Microwave-Assisted Polymer Synthesis: Recent Developments in a ...

Review 

Microwave-Assisted Polymer Synthesis: 

Recent Developments in a Rapidly 

Expanding Field of Research a 

Richard Hoogenboom, Ulrich S. Schubert* 

The use of microwave irradiation has become a common heat source in organic chemistry. 

Inspired by this enormous success, the use of microwave irradiation is also increasingly 

studied for polymerization reactions. The present review discusses developments in this 

rapidly growing field of research. The main areas in which the use of microwave irradiation 

has been explored in the recent years are step-growth polymerizations, ring- opening polymerizations 

as well as radical 

polymerizations. These different 

areas will be addressed in 

detail, whereby special attention 

will be given to observed 

improvements resulting from 

the use of microwave irradiation 

as well as the occurrence 

of non-thermal effects. 

Introduction 

The use of microwave irradiation as an alternative heat 

source is becoming more and more popular in chemistry. 

Nowadays, almost all organic and pharmaceutical chemical 

laboratories are equipped with microwave synthesizers. 

[1–4] Microwave ovens mainly owe their popularity to 

the often observed enhanced reaction rates. Nevertheless, 

these enhanced reaction rates can be often explained by 

R. Hoogenboom, U. S. Schubert 

Laboratory of Macromolecular Chemistry and Nanoscience, 

Eindhoven University of Technology and Dutch Polymer Institute 

(DPI), Den Dolech 2, Eindhoven 5600 MB, The Netherlands 

Fax: þ31 40 247 4786; E-mail: u.s.schubert@tue.nl 

a For a review on earlier literature, see Part I: Macromol. Rapid 

Commun. 2004, 25, 1739. 

the increased reaction temperatures that are allowed by 

the use of closed (pressurized) reactors. The use of such 

closed reaction vials has opened a completely unexplored 

area of high-temperature chemistry under microwave 

irradiation. The closed reaction vessels are also exploited to 

replace high-boiling solvents by low-boiling solvents, 

which simplifies product isolation. In addition, the direct 

heating of molecules under microwave irradiation leads to 

very fast and homogeneous heating that has resulted in 

the reduction of side reactions, cleaner products, and 

higher yields. Microwave heating is based on dielectric 

heating; i.e., molecules exhibiting a permanent dipole 

moment will try to align to the applied electromagnetic 

field resulting in rotation, friction, and collision of molecules 

and, thus, in heat generation. As a result, the heating 

rate and efficiency of microwave heating strongly depends 

on the dielectric properties and the relaxation times of the 

368 

Macromol. Rapid Commun. 2007, 28, 368–386 

ß 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 

DOI: 10.1002/marc.200600749

Microwave-Assisted Polymer Synthesis: Recent Developments in ... 

reaction mixture, whereby the use of good microwave 

absorbing solvents results in very fast heating. [5] Besides 

the advantages of fast and homogeneous heating as well 

as the possible high-temperature chemistry, non-thermal 

microwave effects due to specific heating of polar intermediates 

have been observed, e.g., leading to modified 

Richard Hoogenboom was born in 1978 in Rotterdam 

(The Netherlands). In 2001 he obtained 

his M.Sc. degree in chemical engineering at the 

Eindhoven University of Technology, whereby his 

undergraduate research was performed in the 

group of Bert Meijer (Eindhoven, The Netherlands). 

During the studies, he performed an internship 

within the group of Andrew Holmes (Cambridge, 

United Kingdom). In 2005, he obtained his Ph.D. 

under supervision of Ulrich S. Schubert (Eindhoven, 

The Netherlands) focusing on supramolecular 

initiators for controlled polymerization 

techniques, automated parallel synthesis of 

well-defined polymers and microwave irradiation 

in polymer chemistry. Currently, he is working 

as project leader for the Dutch Polymer 

Institute (DPI) with a major focus on the use 

of high-throughput experimentation and microwave 

irradiation for living/controlled polymerization 

techniques. 

Ulrich S. Schubert was born in Tübingen in 1969. 

He studied chemistry at the Universities of Frankfurt 

and Bayreuth (both Germany) and the Virginia 

Commonwealth University, Richmond (USA). 

His Ph.D. work was performed under the supervision 

of Professor Eisenbach (Bayreuth, Germany) 

and Professor Newkome (Florida, USA). In 1995 he 

obtained his doctorate with Prof. Eisenbach. After 

a postdoctoral training with Professor Lehn at the 

Université Strasbourg (France) he moved to the 

Technische Universität München (Germany) to 

obtain his habilitation in 1999 (with Professor 

Nuyken). From 1999 to spring 2000 he held a 

temporal position as a professor at the Center 

for NanoScience at the Universität München 

(Germany). Since Summer 2000 he is Full- 

Professor at the Eindhoven University of Technology 

(Chair for Macromolecular Chemistry and 

Nanoscience). From 2003 on he is member of 

the management team of the Dutch Polymer 

Institute. His awards include the Bayerischen 

Habilitations-Förderpreis, the Habilitandenpreis 

of the GDCh (Makromolekulare Chemie), the 

Heisenberg-Stipendium of the DFG, the Dozenten- 

Stipendium of the Fonds der Chemischen Industrie 

and a VICI award of NWO. The major focus of 

the research interest of his relates to organic 

heterocyclic chemistry, supramolecular materials, 

combinatorial material research, nanoscience and 

tailor-made macromolecules. 

selectivities and enabling reactions that cannot be performed 

with thermal heating. [6] These non-thermal microwave 

effects are thought to arise from specific microwave 

absorption by polar components of a reaction making 

them more reactive under microwave irradiation when 

compared to thermal heating. 

The use of microwave irradiation in polymer chemistry 

is an emerging field of research that we reviewed in 

2004. [7] Up to that moment, many investigations of 

microwave-assisted polymerizations were conducted in 

domestic microwave ovens making the reproducibility 

and safety of the experiments doubtful due to insufficient 

temperature control. However, the development of commercial 

microwave synthesizers with excellent temperature 

control significantly improved the reliability of the 

reported microwave-assisted polymerizations. As a result, 

the number of publications on microwave-assisted polymerizations 

per year has shown a rapid expansion 

(Figure 1). [8] In fact, a similar figure in the previous review 

showed maximum 90 publications per year, which almost 

doubled in the last two years. 

In the current review, the progress in the field of 

microwave-assisted polymer synthesis since the previous 

review will be discussed with a main focus on step-growth 

polymerizations, ring-opening polymerization, and (controlled) 

radical polymerizations. Special attention will be 

given to the occurrence of non-thermal microwave effects, 

which is still a controversial topic. 

Step-Growth Polymerization 

Step-growth polymerizations are based on the coupling of 

two multifunctional, mostly bifunctional, monomers. 

The resulting coupled product also contains the functional 

groups and thus reacts in the same manner as the 

Figure 1. Number of publications on microwave-assisted 

polymerizations per year. [8] 


ß 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mrc-journal.de 369


monomer eventually leading to polymeric materials. The 

most studied step-growth polymerization methods are 

better known as polycondensations due to the release of 

water during the coupling reactions. 

In this section, microwave-assisted step-growth polymerizations 

are discussed starting with polyamides, polyimides, 

and poly(amide-imide)s, which are the most 

studied class of step-growth polymerizations under microwave 

irradiation. Nevertheless, polymerization via C–C 

coupling reactions resulting in conjugated polymers is 

becoming more popular under microwave irradiation and 

will be discussed as well. The final part of this section deals 

with other step-growth polymerization reactions including 

the synthesis of polyethers, polyesters, and polyurethanes. 

Polyamides, Polyimides, and Poly(amide-imide)s 

Linear aromatic polyamides, polyimides, and poly(amideimide)s 

exhibit excellent thermal, mechanical, and chemical 

stabilities. As a result, these materials are often used 

in high-performance applications. However, the rigid 

structure of these materials makes them hardly soluble 

in organic solvents and, therefore, the use of hightemperature 

microwave-assisted polymerization procedures 

might be advantageous. 

The use of microwave irradiation for the synthesis of 

poly(aspartic acid) starting from maleic anhydride was 

investigated by Pielichowski et al. [9] This multistep procedure 

includes hydrolysis of the maleic anhydride, 

condensation with ammonium hydroxide followed by 

polycondensation resulting in poly(anhydroaspartic acid). 

Subsequent room temperature hydrolysis yielded the 

desired poly(aspartic acid). It was claimed that the use 

of microwave irradiation (multimode microwave reactor) 

accelerated the process by a factor of ten without influencing 

the yield. Faghihi and Hagibeygi have used a 

microwave-assisted polymerization method (domestic 

microwave) for the synthesis of polyamides containing 

azo-benzene moieties. [10] 4,4 0 -Azobenzoyl chloride was 

reacted with eight different 5,5 0 -disubstituted hydantoin 

derivatives as depicted in Scheme 1(a). The hydantoin 

moieties improved the solubility of the resulting polyamides 

while the high thermal stability of the material 

was retained. The authors claimed higher yields and 

efficiencies for the microwave-assisted polymerization 

procedure in o-cresol compared to a standard polymerization 

method with conventional heating in N,Ndimethylacetamide 

(DMAc) or bulk. In a similar work, 

Loupy et al. reported the microwave-assisted synthesis 

(monomode microwave reactor) of chiral polyamides by 

the step-growth polymerization of diphenylaminoisosorbide 

with several diacyl chlorides as depicted in 

Scheme 1(b). [11] Microwave-assisted polymerizations in 

the presence of N-methylpyrrolidone led to faster polymerizations 

and higher molecular weight products when 

compared to standard polymerization methods (however, 

no direct comparison between microwave and thermal 

heating was reported). The N-methylpyrrolidone in the 

microwave polymerization procedure was required to 

induce effective homogeneous heating of the monomers 

and the formed polymers. Lu and coworkers used microwave 

irradiation for the step-growth polymerization of 

Scheme 1. Polyamides (a and b) and polyimide (c) prepared via microwave-assisted step-growth polymerizations: (a) Polyamide synthesis 

from 4,4 0 -azobenzoyl chloride and substituted hydantoins; (b) preparation of polyamides from diphenylaminoisosorbide with several diacyl 

chloride; (c) polyimide synthesis from benzophenone tetracarboxylic dianhydride and p-phenylene diisocyanate. 

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benzoguanamine and pyromellitic anhydride resulting in 

the formation of the p-p conjugated poly(amic acid). [12] 

Although the polymer was synthesized under microwave 

irradiation, no comparison was made to thermal heating. 

The side chains of the resulting poly(amic acid) were 

further functionalized using both azo as well as isocyanate 

coupling procedures at moderate temperatures (no microwave 

irradiation) to study the influence on the fluorescence 

and non-linear optical properties of the materials. 

Direct synthesis of polyimides via the step-growth 

polymerization of isocyanates and anhydrides under 

microwave irradiation was reported by Yeganeh et al. [13] 

The polymerizations were performed in a closed Teflon 

mold inside a domestic microwave oven. The feasibility of 

this approach was first demonstrated by the model 

reaction of phthalic anhydride with p-phenylene diisocyanate 

followed by the model polymerization of benzophenone 

tetracarboxylic dianhydride and p-phenylene 

diisocyanate [Scheme 1(c)]. The effects of microwave 

power, solvent amount, reaction time, and catalyst were 

optimized for this model polymerization reaction. Subsequently, 

the optimal microwave-assisted polymerization 

procedure was applied for the synthesis of novel 

polyimides. 

Most of the recent investigations on microwave-assisted 

polycondensations have been performed on the synthesis 

of poly(amide-imides). The reported polymerizations were 

all performed using domestic microwave ovens. The 

monomers were placed and ground in a porcelain dish. 

After the addition of a small amount of o-cresol, the mixture 

was ground again followed by microwave heating. 

The microwave-assisted synthesis of a series of optically 

active poly(amide-imides), in which the chirality resulted 

from the incorporation of amino acids, was reported by 

Faghihi et al. [14–16] N,N 0 -(pyromellitoyl)-bis(amino acid 

chloride)s were reacted with eight hydantoin derivatives 

as depicted in Scheme 2(a). The polycondensations 

proceeded rapidly compared to the conventional polymerization 

method under thermal heating and was 

completed within 10 min. Nevertheless, the occurrence 

of non-thermal microwave effects was not investigated 

and no direct comparison between the different heat 

sources was made. To provide the optical activity, 

L-leucine, L-valine, or L-alanine were incorporated as amino 

acids. The resulting poly(amide-imide)s might, e.g., be 

suitable as column material for the separation of 

enantiomeric mixtures. Similarly, Faghihi and Hajibeygi 

reported the polycondensation reaction of N,N 0 -(4,4 0 - 

diphenyl ether) bistrimellitimide diacid chloride with 

the same hydantoin derivatives under microwave irradiation. 

[17] The increased solubility of the resulting 

poly(amide-imide)s could be the basis for a novel class 

of processable high-performance plastics. Mallakpour and 

Kowsari investigated the synthesis of optically active 

poly(amide-imide)s by the polycondensation of N,N 0 -(4, 

4 0 -oxydiphthaloyl)-bis(amino acid chloride)s (amino acids 

used are L-leucine, L-valine, and L-isoleucine) and aromatic 

diamines under microwave irradiation [Scheme 2(b)]. [18–20] 

It was demonstrated that comparable polymers can be 

obtained under both microwave and thermal heating 

(different procedures), although shorter reaction times 

were required when using microwave irradiation. 

The resulting optically active polymers were readily soluble 

in organic solvents and exhibited good thermal 

stability. Similarly, Mallakpour and Shahmohammadi 

replaced the central N,N 0 -(4,4 0 -oxydiphthaloyl) group by 

Scheme 2. Poly(amide-imide)s that were synthesized under microwave irradiation: (a) Reaction of N,N 0 -(pyromellitoyl)-bis(amino acid 

chloride)s with hydantoin; (b) copolymerization of N,N 0 -(4,4 0 -oxydiphthaloyl)-bis(amino acid chloride)s with aromatic diamines; (c) 

synthesis of flame-retardant polymers based on N,N 0 -(3,3 0 -diphenylphenylphosphine oxide) bistrimellitimide and aromatic diamines. 




N,N 0 -(pyromellitoyl), [21] N,N 0 -(4,4 0 -sulfone-diphthaloyl), [22] or 

N,N 0 -(4,4 0 -hexafluoroisopropylidenediphthaloyl) [23] groups 

resulting in novel classes of optically active poly(amideimide)s, 

whereby the latter synthesis was also performed in 

the presence of ionic liquids to improve the microwave 

absorption. More recently, Faghihi and Zamani reported the 

microwave-assisted synthesis of phosphine-containing 

poly(amide-imide)s that exhibit flame-retardant properties. 

[24] N,N 0 -(3,3 0 -diphenylphenyl phosphine oxide) bistrimellitimide 

diacid chloride and a variety of aromatic 

diamines were polymerized resulting in processable polymers 

with excellent thermal stability as well as flame 

retardancy [Scheme 2(c)]. In related research, Faghihi and 

coworkers prepared poly(amide-imide)s under microwave 

irradiation from N,N 0 -(4,4 0 -diphenyl ether) bis(trimellitimido) 

[25] or N,N 0 -(pyromellitoyl)-bis-L-alanine [26] diacid 

chlorides with a variety of tetrahydropyrimidinones and 

tetrahydro-2- thioxopyrimidines. 

All previously discussed examples of poly(amideimide)s 

were based on symmetrical monomer units. In 

contrast, Mallakpour and Kowsari reported the synthesis 

of non-symmetrical acid chlorides derived from epiclon 

and L-isoleucine, [27] L-methionine, [28] or L-valine. [29] 

These optically active acid chlorides were subsequently 

polymerized with different aromatic diamines under 

microwave irradiation as depicted in Scheme 3(a). The 

combination of both aromatic and aliphatic spacers in 

poly(amide-imide)s was investigated by Mallakpour and 

Rafiemanzelat. [30] An asymmetric optically active diacid 

based on N-trimellitylimido-L-valine was reacted with 

different (aliphatic) diisocyanates resulting in the corresponding 

optically active poly(amide-imide)s as depicted 

in Scheme 3(b). The resulting polymers were used to study 

structure-property relationships and it was found that the 

incorporation of flexible spacer units improved the 

solubility of the materials but did not negatively influence 

the thermal stability. A similar N-trimellitylimido-Lleucine 

diacid chloride was reacted with eight different 

hydantoin derivatives yielding the corresponding 

optically active poly(amide-imide)s. [31] The L-valinebased 

asymmetric diacid central unit was used for the 

microwave-assisted preparation of poly(amide-imideurethane)s. 

[32,33] The diacid and poly(ethylene glycol diol)s 

were copolymerized using 4,4 0 -methylene-bis(4-phenylisocyanate) 

as coupling agent in a one-step [32] or twostep 

[33] procedure [Scheme 3(c)]. For the two-step procedure, 

the diisocyanate was first reacted with the diol or the 

diacid and subsequently with the other reagent. It was 

found that the properties of the polymers could be influenced 

by changes in catalyst, microwave power, irradiation 

time as well as the molecular weight of the utilized 

poly(ethylene glycol). The resulting thermoplastic 

poly(amide-imide-urethane)s revealed good thermal stability 

and phase mixing. The thermal stability of these 

Scheme 3. Synthesis of poly(amide-imide)s containing asymmetric building blocks: (a) Reaction of a non-symmetrical acid chloride derived 

from epiclon and amino acids with aromatic diamines; (b) Copolymerization of N-trimellitylimido-L-valine diacid with diisocyanates; (c) 

synthesis of poly(amide-imide-urethane)s based on N-trimellitylimido-L-valine diacid, poly(ethylene glycol) and 4, 4 0 -methylene- bis(4- 

phenylisocyanate). 

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polymers improved significantly compared to conventional 

poly(urethanes). 

Polymerizations via C–C Coupling Reactions 

C–C coupling procedures are often applied for step-growth 

polymerization resulting in conjugated polymers that can 

be applied in, e.g., light-emitting diodes, solar cells, and 

organic field effect transistors. [34–36] These C–C coupling 

procedures are often based on metal catalysis which might 

benefit from microwave irradiation by specific absorption 

of the metal ions. 

Khan and Hecht investigated the palladium-catalyzed 

synthesis of poly(m-phenyleneethynylene)s under both 

thermal heating and microwave heating (multimode 

microwave reactor). [37] A novel synthetic method was 

developed in which both deprotection and polymerization 

of AB 0 monomers or AA and BB 0 monomers were 

performed simultaneously resulting in defect-free polymer 

structures as depicted in Scheme 4(a). It was found 

that the microwave-assisted polymerization was comparable 

with thermal heating in toluene, which was ascribed 

to the low dipole moment of the solvent. When the solvent 

was changed to acetonitrile, the polymerization under 

microwave irradiation resulted in higher polymerization 

rates as well as higher molecular weight polymers, 

whereby the microwave-polymerizations were performed 

under different conditions. Tierney and coworkers investigated 

the synthesis of polythiophenes via Stille-type 

cross-coupling [Scheme 4(b)] in a monomode microwave 

reactor. [38] Soluble semi-conducting polythiophenes were 

obtained using both thermal and microwave heating. 

However, it was claimed that the microwave-assisted 

Scheme 4. Microwave-assisted polymerizations via C–C coupling procedures. (a) Palladium-catalyzed synthesis of poly(m-phenyleneethynylene)s; 

(b) Stille-type synthesis of polythiophene; (c) synthesis of poly(phenylenevinylene) via Heck coupling; (d) Ni(0)-mediated copolymerization 

of dibromofluorene with a dichloro platinum-salen complex. 




polymerization method yielded higher molecular weight 

polymers and slightly lower polydispersity indices, 

whereby the direct comparison was performed at different 

polymerization temperatures. The Suzuki C–C coupling 

method was investigated under microwave irradiation 

(monomode microwave reactor) by Scherf et al. [39] 

Three differently substituted naphthalene boronic ester 

monomers were coupled to 4,4 0 -didecyl-2 0 ,5 0 - dibromoterephthalophenone 

using a palladium catalyst. The polymerization 

of the less sterically hindered 2,6-diboronic 

ester naphthalene under both microwave irradiation and 

thermal heating gave similar results. However, the more 

sterically hindered 1,5-diboronic ester naphthalenes could 

not be polymerized using conventional heating, but the 

use of microwave irradiation allowed their polymerization. 

All resulting conjugated polymers served as precursors 

for the formation of ladder-type polymers, which 

have desirable optical and emitting properties. Another 

palladium-catalyzed C–C coupling procedure, namely the 

Heck reaction, was studied for the formation of conjugated 

polymers under both microwave (monomode microwave 

reactor) and thermal heating by Ritter and coworkers. [40] The 

copolymerization of divinylbenzene and 1,4-diiodo-2,5- 

dibutoxybenzene [Scheme 4(c)] was studied in refluxing 

dioxane to ensure the same polymerization temperature in 

both open vessel reactions. This direct comparison revealed 

a slight acceleration of the polymerization under microwave 

irradiation. In addition, the molecular weight of the 

resulting poly(2,5-dibutoxy-1, 4-phenylenevinylene) was 

also a little higher when microwave irradiation was applied 

as heat source. 

The previous examples were all based on C–C coupling 

reactions that require two different functional groups. On 

the contrary, Ni(0)-catalyzed coupling reactions can be 

used for homocoupling reactions. Yamamoto and coworkers 

used a Ni(0) catalyzed polymerization procedure for 

the synthesis of poly(pyrazine-2,5-diyl) starting from 

2,5-dibromopyrazine. [41] The thermal polymerization 

required 2 d polymerization time, while the microwaveassisted 

procedure was finished within 10 min. Unfortunately, 

no temperature was given for the microwave 

procedure and, thus, it is not clear whether the observed 

acceleration is due to thermal or microwave effects. 

Nevertheless, the polymer obtained under microwave 

irradiation had a higher molecular weight. Carter et al. 

reported the use of a Ni(0) catalyzed C–C coupling for 

the synthesis of poly(biphenylmethylene)s starting from 

bistriflate monomers under microwave irradiation (monomode 

microwave reactor). [42] It was demonstrated that the 

polymerization could be performed using both thermal 

and microwave heating, whereby no significant differences 

were observed in the resulting polymers. Nevertheless, 

the microwave-assisted polymerizations were 

performed for only 10 min at 200 8C, whereas the conventional 

polymerizations were performed for 16–24 h at 

80 8C. Surprisingly, endcapping the polymerization by the 

presence of 4-bromostyrene could also be performed at 

200 8C under microwave heating without coupling or 

degradation of the vinyl groups. The Ni(0)-mediated 

polymerization procedure was also applied by Scherf 

and coworkers for the synthesis of polyfluorenes 

with electrophosphorescent platinum-salen chromophores 

[Scheme 4(d)]. [43] The polymerization required 

3 d under thermal heating in tetrahydrofuran (THF) 

at 80 8C and could be accelerated down to 12 min 

under microwave irradiation at 115 or 220 8C in THF of 

a mixture of N,N-dimethylformamide (DMF) and toluene, 

respectively. The resulting copolymers revealed high 

electroluminescence efficiencies due to energy transfer 

from the polyfluorene to the salen complex. 

Other Step-Growth Polymerizations 

Besides poly(amide-imide)s and conjugated polymers, 

several other polymers have been prepared using stepgrowth 

polymerization mechanisms under microwave 

irradiation in the last couple of years. 

The synthesis of biodegradable aliphatic polyesters was 

investigated under microwave irradiation (monomode 

microwave reactor) by Nagahata and coworkers. [44] Direct 

polycondensation of succinic acid and butanediol was 

investigated in the presence of a stannyl catalyst 

[Scheme 5(a)]. The polymerization conditions were investigated 

in detail, whereby the (absence of) solvent, catalyst 

concentration, polymerization temperature, stoichiometry, 

and reaction time were varied. The optimal polymerization 

conditions were also tested in a conventionally 

heated reaction demonstrating a much lower polymerization 

rate compared to the microwave-assisted polymerization 

method. The authors speculate that the ten-fold 

acceleration under microwave irradiation might be due to 

specific microwave absorption by the released water 

molecules leading to quicker evaporation of the water and 

thus a shift in equilibrium towards the polymer. Chatti 

et al. investigated the synthesis of poly(ether-ester)s from 

an isosorbide-based aliphatic diol and two different diacid 

chlorides under microwave irradiation (monomode microwave 

reactor). [45] The used isosorbide-based material is an 

interesting building block for polymer structures because 

it represents a renewable resource. The bulk polymerizations 

revealed a remarkable acceleration under microwave 

irradiation compared to thermal heating under the same 

conditions that was ascribed to the enhanced polarity of 

the transition state during the ester formation. In addition, 

it was found that the microwave-assisted polymerization 

procedure gave less degradation at longer reaction times 

(8 h) compared to conventional heating. The synthesis of 

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Scheme 5. Examples of other polycondensations: (a) Polyester synthesis from succinic acid and butanediol; (b) polycondensation 

of dimethylhydrogen phosphonate and poly(ethylene glycol) resulting in poly(alkylene hydrogen phosphonate); (c) poly(urea) or 

poly(thiourea) synthesis. 

poly(ether)s from trichlorophenol was investigated under 

microwave irradiation by Kisakuerek and coworkers 

(domestic microwave oven). [46] Surprisingly, it was found 

that, depending on the microwave irradiation and polymerization 

time, a conjugated polymer was formed next to 

the expected poly(dichlorophenylene oxide). Moreover, the 

induction period of the polymerization was shorter under 

microwave irradiation compared to conventional heating. 

Troev and coworkers reported the step-growth polymerization 

of dimethyl hydrogen phosphonate with poly(ethylene 

glycol) resulting in biodegradable poly(alkylene 

hydrogen phosphonate) [Scheme 5(b)]. [47] Thermal and 

microwave heating both resulted in comparable polymers, 

whereby the microwave polymerization was performed 

for 55 min at 140–180 8C and the thermal polymerization 

for 9.5 h at 130–140 8C. However, the higher temperatures 

used for the microwave polymerization could not be 

applied in the thermal polymerization process due to 

thermal degradation of the dimethyl hydrogen phosphonate. 

The syntheses of poly(urea)s and poly(thiourea)s 

from the polycondensation of urea or thiourea with a 

series of diamines and a catalytic amount of p-toluenesulfonic 

acid were studied under microwave irradiation 

(domestic microwave oven) by Banihashemi et al. 

[Scheme 5(c)]. [48] The solvent, microwave power as well 

as the polymerization time were optimized for the microwave-assisted 

polymerizations. Even though no comparison 

was made with thermal heating, the authors concluded 

that microwave irradiation is a fast and efficient 

method for such polymerizations. 

Ring-Opening Polymerizations 

Polymerization of cyclic monomers is a popular approach 

for the synthesis of polymers, because these ring-opening 

polymerizations do not suffer from equilibria between the 

polymer with elimination products and the monomers 

that often limit the attainable molecular weights in 

polycondensations. As a result, ring-opening polymerization 

methods allow easier preparation of high-molecular 

weight polymers. In addition, a variety of ring-opening 

polymerizations can be performed via controlled/living 

polymerization mechanisms that allow the formation of 

well-defined (co)polymers. In the field of microwave-assisted 

polymerizations, the main focus has been on 

the ring-opening polymerization of cyclic esters as well as 

the living cationic ring-opening polymerization of 

2-oxazolines that will be discussed in the following 

sections. 

Aliphatic Polyesters 

Ring-opening polymerization of cyclic esters like lactones 

and lactides results in the formation of biodegradable 

aliphatic polyesters. These materials are promising candidates 

for bio-related applications such as drug-delivery or 

as scaffolds in tissue engineering. The majority of the 

investigations on microwave-assisted ring-opening polymerizations 

of cyclic esters were performed using e-caprolactone 

or lactides. 

The effect of microwave irradiation on the chain propagation 

of the benzoic acid initiated polymerization of 

e-caprolactone was investigated in detail by Yu and Liu 

using closed ampoules in a domestic microwave oven. [49] 

The chain propagation was studied as a function of 

microwave power, monomer to initiator ratio, and polymerization 

temperature. Nevertheless, the most interesting 

results were obtained by a direct comparison of the use 

of microwave heating and thermal heating demonstrating 

that the use of microwave heating favors chain growth in 




Figure 2. Polymerization kinetics that were obtained for the enzyme-catalyzed ring-opening 

polymerization of e-caprolactone under microwave heating and oil bath heating in refluxing 

benzene (left) and diethyl ether (right). Reprinted with permission from ref. [50] 

the initial stage and thus limits the number of polymer 

chains, whereas thermal heating favored the formation of 

growing centers in the initial stage. As a result, the 

microwave-assisted polymerization procedure resulted in 

higher molecular weight polymers. Kerep and Ritter 

investigated the enzyme-catalyzed (novozym 435) polymerization 

of e-caprolactone under reflux conditions in toluene, 

benzene, and diethyl ether using both thermal and 

microwave (monomode microwave reactor) heating. [50] A 

strong effect of the used solvents was observed: The 

polymerization was decelerated under microwave irradiation 

in toluene and benzene (Figure 2, left), while it was 

accelerated under microwave irradiation in diethyl ether 

(Figure 2, right). In this particular case, the boiling point 

rather than the nature of the solvents (all apolar), seems to 

be a critical factor. The authors proposed that the observed 

effects might be due to a microwave- enhanced fit between 

the active center of the enzyme and the e-caprolactone 

substrate under mild conditions. 

Loupy et al. investigated the effect of microwave 

irradiation on the polymerization of e-caprolactone with 

lanthanide halide catalysts using different heat profiles. [51] 

When 200 W microwave power was applied constantly, 

broader molecular weight distributions were obtained 

compared to the use of an initial power boost (300 W). This 

observed effect was attributed to the faster heating with 

the higher initial microwave power, which inhibits 

secondary transfer reactions. Moreover, direct comparison 

of thermal and microwave heating demonstrated the 

necessity of longer reaction times with thermal heating as 

well as lower molecular weights and broader molecular 

weight distributions. In degradation studies of the synthesized 

poly(e-caprolactone), it was found that the 

presence of lanthanide catalysts accelerates hydrolytic 

degradation but it inhibits enzymatic degradation. In 

addition, the synthesized acid-functional polymers were 

converted into macromonomers by esterification with 

2-hydroxyethyl methacrylate. Ritter and coworkers 

demonstrated the direct synthesis of similar poly(ecaprolactone) 

macromonomers via the stannous octanoate 

catalyzed ring-opening polymerization of e-caprolactone 

under microwave irradiation. [52] Although no microwaveacceleration 

was observed for the polymerization, the use 

of microwave irradiation allowed rapid optimization of 

the polymerization conditions. Fang et al. also applied a 

microwave-assisted polymerization (domestic microwave 

oven) procedure for the stannous octanoate catalyzed 

ring-opening polymerization of e-caprolactone. [53] The 

amino groups of chitosan were protected with phthalic 

anhydride allowing the use of the primary hydroxyl-groups 

as initiators for the ring-opening polymerization 

as depicted in Scheme 6. After the polymerization, the 

amino groups were deprotected resulting in poly(ecaprolactone) 

grafted chitosan. Compared to conventional 

heating, higher grafting densities were obtained with 

microwave heating. Moreover, the grafting procedure was 

greatly accelerated when more than 450 W of microwave 

power was applied. Yu and Liu have used a catalystfree 

microwave-assisted polymerization procedure for the 

preparation of poly(e-caprolactone)-block-poly(ethylene glycol)-block-poly(e-caprolactone) 

copolymers. [54] The monomer 

conversion as well as the resulting molecular weight of the 

polymers could be adjusted by changes in the irradiation 

time, microwave power as well as length and amount of 

added poly(ethylene glycol). The resulting triblock copolymers 

were studied for the encapsulation and release of 

ibuprofen revealing an almost linear release in time. 

Besides e-caprolactone, a variety of other cyclic esters 

have been used in microwave-assisted polymerization 

procedures. Shu et al. described the stannous octanoatecatalyzed 

ring-opening polymerization of D,L-lactide under 

ambient atmosphere and vacuum using a domestic 

microwave oven. [55] It was found that the efficient heating 

of microwave irradiation resulted in a successful polymerization 

without the need for vacuum or an inert 

atmosphere as required with thermal heating. In addition, 

higher temperatures were attainable before thermal 

decomposition occurred when using microwave irradiation. 

This is most likely due to the 

more homogeneous heat profile. 

Nevertheless, the observed 

acceleration under microwave 

irradiation could not be completely 

designated to the higher 

temperatures and, thus, it was 

concluded that non-thermal 

microwave effects also played a 

role. The same polymerization 

system was studied by Liu 

and coworkers. [56] The focus of 

this study was the effect of 

microwave power on the polymerization 

process under micro- 

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Scheme 6. Grafting procedure that was used for the preparation of chitosan-graft-poly(e-caprolactone). 

Figure 3. Molecular weight versus time evolution at different 

microwave powers for the stannous octanoate catalyzed 

ring-opening polymerization of D,L-lactide. Reprinted with permission 

from ref. [56] 

wave irradiation (domestic microwave oven). It was found 

that, up to 255 W, the molecular weight of the polymer 

increasedandreachedamaximumwhen90% conversion 

was reached (Figure 3). When a higher dose of microwave 

energy was applied, the molecular weight first increased 

and subsequently decreased in time due to transesterification 

reactions. Moreover, the monomer conversion eventually 

decreased on applying 510 W of power indicating 

depolymerization. These results clearly demonstrate the 

effect of microwave power on the ring-opening polymerization. 

However, due to the absence of a direct comparison 

with thermal heating it is not clear whether this is a thermal 

effect or a non-thermal microwave effect. 

Similar observations were made by Wang et al. for 

the microwave-assisted ring-opening polymerization of 

p-dioxanone using a domestic microwave oven. [57] It was 

found that the yield and the molecular weight of the 

polymers go through a maximum when the microwave 

power is increased or when the reaction time at a given 

microwave power is increased due to decomposition of the 

polymers. Jin et al. studied the formation of b-tricalcium 

phosphate/poly(L-lactide-stat-glycolide) composites in a 

domestic microwave oven. [58] The b-tricalcium phosphate 

was dispersed in a melt of the two monomers and 

stannous octanoate and the polymerization was performed 

by applying 100 W microwave power. Up to 

10 wt.-% of the inorganic material, the molecular weight of 

the resulting polymers decreased, but the addition of 

more b-tricalcium phosphate resulted in higher molecular 

weights, which was attributed to superheating of the salt 

under microwave irradiation. The mechanical properties 

of the prepared composites were proportional to the 

molecular weight of the copolymers and not to the 

amount of dispersed particles. Nagahata et al. have 

successfully explored a novel route for the synthesis of 

poly[(ethylene terephthalate)-stat-isophthalate] starting 

from an ethylene isophthalate cyclic dimer and bis(2- 

hydroxyethyl) terephthalate under microwave irradiation. 

[59] However, the influence of microwave heating on 

this polymerization was not addressed in the current 

study. 




Cationic Ring-Opening Polymerizations 

Cationic ring-opening polymerizations seem to be very 

well suited to address non-thermal microwave effects due 

to the cationic propagating species. In recent literature, 

several studies were reported to address this topic for the 

cationic ring-opening polymerization of 2-oxazolines, 

which will be discussed in this section. 

The cationic ring-opening polymerization of 2-ethyl-2- 

oxazoline under microwave irradiation (monomode microwave 

reactor) was first reported by Schubert and coworkers. 

[60] It was demonstrated that the polymerization in 

acetonitrile could be tremendously accelerated under 

superheated conditions up to 180 8C without losing the 

living character of the polymerization. Reference experiments 

in a pressure NMR tube and larger pressure 

reactors [61] revealed that the polymerization was only 

accelerated due to thermal effects. This study was further 

expanded to other 2-oxazoline monomers (methyl, nonyl, 

and phenyl substituted) and it was demonstrated that the 

polymerizations of these monomers could also be accelerated 

when going to superheated conditions. [62] The 

Arrhenius parameters were found to be in the same range 

as for thermal polymerizations and, thus, it was concluded 

that the observed accelerations are only due to the 

increased polymerization temperatures. Nevertheless, it 

was found that the control over the polymerizations was 

slightly better under microwave irradiation due to the 

more homogeneous heat profiles. Additional studies were 

performed on different solvents for the polymerization of 

2-nonyl-2-oxazoline revealing that the polymerization rate 

and the Arrhenius parameters were comparable in both 

acetonitrile and dichloromethane. [63] Sinnwell and Ritter 

also found that the cationic ring-opening polymerization 

of 2-phenyl-2-oxazoline [64] and 2-phenyl-2-oxazine [65] 

could be accelerated in both open and closed reactors 

under microwave irradiation (monomode microwave 

reactor). Surprisingly, reference experiments with thermal 

heating revealed that the acceleration was due to nonthermal 

effects, which was attributed to specific microwave 

absorption of the cationic propagating species. In the 

case of 2-phenyl-2-oxazine, the microwave-acceleration 

was demonstrated using methyl tosylate and butyl iodide 

as initiators. Although these initiators result in different 

polymerization rates due to the different counterions, the 

observed acceleration was in both cases a factor 1.8. In 

addition, it was found that the initiating group can be used 

to tune the glass transition temperature of the resulting 

polymers. A careful evaluation of these opposite results on 

the (non)-existence of non-thermal microwave effects 

revealed that the polymerization rates for 2-phenyl-2- 

oxazoline under microwave irradiation were almost the 

same in both studies, but different polymerization rates 

were found in the thermal reference. [66] Another claimed 

Figure 4. Size exclusion chromatograms as well as pictures of 

upscaling the cationic ring-opening polymerization of 2-ethyl-2- 

oxazoline from 4 mmol (a) via 200 mmol (b) to 1 000 mmol 

(c) under superheated microwave conditions. Reprinted with 

permission from ref. [67] 

advantage of microwave heating, namely direct scalability, 

was addressed by Schubert et al. [67] The superheated 

cationic ring-opening polymerization of 2-ethyl-2-oxazoline 

was performed under microwave irradiation at scales from 

4 mmol up to 1 mol using both monomode and multimode 

microwave reactors yielding highly comparable poly(2- 

ethyl-2-oxazoline)s with low polydispersity indices regardless 

of the scale (Figure 4). Further upscaling using continuous 

flow microwave reactors resulted in broadening of the 

molecular weight distribution due to the residence time 

distribution of the reactors. [68] Nonetheless, reasonably 

well-defined poly(2-ethyl-2-oxazoline)s could be prepared 

using continuous flow microwave set-ups. Very recently, 

Schubert and coworkers investigated the cationic ringopening 

polymerization of 2-ethyl-2-oxazoline and 2-phenyl- 

2-oxazoline under microwave irradiation using ionic liquids 

as solvent to exclude the use of organic solvents. [69,70] The use 

of ionic liquids as strongly polar solvents resulted in an 

acceleration of the polymerization due to a better stabilization 

of the ionic propagating species. However, the same 

acceleration could be reproduced with thermal heating. 

Despite the current debate on non-thermal microwave 

effects for the polymerization of 2-oxazolines, the 

improved microwave-assisted polymerization procedure 

was applied for the fast synthesis of libraries of poly(2- 

alkyl-2-oxazoline)s, [71] quasi-diblock [72] and diblock copoly(2-oxazoline)s 

[73] as well as triblock terpoly(2-oxazoline)s 

[74] to elucidate structure-property relationships (this 

work was recently featured in ref. [75] ). The first successful 

synthesis of triblock terpoly(2-oxazoline)s with polydispersity 

indices below 1.30 was claimed to be facilitated 

by the improved control over the polymerization due to 

more homogeneous heating. In addition, a 2-oxazoline 

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monomer based on unsaturated soy bean fatty acids 

was polymerized successfully under microwave irradiation, 

whereby the unsaturated sites were not affected 

by the polymerization of the 2-oxazoline ring. [76] 

The resulting polymers with unsaturated side-chains 

could be cross-linked by UV-irradiation. This soy-based 

2-oxazoline monomer was also used for the microwaveassisted 

two-step synthesis of amphiphilic poly(2-ethyl- 

2-oxazoline)-block-poly(2-soy-alkyl-2-oxazoline) block 

copolymers that were successfully applied for the preparation 

of cross-linked micelles. [77,78] 

Radical Polymerizations 

Scheme 7. Schematic representation of the different selectivity in 

the synthesis of (meth)acrylamides that was found by Ritter and 

coworkers using microwave and thermal heating. [79,80] 

Radical polymerization techniques are widely used in both 

industry and academia because of the broad range of 

possible monomers and the relatively simple polymerization 

procedures. Moreover, radical polymerizations are 

compatible with water and therefore emulsion and dispersion 

polymerization procedures that exclude the use of 

organic solvents can be applied. 

This section will discuss the recent developments in 

microwave-assisted free radical polymerizations, free 

radical polymerizations in emulsion as well as controlled 

radical polymerizations. The section on free radical polymerization 

will specifically address the issue of copolymerizing 

different monomers under microwave irradiation 

since specific microwave absorption may lead to 

changes in monomer reactivity or in transition states and 

thus in the reactivity ratios. 

Free-Radical Polymerizations 

The free-radical polymerization of vinylic monomers is one 

of the major processes for the industrial production of bulk 

polymers like polystyrene and poly(methyl methacrylate). 

The previous review on microwave-assisted polymerizations 

covered a wide range of investigations on the effect 

of microwave irradiation on free radical homopolymerizations. 

[7] However, in recent years only a few of such 

investigations were reported and the major focus has 

shifted to copolymerizations. 

Nevertheless, Ritter and coworkers have investigated 

the microwave-assisted direct synthesis and polymerization 

of a series of chiral (meth)acrylamides. [79,80] The direct 

synthesis of chiral meth(acrylamide) from (meth)acrylic 

acid and 1-phenylethylamine under microwave irradiation 

yielded the desired vinyl monomers, whereas the 

same reaction under thermal heating resulted mainly in 

the formation of the Michael addition product (Scheme 7). 

The preferred formation of the desired (meth)acrylamides 

under microwave irradiation could be rationalized by the 

(zwitter) ionic intermediates that lead to the formation of 

the meth(acrylamide)s. The direct synthesis of (meth)acrylamides 

under microwave irradiation represents a 

major improvement compared to the conventional methods 

that make use of acid chloride reagents and/or coupling 

agents. In addition, it was demonstrated that the 

synthesis and polymerization of 1-phenylethyl (meth)acrylamide 

can be performed simultaneously in a one-pot 

reaction under microwave irradiation. 

Similarly, Bezdushna and Ritter reported a microwave 

acceleration for the direct synthesis of N-phenylmaleimide 

from maleic anhydride and aniline based on specific 

microwave absorption of the ionic intermediates. [81] Moreover, 

the synthesis of N-(2-ethoxyethyl)maleimide from its 

corresponding maleic acid in acetic anhydride as reactive 

solvent was also investigated under microwave irradiation. 

[82] Although this reaction also proceeds via ionic 

intermediates, no acceleration was observed due to 

specific microwave absorption in this case. Fischer et al. 

investigated the free radical polymerization of N-alkylacrylamides 

with 3-mercaptopropionic acid as chain 

transfer agent in methanol with thermal heating at 

ambient pressure and under superheated conditions as 

well as under microwave irradiation. [83] The chain transfer 

polymerization could be accelerated from 5 to 1 h when 

going to superheated conditions with thermal heating. 

When changing the heat source to microwave irradiation, 

the polymerization was further accelerated down to 

several seconds. However, the microwave-assisted polymerizations 

were performed without solvent in a domestic 

microwave oven under power control. Therefore, it is not 

clear whether the acceleration is due to thermal effects or 

not. Nevertheless, the accelerated microwave polymerization 

procedure was incorporated into university education 

allowing synthesis, isolation and characterization of the 

polymers within a one-day laboratory session. [84] 

The copolymerization of monomers with significantly 

different microwave absorption characteristics is believed 




to result in specific microwave effects resulting in changes 

in the reactivity ratios. Fellows has tried to address these 

speculated effects for the free radical copolymerizations of 

methyl methacrylate and styrene as well as butyl methacrylate 

with styrene or isoprene in toluene under microwave 

irradiation (monomode microwave reactor). [85] 

However, no changes in reactivity ratios were observed 

although more detailed studies were required for the 

copolymerization of butyl methacrylate and isoprene. The 

microwave-assisted polymerization procedure did accelerate 

the polymerizations by a factor of 1.7, which could be 

ascribed to an increase in radical flux. It was proposed that 

the increased radical flux under microwave irradiation is 

due to rapid orientation of the radicals that are formed 

from decomposition of the azoisobutyronitrile as depicted 

in Scheme 8. This orientation would reduce the number of 

direct terminations by recombination of the two radical 

fragments under microwave irradiation and thus cause a 

higher radical flux. 

In similar investigations, Greiner and coworkers investigated 

the free radical copolymerization of methyl methacrylate 

and styrene with different initiators in different 

solvents using both microwave (monomode microwave 

reactor) and thermal heating. [86] In contrast to the findings 

of Fellows, [85] the polymerizations in toluene revealed very 

similar polymerization rates for both heating methods, 

whereas the polymerizations in DMF were all accelerated 

under microwave irradiation. Nevertheless, regardless of the 

used solvent and initiator the reactivity of both monomers 

were not affected by the use of microwave irradiation. 

Agarwal et al. studied the copolymerization of 2,3,4,5,6- 

pentafluorostyrene and N-phenylmaleimide. [87] Comparison 

of microwave heating and thermal heating for this 

copolymerization revealed a higher initial polymerization 

rate and a lower final monomer conversion for the 

microwave- assisted procedure. The authors speculated that 

the lower final monomer conversion under microwave 

irradiation might be ascribed to an increased amount of 

diffusion-controlled termination reactions although no direct 

association was made with microwaves. The synthesized 

copolymers of 2,3,4,5,6-pentafluorostyrene and N-phenylmaleimide 

exhibited both high glass transition temperature 

as well as high hydrophobicity. The copolymerization of 

N,N-dimethylaminoethyl methacrylate with allylthiourea 

was performed under microwave irradiation (domestic 

microwave oven) by Lu et al., whereby both the influence 

of reaction time and microwave power on the copolymerization 

were studied. [88] Subsequently, copper was coordinated 

to this polymer by microwave irradiation of a solution 

of the copolymer with blue vitriod. This polymer-copper 

system was successfully applied as an heterogeneous 

catalyst for the polymerization of methyl methacrylate. 

Besides the free radical copolymerization of different 

monomers, several studies were reported in which vinylic 

polymers were grafted onto natural polymers under 

microwave irradiation using domestic microwave ovens. 

Sanghi and coworkers reported grafting of acrylonitrile [89] 

and acrylamide [90] onto guar gum under both thermal 

heating and microwave irradiation. Grafting with thermal 

heating was performed at 35 8C in the presence of redox 

initiating systems (potassium persulfate and ascorbic 

acid). Under microwave irradiation, grafting could be 

achieved in the absence of this initiating system at 97 8C, 

whereas control experiments with thermal heating at 

100 8C without initiator did not show any grafting, 

indicating the presence of non-thermal microwave effects. 

Grafting of acrylamide onto the guar gum under microwave 

irradiation in the presence of the redox initiating 

system resulted in higher grafting efficiency. The same group 

also reported grafting of acrylonitrile, [91] acrylamide, [92] and 

methyl methacrylate [93] onto chitosan using microwave 

heating. Similar to the grafting on guar gum, it was found 

that radically grafting onto the chitosan could be achieved 

without any redox initiating system when applying 

microwave irradiation. Grafting of both acrylamide and 

methyl methacrylate was demonstrated to improve the 

solubility of the chitosan at neutral pH. Moreover, these 

grafted copolymers showed increased zinc(II) binding 

(methyl methacrylate and acrylamide) and/or calcium(II) 

binding (acrylamide) making them suitable candidates for 

Scheme 8. Schematic representation of the direct orientation of radicals that are formed from the decomposition of azoisobutyronitrile 

under microwave irradiation that was proposed to explain the higher radical flux observed for microwave-assisted polymerizations 

compared to thermal polymerizations. [85] 

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Scheme 9. Grafting of methyl methacrylate on k-carrageenan using potassium persulfate. 

the removal of these ions from waste water. Prasad et al. 

used microwave irradiation as heat source for the grafting 

of methyl methacrylate on k-carrageenan using a 

potassium persulfate initiating system as depicted in 

Scheme 9. [94] The most important advantages of the 

microwave-assisted grafting procedure were the very 

short polymerization times and the simplicity, whereby 

the good control over the polymerization conditions 

prevented thermal degradation of the k-carrageenan. 

Superabsorbing materials have been prepared under 

microwave irradiation by the copolymerization of cornstarch, 

sodium acrylate, and poly(ethylene glycol) diacrylate 

by Zheng et al., where it was found that both the 

inhibitor and oxygen did not have to be removed from the 

polymerization mixture when using microwave irradiation. 

[95] Optimization of the microwave-assisted polymerization 

method resulted in the preparation of a superabsorber 

with a swelling ratio of 520 to 620 g water per 

gram polymer. When the optimal conditions were applied 

for the preparation of the hydrogel using conventional 

heating, the material exhibited lower swelling ratios 

demonstrating the advantage of microwave heating. Xu 

and coworkers prepared superabsorbers by the copolymerization 

of starch, sodium acrylate, and 2-acrylamido-2- 

methylpropanosulfonic acid. [96] Besides the faster polymerization 

under microwave irradiation, it was found 

that the swelling rate of the material prepared under 

microwave irradiation was 

much higher than for the material 

prepared with conventional 

heating. Scanning electron 

microscopy revealed that the 

material produced under microwave 

irradiation consisted of 

many evenly distributed pores, 

whereas the material prepared 

with thermal heating contained 

irregular pores. This 

observation was correlated to 

the different temperatures that 

were used: A higher temperature 

with microwave heating 

causes in situ drying and thus the pores resulted from 

water evaporation during the preparation while thermal 

heating gave a hydrogel that was dried afterwards. 

Another current topic in microwave-assisted free radical 

polymerizations is the preparation of composite materials 

in which the solid materials act as microwave absorbers 

and initiate the polymerization. Zhu and Zhu reported the 

simultaneous one-step preparation of polyacrylamidemetal 

nanocomposites under microwave irradiation as 

depicted in Figure 5. [97] Using this method, monodisperse 

nanocomposites could be obtained with silver, platinum, 

and copper. During these studies, ethylene glycol was used 

as solvent, reducing agent, and microwave absorber. This 

novel method excludes the use of additional initiators, 

surfactants, and stabilizers. 

Polystyrene-silica composites were prepared by Liu and 

Su. [98] Silica particles were dispersed in bulk styrene with 

azoisobutyronitrile as initiator followed by microwave 

irradiation resulting in the polymerization of styrene. The 

effect of microwave power and initiator on the styrene 

conversion and grafting efficiency were investigated. 

Moreover, it was mentioned that the microwave-assisted 

polymerization procedure is the shortest and easiest 

method known in the literature: it results in almost the 

best grafting parameters. Ritter and coworkers used the 

selective heating of iron fibers under microwave irradiation 

for the synthesis of channel containing polymeric 

Figure 5. Schematic representation of the one-pot synthesis of polyacrylamide-metal nanocomposites. 




materials. [99] A tube with steel wool, methyl methacrylate, 

ethylene glycol dimethacrylate, and azoisobutyronitrile 

was heated under microwave irradiation resulting in the 

formation of a cross-linked network around the steel wool. 

These iron fibers were subsequently removed using 

concentrated hydrochloric acid leaving a channel-containing 

cross-linked poly(methyl methacrylate) network. 

The selective heating of the iron fibers was demonstrated 

by applying 25 W power to a monomer-initiator solution 

with and without iron powder. Without iron almost no 

temperature increase was observed while in the presence 

of iron the temperature increased quickly. The use of 

thermal heating resulted in polymerization from the wall 

of the flask and did not give the desired channel containing 

materials. 

Emulsion Polymerizations 

Free radical polymerizations in emulsion are environmentally 

benign alternatives due to the absence of organic solvents. 

Many studies were already performed on microwaveassisted 

emulsion polymerizations often resulting in faster 

polymerizations. Palacios et al. have proposed a modeling 

approach of such microwave-assisted polymerizations in 

which a conventional model was expanded with a second 

free radical chemical initiator to account for the microwave 

acceleration. [100] The concentration of this artificial 

radical initiator was related to the microwave power and 

its half life time was related to the ratio of monomer 

concentration to the rate of microwave absorption. With 

these parameters it was possible to model and reproduce a 

variety of polymerization kinetics for microwave-assisted 

emulsion polymerizations that were published in recent 

literature. Wu and coworkers have replaced thermal 

heating by microwave heating in their recent studies on 

the emulsion polymerization of styrene in the presence [101] 

and absence [102] of surfactants. However, their main 

objectives were related to the principles of emulsion 

polymerization and they did not study the effects of 

microwave irradiation on the emulsion polymerization 

process. Holtze et al. exploited the fast heating and cooling 

that is provided by modern microwave reactors for 

the synthesis of ultrahigh molecular weight polystyrene 

in miniemulsion. [103] Application of alternating short 

microwave-irradiation pulses (10 s) and long cooling 

intervals (15 min) resulted in radical formation in the 

irradiation phase and propagation during the cold phase. It 

was demonstrated that after the hot phase, zero or one 

radical survives per droplet generating high molecular 

weight polystyrene until chain-transfer to monomer 

occurs and a new polymer chain is formed. The occurrence 

of non-thermal microwave effects is excluded by the 

authors and all the observed effects could be explained 

with common radical kinetics for heterophase systems. 

O’Mealey et al. studied the effect of microwave irradiation 

(multimode microwave reactor) on the emulsion polymerization 

of styrene and methyl methacrylate. [104] The 

polymerization kinetics for styrene were similar under 

thermal and microwave heating, whereby only higher 

monomer conversions were observed at longer reaction 

times. Surprisingly, the emulsion polymerization of 

methyl methacrylate was faster with microwave irradiation 

at all investigated reaction times. Additionally, 

the obtained molecular weights for polystyrene and 

poly(methyl methacrylate) were significantly higher when 

the polymerizations were performed under microwave 

irradiation, which was ascribed to a possible higher degree 

of branching when microwave irradiation was applied. 

Surfactant-free emulsion polymerization of methyl methacrylate 

was studied by Bao and Zhang using both thermal 

and microwave heating resulting in very uniform 

poly(methyl methacrylate) particles. [105] It was found that 

the use of microwave irradiation clearly accelerated the 

emulsion polymerizations, which was ascribed to an 

increased thermal decomposition rate of the potassium 

persulfate due to microwave irradiation. This was confirmed 

by an Arrhenius plot of the potassium persulfate 

decomposition that showed a decrease in the activation 

energy from 128 to 106 kJ mol 1 when going from 

thermal heating to microwave heating (Figure 6). 

The microwave-assisted emulsion polymerization of 

methyl methacrylate was also studied in comparison to 

thermal heating by Palacios and coworkers. [106] The 

application of only 50 W microwave power accelerated 

the polymerization compared to thermal heating. In 

addition, higher molecular weight polymers with lower 

polydispersity indices, sometimes even in the range of 

Figure 6. Arrhenius plot for the decomposition of potassium 

persulfate under microwave (40 and 300 W) and thermal heating 

(K p ¼ decomposition rate; reprinted with permission from 

ref. [105] ). 

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controlled radical polymerization techniques (1.18), were 

obtained with microwave irradiation. Yi et al. reported the 

surfactant-free emulsion copolymerization of styrene and 

N-isopropylacrylamide using microwave heating. [107,108] 

The resulting polymer particles were smaller and more 

homogeneous compared to particles made with thermal 

heating. It was demonstrated that these particles were 

thermoresponsive and their size decreased when the 

temperature was increased. Similarly, Zhang et al. synthesized 

thermosensitive poly(methyl methacrylate) coated 

poly(N-isopropylacrylamide) particles using a microwaveassisted 

two-step emulsion polymerization. [109] 

The last reported example of a water-based free radical 

polymerization under microwave irradiation is the dispersion 

polymerization of styrene using poly(N-vinylpyrrolidone) 

as stabilizer and azoisobutyronitrile as initiator 

was reported by Xu et al. [110] The polystyrene particles 

obtained with microwave irradiation were smaller, more 

uniform and more stable than those prepared with 

thermal heating as illustrated by Figure 7. 

Controlled Radical Polymerizations 

In contrast to free radical polymerizations, the occurrence 

of radical termination reactions is suppressed in controlled 

radical polymerization techniques. The suppression of 

termination reactions is achieved by lowering the concentration 

of free radicals by a reversible radical termination 

with metals [atom-transfer radical polymerization (ATRP)] 

or nitroxides [nitroxide-mediated radical polymerization 

(NMP)], or by a reversible chain transfer mechanism 

[reversible addition fragmentation chain-transfer polymerization 

(RAFT)]. Zhu and coworkers investigated the 

ATRP of styrene under pulsed microwave irradiation. [111] 

Controlled polymerization of styrene with pulsed microwave 

irradiation revealed polymerization rates that were 

three times larger than those for thermal heating, suggesting 

that the controlled nature of the polymerization 

was not affected as was demonstrated by 1 H NMR spectroscopy 

and chain extension experiments. Similarly, 

Hou et al. reported that the iron(II)-catalyzed ATRP of 

acrylonitrile could be accelerated under microwave 

irradiation. The Ru(II)-catalyzed ATRP of MMA was also 

enhanced by the use of microwave irradiation (monomode 

microwave reactor). [112] Demonceau and coworkers 

demonstrated acceleration of the methyl methacrylate 

polymerization under microwave irradiation at temperatures 

in the range of 100–140 8C and a deceleration at 

temperatures above 150 8C. In addition, the molecular 

weight distributions were found to be broader when using 

microwave irradiation regardless of the polymerization 

temperature. Further studies to elucidate the underlying 

principles of these investigations are in progress. In 

contrast to the previously described accelerations of ATRP 

reactions, Zhang and Schubert reported that the ATRP of 

methyl methacrylate with both microwave (monomode 

microwave reactor) and thermal heating revealed comparable 

polymerization rates. [113] In addition, increasing the 

polymerization temperature under microwave irradiation 

led to uncontrolled polymerizations due to higher radical 

concentrations. Wu et al. used microwave irradiation for 

the further end-functionalization of telechelic bromopolystyrene 

with C 60 fullerenes. [114] The use of microwave 

irradiation significantly increased the rate of fullerene 

coupling without changing the structure and properties of 

the resulting polymers. The NMP of methyl acrylate 

and tert-butyl acrylate in dioxane was investigated by 

Schubert and coworkers in a monomode microwave 

reactor. [115] Comparative studies with both microwave 

heating and thermal heating revealed similar polymerization 

kinetics. Nevertheless, at high monomer conversion 

above 90% the microwave-assisted polymerization procedure 

resulted in well-defined polymers while the thermal 

polymerization process showed increasing molecular 

weight distributions. This observation was attributed to 

Figure 7. Transmission electron microscope images of polystyrene particles obtained under similar conditions with microwave (left) and 

thermal (right) heating (reprinted with permission from ref. [110] ). 




the more homogeneous heating under microwave irradiation 

that becomes more apparent at high conversions due 

to the increased viscosity of the polymerization mixture. In 

contrast, Zhu et al. observed a clear acceleration of the NMP 

of styrene in bulk under microwave irradiation (monomode 

microwave reactor). [116] The rate of polymerization 

increased with increasing microwave power while the 

control over the polymerization was maintained. The 

microwave-assisted RAFT polymerization of both styrene 

and methyl methacrylate was investigated by Perrier and 

coworkers. [117] For both monomers an increase in polymerization 

rate was observed when microwave irradiation 

was applied as heat source. Moreover, linear first-order 

kinetics were observed and a linear increase in molecular 

weight with conversion demonstrating a good control over 

the polymerizations under microwave irradiation was also 

observed. Zhu et al. reported similar observations for the 

RAFT polymerization of styrene using a domestic microwave 

oven. [118] 

microwave irradiation that were observed in recent years. 

In addition, several open questions such as specific microwave 

absorption in copolymerizations as well as upscaling 

issues have to be addressed in the coming years. 

Nevertheless, it is expected that the use of microwave 

irradiation will evolve from a research topic into a common 

research tool in polymer science. Whether microwave-assisted 

polymerization procedures will be incorporated 

into future commercial processes is still uncertain 

and would only be feasible for processes that show a clear 

(economical) advantage over thermal heating. 

Acknowledgements: This study was supported by the Dutch 

Polymer Institute (DPI) and the Fonds der Chemischen Industrie. 

Received: October 30, 2006; Accepted: December 8, 2006; DOI: 

10.1002/marc.200600749 

Keywords: microwave irradiation; polymer; radical polymerization; 

ring-opening polymerization; step-growth polymerization 

Summary and Outlook 

The use of microwave irradiation in polymer chemistry is a 

rapidly expanding field of research. In the last two years, 

the number of publications per year has doubled. The main 

reason for this increased interest in the use of microwave 

irradiation is the often observed acceleration of polymerizations 

when performed with microwave irradiation. 

Nevertheless, in many cases the acceleration is due to 

increased polymerization temperatures compared to thermal 

heating, whereby it should be noted that these 

increased temperatures are much easier accessible when 

using microwave irradiation. In addition to the increased 

temperatures, many of the observed advantages of microwave 

heating can be ascribed to the fast and homogeneous 

heating that can prevent thermal decomposition and/or 

other side reactions caused by local overheating over the 

polymerization mixtures with thermal heating. Besides 

these improvements that can be ascribed to thermal 

effects under microwave irradiation, several examples 

have been reported in which non-thermal microwave 

effects were observed. These non-thermal microwave 

effects can be rationalized by specific microwave absorption 

of polar intermediates and or reagents making them 

more reactive. However, the observation of such effects 

seems to depend on the choice of microwave reactors 

(domestic, monomode, or multimode microwaves) as well 

as the choice of polymerization conditions. In addition, 

attempts to change monomer reactivity and reactivity 

ratios in copolymerizations of monomers with different 

polarities have not succeeded so far. 

The field of microwave-assisted polymerizations is 

believed to continue its rapid expansion in the coming 

years inspired by the large number of beneficial effects of 

[1] B. L. Hayes, ‘‘Microwave Synthesis: Chemistry at the Speed of 

Light’’, CEM Publishing, Matthews 2002. 

[2] C. O. Kappe, Angew. Chem. Int. Ed. 2004, 43, 6250. 

[3] J. P. Tierney, P. Lidstrom, ‘‘Microwave Assisted Organic 

Chemistry’’, Taylor & Francis Group, Abingdon 2004. 

[4] C. O. Kappe, A. Stadler, ‘‘Microwaves in Organic and Medicinal 

Chemistry’’, Wiley VCH, Weinheim 2005. 

[5] C. Gabriel, S. Gabriel, E. H. Grant, B. S. J. Halstead, 

D. M. P. Mingos, Chem. Soc. Rev. 1998, 27, 213. 

[6] A. d. l. Hoz, A. Diaz-Ortiz, A. Moreno, Chem. Soc. Rev. 2005,34, 

164. 

[7] F. Wiesbrock, R. Hoogenboom, U. S. Schubert, Macromol. 

Rapid Commun. 2004, 25, 1739. 

[8] Results of a search for ‘‘Microwave and Polymerization’’ in 

the SciFinder database on October 23, 2006. 

[9] J. Pielichowski, E. Dziki, J. Polaczek, Polym. J. Chem. Technol. 

2003, 5, 3. 

[10] K. Faghihi, M. Hagibeygi, Eur. Polym. J. 2003, 39, 2307. 

[11] A. A. Caouthar, A. Loupy, M. Bortolussi, J.-C. Blais, 

L. Dubreucq, A. Meddour, J. Polym. Sci., Part A: Polym. Chem. 

2005, 43, 6480. 

[12] N. Li, J. Lu, S. Yao, Macromol. Chem. Phys. 2005, 206, 559. 

[13] H. Yeganeh, B. Tamami, I. Ghazi, Eur. Polym. J. 2004,40, 2059. 

[14] K. Faghihi, Chin. J. Polym. Sci. 2004, 22, 343. 

[15] K. Faghihi, K. Zamani, A. Mirsamie, S. Mallakpour, Polym. Int. 

2004, 53, 1226. 

[16] K. Faghihi, A. Mirsamie, Chin. J. Polym. Sci. 2005, 23, 63. 

[17] K. Faghihi, M. Hajibeygi, J. Appl. Polym. Sci. 2004, 92, 3447. 

[18] S. Mallakpour, E. Kowsari, J. Appl. Polym. Sci. 2005, 96, 435. 

[19] S. Mallakpour, E. Kowsari, Polym. Eng. Sci. 2006, 46, 558. 

[20] S. Mallakpour, E. Kowsari, Iran. Polym. J. 2005, 14, 799. 

[21] S. Mallakpour, M. H. Shahmohammadi, Iran. Polym. J. 2005, 

14, 473. 

[22] S. Mallakpour, E. Kowsari, Polym. Adv. Technol. 2005, 16, 

466. 


384 



DOI: 10.1002/marc.200600749


[24] K. Faghihi, K. Zamani, J. Appl. Polym. Sci. 2006, 101, 4263. 

[25] K. Faghihi, M. Hagibeygi, Macromol. Res. 2005, 13, 14. 

[26] K. Faghihi, N. Foroughifar, S. Mallakpour, Iran. Polym. J. 

2004, 13, 93. 

[27] S. Mallakpour, E. Kowsari, J. Appl. Polym. Sci. 2004, 93, 2218. 

[28] S. Mallakpour, E. Kowsari, Polym. Adv. Technol. 2005,16, 732. 


[30] S. Mallakpour, F. Rafiemanzelat, Eur. Polym. J. 2005,41, 2945. 

[31] K. Faghihi, Macromol. Res. 2004, 12, 258. 

[32] S. Mallakpour, F. Rafiemanzelat, Iran. Polym. J. 2005, 14, 

909. 

[33] S. Mallakpour, F. Rafiemanzelat, J. Appl. Polym. Sci. 2005, 98, 

1781. 

[34] V. Percec, C. Pugh, E. Cramer, S. Okita, R. Weiss, Makromol. 

Chem., Macromol. Symp. 1992, 54/55, 113. 

[35] W. Heitz, Mater. Sci. Technol. 1999, 20, 37. 

[36] M. Leclerc, J. Polym. Sci., Part A: Polym. Chem. 2001,39, 2867. 

[37] A. Khan, S. Hecht, Chem. Commun. 2004, 300. 

[38] S. Tierney, M. Heeney, I. McCulloch, Synth. Met. 2005, 148, 

195. 

[39] B. S. Nehls, S. Fueldner, E. Preis, T. Farrell, U. Scherf, Macromolecules 

2005, 38, 687. 

[40] C. Koopmans, M. Iannelli, P. Kerep, M. Klink, S. Schmitz, 

S. Sinnwell, H. Ritter, Tetrahedron 2006, 62, 4709. 

[41] T. Yamamoto, Y. Fujiwara, H. Fukumoto, Y. Nakamura, 

S.-Y. Koshihara, T. Ishikawa, Polymer 2003, 44, 4487. 

[42] M. Beinhoff, L. D. Bozano, J. C. Scott, K. R. Carter, Macromolecules 

2005, 38, 4147. 

[43] F. Galbrecht, X. H. Yang, B. S. Nehls, D. Neher, T. Farrell, 

U. Scherf, Chem. Commun. 2005, 2378. 

[44] S. Velmathi, R. Nagahata, J.-I. Sugiyama, K. Takeuchi, Macromol. 

Rapid Commun. 2005, 26, 1163. 

[45] S. Chatti, M. Bortolussi, D. Bogdal, J. C. Blais, A. Loupy, Eur. 

Polym. J. 2006, 42, 410. 

[46] O. Cakmak, M. Bastuerkmen, D. Kisakuerek, Polymer 2004, 

45, 5451. 

[47] E. Bezdushna, H. Ritter, K. Troev, Macromol. Rapid Commun. 

2005, 26, 471. 

[48] A. Banihashemi, H. Hazarkhani, A. Abdolmaleki, J. Polym. 

Sci., Part A: Polym. Chem. 2004, 42, 2106. 

[49] Z. J. Yu, L. J. Liu, Eur. Polym. J. 2004, 40, 2213. 

[50] P. Kerep, H. Ritter, Macromol. Rapid Commun. 2006, 27, 

707. 

[51] D. Barbier-Baudry, L. Brachais, A. Cretu, R. Gattin, A. Loupy, 

D. Stuerga, Environ. Chem. Lett. 2003, 1, 19. 

[52] S. Sinnwell, A. M. Schmidt, H. Ritter, J. Macromol. Sci., Part A: 

Pure Appl. Chem. 2006, 43, 469. 

[53] L. Liu, Y. Li, Y.-e. Fang, L. Chen, Carbohydr. Polym. 2005, 60, 

351. 

[54] Z. Yu, L. Liu, J. Biomater. Sci., Polym. Ed. 2005, 16, 957. 

[55] J. Shu, P. Wang, T. Zheng, B. Zhao, J. Appl. Polym. Sci. 2006, 

100, 2244. 

[56] C. Zhang, L. Liao, L. Liu, Macromol. Rapid Commun. 2004, 25, 

1402. 

[57] Y. Li, X.-L. Wang, K.-K. Yang, Y.-Z. Wang, Polym. Bull. 2006,57, 

873. 

[58] H.-H. Jin, S.-H. Min, K. H. Hwang, I.-M. Park, H.-C. Park, 

S.-Y. Yoon, Mater. Sci. Forum 2006, 510–511, 758. 

[59] R. Nagahata, J.-I. Sugiyama, S. Velmathi, Y. Nakao, M. Goto, 

K. Takeuchi, Polym. J. 2004, 36, 483. 

[60] F. Wiesbrock, R. Hoogenboom, C. H. Abeln, U. S. Schubert, 

Macromol. Rapid Commun. 2004, 25, 1895. 

[61] R. Hoogenboom, M. W. M. Fijten, R. M. Paulus, H. M. L. Thijs, 

S. Hoeppener, G. Kickelbick, U. S. Schubert, Polymer 2006,47, 

75. 

[62] F. Wiesbrock, R. Hoogenboom, M. A. M. Leenen, 

M. A. R. Meier, U. S. Schubert, Macromolecules 2005, 38, 

5025. 

[63] R. Hoogenboom, F. Wiesbrock, M. A. M. Leenen, M. A. R. 

Meier, U. S. Schubert, J. Comb. Chem. 2005, 7, 10. 

[64] S. Sinnwell, H. Ritter, Macromol. Rapid Commun. 2005, 26, 

160. 

[65] S. Sinnwell, H. Ritter, Macromol. Rapid Commun. 2006, 27, 

1335. 

[66] R. Hoogenboom, M. A. M. Leenen, F. Wiesbrock, 

U. S. Schubert, Macromol. Rapid Commun. 2005, 26, 1773. 

[67] R. Hoogenboom, R. M. Paulus, Å. Pilotti, U. S. Schubert, 


[68] R. M. Paulus, T. Ermenger, C. R. Becer, R. Hoogenboom, 


[69] C. Guerrero-Sanchez, R. Hoogenboom, U. S. Schubert, Chem. 

Commun. 2006, 3797. 

[70] C. Guerrero-Sanchez, M. Lobert, R. Hoogenboom, 


[71] R. Hoogenboom, M. W. M. Fijten, H. M. L. Thijs, B. M. van 

Lankvelt, U. S. Schubert, Des. Monom. Polym. 2005, 8, 659. 

[72] R. Hoogenboom, H. M. L. Thijs, M. W. M. Fijten, B. M. Van 

Lankvelt, U. S. Schubert, J. Polym. Sci., Part A: Polym. Chem. 

2007, 45, 416. 

[73] F. Wiesbrock, R. Hoogenboom, M. Leenen, S. F. G. M. van 

Nispen, M. van der Loop, C. H. Abeln, A. M. J. van den Berg, 

U. S. Schubert, Macromolecules 2005, 38, 7957. 

[74] R. Hoogenboom, F. Wiesbrock, H. Huang, M. A. M. Leenen, 

H. M. L. Thijs, S. F. G. M. van Nispen, M. van der Loop, 

C.-A. Fustin, A. M. Jonas, J.-F. Gohy, U. S. Schubert, Macromolecules 

2006, 39, 4719. 

[75] R. Hoogenboom, Macromol. Chem. Phys. 2007, 208, 18. 

[76] R. Hoogenboom, U. S. Schubert, Green Chem. 2006, 8, 895. 

[77] H. Huang, R. Hoogenboom, M. A. M. Leenen, P. Guillet, 

A. M. Jonas, U. S. Schubert, J.-F. Gohy, J. Am. Chem. Soc. 

2006, 128, 3784. 

[78] R. Hoogenboom, M. A. M. Leenen, H. Huang, C.-A. Fustin, 

J.-F. Gohy, U. S. Schubert, Colloid Polym. Sci. 2006, 284, 1313. 

[79] M. Iannelli, H. Ritter, Macromol. Chem. Phys. 2005, 206, 349. 

[80] M. Iannelli, V. Alupei, H. Ritter, Tetrahedron 2005, 61, 

1509. 

[81] E. Bezdushna, H. Ritter, Macromol. Rapid Commun. 2005, 26, 

1087. 

[82] P. Eckstein, H. Ritter, Des. Monom. Polym. 2005, 8, 601. 

[83] F. Fischer, R. Tabib, R. Freitag, Eur. Polym. J. 2005, 41, 403. 

[84] F. Fischer, R. Freitag, J. Chem. Educ. 2006, 83, 447. 

[85] C. M. Fellows, Central Eur. J. Chem. 2005, 3, 40. 

[86] H. Stange, M. Ishaque, N. Niessner, M. Pepers, A. Greiner, 


[87] S. Agarwal, M. Becker, F. Tewes, Polym. Int. 2005, 54, 1620. 

[88] J. Lu, J. Wu, L. Wang, S. Yao, J. Appl. Polym. Sci. 2005, 97, 

2072. 

[89] V. Singh, A. Tiwari, D. N. Tripathi, R. Sanghi, J. Appl. Polym. 

Sci. 2004, 92, 1569. 

[90] V. Singh, A. Tiwari, D. N. Tripathi, R. Sanghi, Carbohydr. 

Polym. 2004, 58, 1. 

[91] V. Singh, D. N. Tripathi, A. Tiwari, R. Sanghi, J. Appl. Polym. 

Sci. 2005, 95, 820. 

[92] V. Singh, A. Tiwari, D. N. Tripathi, R. Sanghi, Polymer 2006, 

47, 254. 




[93] V. Singh, D. N. Tripathi, A. Tiwari, R. Sanghi, Carbohydr. 

Polym. 2006, 65, 35. 

[94] K. Prasad, R. Meena, A. K. Siddhanta, J. Appl. Polym. Sci. 2006, 

101, 161. 

[95] T. Zheng, P. Wang, Z. Zhang, B. Zhao, J. Appl. Polym. Sci. 2005, 

95, 264. 

[96] K. Xu, W. D. Zhang, Y. M. Yue, P. X. Wang, J. Appl. Polym. Sci. 

2005, 98, 1050. 

[97] J.-F. Zhu, Y.-J. Zhu, J. Phys. Chem. B 2006, 110, 8593. 

[98] P. Liu, Z. Su, Mater. Chem. Phys. 2005, 94, 412. 

[99] M. Klink, U. Kolb, H. Ritter, e-Polymers 2005, 069. 

[100] M. Aldana-Garcia, J. Palacios, E. Vivaldo-Lima, J. Macromol. 

Sci., Part A: Pure Appl. Chem. 2005, A42, 1207. 

[101] J. Gao, C. Wu, Langmuir 2005, 21, 782. 

[102] T. Ngai, C. Wu, Langmuir 2005, 21, 8520. 

[103] C. Holtze, M. Antonietti, K. Tauer, Macromolecules 2006, 39, 

5720. 

[104] J. O’Mealey, J. Phillips, S. C. Pilcher, J. Undergrad. Chem. Res. 

2006, 5, 89. 

[105] J. Bao, A. Zhang, J. Appl. Polym. Sci. 2004, 93, 2815. 

[106] J. Sierra, J. Palacios, E. Vivaldo-Lima, J. Macromol. Sci., Part A: 

Pure Appl. Chem. 2006, 43, 589. 

[107] C. Yi, Z. Deng, Z. Xu, Colloid Polym. Sci. 2005, 283, 1259. 

[108] Z. W. Deng, X. X. Hu, L. Li, Z. S. Xu, C. F. Yi, J. Appl. Polym. Sci. 

2006, 99, 3514. 

[109] H. Zhao, H. Chen, Z. Li, W. Su, Q. Zhang, Eur. Polym. J. 2006,42, 

2192. 

[110] Z.-S. Xu, Z.-W. Deng, X.-X. Hu, L. Li, C.-F. Yi, J. Polym. Sci., Part 

A: Polym. Chem. 2005, 43, 2368. 

[111] Z. Cheng, X. Zhu, N. Zhou, J. Zhu, Z. Zhang, Radiat. Phys. 

Chem. 2005, 72, 695. 

[112] S. Delfosse, H. Wei, A. Demonceau, A. F. Noels, Polym. Prepr. 

2005, 46, 295. 

[113] H. Zhang, U. S. Schubert, Macromol. Rapid Commun. 2004, 

25, 1225. 

[114] H. Wu, F. Li, Y. Lin, M. Yang, W. Chen, R. Cai, J. Appl. Polym. Sci. 

2006, 99, 828. 

[115] M. Leenen, F. Wiesbrock, R. Hoogenboom, U. S. Schubert, 

e-Polymers 2005, 071. 

[116] J. Li, X. Zhu, J. Zhu, Z. Cheng, Radiat. Phys. Chem. 2006, 75, 

253. 

[117] S. Perrier, F. Vettier, S. I. Brown, Polym. Prepr. 2005, 46, 

291. 

[118] J. Zhu, X. Zhu, Z. Zhang, Z. Cheng, J. Polym. Sci., Part A: Polym. 

Chem. 2006, 44, 6810. 

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