Study of particle growth by seeded emulsion polymerization ...

Colloids and Surfaces 

A: Physicochemical and Engineering Aspects 201 (2002) 131–142 

www.elsevier.com/locate/colsurfa 

Study of particle growth by seeded emulsion polymerization 

accompanied by electrostatic coagulation 

Fuminori Ito, Guanghui Ma, Masatoshi Nagai, Shinzo Omi * 

Graduate School of Bio-Applications and Systems Engineering, Tokyo Uniersity of Agriculture and Technology, 

2-24-16 Nakamachi, Koganei, Tokyo 184-8588, Japan 

Received 5 January 2001; accepted 25 July 2001 

Abstract 

A seeded emulsion polymerization was conducted in order to prepare an emulsion composed of large-sized 

particles, which was carried out in parallel with the controlled coagulation process induced by the formation of 

secondary polymers having an opposite charge to the surface charge of the seed particles. As the first part of this 

study, effects of agitation rate during the seed polymerization, size of the seed polymer particles and controlled pH 

of the reaction mixture were investigated. The lower agitation rates yielded a stable latex composed of large-sized 

grown particles, whereas the higher, intensive agitation rates induced undesirable coagulation between the larger 

particles, forcing them to separate from the latex. It was revealed that the smaller seed particles performed a 

well-controlled coagulation and yielded a larger particle size. The lower pH (8.0–8.5) reduced the solid content in the 

latex due to an uncontrollable formation of coagulums. At the higher pH (9.5–10.0), the controlled coagulation was 

not as effective as those obtained at the intermediate pH (8.75–9.0). © 2002 Elsevier Science B.V. All rights reserved. 

Keywords: Seeded emulsion polymerization; Controlled coagulation; Electrostatic attraction; Styrene; Dimethylaminoethyl 

methacrylate 

1. Introduction 

Emulsion, suspension and non-aqueous phase 

dispersion (NAD) polymerizations are three major 

means to obtain polymer colloid dispersions 

ranging from submicron to millimeter scale [1]. 

Suspension polymerization can cover a wide size 

range from tens of micrometers to 1 mm and has 

a versatility of applications in industry; one for 

sophisticated products such as packing beads for 

* Corresponding author. Tel./fax: +81-42-388-7065. 

E-mail address: omi@cc.tuat.ac.jp (S. Omi). 

liquid chromatography, xerographic toners and 

ion exchange resins, and the other for commodity 

materials such as expandable beads of polystyrene 

[2–4]. Broad size distribution may be a major 

disadvantage of the suspension polymerization. 

NAD polymerization can provide quite uniform 

particles from submicron to somewhere around 10 

m in diameter and are originally developed for 

production of solvent-born paints [5]. The use of 

organic solvents and their recovery may need 

extra care to prevent the release of environmentally 

hazardous chemicals [2]. Microsuspension 

polymerization, the size range covering from sev- 

0927-7757/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. 

PII: S0927-7757(01)01030-5

132 

F. Ito et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 201 (2002) 131–142 

eral submicrons to micrometers, has been developed 

for the commercial production of poly (vinyl 

chloride) (PVC) paste resin. A wide size distribution, 

even a bimodal distribution, is required for 

this purpose, and the microsuspension polymerization 

has been rather limited to the PVC 

process. 

Conventional emulsion and mini-emulsion 

polymerizations have been widely used for the 

commercial production of various lattices and 

extensively investigated from the academic point 

of view as well [1,6]. Their size ranges in most 

cases between several 10 nm and submicrons with 

an exception being the soap-free emulsion polymerization 

from which nearly 1 m uniform 

spheres can be obtained, in particular, in the case 

of the hydrophobic monomers. 

From the survey of the size ranges of polymer 

particles covered by each heterogeneous polymerization 

system, one may note that there is no 

commercially feasible route to obtain fairly uniform 

particles ranging from 0.5 to several microns. 

Agreeably, the seeded emulsion 

polymerization technique, in principle, may cover 

this size range, however, it requires a skilled operation 

to be performed by several stages of polymerization 

with carefully adjusted formulations of 

soap, monomers, initiator and other ingredients. 

One could recall two ultimate seeded processes 

[7,8], one is a repeated seeded emulsion polymerizations 

carried out in the non-gravitational field 

by Vanderhoff et al. and the NASA group [7], 

and the other is the two-step swelling technique 

by Ugelstad et al. [8,9]. Both techniques successfully 

achieved extremely uniform polymeric microspheres 

up to 100 m. 

Going back to more realistic procedures, those 

particles with the above size range (0.5 to several 

microns) are required in certain applications. For 

example, Dainippon Ink Co. (Dic) [10] commercialized 

a particular coating emulsion resistant to 

the shear thinning effect. An ionic monomer, 4- 

sulfonicstyrene, sodium salt (NaSS), was added in 

an ordinary formulation for coating emulsion. A 

controlled partial coagulation of growing polymer 

particles took place in the early stage of soap-free 

emulsion polymerization, and the resultant particle 

size distribution (PSD), including the agglomerates 

of several microns, successfully prevented 

the dripping of paints while brushing down vertically. 

The photograph showed grape-like agglomerates, 

two-dimensional rather than spherical 

shape. The present authors were inspired by this 

patent, and tried to establish an efficient route of 

particle growth which could yield particles of the 

above size range. 

The design scheme for particles is illustrated in 

Fig. 1. By employing an anionic initiator, ammonium 

persulfate (APS), and an anionic surfactant, 

sodium lauryl sulfate (SLS), the seed polymer 

particles of poly(methyl methacrylate-co-methyl 

acrylate) (PMMA-MA) were prepared (Fig. 1(a)). 

The seed polymer particles were swollen with a 

comonomer composed of hydrophobic styrene 

and water-soluble, cationic dimethylaminoethyl 

methacrylate (DM). An adequate amount of nonionic 

surfactant, polyoxyethylene nonylphenyl 

ether (PEO23) was added to stabilize the seed 

particles, and then the polymerization was carried 

out with a cationic initiator, 2,2-azobis(2- 

amidinopropane)·2HCl (V-50). Since DM is 

highly water-soluble, a fair amount of DM is 

partitioned in the aqueous phase which somewhat 

promotes the solubility of styrene as well (Fig. 

1(b)). The polymerization took place in the seed 

particles swollen with monomers and also in the 

aqueous phase, leading to the nucleation and 

growth of the cationic secondary particles of 

poly(styrene-co-DM) (PS-DM). Meanwhile, the 

two-way coagulation and growth process progressed 

in parallel, the one induced by the coulombic 

attraction between the cationic secondary 

particles and the anionic seeds, and the other by 

the viscosity of the seed and coagulated particles 

(Fig. 1(c)). The stability of the reaction system 

was readily maintained by the addition of PEO23 

as well as by the adjustment of pH, and fairly 

spherical, grown particles were obtained having 

DM-rich domains on the surface and inside particles 

(Fig. 1(d)) [11]. 

By carefully designing the compositions of the 

seed polymer particles and the secondary 

comonomer, a variety of morphologies can be 

created with this procedure. Encouraged with this 

result, in the present paper, the authors will report 

the effects of the agitation during the seed poly-

F. Ito et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 201 (2002) 131–142 133 

merization, the particle size of seeds, and the pH 

in the reaction medium to the outcome of growth 

process. The detailed observation of the growth 

mechanism will follow in the next paper. 

2. Experimental 

2.1. Materials 

Styrene (ST), methyl acrylate (MA) and methyl 

methacrylate (MMA) (Kishida Chemical Co.) 

were commercial grade, and distilled under reduced 

pressure. These reagents were stored in a 

refrigerator until use. Dimethyl aminoethyl 

methacrylate (DM, Tokyo Chemical Co.) was 

reagent grade and used as received. Ammonium 

persulfate (APS, Wako Pure Chemical Co.) and 

2,2-azobis (2-amidinopropane)·2HCl (V-50,Wako 

Pure Chemical Co.) were used as initiators to 

prepare seed latex P(MMA-co-MA) and to conduct 

the seeded emulsion polymerization, 

respectively. 

Sodium lauryl sulfate of biochemistry grade 

(SLS, Merck) was used as an emulsifier to prepare 

the seed latex P(MMA-co-MA). Polyoxyethylene 

nonylphenylether with 23 units of ethylene oxide 

(PEO23, Kao Co) was used to stabilize the swollen 

seed latex during the polymerization. t-Dodecyl 

mercaptan (TDM, Tokyo Chemical Co.) was 

used as a chain transfer agent to control molecular 

weight. Distilled and deionized (DDI) water 

was used. 

2.2. Polymerization apparatus 

A flat-bottomed glass separator flask with 500 

or 1000 ml capacity was used as a polymerization 

reactor; the 500-ml flask was used for the seeded 

emulsion polymerization and the 1000-ml flask 

was employed in seed latex preparation. A nitrogen 

inlet, a condenser, a thermocouple, and a 

dropping funnel for the initiator solution were 

connected to the top of the flask. A half-moon 

blade-type impeller was also used in this 

apparatus. 

Fig. 1. Schematic diagram of proposed seed polymerization.

134 


2.3. Preparation of PMMA-MA anionic seed 

latex 

One hundred and fifty grams each of MMA 

and MA dissolving 0.5 g of TDM was mixed with 

700 g of DDI water dissolving 2.0 g SLS with a 

magnet stirrer. The mixture was transferred to the 

reactor, and the nitrogen was bubbled through it 

for 1 h. After the temperature was raised to 333 

K, 30 ml of 0.2–0.8 g APS solution (also bubbled 

with the nitrogen stream) was added through the 

dropping funnel in a stream of nitrogen. The 

nitrogen atmosphere in the reactor was maintained 

throughout the polymerization. The polymerization 

was conducted for 3.0 h. 

2.4. Analyses 

Monomer conversion was measured gravimetrically. 

A weighed latex sample was diluted with 

methanol and the precipitated polymer was separated 

by centrifugation. The polymer was washed 

with methanol by repeating the same procedure. 

The washed polymer was dried in a vacuum oven 

at room temperature and weighed. The resulting 

polymer particles were observed by an SEM 

(JSM-5310.JEOL). The latex was diluted 10 000– 

20 000 times with DDI water, and one drop was 

placed on an aluminum film attached on the stub, 

and dried. Then gold was spattered on the surface 

with a film coater (JFC-1200 JEOL) before viewing. 

More than 200 particles size were measured 

to calculate the average diameter of the particles. 

The molecular weight of copolymers soluble in 

tetrahydrofuran (THF) was measured with a GPC 

(H810, Tosoh) which was calibrated using standard 

polystyrene samples. THF was used as an 

eluent solvent. 

The zeta-potentials of the polymer particles 

were measured with a Zeecom apparatus (Microtech 

Nition). The latex was diluted 10 000 times 

with DDI water, and served for measurement. 

2.5. Seeded emulsion polymerization 

The seed latex obtained was dialyzed with cellulose 

membrane (UC 27-32-100 Sankou Co.) for 24 

h under the continuous flow of tap water. Then 

they were soaked in 5 l DDI water overnight. The 

weight ratio of monomer and seed particles (expressed 

as M/P hereafter) was adjusted to 2.0. 

The weight of total reaction mixture was 400 g. 

All the ingredients minus 25 ml of 0.25 g V-50 

solution were homogenized with an Ace Homogenizer 

(HF 93 SMT Co.) at 5000 rpm for 15 min, 

and transferred to the reactor. The particles were 

allowed to absorb the comonomer for 1 h whilst 

the temperature was raised to 333 K. The initiator 

solution was then added in a similar way as in the 

preparation of seed latex. The polymerization was 

conducted for 20 h. 

3. Result and discussion 

3.1. Preparation of anionic seed latex 

The recipe for conventional emulsion polymerization 

and the resulting characteristics of seed 

latex particles are shown in Table 1. Run 1400 

was employed to investigate the effect of agitation 

rate during the seeded polymerization on the controlled 

coagulation and growth of particles, Run 

1401, 1400, 1404, 1402 and 1403 were used for the 

different sized seeds, and Run 1407, for investigating 

the effect of pH. As 30 wt.% of monomer was 

present in the initial reaction mixture, it was 

difficult to control the reaction temperature at the 

particle nucleation stage due to the intensive heat 

of polymerization of MMA-MA, resulting in the 

poor reproducibility of the products (Run 1401, 

1400 and 1402) concerning the values such as the 

average diameter (number of polymer particles), 

CV and -potential. All these properties are regarded 

to play the key roles in the controlled 

coagulation and growth process. In particular, 

nearly the same values of -potential were desired 

to investigate the effect of particle size, however, 

as shown later, a definite dependence on the seed 

particle size was obtained. 

3.2. Effect of agitation rate 

The effect of agitation rate (in other words, 

effect of shear rate) was investigated by employing 

the Run 1400 seed latex, the agitation rates


Table 1 

Characteristics of prepared seed latex for Runs 1400, 1401, 1402, 1403, 1404 and 1407 

Run Emulsifier (SLS) Initiator (APS) Conversion (%) Average CV (%) Number of seed particles Mn (×10 −5 ) -Potential (mV) 

concentration (g) 

concentration (g) 

diameter (m) (×10 −14 dm −3 ) 

1400 2.0 0.8 

98.6 

0.11 

11.1 4.24 2.16 −60.5 

1401 2.0 0.8 92.0 0.08 

22.4 10.7 2.14 −58.4 

1402 2.0 0.8 98.6 

0.16 6.96 1.40 2.12 −73.1 

1403 0.3 0.4 

82.6 0.25 

8.24 0.32 1.01 −47.5 

1404 2.0 0.2 98.8 0.14 

19.4 2.06 1.50 −69.0 

1407 8.0 

0.2 98.7 

0.10 12.5 5.66 1.51 −78.0

136 


Fig. 2. Agitation rate versus average particle size. Effect of 

agitation rate at seeded emulsion polymerization. 

being selected as 180, 240, 350, 420 and 500 rpm. 

Table 2 shows the mutual recipe and some characteristics 

of the polymer particles in the final latex. 

Fig. 2 shows the effect of agitation intensity on 

the average size of the resultant particles and its 

distribution expressed as the coefficient of variation 

(CV, (standard deviation)/(average diame- 

ter)×100). SEM photographs of the final latex 

particles are shown in Fig. 3. 

Interestingly, a sharp drop in the particle size 

and a broadening of its distribution (high CV) 

were observed beyond 350 rpm as a boundary. 

The normal trend of increasing the agitation rate 

during the polymerization revealed acceleration of 

agglomeration between the particles, leading to 

the larger size. In the present polymerization system, 

intensive agitation beyond 350 rpm may 

have enhanced the coagulation between the larger 

particles which had already grown to a considerable 

size due to the other potential coagulative 

factor (coulombic attraction force). These successive 

coagulation processes deteriorated the stability 

of agglomerated particles until they separated 

from the latex, creaming up to the surface, and 

forming a layer of coagulums there. Notice that 

the polymer particles shown in Fig. 3(d,e) are the 

remnants of those which survived the further coagulation. 

Naturally, the sizes of surviving particles 

are small. Fig. 4 shows substantial evidence 

that the solid content in the resultant latex (minus 

separated coagulum layer) decreased dramatically 

at the higher agitation rate. 

Fig. 3. SEM photographs of final latex particles. Agitation rate (rpm) (a) 180; (b) 240; (c) 350; (d) 420; (e) 500.


Table 2 

Recipe and result of seeded emulsion copolymerization. (I) Effect of agitation rate 

Run Agitation rate Average particle size CV (%) -Potential Solid content in the final latex (g per g-lx) Average number of 

(rpm) (m) 

(mV) coagulation 

408 180 

0.60 

15.4 −43.8 

0.234 

69.4 

404 240 0.57 15.2 −48.3 

0.202 68.9 

405 350 0.63 

18.2 −18.4 0.232 

81.0 

407 420 0.23 41.7 −22.1 

0.173 

– 

406 500 

0.29 

39.2 – 0.162 – 

Recipe: DDI water 189 g, seed latex (Run 1400) 131 g (solid content 40 g), PEO23 0.75 g, styrene 72 g, DM 8 g, TDM 0.24 g, initiator (V-50) 0.25 g; Initial pH of 

the reaction mixture was 8.75; Polymerization was carried out at 333 K for 20 h.

138 


Fig. 4. Agitation rate versus final solid content in latex. 

On the other hand, the lower agitation rates 

(180, 240 and 350 rpm) provided a favorable 

shear field, maintained the controlled coagulation 

process and yielded a large particle size with a 

narrower size distribution (low CV). Also notice 

that the average particle size slightly increased 

until 350 rpm, implying a positive contribution of 

the shear until this level without disrupting the 

controlled coagulation process. This tendency is 

more distinctively reflected in the average number 

of coagulation shown in Table 2, which is obtained 

from the following relationship provided 

that neither secondary nucleation took place, nor 

separated coagulums were present. 

N sp 

= w s d p 3 

(1) 

N p w p d sp 

N sp and N p denote the number of seed polymer 

particles and the number of final particles, respectively; 

w s and w p denote the solid content in the 

initial and final stage of latex, respectively; d sp and 

d p denote the average diameter of seed polymer 

particles and that of the final coagulated particles, 

respectively. 

The average number of coagulation for the 

grown particles is estimated as 70–80, demonstrating 

that the present seed polymerization provides 

an effective growth process. 

Interestingly, -potential of the resultant latex 

remained negative, and its absolute value de- 

creased as the agitation rate was increased. One 

may speculate that the cationic ST-DM domains 

tend to be engulfed inside the grown particles at 

the low shear process, whilst at the higher shear 

rate, those domains tend to be adsorbed on the 

surface (Fig. 1). In our first paper, we confirmed 

these two domains by the TEM observation of 

microtomed cross-sectional area of the particles 

stained with the vapor of methyl iodide [11,12]. 

One of the disadvantages of this growth process is 

a moderate conversion of monomer in the seeded 

polymerization as predicted from Fig. 4. The 

monomer conversion attained at most 67% (Runs 

408 and 405) because the water soluble radicals 

generated from V-50 may not be able to diffuse 

into the grown particles in the later stage of 

polymerization. Attempts to raise the conversion 

at the later stage are being investigated. 

3.3. Effect of seed particle size 

The effect of particle size in the seed latex on 

the controlled coagulation and growth process 

was investigated using the seed lattices with the 

average size changed from 0.08 to 0.25 m. The 

recipe and some characteristics of the polymer 

particles in the final latex is shown in Table 3. The 

final average particle size is in the range of 0.55– 

0.76 m with the coefficient of variation 10–20%. 

Fig. 5 shows the plot of the particle growth ratio, 

Fig. 5. Growth ratio of particles before and after seeded 

emulsion polymerization against the seed particle size.


Table 3 

Recipe and result of the seeded emulsion copolymerization. (II) Effect of seed particle size 

Run Seed particle size Average particle size CV (%) -Potential Solid content in the final latex Average number of 

(m) (m) 

(mV) (g per g-lx) 

coagulation 

409 0.08 

0.62 

12.4 −42.7 

0.260 

179.0 

408 a 0.11 0.60 15.4 −43.8 

0.234 69.4 

437 0.14 0.56 

16.7 −26.5 0.269 

23.8 

417 0.16 0.55 18.1 −27.6 

0.248 

16.4 

421 0.25 

0.76 

16.4 −21.0 0.192 14.6 

Each reaction mixture was made up so that the solid content was 40 g in 320 g of the seed latex diluted with DDI water. PEO23 1.50 g, styrene 72 g, DM 8 g, TDM 

0.24 g, initiator (V-50) 0.25 g; Initial pH of the reaction mixture was 8.75; Agitation rate was 180 rpm; Polymerization was carried out at 333 K for 20 h. 

a 0.75 g of PEO23 was used.

140 


Table 4 

Recipe and result of the seeded emulsion copolymerization. (III) Effect of pH control 

Run pH Average particle CV (%) -Potential Solid content in the final latex Average number of 

size (m) 

(mV) 

(g per g-lx) 

coagulation 

451 8.0 0.24 

23.4 4.60 0.190 – 

452 8.5 0.31 

7.47 11.6 0.170 – 

408 a 8.75 0.60 15.4 −43.8 

0.234 

69.4 

450 9.0 0.45 22.2 −14.0 0.224 40.5 

449 9.5 0.29 13.5 −34.5 0.251 9.64 

448 10.0 0.28 9.55 −27.6 

0.236 

9.27 

Recipe: DDI water 182 g, seed latex (Run 1407) 138 g (solid content 40 g), PEO23 1.5 g, styrene 72 g, DM 8 g, TDM 0.24 g, initiator 

(V-50) 0.24 g; Agitation rate was 180 rpm; Polymerization was carried out at 333 K for 24 h. 

a Run 1400 was employed as a seed latex (see Table 3). 

d p /d sp , against the seed particle size. The average 

number of coagulated seed particles can be estimated 

from Eq. (1) and is shown in Table 3 which 

may reveal more clearly that the efficient growth 

of polymer particles progressed under the controlled 

coagulation of smaller seed particles (Runs 

409 and 408) compared to the larger seed particles 

(Runs 437, 417 and 421). Run 421 yielded the 

highest average diameter of the resultant particles 

(0.76 m), however, the lowest solid content implied 

poor stability with a low absolute value of 

-potential, leading to the formation of 

coagulums. 

On the other hand, the runs with smaller seed 

particles (Runs 409 and 408) maintained reasonable 

values of -potential. Suppose that the resultant 

grown particle size is in same order as shown 

in Table 3. As the surface area, in other words, 

the surface charge of the larger number of small 

size particles is higher than that of the smaller 

number of large size particles, the former grown 

particle still possesses extra anionic charges after 

the controlled coagulation process with cationic 

polymers or particles during the seed polymerization 

period. This speculation may be justified by 

the higher absolute value of -potentials in Runs 

409 and 408. As a conclusion, it can be said that 

the smaller sized seed particles are preferred for 

conducting the growth process involving the controlled 

coagulation of seed particles. This conclusion 

seems to emphasize an importance of the 

establishment of procedure and probably the 

choice of equipment as well in order to maintain 

the reproducible production of seed lattices. Even 

a small perturbation of the reaction temperature 

during the nucleation period is reflected in fluctuations 

in the average diameter of final particles 

and the number of polymer particles. Semi-batch 

(or semi-continuous) operation will be recommended 

to suppress extensive heat generation in 

the earlier stage of batch polymerization. A majority 

of monomers can be added continuously 

after the particle nucleation settled down. 

3.4. Effect of controlling the pH of the reaction 

mixture 

Up to this section, no attempt was made to 

adjust the pH of the reaction mixture before 

undertaking the seeded polymerization. The measured 

pH values were 8.75. The ionization degree 

of DM and V-50 (pK a -values of primary and 

tertiary amines are reported to be in the range, 

10–11) [13] will affect the -potential of seed 

particles as well. Under these predictions, the pH 

of the reaction mixture was adjusted from 8.0 to 

10.0 by adding HCl or KOH after the swelling 

process of DM and styrene. Run 1407 was employed 

as a seed latex. The average diameter of 

seed particles was 0.10 m. The details of the 

recipe and the results of seeded polymerizations 

are shown in Table 4. Run 408, which was carried 

out using a slightly different size of the seed 

particles (0.11 m), is included in the table for 

further discussion. There was a marked change in 

the results as the pH shifted from 8.5 to 9.0. At


the lower pH (8.0 and 8.5), the final solid content 

decreased due to the formation of coagulums just 

as we observed in the experiments employing a 

higher agitation rate. Also, the positive and low 

values of -potential implied that quite a few 

secondary particles were nucleated because of the 

enhanced ionization of DM in the aqueous phase. 

An increase in charged DM will favor its partition 

in the aqueous phase, and stabilize the oligomeric 

chains nucleated in the aqueous phase, allowing 

them to grow independently as secondary particles. 

Unless secondary particles are suppressed, no 

stable growth process may be accomplished even 

though the amount of nonionic surfactant is 

increased. 

On the other hand, at the higher pH (9.5 and 

10.0), only a moderate coagulation proceeded, as 

the ionization of DM was suppressed, reducing 

the electrostatic attraction between the oppositely 

charged particles. The secondary nucleation was 

less enhanced as indicated from the lower values 

of CV. (Note that the lowest CV for Run 452 was 

obtained from the remaining small-sized particles 

after a majority of grown particles uncontrollably 

coagulated.) Definitely, an optimal pH range 

(8.75–9.0) existed where a moderate ionization of 

DM allowed a controllable coagulation process to 

progress, yielding effectively grown particles with 

a reasonably narrow size distribution. 

3.5. Brief outline of coagulation mechanism 

A series of experiments are now in progress in 

which the growth of polymer particle is closely 

observed by SEM photographs of the lattices 

withdrawn at certain time intervals. Although the 

investigations are by no means complete, it is 

implied that substantial coagulation of seed particles 

had already started during the swelling period 

of comonomer into the polymer particles before 

the polymerization. Further growth of polymer 

particles followed and continued until approximately 

50% monomer conversion, thereafter the 

growth levelled off. No more aggressive coagulation 

took place. The amount of PEO23 affected 

the initial coagulation and further growth as well, 

excess addition of PEO23 induced the secondary 

nucleation and poor growth, whereas deficiency 

resulted in an excessive coagulation and poor 

monomer conversion. Investigation of other factors 

and detailed analyses will be submitted later. 

4. Conclusion 

Anion-charged seed particles, poly (MMA-co- 

MA), were prepared using anionic SLS and initiator 

APS, and seeded emulsion copolymerization 

was conducted with a comonomer DM and initiator 

V-50 having counter-ions (cationic) against 

the seed particles, in order to obtain large-sized 

composite particles. The effects of agitation rate, 

seed particle size and controlled pH in the reaction 

mixture were examined. Increasing the agitation 

rate, such as to 420 and 500 rpm, reduced the 

solid content in the lattices due to an uncontrollable 

coagulation between the grown particles 

which resulted in the separation of coagulums. 

The remaining particle size was small and the size 

distribution became broader. Moderate agitation, 

up to 350 rpm, favored the controlled coagulation 

of the seed particles in parallel with the growth, 

leading to the large-sized particles with a reasonably 

narrow size distribution. Smaller size seed 

particles promoted controlled particle growth, 

yielding a larger particle growth ratio, d p /d sp .Reproducibility 

of the anionic particle size is thereby 

essential. The lower pH (8.0–8.5) reduced the 

solid content in the latex because of the formation 

of large amounts of coagulums just as we observed 

at the high agitation rate. At the higher pH 

(9.5–10.0), the controlled coagulation was not so 

effective due to the suppression of cationic ions. 

Consequently, the intermediate pH (8.75–9.0), 

with an adequate balance between the counter 

ions, yielded the large-sized grown particles with a 

narrow size distribution. In the next article, the 

detailed growth and controlled coagulation behavior 

of the seed particles will be reported. 

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