Clickable initiators, monomers and polymers in controlled radical ...

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Table 2
Azide-containing initiators for ATRP (poC ¼ postclick, prC ¼ preclick, simult ¼ simultaneous)
Entry Structure Click CRP Monomer Strategy Ref
11 CuAAC ATRP DMAEMA, St poC 92,106,107
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Published on 20 September 2010 on http://pubs.rsc.org | doi:10.1039/C0PY00168F
12
CuAAC ATRP MMA,
DEAEMA,
HEMA,
KSPMA,
HMA,
NIPAM,
DMAEMA,
DEAM, St
poC, simult 68,82,94,109–112
13 CuAAC ATRP NIPAM poC 113
14 CuAAC ATRP NIPAM poC 110
15 CuAAC ATRP St, nBMA poC, prC 114
16 CuAAC ATRP DEGMA poC 104
control, but on the accessibility of an alkyne-functionalized one.
Practically, a-bromoisobutyryl bromide is commercial available
and is mostly functionalized via esterificiation reaction with
propargyl alcohol.
The most widely employed catalytic system is CuBr and
PMDETA again regardless of the initiator or monomer type.
Besides, other catalytic systems, e.g. CuCl/tris(2-(dimethylamino)-ethyl)amine
(Me 6 TREN) for the polymerization of
NIPAM 91,94 or 1,1,4,7,10,10-hexamethyltriethylenetetramine
(HMTETA), 44 could provide better control over the polymerizations.
The catalytic activity of the metal complex and, hence,
the ability to control the polymerization can be correlated to the
ability to stabilize the Cu(II) oxidation state, thus forming
a reducing Cu(I) complex. 93 The polymerization can proceed
relatively fast even at low temperatures when a catalyst with
a high activity is used. 6 PMDETA is a good ligand for Cu(I) with
moderate activity between the less active bpy (two magnitudes
lower in activation rate) and the more active Me 6 TREN (two
magnitudes higher in activation rate) and, therefore, can be used
for a wide range of monomers. 93
Besides the attachment of propargyl alcohol, the alkyne
moiety can also be incorporated onto an ATRP initiator by the
reaction of propargyl amine with a-haloisobutyryl halides. An
example is shown in Entry 3. 95 Hereby, a combination of the preand
the postclick approach was utilized. The initiator was clicked
prior to the polymerization with azide-functionalized dansyl as
a fluorescent label. By using this compound as initiator in ATRP
different random copolymers of alkyne- or azide-functionalized
acrylamides were obtained: Poly(NIPAM-r-propargylacrylamide)
(M n ¼ 20 000 g mol 1 ,PDI¼ 1.3) and poly[NIPAM-r-(3-azidopropylacrylamide)]
(M n ¼ 10 000 g mol 1 , PDI ¼ 1.2). The
pendant clickable polymers were attached onto an azide-functionalized
silica particle in an elegant layer-by-layer click approach
to yield thermoresponsive microcapsules after removal of the silica
template. 95
In Entry 4 an initiator is shown where the alkyne is linked to
the mediating bromide via an o-nitrobenzyl ester as a photocleavable
group. 96 The initiator was used in a one-pot click-CRP
reaction for the polymerization of either St, tBA or MMA in the
presence of azide-functionalized PEO or PS to prepare photocleavable
block copolymers as clicked structures with the
labile group between the polymer blocks: PEO-b-PS (M n ¼
38 000 g mol 1 , PDI ¼ 1.2), PEO-b-PtBA (M n ¼ 63 000 g mol 1 ,
PDI ¼ 1.2), PS-b-PMMA (M n ¼ 38 000 g mol 1 , PDI ¼ 1.2–1.3).
This journal is ª The Royal Society of Chemistry 2010 Polym. Chem., 2010, 1, 1560–1598 | 1567