Tandem Photoinduced Cationic Polymerization and CuAAC
for Macromolecular Synthesis
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Abstract
A novel
synthetic strategy involving sequential photoinduced cationic
and copper-catalyzed azide–alkyne cycloaddition (CuAAC) click
processes for the synthesis of complex macromolecular structures such
as side-chain functional polymers, graft copolymers, and organogels
is described. In the approach, first a set of copolymers possessing
side-chain alkyne or halide functionalities, namely, poly(cyclohexene
oxide-<i>co</i>-glycidyl propargyl ether) (P(CHO-<i>co</i>-GPE)), poly(cyclohexene oxide-<i>co</i>-epichlorohydrin)
(P(CHO-<i>co</i>-ECH)), and poly(tetrahydrofuran-<i>co</i>-epichlorohydrin) (P(THF-<i>co</i>-ECH)), were
synthesized by photoinitiated free-radical-promoted cationic copolymerization
of the corresponding monomers using phenylbis(2,4,6-trimethylbenzoyl)phosphine
oxide (BAPO) and diphenyl iodonium hexafluorophosphate (Ph<sub>2</sub>I<sup>+</sup>PF<sub>6</sub><sup>–</sup>) as free radical photoinitiator
and oxidant, respectively. While P(CHO-<i>co</i>-GPE) readily
contained clickable alkyne side-chains, the halide groups of P(THF-<i>co</i>-ECH) were converted
to azide groups by conventional azidation procedure using NaN<sub>3</sub> in DMF. Model side-chain functionalization, grafting onto,
and organogel formation were demonstrated by using P(CHO-<i>co</i>-GPE) and azidated P(THF-<i>co</i>-ECH) via photoinduced
CuAAC reactions. The intermediate polymers formed in various stages
and final polymers were characterized by spectral analysis and gel
permeation chromatography
