Tandem Photoinduced Cationic Polymerization and CuAAC for Macromolecular Synthesis

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-co-glycidyl propargyl ether) (P(CHO-co-GPE)), poly(cyclohexene oxide-co-epichlorohydrin) (P(CHO-co-ECH)), and poly(tetrahydrofuran-co-epichlorohydrin) (P(THF-co-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 (Ph₂I⁺PF₆^-) as free radical photoinitiator and oxidant, respectively. While P(CHO-co-GPE) readily contained clickable alkyne side-chains, the halide groups of P(THF-co-ECH) were converted to azide groups by conventional azidation procedure using NaN₃ in DMF. Model side-chain functionalization, grafting onto, and organogel formation were demonstrated by using P(CHO-co-GPE) and azidated P(THF-co-ECH) via photoinduced CuAAC reactions. The intermediate polymers formed in various stages and final polymers were characterized by spectral analysis and gel permeation chromatography.