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-<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 (Ph₂I⁺PF₆^–) 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 NaN₃ 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