Catalyst-free and visible light-induced RAFT alternating polymerization of 1,3-pentadiene isomers and maleic anhydride

Visible light-mediated photoinduced reversible addition-fragmentation chain transfer polymerization (RAFT) copolymerization of 1,3-pentadiene isomers and maleic anhydride (MAH) in the absence of photocatalysts or photoinitiators was realized in tetrahydrofuran (THF) solvent at r.t. under various visible wavelengths. The well-defined alternating copolymers were successfully and efficiently synthesized by directly using O-ethyl-S-benzoic thioanhydride (EBT) as chain transfer agent activated by blue light (460 nm). The conventional thermal-initiated radical copolymerization of 1,3-pentadiene (PD) isomers (except cis-1,3-pentadiene (CP)) and MAH gave both DA cycloaddition products and alternating sequence copolymers. In contrast, the alternating copolymer was the only isolated product in this photoinitiated polymerization system, in which the DA reaction was completely suppressed. Moreover, both trans-1,3-pentadiene (TP) and PD isomers can be copolymerized with MAH to give alternating copolymers with high yields up to 100%, although the photopolymerization rates are in the order: PD > CP > TP. And the copolymerization can be implemented by simply switching the light source ON/OFF. We supposed that the donor–acceptor interaction between the PD and MAH (similar to St (styrene)/MAH system) plays an important role in this novel light-induced RAFT alternating copolymerization behavior.