Study on the photopolymerization mechanism of allyl monomers: A photo-driven radical-mediated [3+2] cyclopolymerization mechanism to reduce degradation chain transfer

A novel mechanism for the photopolymerization of multi-functional allyl monomers, namely, photodriven radical-mediated [3 + 2] cyclopolymerization (PRMC), was proposed based on the results of theoretical calculations and experimental measurements. The E-a of the transition state (TS) is calculated using density functional theory to be under 25 kcal/mol. The driving forces of the product are close to -6 kcal/mol, indicating that PRMC can proceed spontaneously. NMR chemical shifts indicate that the cyclization reaction and traditional free radical addition reaction occur at the same time. The photopolymerization kinetics of allyl monomers and the initial radical structure of PRMC were obtained using real-time infrared spectroscopy and electron spin resonance spectroscopy respectively. The results of thermogravimetry and gel permeation chromatography show that high molecular weight polymers are obtained by photopolymerization, in contrast to the miniscule yield obtained by thermal polymerization. These observations show that PRMC can activate the polymerization of inert monomers and reduce the hindrance from degradation chain transfer at a low temperature.