Photocatalyzed HAT-Degradation of Vinyl Polymers: Cleavage of C-C Bond in Backbone Triggered by Radical Activation of C-H Bond in Pendant.

Abstract

In this work, we achieved a triggering degradation of polymers composed of carbon-carbon (C-C) bonded backbone without relying on introduction of labile heteroatom-based bond. The crucial point for the achievement is using vinyl ether (VE) as a comonomer in radical copolymerization of (meth)acrylate for introduction of the carbon-hydrogen (C-H) bonds active for photocatalyzed hydrogen atom transfer (HAT) as triggers in the pendant. Interestingly, methyl methacrylate (MMA)-n-butyl vinyl ether (NBVE) copolymer underwent degradation in acetonitrile in the presence of benzophenone (Ph2CO) under UV irradiation at 80˚C. The degradation did not take place, when any one of UV, Ph2CO, heat, and NBVE unit was removed or HAT-active solvent such as toluene and 1,4-dioxane was used. These control experiments strongly supported the HAT-triggering degradation. Furthermore, the degradation behaviors of the copolymers with other vinyl ethers such as tert-butyl vinyl ether and methyl isopropenyl ether indicated that the C-H bond neighboring to oxygen on the pendant is mainly responsible for the trigger leading to degradation. The HAT-triggering degradation was also demonstrated even with the acrylate-based copolymer.