Well-defined triblock copolymers with a photolabile middle block of poly(phenyl vinyl ketone): facile synthesis, chain-scission mechanism and controllable photocleavability

Abstract

The effective preparation of photoresponsive polymers with precisely controlled location and number of photolabile units in the main chain is essential for their applications. In this study, a series of photocleavable well-defined triblock copolymers with the photocleavable middle block of poly(phenyl vinyl ketone) (PPVK) were readily synthesized by RAFT polymerization. The chain structure and chemical composition of copolymers were characterized by ¹HNMR, FTIR and GPC. The well-controlled molecular weights and low polydispersity (<1.30) demonstrated the excellent controllability and living characteristics of the RAFT process for the polymerization of PVK. Then the photocleavage mechanism and kinetics of PPVK-functionalized copolymers were systematically investigated by tracking, fractionating and quantifying the photolysis products using gradient polymer elution chromatography (GPEC). The results not only confirmed the rapid photocleavability of PPVK-based polymers, but also firstly provided direct evidence for the proposed Norrish type reaction mechanism of the chain scission of PPVK. Moreover, the investigation of the effect of the PPVK chain on the photolysis kinetics demonstrated that the photodegradation rate of PPVK-based polymers can be controlled by adjusting the PPVK chain length in block copolymers. As a preliminary application study, the self-assembled micelles of the obtained PPVK-based amphiphilic polymers under light irradiation were found to undergo photo-triggered rapid disassembly and exhibited photo-controllable emulsifiability. In sum, the incorporation of the highly photolabile PPVK into block copolymers by RAFT polymerization provides a promising strategy for the construction of complex polymeric architectures or nanostructures with controllable photocleavability.