Wavelength-Controlled Synthesis and Degradation of Thermoplastic Elastomers Based on Intrinsically Photoresponsive Phenyl Vinyl Ketone

Abstract

Phenyl vinyl ketone (PVK) is known for its responsiveness to light, with initiation promoted under visible light and degradation of poly(PVK) promoted under UV radiation. Thus, expensive radical sources such as photocatalysts and initiators can be substituted by PVK to promote intrinsic photoinitiation giving well-defined polymers. Homo polymers and block copolymers are readily synthesized by reversible deactivation radical polymerization techniques; this study is the first approach of formation of block polymers through the intrinsically generated radicals of PVK monomers, where the monomer serves as both the chain forming unit and the radical source. In this work, the photoinitiation of PVK was used to generate poly(PVK) homopolymers, which were chain extended with butyl acrylate (BA) and PVK to synthesize poly(PVK-BA-PVK) block polymers. The structural differences of PVK and BA caused microphase separation of the block segments to form thermoplastic elastomers (TPEs) with interesting thermomechanical properties. Due to the differences in glass transition temperature, the poly(PVK) blocks formed the hard segments of the TPE, with the poly(BA) segments forming the soft elastic domains. The TPE materials could achieve a maximum of 1000 kPa stress and 400% strain at break. Irradiation of the TPE materials with 310 nm UV light promoted the degradation of poly(PVK) segments, with associated changes such as a decrease in mechanical strength and elasticity. Molecular dynamics simulations confirmed the trends observed in TPE mechanical properties with the changes in the polymer composition. Further, the simulations provided atomistic insights into the underlined degradation mechanism of PVK in block polymers and its effect on TPE mechanical properties.