One-pot synthesis of core-crosslinked star polymers from poly(methyl methacrylate) with unsaturated chain ends and encapsulation of UV absorbing molecules

Abstract

Core-crosslinked star polymers were synthesized via a “grafting-through” approach. PMMA–P_A block copolymer arms were first prepared via addition–fragmentation chain transfer polymerizations of styrene or acrylate monomers using PMMA–Y, where P_A is polystyrene or polyacrylate and PMMA–Y is poly(methyl methacrylate) with an unsaturated chain end. The PMMA–P_A block copolymers were used as macroinitiators in the polymerizations of a crosslinkable monomer, generating core-crosslinked star polymers. Using PMMA–Y with different molecular weights and functional acrylates, various star polymers were obtained. A “one-pot” synthesis of star polymers was also achieved. The PMMA–P_A macroinitiators were not purified but directly used in the star polymer synthesis, enabling facile synthesis of star polymers, which is industrially preferred. Star polymers with different core sizes and crosslinking densities were also obtained. As a demonstration, a PMMA–PTHFA core-crosslinked star polymer was synthesized and used for encapsulating a UV absorber (UVA) molecule, i.e., (2-(2-hydroxy-5-methylphenyl)benzotriazole) that is commonly used in coating and cosmetic formulations, where PTHFA is poly(tetrahydrofurfuryl acrylate). The UVA-containing star polymer was embedded in a PMMA matrix, and the obtained film showed UV-cut properties. Notably, the obtained film significantly suppressed leaching of the UVA due to the encapsulation of the UVA in the star polymer even at high temperature without impeding the visual appearance (transparency) of the film, which is attractive for possible industrial applications.