Comprehensive studies of continuous flow reversible addition–fragmentation chain transfer copolymerization and its application for photoimaging materials

Abstract

We performed thorough studies of reversible addition–fragmentation chain transfer (RAFT) copolymerization of industrially relevant functional monomers utilizable for chemically amplified resist systems using an industry-friendly solvent, propylene glycol monomethyl ether, in a continuous flow to gain deeper insights into its kinetics, reactivity, and applicability. Kinetic examinations reveals that the RAFT copolymerization in flow mode exhibits typical pseudo-first-order kinetics with a large increase in the apparent propagation rate constant up to approximately 10 times that of a conventional batch process. The products obtained at the same residence time exhibit outstanding homogeneity in molecular weight, dispersity, and composition. Furthermore, flow chemistry allows easy access to the reactivity ratio of eight different monomer pairs, which is validated by the comparison of the theoretically estimated compositions from the reactivity ratio values with the empirically determined compositions in a full conversion range. The applicability of flow copolymerization toward practical photolithography is confirmed by photolithographic positive tone pattern formation in a chemically amplified resist formulation including the flow-derived copolymer. Our comprehensive exploration provides fundamental insights into the nature of continuous flow RAFT copolymerization in terms of reactivity and kinetics, which further enables the simultaneous achievement of target complex copolymers with precise, uniform, and homogeneous control of structural and compositional parameters on a large scale, maximizing its potential capability to address the challenges in pioneering technologies such as photolithography toward the development of polymers for the patterns with single-nanometer digit dimensions.