Aerobic Mechanochemical RAFT Copolymerization of Thioctic Acid with Solid Monomers

Abstract

Controlled radical polymerization in the solid state remains a formidable challenge, primarily due to restricted mass transport and inefficient initiation under such conditions. In this work, we present a robust mechanochemical approach for the solvent-free RAFT copolymerization of lipoic acid (TA) with various solid monomers—including acrylamide-type and styrenic derivatives—under aerobic conditions. By utilizing mechanical-to-chemical energy transduction, we achieved programmed dissociation of amine-coordinated alkylborane initiators, thereby enabling precise control over radical generation within a heterogeneous solid matrix. Under optimized ball-milling conditions at 30 Hz, copolymers of N-isopropylacrylamide (NiPam) and TA were synthesized with high conversions (up to 81.0%) and narrow dispersities (Đ < 1.61). The system also exhibited broad compatibility with styrenic monomers such as vinylbenzoic acid (VBA), yielding well-defined copolymers. Systematic studies revealed that the coordination strength of the initiator and the structural compatibility of the chain transfer agent (CTA) play critical roles in regulating polymerization kinetics. This work establishes a versatile mechanistic framework for the design of dynamic covalent materials via sustainable, solvent-free mechanochemical pathways.