Design and Synthesis of Mechano-Responsive Color-Changing Thermoplastic Elastomer Based on Poly(n-Butyl Acrylate)-Spiropyran-Polystyrene Comb-Structured Graft Copolymers

Colorimetric mechanophores like spiropyran (SP) represent an emerging type of interesting signal molecule that can be incorporated into polymers or other materials as a stress transducer. In this work, a new type of spiropyran-containing inimer molecule MA-SP-Br are designed and synthesized, which is incorporated into polybutylacrylate (PBA) chains through reversible addition-fragmentation chain transfer (RAFT) copolymerization with n-butyl acrylate (BA). PBA-SP-Br is then used as a macro-initiator to graft polystyrene (PS) side chains from the PBA backbone through atom transfer radical polymerization (ATRP) of styrene. The resulting comb-structured graft copolymer PBA-SP-PS contains 0.15-0.34% SP and exhibits a characteristic feature of thermoplastic elastomers. Under uniaxial stretch, the materials possess an excellent mechano-responsivity and change color at strains as low as about 14%.