Synthesis, properties, and light-induced shape memory effect of multiblock polyesterurethanes containing biodegradable segments and pendant cinnamamide groups

Novel multiblock polyesterurethanes containing crystalline hard and amorphous soft segments and pendant cinnamamide moieties were designed and synthesized via a two-step polyaddition reaction using N,N-bis(2-hydroxyethyl) cinnamamide (BHECA), biodegradable poly(l,l-lactide) (PLLA), and poly(ε-caprolactone) (PCL) diols as raw materials and hexamethylene diisocyanate (HDI) as coupling agent and characterized by (1)H NMR, FTIR, UV, DSC, tensile and photomechanical tests, and so on. The copolymers behaved as typical thermoplastic elastomers and showed satisfactory thermal and mechanical properties. They also exhibited light-induced shape memory effect (LSME) at room temperature on exposure to light stimuli. The pendant cinnamamide groups work as photoresponsive molecular switches and provide the polymer with LSME via reversible 2 + 2] cycloaddition cross-linking. The strain fixity (R(f)) increases with the content of BHECA and the strain recovery (R(r)) increases with the content of PLLA. The R(f) reaches 50% at a BHECA content of 20 wt % and the R(r) reaches >95% at PLLA content of 50 wt %.