Synthesis, structure and tunable shape memory properties of polytriazoles: dual-trigger temperature and repeatable shape recovery

Thermally induced shape memory polymers (SMPs) are capable of storage, release of energy and shape recovery on the macro-scale. In this work, cross-linked SMPs were synthesized from the monomers tris(4-(1-azido 3-oxy propan-2-ol) phenyl) methane (A(3)), and 1,4-bis(propargyloxy) benzene (B-2), and the propargyl functionalized novolac oligomer (B-3). The A(3)B(2) polymer exhibited a low trigger temperature of 92 degrees C, whereas A(3)B(3) registered a higher trigger temperature of 125 degrees C. The extent of shape recovery of both the SMPs was above 95% and it was repeatable for at least 10 times. On repeating the shape memory cycles, the response time for shape recovery increased, but nearly a complete shape recovery was observed in both polymers. In addition, a polymer with dual trigger temperature (83 and 113 degrees C) was synthesized by click polymerization between the A3 monomer and stoichiometric equivalence of B-2 and B3 monomers. The polytriazole networks bearing monophenyl and oligomer structures in tandem enabled both low and high trigger temperature in a single polymeric structure. The SMP possesses a shape recovery to an extent as high as 98% at both the trigger points even on the 10th shape memory cycle. These polymers exhibited hydrophobicity with a static water contact angle of about 90 degrees and very low water absorption (<0.05 weight%). The enhanced water repellency is attributed to the inter/intra-chain hydrogen bonding characteristics of triazole bridges. The low/high/dual trigger temperature SMPs are thermally stable (T-10% > 230 degrees C) and are suitable for actuator applications.