Thermomechanical Actuator Based on a Molecular-Spring Polymer with a Long Alkyl Side Chain

A disubstituted acetylene polymer, with a molecular-spring main chain and a long alkyl side chain of the octadecyl group (PDMC₁₈SP), was examined as an active material for a thermomechanical actuator and its thermodynamic and (thermo)mechanical properties were compared to those of other two polymer derivatives [i.e., a polymer without a long alkyl side chain (PTMSP) and a polymer with the same long alkyl side chain with a phenyl ring (PDMC₁₈SDPA)]. Unlike PTMSP, PDMC₁₈SP and PDMC₁₈SDPA produced soft films, which could be considerably elongated by an external tensile force at room temperature. When the external force was removed, PDMC₁₈SP recovered to its original form, while PDMC₁₈SDPA did not. Both polymers showed apparent thermodynamic phase transition. PDMC₁₈SP underwent a much greater change under both strain and stress with temperature compared to PDMC₁₈SDPA. PDMC₁₈SP was used as an active layer to prepare a bilayer-type actuator, which showed apparent mechanical actuation with temperature. The direction of mechanical actuation was easily controlled by shearing the active layer.