Effect of multi-armed chain extender on microphase morphology, stress-strain behavior and electromechanical properties of polyurethane elastomers

Abstract

High dielectric constant and low modulus of thermoplastic polyurethane elastomers (PUEs) are required for various applications in actuators, sensors and energy harvestings. In this work, we controlled the microphase separated morphology of PUEs by regulation of the content of hydroxyl-terminated four-armed polycaprolactone (4amPCL) chain extender to achieve J-shaped stress-strain curve with low modulus and high electromechanical properties. Our results showed that the hydrogen bonding between hard segments (HSs) and crystallization of soft segment (SS) are significantly impeded by long-chain branched structure when added lower molar fraction (<20% of chain extenders) of 4amPCL as chain extender, whereas the branched long-chains are embedded in microphase separated hard and soft domains (HD and SD) to form strip shaped interconnected hard domain (HD) rich regions when added higher molar fraction (>20% of chain extenders) of 4amPCL as chain extender. The PUE with 29% of 4amPCL (PU-4amPCL-0.29) showed lower modulus (1.5 MPa), higher tensile strength (17.5 MPa) at 1048% of elongation, and 3.9% of actuation strain at 20 kV/mm, and higher contribution (48.1%) of Maxwell stress on actuation strain at 20 kV/mm. We found that the microphase separation of branched long-chains induced semi-interpenetration polymer network like structure of PUEs played an important role in exhibiting J-shaped stress-strain behavior. Our results can provide new insight on fabrication of high electromechanical performance of dielectric polyurethane elastomers.