Effect of the symmetry of polyether glycols on structure-morphology-property behavior of polyurethane elastomers

The macroscopic properties of polymers could be significantly affected by subtle structural changes in the building blocks, either in a beneficial or detrimental manner. Therefore, it is of essential importance to investigate the structure−property relationships of polymeric materials and provide guiding principles for realizing the optimal thermal, mechanical, and optoelectrical characteristics. Polyurethane (PU) is a kind of widely applied functional polymers with alternating soft and hard segments. The structure-morphology-property behavior of PU is dictated by both segments. Herein, PU elastomers (PUEs) are synthesized with identical hard segment and four kinds of soft segments (polyether diols) with similar chain length but different chain symmetry. The chosen polyether diols either have symmetrical and linear structure like poly(trimethylene ether) glycol (PO3G) and poly(tetramethylene ether) glycol (PTMG), or have asymmetrical chain structure with side methyl groups like poly(propylene glycol) (PPG), and 3-methyltetrahydrofuran/tetrahydrofuran copolyether glycol (3MCPG). The effects of structural symmetry of polyether diols on the structure, morphology, and mechanical properties of the as-prepared PUEs are investigated. The results reveal that the PO3G based PUE exhibits the highest value of hydrogen bonding (74.7%) and the highest degree of microphase separation among four PUE samples, along with the highest Young's modulus (42.7 MPa), tear strength (112.8 kN/m), and the best elastic resiliency capability, thanks to the high structural regularity of the PO3G chains. On the contrary, PPG based PUE typically have the deteriorated thermal and mechanical performance due to the interfered microscopic packing. This work highlights how the small structural changes of building blocks in PU would manipulate its macroscopic feature and provide an additional structural handle for designing advanced PU materials.