Properties of thermoplastic polyurethane elastomers containing liquid crystalline chain extender (I) synthesis and properties of hard segments

Abstract

Polyurethanes prepared from 1,6-diisocyanate hexane (HDI) and 2,4-tolylene diisocyanate (2,4-TDI) with liquid crystalline chain extender 4,4′-bis( n-hydroxyalkyloxy)biphenyl ( n-PBP, n = 2, 3, 6) were reported. Characterizations of monomers and polymers were performed by infrared spectroscopy (IR), 1H-NMR, solid-state C 13-NMR, and elemental analysis. The phase transition behaviors of polyurethanes were investigated by Global TSC, DSC, and polarized microscopy (POM). Our results showed that monomers 4,4′-bis(n-hydroxyalkyloxy) biphenyl exhibit smectic type mesophase. It was observed that the longer the spacer length of polyurethanes, the higher the chain mobility, the larger DOD (degree of disorder) value and the lower the relaxation time. Also the phase transition temperature of polyurethanes decreases with increasing spacer length. DSC measurements and texture observations indicated that H2, H3, H6 and T6 exist in both mesophase and crystal phase. Quantitative analysis of temperature dependence hydrogen bonding revealed that hydrogen bonded content ( X b) of the C group for all samples decreased with increasing temperature. For the H series, both X b and ΔH decrease with increasing spacer length of the mesogenic diol.