The Influence of Cross-Linking/Chain Extension Structures on Mechanical Properties of HTPB-Based Polyurethane Elastomers

摘要

Cross-linked and chain-extended polyurethane networks based on hydroxyl-terminated polybutadiene are synthesized by one-step reaction with isophorone diiso-cyanate. The degree of cross-linking is controlled by varying the triol to diol ratio. Chain extension is optimized by appropriate adjustment in the concentration of the diols. The influence of cross-linking agents and chain-extenders on mechanical properties of cured elastomers is investigated. IR-spectroscopy is employed to observe the curing reaction and inter-segment hydrogen bonding. It is demonstrated that the chain-extended polymer is phase segregated at sub-micron level and registers far better mechanical properties as compared to cross-linked polymer. Incorporation of 1,4 butanediol yields the maximum tensile strength, elongation and modulus. The polymer fabricated with trimethy-lolpropane is stronger than that of hexanetriol but exhibits lower stretching properties. However, butanediol exhibits superior mechanical properties in comparison to hexanediol. Equilibrium swelling behaviour follows the expected norm; degree of swelling varies inversely with the cross-link density. The chain-extended polymers show reduced degree of swelling due to plausible association between the hard segment domains formed in the micro-phase segregated structures.