Polyurethanes from crystalline prepolymers

Abstract

Cast, segmented urea–urethane polymers, obtained from crystalline urethane prepolymers in a reaction with water, were studied. Hitherto the reaction with water was conducted exclusively with liquid prepolymers. If the polycondensation reaction with water is carried out with the prepolymer solidified as a result of its crystallization, rather than the liquid prepolymer, in the cast products the formation of discontinuities in the polymer bulk as carbon-dioxide gaseous phase is eliminated or significantly suppressed. A similar method of cast polyurethane preparation is not known from available literature. Terathane 2000 oligomer was used for prepolymer preparation. The prepolymer was crystallized at various temperatures, and subsequently chain-extended with water. The crystalline polymers thus produced were examined prior to, and after samples were heated to transform the soft-segment crystalline phase into an amorphous state. The effect of prepolymer crystallization temperature and of the chain-extension conditions on the structure of the polymers obtained was investigated. Relations between certain structural features and mechanical properties of the polymers studied were learned. The polymer structure, hence soft-segment crystalline phase content and the degree of phase separation were found to be affected by the prepolymer crystallization point. An analogous effect of crystallization point on the Terathane 2000 oligomer and its prepolymer structures was observed. The effect of prepolymer crystallization point on the crystallizability of hard segments was also revealed.