Computer simulation of the structure and elasticity of polyurethane networks: 2. Polyoxypropylene triols and 4,4′-diphenylmethane diisocyanate

Abstract

Polyoxypropylene triol-based urethane networks have been simulated with a computer. Simulations show that cyclic molecules are present in substantial amounts in the sol fraction when the stoichiometric ratio r s ∼ 1.0. Simulations also show that the fractions of loops are much higher than those obtained from modified cascade theory. The population of loops is dependent on molecular weight, dilution and stoichiometric ratio. The proportion of dangling ends is independent of molecular weight and dilution, but depends upon r s. It is found that, for r s ∼ 0.8–1.0, the simulations underestimate moduli, but they give very good agreement either for the affine model or for the phantom model when r s is below 0.8. Reasons for the discrepancy are given in terms of segmentation effects known to occur with the 4,4′-diphenylmethane diisocyanate used in the experimental work.