Diisocyanate‐linked polymers. II. Mechanical and swelling properties of some polyurethane elastomers

Abstract

AbstractA study was made of the mechanical and equilibrium swelling properties of five series of polyurethane elastomers prepared from polyoxypropylene glycol 2025, dipropylene glycol, trimethylol propane, and either toluene diisocyanate (TDI) or hexamethylene diisocyanate (HDI). The study included the dependence of the properties on the ratio of isocyanate to hydroxyl groups, the concentration of urethane groups, [U], and the triol concentration; the triol concentration and [U] were varied independently in four series of elastomers. It was found that the glass transition temperature for both the TDI elastomers and HDI elastomers increased linearly with [U]. For elastomers having a constant [U], the quasi‐equilibrium elongation at a given value of T − Tg increased linearly with the reciprocal of the number of effective chains per unit volume, but the tensile strength depended only slightly on this quantity. For elastomers having the same triol concentration, the ultimate properties over a wide temperature range were compared at equal values of T − Tg and were found to depend on [U], especially for elastomers having the largest [U]‐values. Several factors that might contribute to this behavior are considered. No major differences between TDI and HDI elastomers were observed except in Tg values. The equilibrium swelling ratios in benzene were used along with equilibrium modulus data to calculate the polymer–solvent interaction parameter χ1. This parameter was found to be independent of crosslinking density, but it increased with [U] and was slightly less for the HDI elastomers than for the TDI elastomers.