The role of the soft phase in the hardening effect and the rate dependence of the ultimate physico-mechanical properties of urethane-containing segmented elastomers

Segmented urethane elastomers (SUE) with polytetramethylene oxide soft segments, toluene diisocyanate (TDI)/methylene-bis-o-chloroaniline (MOCA) hard segments, TDI/ MOCA + TDI/butanediol (BD) and TDI/MOCA + isophorone diisocyanate/MOCA mixed segments were investigated. A microphase separation in SUE was adjusted by the variation in the composition of the hard segments or preparation conditions. It was shown that non-linear relationships of SUE’s thermo-mechanical, thermal and mechanical properties on the composition of hard segments, including an extremal one, were typical. Basic dependence types of SUE strength on the stretching rates (direct, reciprocal, extremal) were determined at various stages of the elastomer structure evolution. A significant increase in the SUE strength was found at a low degree of microphase separation. A strong effect of interaction in the soft phase on the physicochemical properties of block copolymers was shown. An improvement of the miscibility between hard and soft phases and a loose structure of the hard phase promote a stabilisation of the strength value in a wide range of the stretching rates. The effect of the strength increase equals to 30–50 %.