Phase segregation kinetics in segmented linear polyurethanes: Relations between equilibrium time and chain mobility and between equilibrium degree of segregation and interaction parameter

Abstract

Abstract The kinetics of phase segregation of segmented linear polyurethanes, from a homogeneous single‐phase system into a two‐phase one, have been studied by measuring the heat capacity change at the glass transition of the soft phase. The extent of phase segregation at equilibrium is a linear function of the Flory–Huggins interaction parameter χ. For χ lower than about 3, no segregation can take place. This value, higher than expected theoretically, indicates forced compatibility due to chemical links between soft and hard blocks of the segmented polyurethanes. The time required to attain equilibrium is not a function of thermodynamic parameters but of the chain mobility. A linear relation is proposed between the logarithm of equilibrium time and the viscosity of the pure soft phase.