The thermal analyses of polymers. II. Thermomechanical analyses of segmented polyurethane elastomers

Abstract

AbstractThe development of new and more sensitive techniques in thermal analyses aids in a more complete understanding of the contributions of individual components in urethane elastomers regarding their mechanical and thermodynamic behavior. The behavior of various segments of the elastomers reported in this work illustrates a clearer interpretation of reasons for changes in mechanical behavior caused by changes in heat capacity, volume and tensile properties; the gross changes previously reported for polyurethane properties as a function of temperature are also confirmed with a more exact definition of their origin.The sub‐ambient temperature behavior and response of physical measurements near the melting point of the backbone polyol are largely a function of the so‐called “soft block.” The soft block does not contribute to the mechanical properties above the melting point of the polyol unless some urethane segments from the diisocyanate and extender are structured into the soft block, that is, excess diisocyanate and extender are added to build in the “hard” block. The extender and isocyanate influence for both low and high temperature properties is observed by the lack of molecular fit imparted to the backbone polyol as well as some crystallinity in the polymer hard block. The usual Tg transition reported in urethane elastomers corresponds to a first‐order transition in the polyester or polyether backbone.