Thermodynamics and mechanisms of the deformation of thermoelastoplastic block copolymers

Abstract

Thermodynamic aspects and mechanisms of the deformation of thermoelastoplastic block copolymers of the styrene-diene, segmented polyurethane and polyester types are discussed. Deformation calorimetry was used to study energy and entropy effects resulting from the deformation and small angle X-ray scattering method was used to obtain information concerning structural changes during deformation. The largestrain tensile deformation of thermoelastoplastics which possess domain structure leads to a “plasticrubber” transition (stress softening effect), which under appropriate time and temperature conditions is reversible. A comparative thermodynamic analysis of the stress softening in block copolymers and filled rubbers as carried out and results dealing with recovering kinetics of initial domain morphology in stress-softened block copolymers are discussed. Particular attention is paid to the structural changes and thermodynamics of deformation of “single crystal” morphology, which can arise in diene-styrene block copolymers under appropriate thermo-mechanical treatment. The role of the chemical nature of soft and hard blocks as well as the morphology and size of hard blocks in thermodynamics and mechanisms of the deformation is analyzed. The problem of the limited extensibility of soft block polymer chains at high deformations is also discussed.