Interfacial morphology and mechanical hysteresis in S‐B‐S triblock copolymers

Significant aspects of the interfacial phase continuity and mechanical stress‐strain hysteresis in S‐B‐S triblock copolymers, where S is polystyrene and B is polybutadiene, are analyzed in terms of a cavitation model for interfacial debonding. Extension‐recovery data in tensile deformation at temperatures from −120°C to 90°C include the glass temperatures of both the S and B phases. The correlation of rheological response at low deformation ϵ = ΔL/L O ⩽ 0.02, where the interfacial phase is intact, with high deformation response ϵ ⩾ 1.0, where interfacial debonding is substantially complete, isolates the strain‐time‐temperature function B(t,ϵ) which defines the interfacial continuity. Analysis of this function by use of the Halpin‐Polley model for kinetics of micro defect growth isolates an intial cavity nucleation process and subsequent propagation and coalescence of cavities at distinct levels of B(t,ϵ). At temperatures above 20°C the work lost W L due to mechanical hysteresis in stress‐strain response is correlated directly with the interfacial work of adhesion W a between S and B phases of Kraton 101 by means of the model for interfacial morphology.