Microstructural diagnosis of block copolymer nonlinear mechanical properties. II: Free recovery from large tensile deformations

Abstract

Abstract Three styrene‐butadiene‐styrene (SBS) block copolymers were cast into sheet form, and the resulting microphase‐separated specimens were tested in tensile free recovery. After an initial strain of 300%, specimens were released and their lengths measured for about a week. For one polymer, the recovery curves are presented for seven temperatures in the range −40 to +80°C; other data are given at 22°C. Analysis of the recovery curves, using as the model a series assembly of Kelvin elements, obtains time constants for microstructural repair and explains the temperature dependence in terms of the microstructural interphase and its partial vitrification. Differences among the three polymers can be interpreted by recognition of styrene‐block molecular weights, as well as by the volume fractions of the domain styrene cores and interphases. Additional structural information arises from torsion pendulum experiments over −120 to 100°C for unstretched, stretched (300%), and partially recovered samples.