Viscoelastic Characterization of an Order−Order Transition in a Mixture of Di- and Triblock Copolymers

Abstract

The phase behavior and linear viscoelasticity of a mixture of a matched diblock and triblock copolymer of styrene and ethylene−butene-1 are reported. The mixture undergoes reversible thermotropic transitions from a cylindrically ordered state at low temperatures to a spherically ordered state at intermediate temperatures to a disordered state at high temperatures. The morphological assignments were based on TEM and SANS measurements, which also revealed a decrease in the domain size in the spherically ordered state as compared to the cylindrically ordered state. The kinetics of the order−order transition are extremely slow, with the sample exhibiting rheological characteristics similar to a disordered material immediately after heating from the cylindrical to the spherical state. The transition exhibits a long induction period wherein the sample continues to behave like a disordered material followed by a rapid increase in the storage modulus and a final plateau value. The kinetics and rheological charact...