Structure-Property Relations in Amorphous and Crystallizable ABA Triblock Copolymers

Abstract

Abstract The properties of the thermoplastic elastomers derived from ABA triblock copolymers depend largely on the nature of the A blocks, which form rigid, thermoplastic domains holding the elastic network together. These domains may be either amorphous or crystalline in nature, the former resulting from an inherent incompatibility between the A and B blocks, while the latter form by normal crystallization processes. It can be demonstrated convincingly that the formation of the amorphous (glassy) domains is enhanced by a higher degree of incompatibility between the A and B blocks and that the strength of the material depends on the degree of phase separation and on the integrity of the amorphous domains. However, the viscosity increases with increasing incompatibility between the two phases, presumably because the two-phase morphology persists even in the melt. On the other hand, the presence of crystallizable A blocks, which do not phase separate in the melt, leads to good flow properties. However, the strength of the material and other mechanical properties are strongly dependent on the molecular weight and crystallization of the A blocks.