Block copolymers from coordinative chain transfer (co)polymerization (CCT(co)P) of olefins and 1,3-dienes and mechanical properties of the resulting thermoplastic elastomers

Abstract

Coordinative chain transfer (co)polymerization (CCT(co)P) is a degenerative chain transfer polymerization mechanism that allows for rapid and efficient chain exchanges between a main group metal/zinc (dormant site) and a transition metal (active site). The ability to generate multiple chains per catalyst molecule during this process leads to significant atom economy, addressing both economic and ecological concerns. In addition to enabling the polymerization of olefins, styrene, and conjugated dienes with high stereospecificity, this technique also provides access to highly reactive polymeryl–metal chain ends. Such extremities can serve as initiation sites for other polymerization techniques, either directly or after an exchange of functional end-group, and may lead in this way to linear block copolymers (BCPs) with a large variety of compositions. Bulk self-assembly of BCPs with adequate architectures enables the ingenious combination of the characteristics of different domains, imparting unique properties that make them suitable for a wide range of applications, such as adhesives, compatibilizers for polymer blends, and thermoplastic elastomers (TPEs). The latter are particularly attractive in the context of a sustainable circular economy: TPEs exhibit at service temperature the elastic properties of crosslinked elastomers, yet they can be molded and extruded like thermoplastics at higher temperatures. This review describes the state-of-the-art synthesis strategies employing CCT(co)P and chain shuttling polymerization (CSP) of olefins and conjugated dienes, either independently or combined with other controlled polymerization techniques, for the synthesis of linear BCPs and multiblock copolymers (MBCs). Some of these polymers constitute a new class of TPEs. In a second section, the control of the morphology of these materials by the architectures of the BCPs and crystallization-driven self-assembly and their thermomechanical properties are discussed.