Propene based thermoplastic elastomers by early and late transition metal catalysis

Thermoplastic elastomers combine rubber elastic behavior with advantages of thermoplastic materials. Two homogeneously dispersed phases, a crystalline hard phase and a soft elastomeric phase, are responsible for the thermoplastic, elastomeric properties. This review focuses on propene based thermoplastic elastomers, where both phases consist of a single monomer (propene) or a defined monomer combination (propene/carbon monoxide), which are polymerized by homogeneous transition metal catalysis of a single polymerization step. Certain metallocene catalysts are capable of producing homopolypropenes with elastomeric properties. These catalysts allow the control over the polymer microstructure by adjusting external polymerization conditions like temperature or monomer concentration. Improvements of the catalysts' polymerization performance were achieved by modification of the ligand framework. Flexible to elastomeric propene/CO copolymers can be prepared by controlling the polymerization conditions of the palladium catalyzed copolymerization reaction. Incorporation of the polar CO functionality in the polymer backbone leads to a polymer with distinct differences in the material properties, compered to homopolypropenes produced by metallocenes catalysis. For both types of the catalysis/polymers a short historical overview as well as detailed information on the catalytic cycle will be given. The nature and the origin of the network formation are described in both cases. (C) 2002 Elsevier Science Ltd. All rights reserved.