Allyl-Terminated Polypropylene Macromonomers: A Route to Polyolefin Elastomers with Excellent Elastic Behavior

We report the design, synthesis, and physical/mechanical properties of graft copolymers containing semicrystalline polypropylene side chains and amorphous ethylene/alpha-olefin copolymer backbones. These materials, a new class of semicrystalline, polyolefin-based thermoplastic elastomers, are made in two steps. First, allyl-terminated syndiotactic or isotactic polypropylene macromonomers are synthesized with controlled microstructure and molecular weight using bis(phenoxyimine)titanium or chiral ansa-zirconocene catalysts, respectively. Second, a pyridyl-amido hafnium catalyst is used to copolymerize the macromonomer, ethylene, and an alpha-olefin with precise control of composition and side chain incorporation. With highly crystalline polypropylene side chains and amorphous backbones of low glass-transition temperatures (<-55 degrees C), the samples have strain-to-break values up to 1400% and elastic recovery above 85% at maximum strains up to 1000%. The synthetic method described herein does not require the use of a living polymerization catalyst; in addition, the mechanical properties of these graft copolymers exceed those of the best linear block polyolefins.