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

Abstract

We report the design, synthesis, and physical/ mechanical properties of graft copolymers containing semicrystalline polypropylene side chains and amorphous ethylene/α-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 α-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°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.T hermoplastic elastomers (TPEs) are an important class of industrial materials that are an attractive alternative to vulcanized rubber. 1 TPEs can be melt-processed, do not require vulcanization, and, unlike thermoset rubbers, can be recycled. TPEs are blocky polymers that derive their elastomeric properties from a combination of "hard" segments with high melting points (T m ) or high glass-transition temperatures (T g ) and "soft" segments with low T g . Elastomeric properties can be obtained in structures having at least two hard sequences separated by a soft sequence and are typically linear triblock or multiblock copolymers. In the solid state, the hard segments are dispersed throughout the amorphous matrix and form physical cross-links that produce recoverable elasticity after straininduced deformation. 1 A well-known example of a commercial TPE is a triblock polystyrene-block-poly(ethylene-co-butene)-block-polystyrene copolymer (SEBS). Although many commercial TPEs are prepared via anionic polymerization and contain polystyrene, there has been longstanding interest in the synthesis and properties of TPEs based on other monomers. Bates and co-workers prepared model polyolefin TPEs by anionic polymerization followed by hydrogenation. 2 More recently, bio-derived TPEs have been reported. 3Given the low cost of ethylene, propylene, and α-olefins, considerable academic and industrial efforts have focused on the development of catalysts and reaction conditions to prepare blocky polyolefins. 4 Several approaches are shown in Scheme 1. Early efforts focused on elastomeric polypropylene (Scheme 1A) prepared with nonliving catalysts. Natta reported the first elastomeric polypropylene in 1959 using TiCl 3 /AlR 3 catalyst mixtures, 5 and more recently similar materials were obtained using zirconium and titanium alkyl complexes supported on alumina. 6 In the 1990s, the synth...

Copolymerization of Propylene with Higher α-Olefins by a Pyridylamidohafnium Catalyst: An Effective Approach to Polypropylene-Based Elastomer

“…Integrating these ordered microstructures in the atactic PP (aPP) or other amorphous copolymer will develop novel POEs with structural diversity and tunable properties, for example, sPP-b-poly(ethylene-co-propylene)-sPP triblock copolymer, iPP-b-aPP-block(b)-iPP multi-block copolymer, poly(ethylene-co-propylene)-graft(g)-iPP and poly(ethylene-co-propylene)-g-iPP copolymer. These new PP-based elastomers showed outstanding performance, including remarkable elastic properties, excellent stiffness-flexibility balance and easy processability [20][21][22]. With the development of group IV single-site catalysts, we can easily control the chain microstructure and the final material properties [23].…”

Preparation of polystyrene–polyolefin multiblock copolymers by sequential coordination and anionic polymerization

“…Preparation of PO-based block copolymers is currently highly topical. [33][34][35][36][37][38][39][40][41][42][43]…”

Polystyrene Chain Growth from Di-End-Functional Polyolefins for Polystyrene-Polyolefin-Polystyrene Block Copolymers

“…The subtle architecture of the PO chains is of particular interest in the bulk polyolefin industry. For example, sequence control to form olefin block copolymers (OBCs) is a formidable task in olefin polymerizations [1][2][3][4][5]. Following the commercialization of OBCs by the Dow Chemical Company [6][7][8], Coates et al recently reported the preparation of PE/iPP (iPP = isotactic polypropylene) multiblock copolymers to enhance capabilities of plastic recycling [1].…”