Semicrystalline thermoplastic elastomeric polyolefins: Advances through catalyst development and macromolecular design

Abstract

We report the design, synthesis, morphology, phase behavior, and mechanical properties of semicrystalline, polyolefin-based block copolymers. By using living, stereoselective insertion polymerization catalysts, syndiotactic polypropylene-blockpoly(ethylene-co-propylene)-block-syndiotactic polypropylene and isotactic polypropylene-block-regioirregular polypropyleneblock-isotactic polypropylene triblock copolymers were synthesized. The volume fraction and composition of the blocks, as well as the overall size of the macromolecules, were controlled by sequential synthesis of each block of the polymers. These triblock copolymers, with semicrystalline end-blocks and mid-segments with low glass-transition temperatures, show significant potential as thermoplastic elastomers. They have low Young's moduli, large strains at break, and better than 90% elastic recovery at strains of 100% or less. An isotactic polypropylene-block-regioirregular polypropylene-block-isotactic polypropylene-block-regioirregular polypropylene-block-isotactic polypropylene pentablock copolymer was synthesized that also shows exceptional elastomeric properties. Notably, microphase separation is not necessary in the semicrystalline isotactic polypropylenes to achieve good mechanical performance, unlike commercial styrenic thermoplastic elastomers.block copolymer ͉ polypropylene T he applications of a polymer are largely determined by its chemical, physical, and mechanical properties. These properties are in turn determined by polymer morphology, which is dictated by polymer structure and composition. Thermoplastic elastomers are a classic example where polymer architecture engenders unique properties. Block copolymers that contain at least two blocks that are hard at room temperature, separated by blocks with a glass transition temperature (T g ) below room temperature, typically exhibit elastomeric properties if the low T g block volume is large (1-5). The most well known elastomers of this type are the polystyrene (PS)-block (b)-polybutadiene-b-PS triblock copolymers, sold commercially by Kraton Polymers. Such materials normally possess a microphase-separated morphology in which 10-nm-scale domains of the hard blocks (e.g., PS) are embedded as spheres or cylinders within a continuous phase of the low T g soft blocks. The hard domains serve as thermally reversible crosslinks that at room temperature produce high levels of recoverable elasticity in the soft phase.Sequence control of a synthetic polymer is most easily accomplished by using a synthetic technique that allows the sequential addition of one or more monomers to the macromolecule in a chain growth process without spontaneous termination. These techniques are collectively called living polymerizations, and despite many successes over the last half century, their further development remains one of the most important frontiers in polymer science. In the case of the Kraton triblock copolymers, a living anionic polymerization process is used to synthesize the materials. Because approximately t...

Mechanism of resilin elasticity

“…Exon I tends to be the ‘soft’ segment and possess resilience of more than 90% 3,7 . The resilin network can be biochemically cross-linked between tyrosine residues, which help to construct a similar thermoplastic elastomeric polymer network 26,27 . In addition, transmembrane segments of full length resilin were predicted (Fig.…”

Synthesis of ethylene/1‐octene copolymers with controlled block structures by semibatch living copolymerization

“…16,17,19 These block copolymers exhibited superior extensibility and toughness compared to their random counterparts. 20 However, kinetic modeling, an important reaction engineering tool, has not been extensively applied in living olefin polymerization systems for precise control over polyolefin chain microstructure.…”

Stereoregular Polymers

“…Addition of a small amount of ethylene during the living polymerization of propylene by V(acac) 3 /Et 2 AlCl/anisole results in a triblock copolymer syndio-PP-block-P(E-random-P)-block-syndio-PP (192). The FI Ti complex (28), which is effective for syndiotactic polymerization of propylene, can also be utilized for the synthesis of copolymer containing the syndiotactic polypropylene block and poly(ethylene-random-propylene) block (193,194). In contrast, the Ti complex with the phenoxy-ketimine ligand (29) affords the similar block copolymer containing the isotactic polypropylene block (86).…”