Synthesis of Semicrystalline Polyolefin Materials: Precision Methyl Branching via Stereoretentive Chain Walking.

We report the discovery of C-symmetric nickel catalysts capable of the regio- and isoselective polymerization of 1-butene to produce isotactic 4,2-poly(1-butene), a new semi-crystalline polyolefin. The catalyst exhibits enantioface selectivities as high as 84% and the resulting polymers display melting temperatures up to 86 °C. This system marks a rare example of preserving stereochemistry through a chain walking polymerization process.

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

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-block-poly(ethylene-co-propylene)-block-syndiotactic polypropylene and isotactic polypropylene-block-regioirregular polypropylene-block-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.

Living polymerization of alpha-olefins with an alpha-diimine Ni(II) catalyst: formation of well-defined ethylene-propylene copolymers through controlled chain-walking.

A C2-symmetric Ni(II) catalyst was found to polymerize alpha-olefins with high levels of omega,2-regiochemistry. The resulting products are ethylene-propylene-type copolymers with methylene sequences of precise length between methyl branches. Modification of reaction conditions can introduce omega,1-enchainments into the polymers which increases the average length of methylene sequences between methyl branches.

Acid-catalyzed ortho-alkylation of anilines with styrenes: an improved route to chiral anilines with bulky substituents.

[reaction: see text] Reaction of para-substituted anilines with styrene derivatives at elevated temperatures, when catalyzed by CF3SO3H, results in highly chemoselective ortho-alkylation of the aniline. When R = H, dialkylation can be achieved by varying the ratio of styrene to aniline. Several different substituted anilines and styrenes were examined, and good yields (42-87%) were obtained, except in the case where electron-withdrawing substituents are present on the styrene.

A C2-symmetric, living alpha-diimine Ni(II) catalyst: regioblock copolymers from propylene.

An isomerically pure, C2-symmetric Ni(II) complex was synthesized and found to be living for propylene polymerization. The regioselectivity of the catalyst varied greatly with reaction temperature, with regioregular, highly isotactic polypropylene (PP) produced at low temperatures, and regioirregular PP produced at high temperatures. Regioblock PP was formed by changing the reaction temperature during the polymerization.