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

Abstract

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.

Branched polyethylenes attainable using thermally enhanced bis(imino)acenaphthene-nickel catalysts: Exploring the effects of temperature and pressure

“…In general, the Tm's of the polymers generated in this study using either alkyl-aluminum co-catalyst (MAO or EASC), fall in the range 92.4 -12.3 °C which is in accord with various levels of branching; an observation that is common for nickel polymerization catalysts [27,29] due to their propensity to mediate chain migration/walking [57,58,[76][77][78][79]. The commonly accepted mechanism is shown in Scheme 2, in which the capacity of the active nickel species to mediate chain isomerization through a sequence of β-H elimination/re-insertion steps is key to the observed branched structures; alternative proposals involving γand δ-eliminations have also been proposed [78].…”

Stereochemical enhancement of polymer properties

“…[120][121][122][123] Stereopure PPG is a crystalline, yet rubbery, polyester that has been synthesised with many different catalysts. [124][125][126][127][128][129][130][131] Surprisingly, the T g and T m seem to be independent of stereochemistry 126,130-132 since both isotactic 131,133,134 and atactic 132 isomers are crystalline. Moreover, the stereochemistry of the PPG unit in triblock architectures of PPG-b-PEG-b-PPG copolymers has little effect on material properties.…”

A continuing legend: the Brookhart-type α-diimine nickel and palladium catalysts

“…49 In addition, the control of the chain walking process to achieved regio-and stereo-selectivity in α-olefin polymerization represents a great challenge. [49][50][51][52][53] Coates and co-workers reported living polymerization of propylene and higher α-olefins catalyzed by a C 2 -symmetric chiral sec-phenethyl substituted α-diimine nickel complex. 50,51 The regioselectivity of these catalysts varied significantly with reaction temperatures: regioregular polypropylene (PP) with a high isotactic content was generated at −60°C, but regioirregular PP was formed at elevated temperature.…”