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Ultrahigh Branching of Main-Chain-Functionalized Polyethylenes by Inverted Insertion Selectivity.

ABSTRACT: Branched polyolefin microstructures resulting from so-called "chain walking" are a fascinating feature of late transition metal catalysts; however, to date it has not been demonstrated how desirable branched polyolefin microstructures can be generated thereby. We demonstrate how highly branched polyethylenes with methyl branches (220?Me/1000?C) exclusively and very high molecular weights (ca. 106 ?g?mol-1 ), reaching the branch density and microstructure of commercial ethylene-propylene elastomers, can be generated from ethylene alone. At the same time, polar groups on the main chain can be generated by in-chain incorporation of methyl acrylate. Key to this strategy is a novel rigid environment in an ?-diimine PdII catalyst with a steric constraint that allows for excessive chain walking and branching, but restricts branch formation to methyl branches, hinders chain transfer to afford a living polymerization, and inverts the regioselectivity of acrylate insertion to a 1,2-mode.

SUBMITTER: Zhang Y

PROVIDER: S-EPMC7496749 | biostudies-literature | 2020 May

REPOSITORIES: biostudies-literature

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Ultrahigh Branching of Main-Chain-Functionalized Polyethylenes by Inverted Insertion Selectivity.

Zhang Yuxing Y Wang Chaoqun C Mecking Stefan S Jian Zhongbao Z

Angewandte Chemie (International ed. in English) 20200706 34

Branched polyolefin microstructures resulting from so-called "chain walking" are a fascinating feature of late transition metal catalysts; however, to date it has not been demonstrated how desirable branched polyolefin microstructures can be generated thereby. We demonstrate how highly branched polyethylenes with methyl branches (220 Me/1000 C) exclusively and very high molecular weights (ca. 10<sup>6</sup> g mol<sup>-1</sup> ), reaching the branch density and microstructure of commercial ethyl ...[more]

PMID: 32441874

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Project description:Polyolefins account for 60% of global plastic consumption, but many potential applications of polyolefins require that their properties, such as compatibility with polar polymers, adhesion, gas permeability, and surface wetting, be improved. A strategy to overcome these deficiencies would involve the introduction of polar functionalities onto the polymer chain. Here, we describe the Ni-catalyzed hydroxylation of polyethylenes (LDPE, HDPE, and LLDPE) in the presence of m CPBA as an oxidant. Studies with cycloalkanes and pure, long-chain alkanes were conducted to assess precisely the selectivity of the reaction and the degree to which potential C-C bond cleavage of a radical intermediate occurs. Among the nickel catalysts we tested, [Ni(Me4Phen)3](BPh4)2 (Me4Phen = 3,4,7,8,-tetramethyl-1,10-phenanthroline) reacted with the highest turnover number (TON) for hydroxylation of cyclohexane and the highest selectivity for the formation of cyclohexanol over cyclohexanone (TON, 5560; cyclohexanol/(cyclohexanone + ?-caprolactone) ratio, 10.5). The oxidation of n-octadecane occurred at the secondary C-H bonds with 15.5:1 selectivity for formation of an alcohol over a ketone and 660 TON. Consistent with these data, the hydroxylation of various polyethylene materials by the combination of [Ni(Me4Phen)3](BPh4)2 and m CPBA led to the introduction of 2.0 to 5.5 functional groups (alcohol, ketone, alkyl chloride) per 100 monomer units with up to 88% selectivity for formation of alcohols over ketones or chloride. In contrast to more classical radical functionalizations of polyethylene, this catalytic process occurred without significant modification of the molecular weight of the polymer that would result from chain cleavage or cross-linking. Thus, the resulting materials are new compositions in which hydroxyl groups are located along the main chain of commercial, high molecular weight LDPE, HDPE, and LLDPE materials. These hydroxylated polyethylenes have improved wetting properties and serve as macroinitiators to synthesize graft polycaprolactones that compatibilize polyethylene-polycaprolactone blends.

Project description:ATP-sensitive K+ (KATP) channels couple cellular metabolism to electrical activity in many cell types. Wild-type KATP channels are comprised of four pore forming (Kir6.x) and four regulatory (sulfonylurea receptor, SURx) subunits that each contain RKR endoplasmic reticulum retention sequences that serve to properly translocate the channel to the plasma membrane. Truncated Kir6.x variants lacking RKR sequences facilitate plasma membrane expression of functional Kir6.x in the absence of SURx; however, the effects of channel truncation on plasma membrane orientation have not been explored. To investigate the role of truncation on plasma membrane orientation of ATP sensitive K+ channels, three truncated variants of Kir6.2 were used (Kir6.2ΔC26, 6xHis-Kir6.2ΔC26, and 6xHis-EGFP-Kir6.2ΔC26). Oocyte expression of Kir6.2ΔC26 shows the presence of a population of inverted inserted channels in the plasma membrane, which is not present when co-expressed with SUR1. Immunocytochemical staining of intact and permeabilized HEK293 cells revealed that the N-terminus of 6xHis-Kir6.2ΔC26 was accessible on both sides of the plasma membrane at roughly equivalent ratios, whereas the N-terminus of 6xHis-EGFP-Kir6.2Δ26 was only accessible on the intracellular face. In HEK293 cells, whole-cell electrophysiological recordings showed a ca. 50% reduction in K+ current upon addition of ATP to the extracellular solution for 6xHis-Kir6.2ΔC26, though sensitivity to extracellular ATP was not observed in 6xHis-EGFP-Kir6.2ΔC26. Importantly, the population of channels that is inverted exhibited similar function to properly inserted channels within the plasma membrane. Taken together, these data suggest that in the absence of SURx, inverted channels can be formed from truncated Kir6.x subunits that are functionally active which may provide a new model for testing pharmacological modulators of Kir6.x, but also indicates the need for added caution when using truncated Kir6.2 mutants.

Dataset Information

Ultrahigh Branching of Main-Chain-Functionalized Polyethylenes by Inverted Insertion Selectivity.

Publications

Ultrahigh Branching of Main-Chain-Functionalized Polyethylenes by Inverted Insertion Selectivity.

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