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RAFT polymerization of ethylene for the synthesis of polar-apolar olefin block copolymers

Abstract : The synthesis of polar-apolar olefin block copolymers, combining a semi-crystalline polyethylene (PE) block and a polar block (poly(vinyl acetate) (PVAc), poly(methyl methacrylate) (PMMA), poly(ethylene oxide) (PEO)) was investigated by RAFT polymerization. A preliminary study on ethylene homopolymerization revealed parasite cross-termination reactions happening at the intermediate radical, resulting in the loss of chain-end fidelity when using aromatic xanthates as chain transfer agents (CTA) under relative mild conditions (T = 70 – 80 °C, P = 200 bar). The extent of cross-termination was greatly reduced with aromatic dithiocarbamates, and for the first time, PE chains with a high livingness were obtained. These first results were used to equip polar macromolecular CTAs (PVAc, PMMA, PEO), with selected aromatic xanthates and dithiocarbamates, that were further used for block copolymerization with ethylene in a low-transferring organic solvent (dimethyl carbonate, DMC). A critical influence of the ethylene pressure was evidenced as block polymerization at 200 bar could not be achieved due to solubility issues in the resulting supercritical DMC/ethylene mixture. This was circumvented by performing the block copolymerization below the supercritical point of the mixture (P < 100 bar) and well-defined PVAc-b-PE, PMMA-b-PE and PEO-b-PE copolymers were eventually obtained. The block copolymers were found to feature self-assembly properties and worm-like morphologies were observed for PMMA-b-PE and PEO-b-PE synthesized in DMC, hinting at a plausible polymerization-induced self-assembly (PISA) mechanism. The successful switch from DMC to water for the synthesis of PEO-b-PE copolymers enabled the observation of various particle morphologies: spheres, vesicles and ellipsoidal particles, depending on the initial macro-CTA:initiator molar ratio
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https://tel.archives-ouvertes.fr/tel-03018585
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Submitted on : Monday, November 23, 2020 - 1:02:33 AM
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  • HAL Id : tel-03018585, version 1

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Cédric Bergerbit. RAFT polymerization of ethylene for the synthesis of polar-apolar olefin block copolymers. Polymers. Université de Lyon, 2019. English. ⟨NNT : 2019LYSE1276⟩. ⟨tel-03018585⟩

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