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Isospecific Group-Transfer Polymerization of Diethyl Vinylphosphonate and Multidimensional NMR Analysis of the Polymer Microstructure

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journal contribution
posted on 11.09.2019, 17:38 by Michael Weger, Philipp Pahl, Fabian Schmidt, Benedikt S. Soller, Philipp J. Altmann, Alexander Pöthig, Gerd Gemmecker, Wolfgang Eisenreich, Bernhard Rieger
Control of stereoregularity is an integral part of a precision polymerization method and for the development of functional materials. Yttrium- and aluminum-based catalysts are known for converting diethyl vinylphosphonate (DEVP) into its stimuli-responsive polymer in a precise but stereoirregular way. Herein, we present Y- and Al-based constrained geometry complexes (CGCs) to induce isotacticity without losing control over other macromolecular parameters. After having established convenient synthesis routes and detailed structural analyses, these CGCs showed exceedingly high turn-over frequencies (up to 45 000 h–1) in the group-transfer polymerization of DEVP. The initiator efficiencies (≤99%) and dispersities (≤1.02) strongly depended on the substitution pattern of the applied ligands. An analysis of the microstructure using multidimensional NMR (1H–1H and 1H–13C­(−31P)) correlation experiments demonstrated significant disparities for the stereospecificity of the CGCs and enabled a reliable signal assignment. The yttrium catalysts produced highly isotactic poly­(diethyl vinylphosphonate), likely following a chain-end control mechanism, whereas the aluminum complexes produced less defined polymers.