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

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.