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Approach for Introducing a Single Metal Complex into a Polymer Chain: Metallo-Chain Transfer Agents in CO2 or COS/Epoxide Copolymerization Processes

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journal contribution
posted on 08.07.2019, 19:03 by Tucker M. Folsom, Gulzar A. Bhat, Ahmed Z. Rashad, Donald J. Darensbourg
We have designed and synthesized poly­(monothiocarbonate)­s containing a single well-defined metal complex in the polymers’ backbone via the immortal copolymerization of carbonyl sulfide and propylene oxide in the presence of chain transfer agents (CTAs). Our initial studies in this area have involved the utilization of metal carbonyl diols, which serve as CTAs. Included in this investigation are the metal complexes ()­Cr­(CO)3 and ()­Re­(CO)3Br. Because of the electron-withdrawing abilities of the metal carbonyl fragments, the CTA afforded catalyst-alkoxide bonds are not sufficiently nucleophilic to react with CO2; hence, the more reactive carbonyl sulfide analog was employed. As anticipated, the molecular weights of the resulting copolymers decreased with increasing quantities of added metal complexes. The incorporation of the metal complexes directly into the polymers’ backbone was noted by νco infrared and 1H NMR spectroscopies. Estimates of metal loading were obtained using calibration curves of the pure metal complexes based on νco infrared or electronic spectra. Thermal decomposition of the copolymers occurred above 180 °C.