Postpolymerization Functionalization of Copolymers Produced from Carbon Dioxide and 2-Vinyloxirane: Amphiphilic/Water-Soluble CO2-Based Polycarbonates
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Common CO2-based polycarbonates are known to be highly hydrophobic, and this "inert" property makes them difficult for the covalent immobilization of bioactive molecules. A practical method for modifying polymers is to introduce various functional groups that permit decoration of polymer chains with bioactive substances. In this report, CO2-based poly(2-vinyloxirane carbonate) (PVIC) with more than 99% carbonate linkages is isolated from the CO2/2-vinyloxirane alternating copolymerization catalyzed by the bifunctional catalyst [(1R,2R)-SalenCo(III)(DNP)2] (1) (DNP = 2,4-dinitrophenolate) bearing a quaternary ammonium salt on the ligand framework. It was also observed that the presence of propylene oxide significantly activates 2-vinyloxirane for incorporation into the polymer chain as well as inhibits the formation of cyclic carbonate in the terpolymerization process. DSC studies demonstrate that the glass transition temperature (T g) decreases with the increase in the content of vinyl groups in the polycarbonate. By way of thiol-ene coupling, showing mainly "click" characteristics and nearly quantitative yields, amphiphilic polycarbonates (PVIC-OH and PVIC-COOH) with multiple hydroxy or carboxy functionalities have been prepared, providing suitable reactivities for further modifications (ring-opening of l-aspartic acid anhydride hydrochloride salt and deprotonation by aqueous ammonium hydroxide (NH4OH(aq))) to successfully isolate the water-soluble CO2-based polycarbonate PVIC-COONH 4, and the PVIC-OH-Asp polymer which shows particles dispersed in water with an average hydrodynamic diameter Dn = 32.2 8.8 nm. It is presumed that this emerging class of amphiphilic/water-soluble polycarbonates could embody a powerful platform for bioconjugation and drug conjugation. In contrast to lower Tgs of PVIC, (PVIC-co-PC), PVIC-OH, and PVIC-COOH, the polycarbonates PVIC-OH-Asp and PVIC-COONH4 show higher Tgs as a consequence of their intrinsic ionic property (ammonium salts). 2014 American Chemical Society.
