Tandem metal-coordination copolymerization and organocatalytic ring-opening polymerization via water to synthesize diblock copolymers of styrene oxide/CO2 and lactide.
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abstract
Selective transformation of carbon dioxide and epoxides into degradable polycarbonates (CO(2)-based copolymer) has been regarded as a most promising green polymerization process. Although tremendous progress has been made during the past decade, very few successful examples have been reported to synthesize well-defined block copolymers to expand the scope of these green copolymers. Herein, we report a tandem strategy combining two living polymerization techniques, salenCo(III)X-catalyzed styrene oxide SO/CO(2) copolymerization and ring-opening polymerization of lactide with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), for the synthesis of poly(styrene carbonate-block-lactide) copolymers. The key to the success of this tandem strategy is the judicious choice of water as the chain transfer and/or chain terminator reagent, which is added at the end of the salenCo(III)X-catalyzed SO/CO(2) copolymerization to in situ generate hydroxyl groups at the end of the polymer chains. The resulting polycarbonates with -OH end groups can thus be directly used as macroinitiators to subsequently initiate ring-opening polymerization of lactide to synthesize the diblock copolymers. Because of the living polymerization nature of both steps in this tandem strategy, we have demonstrated that the diblock copolymers synthesized possess well-defined structures with narrow molecular weight distributions and controllable lengths of both styrene carbonate and lactide blocks.
