Synthesis of functional CO2-based polycarbonates via dinuclear nickel nitrophenolate-based catalysis for degradable surfactant and drug-loaded nanoparticle applications

Abstract

Functionalized polycarbonates from carbon dioxide have become an emerging topic owing to a large number of potential applications recently. In this contribution, we have developed efficient catalysis strategies along with dinuclear nickel catalysts to synthesize functional CO₂-based polycarbonates and investigated their unique applications in the field of biomaterials. Novel bimetallic nickel catalysts based on bis(benzotriazole iminophenolate) (BiIBTP) ligands have been prepared for copolymerization of carbon dioxide (CO₂) with epoxides to produce CO₂-derived polycarbonates. Nickel complexes [(^C83CBiIBTP)Ni₂(DNP)₂(MeOH)₂] (1), [(^C83CBiIBTP)Ni₂(DNP)(H₂O)₃][DNP] (2) and [(^C83CBiIBTP)Ni₂(NP)(MeOH)₂][NP] (3) (DNP = 2,4-dinitrophenolate; NP = 2-nitrophenolate) from the facile one-pot synthesis have been structurally characterized by single crystal X-ray crystallography, and their molecular structures belong to dinuclear Ni(II)/Ni(II) species containing a hexadentate BiIBTP ligand and two nitrophenolate coligands. We found that alternating copolymerization of CO₂ with cyclohexene oxide (CHO) could proceed efficiently via catalysis using dinickel complex 1 or 3 to afford CO₂-based poly(cyclohexene carbonate)s (PCHCs) with >99% carbonate linkages under optimized conditions. Beyond CO₂/CHO copolymerization, copolymerization of 4-vinyl-1,2-cyclohexene oxide (VCHO), CHO and CO₂ to obtain the corresponding polycarbonates with the vinyl functionalities (PCHC-co-PVCHC) was also studied. Utilizing the vinyl functionalities, one copolymer PCHC-co-PVCHC was successfully converted into charged PCHCs (CPCHCs) with different levels of charge density through thiol–ene click functionalization. Having an amphiphilic structure, these CPCHCs have been used as a biodegradable polymeric surfactant to prepare an oil-in-water (O/W) mini-emulsion. CPCHCs were further converted into degradable nanoparticles (NPs) through our developed mini-emulsion interfacial cross-linking technique and biomedical functions of the NPs such as drug loading capacity, drug release profile and cytotoxicity have been demonstrated.