Well-defined polyurethane-graft-poly(N,N-dimethylacrylamide) copolymer with a controlled graft density and grafted chain length: synthesis and its application as a Pickering emulsion

摘要

A robust method for the synthesis of well-defined polyurethane-graft-poly(N,N-dimethylacrylamide) (PU-g-PDMA) copolymers with good control over the graft density and the grafted chain length was presented in this study. Firstly, a functional polyurethane (fPU) polymer with lateral trithiocarbonate-based chain transfer agent group was synthesized by the polyaddition reaction of 2,2-bis(hydroxymethyl) butyl 2-(ethylthiocarbonothioylthio)-2-methylpropanoate (BEMP) with hexamethylene diisocyanate (HDI), and the subsequent chain extension reaction with 1,4-butanediol (BDO). The content of the chain-transfer groups in the synthesized fPU could be well tuned by altering the mole ratio of BEMP to HDI during the synthesis of the prepolymer. The produced fPU was then applied as the macro-RAFT agent to mediate the radical polymerization reaction of the N,N-dimethylacrylamide (DMA) monomers that were initiated by azobisisobutyronitrile (AIBN), resulting in well-defined amphiphilic PU-g-PDMA graft copolymers with a known graft density and tunable grafted chain lengths. The structure of the obtained PU-g-PDMA was characterized carefully using FTIR and H-1 NMR. The average molecular weight and polydistribution of PU-g-PDMA copolymers were analyzed by GPC. The thermal properties of fPU and PU-g-PDMA copolymers were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The amphiphilic PU-g-PDMA graft copolymers could self assemble into spherical nanoparticles with a core-shell structure in water. The core-shell structured nanoparticles could be applied as emulsifiers for the formation of stabilized toluene-in-water Pickering emulsions, and an extremely low content of emulsifiers (similar to 0.01%) relative to the total weight of oil and water was required.