Synthesis Of Amphiphilic PU Graft Copolymers And Their Application As Stabilizers For Emulsion

Graft copolymer refers to a kind of polymer that the side chains are regularly or densely tethered on the linear backbone.The physical properties of graft copolymers differ distinctly from those of normal linear polymers,especially for those with a high graft density,and these distinguished properties endow graft copolymers many advantages in versatile application fields,such as coating,biomedicine and nanoscience etc.A great deal of effort has been devoted to the synthesis of well-defined graft copolymers with desired chemical compositions,controlled lengths of side chains and backbone,as well as adjustable grafting densities during the past years.In this study,we reported the synthesis of the amphiphilic polyurethane-based graft copolymers by the combination of controlled radical polymerization with the polyaddition reaction.And the detailed contents included the following two parts:(1)Synthesis of well-defined polyurethane-g-poly(N,N-dimethylacrylamide)(PU-g-PDMA)copolymers with good control over the graft density and the grafted chain length and their application as emulsifiers.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 produced fPU was then applied as the macro-RAFT agent to mediate RAFT polymerization reaction of the DMA monomers that were initiated by azobisisobutyronitrile(AIBN).The structure of the obtained PU-g-PDMA was characterized carefully.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(~0.01%)relative to the total weight of oil and water was required a method for the preparation of PDMA grafted from polyurethane(PU)surface is presented.(2)Synthesis of amphiphilic PU-based supramolecular graft copolymers with detachable side chains via the polyaddition reaction and reversible addition–fragmentation chain transfer(RAFT)polymerization reaction combination.A functional trithiocarbonate compound containing a disulfide bond and two hydroxyl groups was firstly synthesized.After the reaction of the synthesized functional trithiocarbonate with 4,4'-diphenylmethane diisocyanate together with the followed chain extension reaction with 1,4-butanediol(BDO),polyurethane polymers(PUs)carrying trithiocarbonate lateral groups were obtained.The as-obtained PUs were further utilized as macromolecular chain transfer agents for the RAFT polymerization of N,N-dimethylacrylamide(DMA)monomers,resulting in well-defined amphiphilic PU-g-PDMA copolymers with pendant PDMA side chains that were tethered on the PU backbone via reversible disulfide bonds.The PU-g-PDMA copolymers could be self assembled core-shell micelle nanoparticles with PU as core and PDMA as shell in water.Using the formed star core-shell micelle nanoparticles as emulsifiers,high stable oil in water Pickering emulsions were generated.Moreover,the formed oil in water Pickering emulsions showed redox-triggered deemulsification features.The structures of the synthesized compounds were carefully characterized by FTIR,1HNMR,and GPC.