Preparation Of Uniform Polystyrene Particles With Environmental Responses Macromolecular Brushes By RAFT Technology

The Uniform polystyrene(PS) particles with environmental responses brushes were preparaed by Reversible Addition-Fragmentation Transfer(RAFT) agent and classical free radical photo-initiated emulsion polymerization with three steps. Firstly, the uniform PS particles were prepared by emulsifier-free polymerization. Secondly, the photo-initiator with end double bond and ester group were attached on the surface of the above PS particles as paper-thin shell by copolymerization using "starve" addition with and without styrene, which control the composition of the surface. Finally, pH value responses brush and thermo-sensitive brush were obtained by photo-initiated emulsion polymerization.with or without RAFT agent.Synthesis and comparison of uniform PS particles with polyvinyl pyrrolidone(PVP) brush using photo-initiated emulsion polymerization with or without the direct addition of aqueous RAFT agent in the continuous phase were discussed. As a result in the polymerization at the presence of RAFT agent, the thickness change of PVP brush kept line-increase which was known from "S" type curve by classical free radical polymerization without RAFT agent. It was implied that the RAFT agent should be taken part in the polymerization and some characterization of controlled polymerization was shown. However, the retardance phenomenon obviously happened. Furthermore, rhe hairy chains were cutted by hydrolysis and characterized by IR. It was found that there were C=S group on the brush chains.The Z-group of the aqueous RAFT agent attached on the surface of uniform PS particles(Poly(St-co-HEMA)-g-RAFT) by the Z-group with CI end bond of the aqueous RAFT agent reacted with the hydroxyl group which containing 2-Hydroxyethyl methacrylate(HEMA) on the surface based on copolymerization using"starve"addition together with styrene. The uniform poly(N-isopropylacrylamide) (PNIPA) brush was obtained by both Poly(St-co-HEMA)-g-RAFT particles and above PS particles on the surface with photo-initiator. Brushes growth precesses between the two types particles with different diameter were investigated by conversion, thickness and morphology etc.At last, the hairy PNIPA grafting on the surface of above PS particles was prepared by classical photo-initiated emulsion polymerization. The characteristic of thermo-sensitivity and the effect of pH value and ion concentration were studied. Moreover, Hybrid PNIPA/PVP brushes were discussed by succeeding addition approach. We found that the particles with hybrid PNIPA/PVP brushes would be more stable than the particles with just PNIPA brush.