Regulating And Controlling Of Macromolecular Brushes With Different Structures On The Surface Of Polystyrene Particles

The monodisperse PS particles with PAA homo-type and PNIPA co-type brushes were successfully synthesized by "grafting from" three-steps method. Firstly, the uniform PS particles were prepared by emulsifier-free/soapless polymerization. Secondly, the photo-initiator with 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 styrene, which control the composition of the surface. Finally, macromolecular brushes were obtained by photo-initiation emulsion polymerization. On the basis of this, molecular weight and grafting-density of PAA brushes and thermo-sensitive characteristics of PNIPA type brushes were investigated. Additionally, the PVP brushes were prepared by RAFT polymerization. Moreover, the mechanism of RAFT polymerization was also studied.At first, the monodisperse submicron-size PS particles were prepared by soapless/emulsifier-free polymerization using 2,2-azobis(2-amidinopropane) dihydrochloride (V50) as cationic initiator. The effect of polymerization recipes and conditions were mainly investigated. The results indicated that the conversion of styrene did not increase obviously in emulsifier-free emulsion polymerization whatever condition was adjusted. Besides that, the polymerization system used to be unstability. Combining the advantages of emulsion-free polymerization and conventional emulsion polymerization, some emulsifier (CTAB) was added in polymerization. In a short polymerization time, high conversion was obtained. The optimum reaction temperature was 65 ℃. In polymerization process, moderate ionic strength was 0.04M. With higher or lower ionic strength, the final conversion might be lower or broad distribution of particle size occurred. The content of initiator affected the reaction rate and particle size distribution (PDI). The appropriate value was 2% of monomer. The content of emulsifier influenced reaction mechanism. Adding 0.3% emulsifier, narrow PDI was obtained. With polymeric emulsifier, large-size particleswere synthesized, but PDI of the particles was broad.With regard to preparation of PAA brushes on the surface of above PS particles, the total conversion of AA was confirmed by measuring the content of residual AA in photo-initiation polymerization system using GC. As a result, the reaction was rapid and it got to constant in a short time. Comparatively, the thickness of brushes shell increased with hysteresis effect. Increasing AA concentration, the total conversion increased. The solid content of seeds also affected the final conversion. When it got to 1.5%, the conversion was highest. The resultant PAA brushes could be cutted from the surface of PS microspheres by hydrolyzation. And then the molecular weight and its distribution of PAA prepared by different polymerization conditions were directly measured by GPC. It was found that the molecular weight of PAA was almost constant during the photo-polymerization. The molecular weight of PAA increased with AA concentration increasing. As the solid content of added seeds was 1.5%, the molecular weight of PAA had an extremum due to relative changed AA concentration, but it was not obvious. Based on both the molecular weight of PAA and conductance titration of cleaned PS particles with PAA brushes, another important parameter grafting-density on the surface of PS particles could be calculated.Different structures of the thermo-sensitive PNIPA macromolecular brushes were obtained by different feed composition and strategy. As for the PS microspheres with negative charge on the surface, the thermo-sensitive characteristics of the above resulting brushes were investigated. Furthermore, the influences of pH value and ionic strength of water medium were also studied. The results indicated that the phase transition temperature of the PNIPA homopolymer brushes grafted on the surface of polystyrene particles was between 29℃ and 33℃. The phase transition temperature increased and the transition ranges tended to be broad when the PNIPA brushes were substituted with P(NIPA-co-AA) or P(NIPA-co-NVP) brushes obtained by the copolymerization of NIPA with AA and NVP, respectively. However, the phase transition was not obvious if adding excessive hydrophilic comonomer. Two transition regions appeared when both PNIPA and P(NIPA-co-AA) brushes were jointly existingon the surface of polystyrene particles. The interesting fluctuant thermosensitivity with wide ranges was found if both PAA and PNIPA brushes were simultaneously anchored on the surface. Moreover, swelling ratio of the P(NIPA-co-AA) brushes increased in water medium with higher pH value. On the contrary, the above swelling ratio decreased with higher ionic strength and the excursion of its phase transition region was observed. As for the PS particles with positive charge on the surface, the phase transition temperature of the PNIPA homopolymer brushes grafted on the surface of polystyrene particles was between 30°C and 35°C. It tended to be broad adding comonomer NVP. With excessive NVP, two phase transition temperature occurred. The different comonomer such as AA and NVP made different brushes thickness.4-cyanopentanoic acid dithiobenzoate was synthesized as soluble RAFT reagent. Both NMR and FTIR were used to confirm the structure of the given RAFT reagent. The prepared RAFT reagent was added in photo-polymerization of VP. The diameter of PS with PVP brushes was measured and the thickness of brushes shell was calculated. The PS microspheres with PVP brushes and individual cutted PVP brushes were characterized by IR. Furthermore, they were compared with the produce was prepared without RAFT reagent in photo-polymerization. The results indicated that the thickness of PVP brushes increased. According to thickness-conversion curve, it was estimated that the RAFT reagent reacted as chain transfer reagent. In IR spectrogram of cutted PVP brushes, characteristic peak of C=S double bond also confirmed it. But more investigated should be needed to assure the accurate reaction mechamism.