Cationic Latex Of Polystyrene And Its Block Copolymer Prepared By Emulsifer-free RAFT Emulsion Polymerization

Emulsion polymerization is the main process to prepare polymer latex. The performance of the latex is closely related with polymer compositions, particle size and size distribution, surface charge of the latex, and residual amount of emulsifiers. Recently, living emulsion polymerization with amphiphilic macroRAFT agent as an emulsifier received much attention. The reason is that nano-structured latex particles consisting of block copolymer could be prepared by this method, and with the amphiphilic macroRAFT agents bonded at the end of the product polymer chains, there would be no problem concerned with the residual emulsifiers. In most casese, nonionic or anionic amphiphilic macroRAFT agents were used. In this thesis, I explored to prepare emulsifier-free cationic latex with cationic amphiphilic macroRAFT agents. A series of cationic amphiphilic macroRAFT agents P4VPm-b-PSn-CPDTTC (m=10,15,20.30, n≈6) was synthesized by design and was used as a sufactant in RAFT emulsion polymerization of styrene. The polymerization kinetics, controllability of the molecules weight, latex particle diameter, and synthesis of block copolymer were investigated, in emulsifier-free RAFT ab initio emulsion polymerization of styrene. The following conclusions were drawn:(1)4-Vinyl pyridine (4VP) was selected as the monomer for the hydrophilic block of the macroRAFT agent. With2-cyanopropan-2-yl dodecyl carbonotrithiate (CPDTTC) as the RAFT agent, we successfully synthetized a series of amphiphilic macroRAFT agent P4VPm-b-PSn-CPDTTC (m=10.15,20,30, n≈6) under control manner, with a narrow molecular weight distribution. Take P4VP2o-b-PS6.2-CPDTTC with25%of4VP units neutralized for an example, micelle with average diameter (by volume) of6.1nm was found by DLS which was formed in water.(2) Taking P4VP15-b-PS6.3-CPDTTC for an example, we investigated how different neutralization percents (with33.3%,66.7%,100%of4VP units neutralized) of the macroRAFT agents influenced the RAFT ab initio emulsion polymerization of styrene (with20%solid content). It was found that the higher the neutralization percent was, the longer the inhibition period would be. The diameters of the final latex of the experiments were about40nm, which was one order of magnitudes smaller than those prepared by traditional emulsifier-free emulsion polymerization. Particle diameter distribution of the final latex was very broad, with many small particles bellow30nm, which indicated a continuous and long nucleation period. In early stage of the polymerizations, the molecular weight agreed well with the theoretically predicted molecules weight, but later, it began to deviate. All PDI first went up, then fell down. At the end of the polymerization, all PDI was high, and rose up as the neutralization percent became higher. A high fraction of macroRAFT agent molecules remained un-reacted in the final product.(3) Taking the four above-mentioned macroRAFT agents with54VP units neutralized for examples, we investigated how different lengths of the4VP block of the macroRAFT agents influenceed the RAFT ab initio emulsion polymerization of styrene (with20%solid content). We found that longer4VP block would end up with shorter inhibition period, and faster polymerization rate. All the diameter of the four experiments was close, about41nm, but the size distribution was still very broad. Take P4VP15-b-PS6.3-CPDTTC with54VP units neutralized for example, we investigated how different design moleculer weights (30,100,200k·mol-1) influenced the RAFT ab initio emulsion polymerization of styrene (with20%solid content). We found all the three experiments had the same inhibition periods, but the higher design moleculer weight led to the slower polymerization rate, and the larger particle diameters (41.4nm,64.0nm,85.1nm, accordingly). The particle size distributions were still very broad in all cases.(4) Using P4VP15-b-PS6.3-CPDTTC and P4VP30-b-PS6.5-CPDTTC as surfactants, the diblock copolymer of PS-b-PBA (molecules weight of the blocks was30and70kg· mol-1, respectively) was synthesized with good livingness but poor control in molecular weight and distributions. While synthesizing diblock copolymer PBA-b-PS, molecules weight went out of control.