Synthesis Of Amphiphilic Diblock Copolymer Based On RAFT Polymerization And Its Application In Emulsion Polymerization

From the end of the 1990s, Reversible Addition-fragmentation Chain Transfer (RAFT) polymerization has received more and more attention. By this method, not only controlled molecular weight and narrow molecular weight distribution can be obtained, but the polymer with different compositions and well-defined macrostructures can also be obtained. Compared with the other controlled radical polymerizations, the RAFT has many advantages such as widely proper monomers, mild conditions with polymerization, no limitation of polymerization processes. Meanwhile, because of the living polymeric characteristics, the polymers with various topological structures, such as block, graft, star, could be obtained. So the RAFT to synthesize block copolymers receives more and more attention. And the amphiphilic block copolymers with special structures can form micelles in selective solvents by self-assembly, which can provide polymeric site for emulsion polymerization. At the same time, the block copolymers can anchor on the surface of latex particle to make the stability. So the amphiphilic block copolymers used as emulsifier are becoming the development trend for emulsion polymerization.Reversible addition-fragmentation chain transfer (RAFT) free radical polymerization of acrylic acid ( AA ) was investigated by using 2-([(dodecylsulfanyl)carbonothioyl]sulfanyl}succinic acid (DCTSS) which was synthesized according to patent as chain transfer agent (CTA) and 4,4`-Azobis(4-cyanovaleric acid)(V501) as initiator in water and ethanol. Then the well-controlled amphipathic block copolymer PAA-b-PBA was prepared by using PAA-RAFT as macromolecular RAFT agent and n-butyl acrylate (BA) as second monomer. The structures of these products were characterized by 1HNMR, FTIR and GPC. Reaction kinetics was investigated. The effects of some parameters on polymerization were investigated, such as n(V501):n(CTA), n(AA):n(CTA), n(V501):n(PAA-RAFT) and n(BA):n(PAA-RAFT). The surface activity, emulsifying property, foamability and foam stability of PAA-b-PBA used as a polymeric surfactant were investigated too. Then BA/MMA mixed monomer was polymerized by emulsion polymerization with the PAA-b-PBA as emulsifier which was synthesized in ethanol. The effects of block copolymers synthesized in different conditions on monomer conversion, gel content, solid content, latex particle size and distribution, zeta potential and centrifugal stability of emulsion polymerization were investigated systematically. At last, the most suitable emulsifier with its polymerized conditions was chosen to emulsion polymerization. The effects of the dose of base and emulsifier on emulsion polymerization were investigated, and the morphology of latex particle was characterized by TEM.The polymerization showed"living"/controlled characteristics by using V501 as initiator, DCTSS as CTA,AA as monomer in water. Reaction kinetics was linear. The molecular weight of polyacrylic acid (PAA) was controllable and increased linearly with monomer conversion. The molecular weight distribution of PAA was as narrow as 1.50. Rising the temperature could increase the rate of reaction, reduce the molecular weight distribution, and control the reaction better. Reducing the molar ratio of initiator to RAFT agent could cause the molecular weight larger, but the rate of the reaction was also lower. Increasing the molar ratio of acrylic acid to RAFT agent, the molecular weight was larger, and the relationship between them was linear. And the best reaction time was 2 hours. The well-controlled amphipathic block copolymer PAA-b-PBA was prepared by using PAA as macromolecular RAFT agent and n-butyl acrylate as second monomer in water. when n(V501):n(CTA) was 0.2, n(AA):n(CTA) was 20, n(V501):n(PAA-RAFT) was 0.1, n(BA):n(PAA-RAFT) was 20, the surface tension of PAA-b-PBA aqueous solution was as low as 30.89N/m ,the emulsifying property was the strongest and the emulsion can be stabilized for 1082s, the foamability and the foam stability were the weakest, the foam height was as low as 17.01mm, and the foam could be stabilized for 210s.The polymerization showed"living"/controlled characteristics by using V501 as initiator, DCTSS as CTA, in ethanol. Reaction kinetics was linear. The molecular weight of polyacrylic acid was controllable and increased linearly with monomer conversion. The molecular weight distribution of PAA was as narrow as 1.044. By adjusting the reactant ratios of n(V501):n(CTA), the effects of the Mn and PDI were not obvious under certain conditions. The Mn and PDI was increased proportionally with n ( AA ) :n ( CTA ) . The well-controlled amphipathic block copolymer PAA-b-PBA was prepared by using PAA as macromolecular RAFT agent and n-butyl acrylate as second monomer in ethanol. The PAA and PAA-b-PBA were characterized by FTIR and GPC. By adjusting the reactant ratios, we were able to obtain PAA-b-PBA copolymer with narrow polydispersities (~1.23). Rising n(V501):n(PAA-RAFT) ratios had a small effect on the Mn values throughout the reaction. Moreover, when n(V501):n(PAA-RAFT)=0.15, the lowest PDI could be obtained. The Mn of PAA-b-PBA was increased proportionally with n(BA):n(PAA-RAFT) ratios and the controlled behavior was also weakened. In addition, the effects of n(AA):n(CTA), n(V501):n(PAA-RAFT) and n(BA):n(PAA-RAFT) ratios on property in water were also investigated. All in all, the CMC of the PAA-b-PBA was far lower than sodium dodecyl benzene sulfonate. When n(AA):n(CTA)=20 and n(V501): n(PAA-RAFT)=0.2, the CMC of the PAA-b-PBA was lowest. If there was no base, the surface tension was lowest. But when a little base was added into this system, the surface tension was rising rapidly and reached the maximum value. With increasing the dose of base, the surface tension was decreased again. Continuing increasing the dose of base, the surface tension approached equilibrium. The CMC of PAA-b-PBA had no effect on base. Narrow PDI of PAA-b-PBA could improve the emulsifying property. As the n(BA):n(PAA-RAFT) and n(AA):n(CTA) ratios were both 20, the emulsifying property of the PAA-b-PBA solution was the best. And the emulsifying property of the PAA-b-PBA was better than sodium dodecyl sulfate, MS-1 and sodium dodecyl benzene sulfonate. But the foamability and the foam stability was lower.In the emulsion polymerization with PAA-b-PBA as emulsifier which was synthesized in ethanol, adding the base could improve the stability of the reaction and the final emulsion. And there were complex impacts on emulsion polymerization with PAA-b-PBA as emulsifier synthesized in different conditions. In a word, when n(V501):n(CTA)=0.15, n(AA):n(CTA)=10, n(V501):n(PAA-RAFT)=0.15, n(BA):n(PAA-RAFT)=10, the PAA-b-PBA was the most suitable for BA/MMA emulsion polymerization. When n(NaHCO3): n(AA)=1.6 and the concentration of emulsifier was 4%, the stability of the reaction process and the final emulsion was the best.At last, the core-shell structure of latex particle was discovered, and the latex particle distribution was wide.