Preparation Of Macromolecular Emulsifier PAA-b-PMMA And Its Application In Emulsion Polymerization

Reversible addition-fragmentation chain transfer Polymerization(RAFT),as an important branch of Controlled/Living Radical Polymerization,has received widespread attention in academia and industry for its advantages of precise control of polymer chain structure.In this paper,an amphiphilic block copolymer poly(acrylic acid-b-methyl methacrylate),PAA-b-PMMA))with clear structure and molecular weight control was prepared by RAFT polymerization,which was used as macromolecular emulsifier for emulsion polymerization.The influencing factors of MMA macromolecule RAFT emulsion polymerization system were explored.The stability of the polymerization process was evaluated by changing the initiator concentration,temperature,stirring rate and adding alkali.The conversion rate and Zeta potential of the polymerization products were tested,and finally PMMA latex with high conversion rate and good stability was successfully obtained.Macro RAFT agent acts as both emulsifier and chain transfer agent during emulsion polymerization,and also acts as a switchable surfactant in emulsion condensation and redispersion,which gives polymer the properties of condensation under acidic conditions,recovery under alkaline conditions,and re-stable dispersion in water.This process was evaluated by particle size test.Results The redispersion performance of the emulsion was good in three cycles.The application range of PMMA latex is limited.Usually,the latex with good comprehensive performance needs to be copolymerized with other monomers,so the copolymerization system of methyl methacrylate(MMA)and butyl acrylate(BA)is further discussed.According to the experience of PMMA emulsion system,we improve solid content by adding monomers to the reaction system.Finally,the solid content was successfully increased to 55.66%.The results of permeable gel chromatography(GPC)showed that the molecular weight of the copolymerization product was controlled and the molecular weight distribution was narrow,which proved the activity characteristics of the reaction.The results of differential scanning calorimeter(DSC)confirm that the polymer structure is controlled.In the case of piecewise feeding,the polymer should be core-shell structure,and the T_g is mainly controlled by the content of BA.In the case of mixed feeding,the polymer structure should be random copolymer,which can be predicted by theoretical formula,and the predicted value is consistent with the test results.Based on the results of GPC and DSC,we conclude that the molecular weight and structure of the copolymerized emulsion are controlled.Similarly,the copolymerization emulsion also has reversible condensation and redispersion.The results of GPC showed that the molecular weight of the copolymerization emulsion before and after the condensation and redispersion was not much different from that of the initial emulsion,and the molecular weight distribution was still narrow,showing good reversible condensation and redispersion.