Emulsion Polymerization Of VC-VAc-MAH And Study On Structure/Performance Of Copolymer

Vinyl chloride-vinyl acetate (VC-VAc) copolymer is one of the most important vinyl chloride copolymers. As low polarity solvents (i.e, ethyl acetate) required to be used in the coating industry, VC-VAc copolymers used as the adhesive component of coatings are required to have good solubility in this kind of solvents. The adhesive strengths of VC-VAc copolymers are also needed to improve. The solubility of VC-VAc copolymers can be improved by optimizing the copolymer composition, and the adhesive strength can be improved by incorporating maleic anhydride (MAH) unit into VC-VAc copolymer chains. Considering the lack of fundamental studies on VC-VAc-MAH emulsion copolymerization and the relationship between the structure and properties of VC-VAc-MAH copolymers, the kinetics and the composition control of VC-VAc and VC-VAc-MAH emulsion copolymerizations were investigated in this thesis, and the solubility of VC-VAc and VC-VAc-MAH copolymers were determined.Firstly, VC-VAc emulsion copolymerizations were carried out by using ammonium persulfate (APS) as the initiator, emulsifier A as the emulsifier system. The kinetics of emulsion copolymerization were studied and the obtained VC-VAc copolymers were characterized by using particle size analyzer, scanning electron microscopy, nuclear magnetic resonance, Fourier transform infrared spectroscopy, gel permeation chromatography, element analysis and differential scanning calorimeter. The results showed that VAc weight fractions in copolymers determined by1H-NMR and EA were lower than that predicted by Mayo-Lewis equation. The solubility of VC-VAc copolymers prepared by emulsion copolymerization was better than that of copolymers synthesized by suspension polymerization using the same feeding monomer composition. The uniformity of copolymer composition can be improved by feeding VC semi-continuously.Secondly, VC-VAc-MAH emulsion copolymerizations were conducted by using different initiators. It was found that the polymerization conversions were very low when copolymerizations were initiated by APS or APS/Na2SO3/CuSO4. Using 2,2-azobisisobutyronitrile (AIBN) or dibenzoyl peroxide (BPO) as initiator resulted the coagulation of copolymer latex particles. Using initiator A, the copolymerization were proceeded smoothly to high conversion, and the as-prepared copolymer latexes were stable. So, initiator A was the ideal initiator for VC-VAc-MAH emulsion copolymerization.The kinetics of VC-VAc-MAH emulsion copolymerization was also investigated. The results showed that the polymerization rate was increased as the concentration of initiator increased. The polymerization rate was increased as the reaction temperature increased, while the molecular weight of the copolymer would be decreased. The concentration of emulsifiers had little effect on the reaction rate and the molecular weight of copolymers. As the initial VAc weight fraction in the feeding monomers increased, the reaction rates would be decreased, but the molecular weights of copolymers had no significant change. As the MAH concentration in the feeding monomers increased, the reaction rate and the molecular weight of copolymer were significantly decreased.Finally, the structure and properties of VC-VAc-MAH copolymer latexes and the copolymers was studied. The results showed that the particles size of latex was decreased as the SDS concentration increased. Emulsifier A could improve the stability of emulsion and reduce the particle size of the copolymer latex. The glass transition temperature of the copolymer was decreased as the content of VAc in the copolymer increased. The solubility of copolymer prepared by semi-continuous emulsion copolymerization was better than that of copolymer prepared by the batch process. VC-VAc-MAH had better adhesion than VC-VAc, and the adhesive strength was increased as MAH content in the copolymers increased.