Emulsion Copolymerization Of Vinyl Chloride With Poly(Ethylene Glycol) Methyl Ether Methacrylate

Poly(vinyl chloride)(PVC)is one of the world’s major thermoplastics and produced worldwide for its excellent mechanical and physical properties.It has been widely applicated in consumer products ranging from packaging to construction materials to health care devices due to the biological properties such as non-specific adsorption with hemoglobin.However,the pure PVC showed poor thermal stability and processing properties towing to its intrinsic structural.Thus,the physical or chemical modifications was commonly required to improve the material properties.Actually,the copolymerization of functional monomers with vinyl chloride monomer(VCM)is a relatively simple but effective technology to endow PVC with desirable properties compared to physical and other chemical modifications.On the one hand,the copolymerized segments can hinder the zippered elimination of HCl and enhance heat resistance.On the other hand,the introduced segment in the PVC based copolymer can afford“free volume”for the movement of polymer chains and reduces the glass transition temperature(T_g)of the copolymer.In terms of the choice of polymerization method,the advantage of emulsion polymerization is that water is the reaction medium,which can reduce the use of volatile organic solvents and improve the transfer of reaction heat.Besides,both of high conversion and molecular weight of polymer latex can be achieved concurrently stemming from its polymerization mechanism features.More importantly,the obtained latex can be directly used as products without further treatment.In my thesis,emulsion polymerization was employed and poly(ethylene glycol)acrylate monomers with good biocompatibility and hydrophilicity was selected to copolymerize with VCM.The effect of the polymerization conditions,such as comonomer concentration,emulsifier dosage,comonomer feed ratio,and chain transfer agent on the monomer conversion,particle size of latex,number-average molecular weight,chemical composition,thermal and mechanical properties were investigated systematically.The main results were summarized as followings:1.The emulsion copolymerization of VCM and poly(ethylene glycol)methyl ether methacrylate(PEGMA,M_w～475)can be conducted successfully when the mass ratio of PEGMA higher than 10%(to total monomer mass).While,the obtained copolymer formed high content of gel fraction.Interestingly,it could be reduced from about 30%to less than 5%by the addition of 2-mercaptoethanol.2.The effect of the conditions,such as polymerization temperature,emulsifier dosage,comonomer feed ratio on the copolymerization system and the structure of copolymer were investigated systematically.The experimental results showed that the VCM/PEGMA ratio in the copolymer composition was close to the initial feed ratio.The T_gvalue of the copolymer was reduced from83.1°C to 59.6°C,and the thermal stability was improved(270°C to 290°C).The hydrophilicity of the P(VCM-co-PEGMA)copolymer was improved and the water contact angle decreased from 91.7°to 63.1°.The elongation at break of the copolymer increased from 2.3%to 45.85%.3.The emulsion copolymerization of PEGMA with VCM at a fixed monomer feed ratio(PEGMA:VCM=20:80)under varied SDS content from1.0%to 0.05%was carried out.It can be drawn that at least 0.2%SDS was required to form micelles and afford sufficient places for the ho-polymerization of VCM.Interestingly,in the present of PEGMA,only 0.05%SDS can maintain the copolymer emulsion colloid with excellent stability,which is quite lower than the CMC value of SDS.Also,the copolymer latexes are uniform in micromorphology.According to the classical emulsion polymerization theory and the polymerization behaviors of the present system,a plausible mechanism that mainly arise from the homogeneous nucleation with the synergy effect of SDS was proposed.4.P(VCM-co-BA-co-PEGMA)copolymer was prepared via emulsion copolymerization.The experimental results showed that the comonomer conversion was about 85%,the M_nwas about 90,000,and the particle size was about 500 nm.What’s more,the BA content was higher while the PEGMA content was lower than the initial feed ratio.The T_g of the copolymer was as low as 31.2°C,and the thermal stability was slightly improved.The transmittance of the copolymer film increased from 74%to 93%.