Study On Syndiotactic-rich And High Molecular Weight PVA

The synthesis of vinyl pivalate (VPi) was studied in this paper, the effect of reaction conditions such as the temperature, the pressure, the reaction time and the catalyst were investigated and a reasonable way for synthesizing VPi was found in the laboratory. The structure of the VPi was characterized by IR spectrum. The syndiotactic-rich and high molecular weight poly(vinyl pivalate)(PVPi) was obtained by solution polymerization and suspension polymerization, respectively.PVPi was synthesized by solution polymerization in dimethyl sulfoxide (DMSO) using 2,2-azobis(2,4-dimethylvaleronitrile) (ADMVN) as initiator at 30℃. The optimum conditions were obtained by orthogonality design, the ratio of monomer to solvent is 15mL:10mL, the concentration of ADMVN is 2.88×10^-3mol·L^-1, the reaction time is 19h. PVPi was obtained with M n 3008 and MWD 3.07. The stereoregularity of PVPi is 80% measured by 1HNMR spectrum.PVPi was also synthesized by suspension polymerization using ADMVN as initiator and poly(vinyl alcohol) as stabilizer. The optimum conditions were gained by orthogonality design, the ratio of oil and water is 5mL:30mL, the concentration of ADMVN is 1.65×10^-3mol·L^-1, the concentration of stabilizer is 1.5% in distilled H2O, the reaction temperature is 30℃, the reaction time is 26h. High molecular weight PVPi was obtained by suspension polymerization, having a number-average degree of polymerization of 6365, the molecular weight distributing of 2.74 measured by GPC spectrum. The stereoregularity of PVPi is 86% measured by 1HNMR spectrum.Suspension polymerization has more advantage than solution polymerization for synthesizing syndiotactic-rich and high molecular weight PVPi by contrast the two different process conditions. Finally the saponification conditions of PVPi were investigated and the process conditions of saponification were discussed, such as the concentration of activator, the temperature of saponification, the drop speed of NaOH-CH₃OH solution and the reaction time and so on. In the end, PVA was obtained with M_n|─6100 and stereoregularity 80%.