Study On Non-Nitrile Compound Initiator Used For Biological Vinyl Acetate Solution Polymerization

The polymerization of vinyl acetate (VAc) is induced by free radical and generates poly (vinyl acetate) (PVAc), then the PVAc is catalyzed alcoholysis by acid or alkali and generates poly (vinyl alcohol) (PVA). Traditional initiator of solution polymerization of VAc is azobisisobutyronitrile (AIBN), resulting in CN residue connects to the end of macromolecular chain, PVAc contains toxic CN residue. In this paper, the solution polymerization reaction was studied with VAc made by biological ethylene method (Bio-VAc) as monomer, lauroyl peroxide (LPO) and di-tert-butyl peroxide (DTBP) as non-nitrile compound initiator and methanol (MeOH) as solvent, then the optimum polymerization condition was determined and kinetics model of the solution polymerization reaction was established. The principal researches were as follows:Influences of speed of agitator, reaction temperature, reaction time, dosage of methanol and dosage of initiator on polymerization conversion and degree of polymerization were investigated through single factor experiment and orthogonal experiment. Through variance analysis, the influence extent of these factors for polymerization conversion were in following order:dosage of initiator>reaction time>reaction temperature>dosage of methanol; the influence extent of these factors for degree of polymerization were in following order: dosage of methanol>dosage of initiator>reaction temperature>reaction time. Through comprehensive evaluation of two indicators about polymerization conversion and degree of polymerization, the optimum polymerization condition was as follows:speed of agitator 200 r·min-1, reaction temperature 65℃, reaction time 3 h, dosage of methanol 10%, dosage of initiator 0.010%. PVA was obtained by optimum reaction condition, it’s average degree of polymerization was 3755, and average polymerization conversion was 45.00%.The changes of polymerization conversion of Bio-VAc with reaction time and the kinetics model of initial stage of solution polymerization were studied. The results showed solution polymerization of Bio-VAc over non-nitrile compound initiator was typical free radical addition polymerization; in initial stage of solution polymerization, pre-exponential factor of reaction (A) was 150.4, activation energy (Ea) was 32.37 kJ·mol-1, the kinetics model was as follows:Properties of LPO-DTBP non-nitrile products and AIBN nitrile products were compared. Structure, molecular weight and its distribution, surface appearance, glass-transition temperature of products and character about mass of the products changed with temperature were characterized by using FT-IR, GPC, SEM, DSC, TG. The results showed structure of non-nitrile products and nitrile products almost had no difference, they were PVAc and PVA, non-nitrile initiator had no effect on structure of the products; molecular weight distribution of LPO-DTBP-PVAc and AIBN-PVAc were 1.66 and 1.70 respectively, they were very close; surface appearance of LPO-DTBP-PVAc was more smooth and level than it of AIBN-PVAc, surface of LPO-DTBP-PVA was level, but surface of AIBN-PVA was not level and had big lumpy appearance; comparing glass-transition temperature (Tg) of products, Tg of LPO-DTBP-PVAc was 34.8·, Tg of AIBN-PVAc was 26.7·, Tg of LPO-DTBP-PVA was 91.6· and Tg of AIBN-PVA was 85.1·, Tg of non-nitrile products were higher than it of nitrile products, this was because non-nitrile products had high molecular weight, narrow distribution and neat surface appearance; LPO-DTBP-PVAc and AIBN-PVAc had two weightlessness, but they had different degree of heat weightlessness under different range of temperature, LPO-DTBP-PVA and AIBN-PVA just had one weightlessness, and they also had different degree of heat weightlessness under different range of temperature.