Synthesis Of PVA And Control Of The Degree Of Polymerization

Polyvinyl alcohol is white flocculent or sheet body, non-toxic and tasteless. It has excellent mechanical properties and surface activity, it is water-soluble high polymer that has been used in many industries such as textile, construction, packaging, polymer chemical etc. The degree of polymerization and alcoholysis of PVA determine its nature and application. The impact of reaction temperature, reaction time, initiator and solvent on the degree of polymerization of PVAc and PVA have been studied, the molecular weight distribution of PVAc is detected by gel chromatography, the degree of polymerization of PVA is detected by Albright Viscometer, according to the differences of molecular weight of PVAc before and after alcoholysis to determine the branched chain situation of polymer, PVA is characterized by infrared spectroscopy.Using AIBN as initiator and methanol as solvent, PVAc is synthesized by solution polymerization in water bath temperature of 70℃, adding solvent step by step, controlling the the average polymerization degree of PVA by different ratio of solvent when solvent added step by step, the good process parameters of synthesis of PVA is:initiator for the monomer mass is 0.00065%, solvent content is 20%, which is added in two steps, step by step by the ratio of 14.77%+6.32%,the reaction time is 2.5h+2.5h, the conversion rate is 32.82%, the average polymerization degree of PVAc is 3311, the average polymerization degree of PVA is 3083, Mw/Mn is 1.549.The conversion rate of vinyl acetate increases when reaction time extends, the average polymerization degree of PVA firstly increases when reaction time extends, raises to a certain optimal value then drops off with reaction time extending. Reaction time is controlled in order to keep the balance between conversion rate of vinyl acetate and polymerization degree of PVA, the good process parameters of synthesis of PVA is:initiator for the monomer mass is 0.00065%, solvent content is 20%, which is added in two steps, step by step by the ratio of 11%+10.28%,the reaction time is 2.5h+2.5h, the conversion rate is 29.51%, the average polymerization degree of PVAc is 2956, the average polymerization degree of PVA is 2917, Mw/Mn is 1.424; the conversion rate is 44.94%, the average polymerization degree of PVA is 2588 when the reaction time is 2.5h+3.5h.