Study On Azo Initiators In The Synthesis Of Ultra-low Polymerization Degree Polyvinyl Alcohol

In this paper,first of all vinyl acetate is raw material,methanol is solvent,azodiisobutyronitrile is initiator.We synthesized ultra-low degree polyvinyl alcohol by solution polymerization.In the experiment,we studied the influence of the ratio of monomer to solvent,the concentration of initiator,reaction time,reaction temperature and the ratio of chain transfer agent on the degree of polymerization of polyvinyl acetate.The optimum reaction conditions were obtained by orthogonal experiments:the ratio of monomer to initiator was 25:1,the ratio of monomer to solvent was 4:5,the reaction time was 4 hours,and the temperature was 67?.Ultra-low molecular weight polyvinyl alcohol with a degree of polymerization of about 300 was obtained.Compared with the experiments of benzoyl peroxide(BPO)and propylbenzene hydrogen peroxide(CHP),we found that the lowest degree of polymerization of PVA synthesized by BPO and CHP were 465 and 334 at 60~70?.The yields of PVA synthesized were 80%and 75%.The degree of polymerization of the product synthesized by AIBN as initiator was lower,about 300,and the yield was higher,reaching about 85%in actual production.Initiators are easy to store and the products are transparent or white.Because of the above advantages,we choose azo initiators for further research.Using azodiisopentanitrile(AMBN),azodicyclohexyl formamide(ACCN),dimethyl azobutyrate(AIBME)and azodiisoheptanitrile(ABVN)as initiators,the optimum reaction conditions were explored in the system of polyvinyl alcohol polymerization:the ratio of monomer to initiator was 25:1,the ratio of monomer to solvent was 1:1,and the lowest polymerization was obtained at 67?,65?,70?,70? degrees respectively.The fitness was 689,484,255 and 156.By means of infrared spectroscopy(IR),nuclear magnetic resonance(NMR),differential scanning calorimetry(DSC),thermogravimetric analysis(TGA),scanning electron microscopy(SEM),gel permeation chromatography(GPC)and other means,it is found that the homemade PVA is low melting and crystallization temperatures,and the heat resistance is better,which is about 100?.It can dissolve completely and has better water solubility.