Investigation of Reaction Conditions for Preparation of Medium MolecularWeight Poly(vinyl alcohol) as Emulsifier

Poly(vinyl alcohol) (PVA) is a water soluble polymer with excellent physical and chemical properties. The basic properties of this polymer depend on its molecular weight, degree of hydrolysis and distribution. Since the commercial applications of PVA are many and varied, therefore, a special grade of PVA with considerable properties is required as an emulsifier. A polymerized ester can be used for preparation of PVA types, because vinylalcohol monomer does not exist in the free state. The characteristics of the preparation of poly(vinyl acetate) (PVAc) are very important in the manufacture of PVA. In this work, a partially hydrolyzed grade of PVA having characteristics suitable for application in emulsion polymerization of vinyl acetate (VAc) (Mv: 77200, hydrolysis degree: 89.2%) was prepared by investigation of reaction conditions for solution polymerization of VAc by the aids of α,α'' azobisisobutyronitrile (AIBN) initiator in methanol and the subsequent saponification reaction of the resulted PVAc in the presence of NaOH. This was including investigation of the effect of [VAc]/[AIBN] ratio and polymerization time for preparation of PVAc at 60ºC in terms of VAc conversion and PVAc molecular weight, then the effect of saponification time of PVAc in terms of the molecular weight and hydrolysis degree of PVA product. In case of some samples, concentration of the monomer relative to that of the initiator plays an important role in VAc conversion value and controlling the PVAc molecular weight. The results from saponification of PVAc samples revealed that, only one of the samples was that its saponification resulted in PVA material desired molecular weight at 1 h. 1H NMR Spectra of PVAc and PVA were used to show a branched molecular structure of PVAc and estimation of the degree of hydrolysis of a PVA sample. The presence of typical characteristics absorption bands in IR spectra of PVAc and PVA samples agrees with proposed structures. To confirm the result earned, the characteristics of PVA obtained were compared with those of the commercially used PVA grades (Mowiols).