Atactic poly(vinyl alcohols) (a-PVAs) having number-average degrees of polymerization [(P n )s] of 1700 and 4000 were prepared by the solution polymerization of vinyl acetate, which was followed by the saponification of poly(vinyl acetate) to investigate the effects of molecular weights of a-PVA on the characteristics of electrospun a-PVA nanofabrics. A-PVA nanofabrics were prepared by electrospinning with controlling the process parameters including the electrical field, conductivity, tip-to-collector distance, and solution concentration. Through a series of characterization experiments, we identified that the molecular weight of a-PVA had a marked influence on the structure and properties of nanofabrics produced. That is, the higher the molecular weight of PVA, the superior the physical properties of PVA nanofabric.
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ABSTRACT:To prepare high molecular weight (HMW) poly(vinyl acetate) (PVAc) with high yield and high linearity as a precursor of HMW poly(vinyl alcohol) (PVA), vinyl acetate (VAc) was emulsion polymerized using, azo initiator, 2,2Ј-azobis(2-amidinopropane) dihydrochloride (AAPH). This was compared with the polymerization using potassium peroxodisulfate (KPS) as an initiator at various polymerization conditions. PVA, having a maximum number average degree of polymerization (P n ) of 3500 was obtained by the saponification of PVAc with P n of 13,000 -14,000, degree of branching (DB) for the acetyl group of about 3.4 -3.5, and a maximum conversion of VAc into PVAc of 95%, which was polymerized by AAPH. These numerical values were superior compared with 14,500 -15,000 of P n of PVAc, obtained by KPS, and 3100 of maximum P n of resulting PVA, DB of about 3.7-3.8, and maximum conversion of 90%. From the foregoing experimental results, we found that AAPH was a more efficient initiator than KPS in increasing both conversion of PVAc and molecular weight of PVA. In addition, PVAc microspheres, obtained by these emulsion polymerizations, can be converted to PVA / PVAc shell / core microspheres through a series of surface-saponifications, maintaining their spherical morphology. Various surface morphologies, such as flat or wrinkled and swellable or nonswellable ones formed by the various molecular parameters and saponification conditions, were examined.
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