Study on chain transfer reaction of poly(vinyl acetate) radical with poly(vinyl alcohol) in a homogeneous system.

The first purpose of this study is to obtain effectively the graft copolymer of poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc). Polymerization of VAc in the presence of PVA in dimethyl sulfoxide (DMSO) was investigated. The second purpose of the study is to obtain a PVA having a long branch whose properties have not been clarified yet. By hydrolyzing the PVAc portion in the graft copolymer, the PVA having a long branch might be obtained. The polymerization system was thought to be homogeneous since DMSO is a common solvent for PVA and PVAc at 60°C. Prior to the experiment, solution polymerization of VAc in DMSO was carried out in the absence of PVA to know the chain transfer constant (C_S) to DMSO. The C_S value was determined to be 0.7×10^-4. Then the chain transfer constant to PVA (C_P) on the basis of monomer unit was measured to be 9.9×10^-4. The C_P value was much smaller than the value we had expected, since the C_S to isopropanol, whose structure resembles that of the vinyl alcohol unit in PVA, had been reported to be about 5-times larger than this. The reason of the rather smaller value of C_P appeared arise from the substantial decrease in concentration of the reactive sites that are buried in the polymer coil. The aimed graft copolymer of PVA and PVAc, as well as the PVA having a long branch, was proved to be rather difficult to obtain, since the reactivity of PVA molecule in the chain-transfer reaction is much lower than that of isopropanol. [ABSTRACT FROM AUTHOR]