| 초록 |
Poly(vinyl alcohol) (PVA) is a semicrystalline polymer, which have inter- and intramolecular hydrogen bondings. PVA is classified into three types, such as isotactic, atactic, and syndiotactic ones according to the stereoregularity of hydroxyl groups. In this study, high molecular weight (HMW) atactic PVA (a-PVA) was prepared by suspension polymerization of vinyl acetate at 40 ℃ and subsequent saponification. A-PVA with number-average degree of polymerization of 4,000 and degree of saponification of 99.9% was dissolved in a mixture of dimethyl sulfoxide (DMSO) and water at three different high polymer concentrations: 7.5, 10, 12.5% (g/dL). Viscoelastic behaviors of HMW a-PVA/DMSO/water solutions during sol-gel transition were investigated through rheological response at different solution temperatures of 90, 80, and 30 ℃. Complex viscosity was decreased with increasing solution temperature when other parameters were held the same. Dynamic storage modulus (G') of a-PVA solutions was smaller than dynamic loss modulus (G") at the sol state. At the post gel state, G' became larger than G", indicating the evolution of viscoelastic solid properties.
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