Mori Takeshi, Nakashima Masashi, Fukuda Yasuhisa, Minagawa Keiji, Tanaka Masami, Maeda Yasushi
Department of Chemical Science and Technology, Faculty of Engineering, University of Tokushima, 2-1 Minamijosanjima, Tokushima 770-8506, Japan.
Langmuir. 2006 Apr 25;22(9):4336-42. doi: 10.1021/la060212v.
Several poly(N-vinylacetamide-co-acrylic acid)s with various copolymer compositions have been synthesized, and their unique phase-transition behavior in aqueous salt (Na2SO4 or NaCl) solutions was investigated. Copolymers containing more than 51 mol % N-vinylacetamide (NVA) show reentrant soluble-insoluble-soluble transitions with increasing temperature. The soluble-insoluble transition temperature (T(p1)) increased linearly with increasing NVA content, whereas the insoluble-soluble transition temperature (T(p2)) was almost constant irrespective of the NVA content. Potentiometric titration of the copolymer solutions suggested that the acrylic acid (AA) carboxyl groups form hydrogen bonds with the NVA amide groups even under soluble conditions. Dehydration of the NVA amides and their consequent hydrogen bonding with the AA carboxyl groups during the soluble-insoluble transition process was indicated by FTIR measurements. Addition of salt (Na2SO4 or NaCl) to the aqueous media reduces the solvent quality and enhances the intra- and interchain interactions of the copolymers. Thus, T(p1) was observed to decrease and T(p2) was observed to increase with increasing salt concentration. However, the addition of urea to the media reverses the concentration dependence of T(p1) and T(p2) by disturbing the intra- and interchain interactions of the copolymers.
合成了几种具有不同共聚物组成的聚（N - 乙烯基乙酰胺 - 共 - 丙烯酸），并研究了它们在盐水（Na2SO4或NaCl）溶液中独特的相变行为。含氮乙烯基乙酰胺（NVA）超过51摩尔％的共聚物随着温度升高呈现再入式可溶 - 不溶 - 可溶转变。可溶 - 不溶转变温度（T(p1)）随NVA含量增加呈线性增加，而不溶 - 可溶转变温度（T(p2)）几乎与NVA含量无关，保持恒定。共聚物溶液的电位滴定表明，即使在可溶条件下，丙烯酸（AA）羧基也与NVA酰胺基团形成氢键。傅里叶变换红外光谱（FTIR）测量表明，在可溶 - 不溶转变过程中，NVA酰胺发生脱水，并因此与AA羧基形成氢键。向水介质中添加盐（Na2SO4或NaCl）会降低溶剂质量，并增强共聚物的链内和链间相互作用。因此，观察到T(p1)随盐浓度增加而降低，T(p2)随盐浓度增加而升高。然而，向介质中添加尿素会扰乱共聚物的链内和链间相互作用，从而逆转T(p1)和T(p2)对浓度的依赖性。
