Horváth Judit, Nagy Miklós
Institute of Chemistry, Eötvös LorAnd University, P.O. Box 32, H-1518 Budapest 112, Hungary.
J Phys Chem B. 2007 May 17;111(19):5140-8. doi: 10.1021/jp070427t. Epub 2007 Apr 18.
Stoichiometric La3+, Ce3+, and Nd3+ salts of poly[(vinyl alcohol)-co-(vinyl sulfate)] (PVAS) copolymer polyacids have been studied in aqueous solution without added salt. All LnPVAS salts were entirely water-soluble in the composition and concentration range investigated. Ratios of the vinyl sulfate and vinyl alcohol units in the copolymers were between 1:5 and 1:107, leading to structural charge densities both above and under the critical value needed for counterion condensation of trivalent counterions. Solvent activity, a1, has been measured by the gel deswelling method in the concentration range of 5 x 10(-4) to 1 x 10(-1) mol of counterion/kg of water (0.2-9 w/w% of the polyelectrolyte). Results are unusually high for polyelectrolytes (-2 x 10(-6) > ln a1 > -3 x 10(-4)), and they are comparable with values determined in solutions of uncharged polymers. Nevertheless, the different copolymers can be clearly distinguished; the water activity is lowered in the order of the vinyl sulfate content of the polyelectrolytes, except for the one above the critical charge density. No observable difference was caused in the thermodynamic properties by the different lanthanide counterions. Reduced osmotic pressure curves and Flory-Huggins pair interaction parameters have been calculated; both of them were used to estimate degrees of dissociation at zero as well as at finite concentrations. Degrees of dissociation are decreasing with increasing concentration or vinyl sulfate content of the copolymer. They take values between 8-36% at zero polymer concentration and they reach zero value simultaneously at approximately 1 x 10(-3) mol of polymer chains/kg of water. The average number of released counterions per polymer chain (DPn = 1005) approaches to a limit of about 4.4 with increasing vinyl sulfate content. This corresponds to average charge distances of b > or = 19 nm and charge density parameters of xi < or = 0.037. The latter is, however, a very low value and indicates a 1/9 contraction compared to the rod-like assumption.
已对聚[（乙烯醇）-共-（乙烯基硫酸盐）]（PVAS）共聚物多元酸的化学计量La3+、Ce3+和Nd3+盐在未添加盐的水溶液中进行了研究。在所研究的组成和浓度范围内，所有LnPVAS盐在水中完全可溶。共聚物中乙烯基硫酸盐和乙烯醇单元的比例在1:5至1:107之间，导致结构电荷密度高于和低于三价抗衡离子进行抗衡离子凝聚所需的临界值。通过凝胶溶胀法在5×10(-4)至1×10(-1)摩尔抗衡离子/千克水（0.2-9 w/w%的聚电解质）的浓度范围内测量了溶剂活度a1。对于聚电解质来说，结果异常高（-2×10(-6)＞ln a1＞-3×10(-4)），并且与在不带电聚合物溶液中测定的值相当。然而，不同的共聚物可以明显区分；除了高于临界电荷密度的那种共聚物外，水活度按照聚电解质中乙烯基硫酸盐含量的顺序降低。不同的镧系抗衡离子在热力学性质上未引起可观察到的差异。已计算了比渗透压曲线和弗洛里-哈金斯对相互作用参数；二者都用于估计零浓度以及有限浓度下的解离度。解离度随共聚物浓度或乙烯基硫酸盐含量的增加而降低。在聚合物浓度为零时，它们的值在8-36%之间，并且在大约1×10(-3)摩尔聚合物链/千克水时同时达到零值。随着乙烯基硫酸盐含量的增加，每条聚合物链释放的抗衡离子的平均数（DPn = 1005）接近约4.4的极限值。这对应于平均电荷间距b≥19 nm和电荷密度参数ξ≤0.037。然而，后者是一个非常低的值，表明与棒状假设相比收缩了1/9。
