Department of Chemistry, University of Cologne , Luxemburger Strasse 116, D-50939 Cologne, Germany.
Langmuir. 2011 Mar 15;27(6):2997-3005. doi: 10.1021/la104585k. Epub 2011 Feb 3.
Copolymer hydrogels were prepared from an aqueous micellar solution of the nonionic surfactant monomer (surfmer) ω-methoxy poly(ethylene oxide)40undecyl-α-methacrylate (PEO-R-MA-40) and acrylic acid (AA) in a one-step reaction using γ-irradiation. The hydrogels were transparent if the polymerization was carried out at pH ≥ 4, whereas turbid gels were obtained if the polymerization was carried out at lower pH. Exposure of the turbid gels to an aqueous solution of pH 11 led to swelling and clearing, whereas subsequent exposure to pH 1 had the reverse effect. Clear gels prepared at pH 4 became turbid, if exposed to an aqueous solution of lower pH and became clear again if reswollen at higher pH. The pH at which clouding set in increased with the amount of surfmer copolymerized in the gel. Pure poly(acrylic acid) (P-AA) hydrogels did not show any changes in transparency if the pH was varied. The presence of surfmer led to more pronounced shrinking and swelling, especially if the gels were prepared at pH 4. The mechanical stability of P-AA and copolymer hydrogels was studied using elongational flow measurements. The presence of surfmer led to increased mechanical stability of the hydrogels. The increase originates from copolymerized micellar aggregates acting as additional, stable cross-linking units in the gel. The true stress at break of copolymer hydrogels prepared at pH 2.4 (or 4) was 5.5 (or 3.4) times larger than for surfmer-free P-AA gels. Possible origins for the higher stability such as complex formation between P-AA and oxyethylene segments of copolymerized PEO-R-MA-40 are discussed.
共聚水凝胶由非离子表面活性剂单体（surfmer）ω-甲氧基聚（氧化乙烯）40 十一烷基-α-甲基丙烯酸酯（PEO-R-MA-40）和丙烯酸（AA）在水溶液中的胶束溶液中一步反应γ-辐照制备。如果聚合在 pH≥4 下进行，则水凝胶是透明的，而如果在较低 pH 下进行聚合，则得到混浊凝胶。将混浊凝胶暴露于 pH 11 的水溶液中会导致溶胀和澄清，而随后暴露于 pH 1 会产生相反的效果。在 pH 4 下制备的透明凝胶如果暴露于较低 pH 的水溶液中会变得混浊，如果在较高 pH 下重新溶胀则会再次变澄清。混浊开始出现的 pH 值随凝胶中共聚的 surfmer 量增加而增加。如果改变 pH 值，纯聚丙烯酸（P-AA）水凝胶不会显示透明度的任何变化。存在 surfmer 会导致更明显的收缩和溶胀，尤其是如果在 pH 4 下制备凝胶。使用拉伸流测量研究了 P-AA 和共聚物水凝胶的机械稳定性。存在 surfmer 会增加水凝胶的机械稳定性。这种增加源自共聚胶束聚集体在凝胶中充当额外的、稳定的交联单元。在 pH 2.4（或 4）下制备的共聚物水凝胶的断裂真实应力（或 3.4）是无 surfmer 的 P-AA 凝胶的 5.5（或 3.4）倍。讨论了更高稳定性的可能起源，例如共聚的 PEO-R-MA-40 与 PAA 之间的络合形成和与氧乙氧基段之间的络合形成。
