Department Chemie, Universität zu Köln, Luxemburger Str. 116, D-50939 Köln, Germany.
J Phys Chem B. 2010 May 6;114(17):5666-77. doi: 10.1021/jp911358z.
Thermoresponsive hydrogels were prepared upon radiation-induced copolymerization of aqueous micellar solutions containing N-isopropylacrylamide (NiPAAm) and a cationic surfactant monomer (surfmer), and of microemulsions containing NiPAAm, surfmer, and styrene. Three surfmer compounds were used: (11-(acryloyloxy)undecyl)trimethylammonium bromide (AUTMAB), (11-(methacryloyloxy)undecyl)trimethylammonium bromide (MUTMAB), and (2-(methacryloyloxy)ethyl)dodecyldimethylammonium bromide (MEDDAB). Comonomer solutions were studied on their phase behavior and structure using small-angle neutron scattering (SANS). The presence of surfmers increased the solubility of NiPAAm in the aqueous phase. SANS studies indicate that the surfmers form spherical micelles, which in the presence of styrene are increased and in the presence of NiPAAm are decreased in size. Styrene is incorporated in the core, and NiPAAm is incorporated in the shell of the micelles. If styrene and NiPAAm are present, the effects of both compensate each other, the micelle size remains unchanged, and only small amounts of styrene are solubilized. Evaluation of scattering curves indicated remarkable changes in headgroup dissociation of surfmers in the presence of NiPAAm in the micellar solutions. If exposed to (60)Co-gamma irradiation (dose: 80 kGy), stable, transparent, and thermoresponsive hydrogels were directly obtained. The lower critical solution temperature (LCST) of gels containing surfmer in low concentration was higher than that for pure NiPAAm gels, whereas in gels with high surfmer concentration it was lower. The lowest LCST was observed if MEDDAB was present in the gel. 1 % (w/w) was already sufficient to lower the LCST from 33.2 to 28.5 degrees C. Gels with low surfmer concentration (< or = 1 wt %) exhibited a strong, rapid swelling in water at 20 degrees C and a rapid and reversible shrinking at 50 degrees C. For a gel containing 1% AUTMAB, the swelling ratio was 2.4 times higher (MUTMAB, 2.8; MEDDAB, 1.5) than that for a pure NiPAAm gel. Copolymer gels containing more than 1 wt % surfmer exhibited a strong and rapid swelling below and above the LCST, because the copolymerized ionic surfmer induced an osmotic pressure in the gel. The effects of a variation of NiPAAm and surfmer concentration were studied, and the origins of the thermoresponsive properties are discussed.
制备了温敏水凝胶，方法是将包含 N-异丙基丙烯酰胺（NiPAAm）和阳离子表面活性剂单体（surfmer）的水性胶束溶液以及包含 NiPAAm、surfmer 和苯乙烯的微乳液进行辐射共聚。使用了三种 surfmer 化合物：（11-（丙烯酰氧基）十一烷基）三甲基溴化铵（AUTMAB）、（11-（甲基丙烯酰氧基）十一烷基）三甲基溴化铵（MUTMAB）和（2-（甲基丙烯酰氧基）乙基）十二烷基二甲基溴化铵（MEDDAB）。使用小角中子散射（SANS）研究了共聚单体溶液的相行为和结构。表面活性剂的存在增加了 NiPAAm 在水相中的溶解度。SANS 研究表明，表面活性剂形成球形胶束，在存在苯乙烯的情况下，胶束的尺寸增加，而在存在 NiPAAm 的情况下，胶束的尺寸减小。苯乙烯被包含在核心中，而 NiPAAm 被包含在胶束的壳中。如果存在苯乙烯和 NiPAAm，两者的影响会相互补偿，胶束的尺寸保持不变，并且只有少量的苯乙烯被溶解。对散射曲线的评估表明，在胶束溶液中存在 NiPAAm 时，表面活性剂的头基离解发生了显著变化。如果暴露于（60）Co-γ辐射（剂量：80 kGy），则可以直接获得稳定、透明和温敏水凝胶。含有低浓度 surfmer 的凝胶的低临界溶液温度（LCST）高于纯 NiPAAm 凝胶的 LCST，而在高浓度 surfmer 的凝胶中则低于 LCST。如果凝胶中存在 MEDDAB，则观察到最低的 LCST。存在 1%（w/w）就足以将 LCST 从 33.2 降低到 28.5°C。LCST 较低的凝胶在 20°C 下具有强烈、快速的水膨胀，在 50°C 下具有快速且可逆的收缩。对于含有 1% AUTMAB 的凝胶，其溶胀比（MUTMAB，2.8；MEDDAB，1.5）是纯 NiPAAm 凝胶的 2.4 倍。含有超过 1% surfmer 的共聚凝胶在 LCST 以下和以上都表现出强烈和快速的溶胀，因为共聚离子型 surfmer 在凝胶中引起渗透压。研究了 NiPAAm 和 surfmer 浓度变化的影响，并讨论了温敏性能的起源。
