Changchun Institute of Applied Chemistry Chinese Academy of Sciences, Changchun 130022, China.
J Colloid Interface Sci. 2010 May 15;345(2):360-8. doi: 10.1016/j.jcis.2010.01.058. Epub 2010 Jan 28.
Series of hydrophilic core-shell microgels with cross-linked poly(N-isopropylacrylamide) (PNIPAAm) as core and poly(vinyl amine) (PVAm) as shell are synthesized via surfactant-free emulsion polymerization. Then, the microgels are treated with a small amount of potassium persulfate (KPS) to generate free radicals on the amine nitrogens of PVAm, which subsequently initiate the graft copolymerization of acrylic acid (AA), acryloyloxyethyl trimethyl ammonium chloride (DAC), and acrylamide (AAm) onto microgels to prepare multi-responsive composite hydrogels. The composite hydrogels consist of cross-linked ungrafted polyampholyte chains as the first network and microgels with grafted polyampholyte chains as graft point and second network and show surprising mechanical strength and rapid response rate. The investigation shows the compress strength of composite hydrogels is up to 17-30 MPa, which is 60-100 times higher than that of the hydrogel matrix. The composite hydrogel shows reversible switch of transmittance when traveling the lowest critical temperature (LCST) of microgels. When the composite hydrogel swollen in pH 2.86 solution at ambient condition is immersed into the pH 7.00 solution at 45 °C, a rapid dynamic shrinking can be observed. And the character time (τ) of shrinking dynamic of composite hydrogel is 251.9 min, which is less than that of hydrogel matrix (τ=2273.7 min).
通过无皂乳液聚合合成了一系列以交联聚 N-异丙基丙烯酰胺（PNIPAAm）为核、聚（乙烯基胺）（PVAm）为壳的亲水性核壳微凝胶。然后，将微凝胶用少量过硫酸钾（KPS）处理，在 PVAm 的胺氮上生成自由基，随后引发丙烯酸（AA）、丙烯酰氧基乙基三甲基氯化铵（DAC）和丙烯酰胺（AAm）接枝共聚到微凝胶上，制备多响应复合水凝胶。复合水凝胶由交联的未接枝聚两性电解质链作为第一网络和带有接枝聚两性电解质链的微凝胶作为接枝点和第二网络组成，表现出惊人的机械强度和快速响应速度。研究表明，复合水凝胶的压缩强度高达 17-30 MPa，是水凝胶基质的 60-100 倍。当复合水凝胶在环境条件下的 pH 2.86 溶液中溶胀，然后浸入 45°C 的 pH 7.00 溶液中时，会出现透光率的可逆开关。并且复合水凝胶的收缩动态的特征时间（τ）为 251.9 min，小于水凝胶基质的特征时间（τ=2273.7 min）。
