We prepared poly(N-isopropylacrylamide-r-N-3-(aminopropyl)methacrylamide) (poly(NIPAAm-r-NAPMAm)) gels with poly NIPAAm (PNIPAAm) grafted only in the surface region (so-called thermoresponsive surface-grafted gels) with various graft densities and investigated the effect of the graft density on the bulk volume change properties, shrinking and swelling, in response to temperature changes. Initiators for atom-transfer radical polymerization (ATRP) and structurally analogous compounds were introduced at certain ratios onto the surface regions of the gels, and a subsequent activator regeneration by electron transfer ATRP of NIPAAm was conducted in aqueous media. The graft densities and molecular weights of the grafted polymers were evaluated from the increment in the dry mass of the gels and the amount of introduced ATRP initiators, which was measured by elemental analyses. Three-dimensional measuring laser microscopy revealed that the prepared gels had graft-density-dependent fine wrinkle structures on their surfaces. The surface-grafted gels induced the formation of skin layers during the shrinking process in response to a temperature increase, and their permeability strongly depended on the graft density. The graft density also controlled the kinetics of the swelling behavior in response to a temperature decrease. These physical properties were discussed on the basis of Young’s modulus of the surface determined by an atomic force microscopy force curve measurement and the homogeneity of the surface polymer network observed by cryo-scanning electron microscopy. This makes it possible to arbitrarily control the characteristics of gels as open or semiclosed systems, which was uniquely determined by the designs of the surface gel networks.

中文翻译：

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热响应性表面接枝凝胶：通过各种密度的表面局部聚合物接枝来控制体积变化特性

我们制备了聚（N-异丙基丙烯酰胺-r - N -3-（氨基丙基）甲基丙烯酰胺）（聚（NIPAAm- r-NAPMAm））凝胶，仅在具有不同接枝密度的表面区域接枝有聚NIPAAm（PNIPAAm）的凝胶（所谓的热响应表面接枝凝胶），并研究了接枝密度对体积变化特性，收缩和溶胀的影响响应温度变化。将原子转移自由基聚合引发剂（ATRP）和结构类似的化合物以一定比例引入到凝胶的表面区域，然后在水性介质中通过NIPAAm的电子转移ATRP进行随后的活化剂再生。由凝胶的干质量的增加和引入的ATRP引发剂的量来评估接枝聚合物的接枝密度和分子量，这通过元素分析来测量。三维测量激光显微镜显示，所制备的凝胶在其表面上具有依赖于移植物密度的细皱纹结构。在温度升高的过程中，表面接枝的凝胶在收缩过程中诱导了表皮层的形成，其渗透性强烈取决于接枝密度。接枝密度还控制了响应温度降低的溶胀行为的动力学。在通过原子力显微镜力曲线测量确定的表面的杨氏模量和通过冷冻扫描电子显微镜观察到的表面聚合物网络的均匀性的基础上，讨论了这些物理性质。这样就可以任意控制凝胶的特性，如开放式或半封闭式系统，