【作者】 赵趱；

【导师】 沈家骢； 王力彦；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2012， 博士

【摘要】 层状组装是一种强有力的制备具有可控结构和组成的薄膜的方法，利用这种方法科学家们已经制备出多种功能膜材料。近年来，一些研究组对于使用层状组装的方法来制造温度响应薄膜的兴趣逐渐增加，通过改变温度可以控制表面湿润性、表面粘附性和薄膜的渗透性等。目前制备温度响应性多层膜的途径主要有两条，一是通过共聚把具有组装能力的单体引入温度响应性聚合物中，然后通过静电力或者化学反应组装成膜。这种方法相对繁琐，需要合成共聚物。二是直接使用温度响应性的均聚物基于氢键组装成膜，一般是和聚羧酸类在酸性溶液中组装成膜，限制了此类温度响应性薄膜在生理条件下的应用。在本论文中，我们测量了一些温度响应性高分子在两两混合后的溶液浊点，发现某些混合溶液的浊点显著降低，表明高分子间存在相互作用，利用这一特性，选择了五种温度响应性均聚物，分别是：聚乙烯基己内酰胺（PVCL）、聚（2-羟丙基丙烯酸酯）（PHPA）、聚（N-L-(1-羟甲基丙基)甲基丙烯酰胺）（P(L-HMPMAm)）、聚（N-异丙基丙烯酰胺）（PNIPAAm）和聚（N-正丙基丙烯酰胺）（PnPMAm），在中性pH下组装多层膜，研究了多层膜在逐步降温的水中的溶解行为，以及四甲基尿素和几种无机盐对高分子多层膜的温度响应性的影响。在论文的第二章，比较了几种中性温度响应性聚合物水溶液的浊点与它们两两混合后的浊点，发现有些混合溶液浊点明显降低，其中包括PVCL/PHPA、PVCL/P(L-HMPMAm)和PNIPAAm/PHPA混合体系。浊点的明显降低意味着不同种的聚合物链之间的相互作用强于同种的聚合物链之间的相互作用，而高分子间的相互作用是层状组装的先决条件。接下来，我们在一恒定温度下将中性的温度响应性聚合物PVCL和PHPA在中性pH组装成膜。该薄膜在温度比组装时更低的纯净水中能被部分溶解；然而在中性pH值的缓冲溶液中，在组装温度时薄膜则相对稳定。此外，PVCL/P(L-HMPMAm)和PNIPAAm/PHPA同样都能在中性pH组装成膜，表明这种在中性pH组装温度响应性多层膜的方法并不是特例，通过混合溶液的相图可以预测哪对高分子适合于进行层状组装。为了详细说明温度对PVCL/PHPA多层膜溶解的影响，我们使用了一种简单的扩散限制的脱附模型来描述多层膜在固定温度纯净水中的溶解过程。随温度降低多层膜的溶解速率增加，最终剩余分数也逐渐减小，因而可以用温度控制多层膜的剩余分数。在论文的第三章，我们在28°C下将中性的温度响应性聚合物PnPMAm和PHPA组装成膜，随温度降低该薄膜能溶解于纯净水中。加入四甲基尿素使多层膜的溶解温度升高，在不同浓度的四甲基尿素溶液中，高分子混合溶液的浊点越高，薄膜的溶解温度也越高，也就是说，四甲基尿素对薄膜的溶解温度的影响和对高分子混合溶液的浊点的影响是正相关的。接下来，在28°C通过改变四甲基尿素溶液的浓度，实现了剩余分数可控的薄膜溶解。在论文的第四章，我们在一恒定温度下将中性的温度响应性聚合物PVCL和P(L-HMPMAm)组装成膜，发现随温度降低高分子的组装量逐渐减少，并且随温度降低，组装好的多层膜能逐渐溶解于纯净水中。加入不同种类不同浓度的盐酸盐，PVCL和P(L-HMPMAm)混合溶液的浊点降低。并且多层膜在盐酸盐溶液中的溶解温度比在纯净水中更低。经过对比分析，这几种盐酸盐对薄膜的溶解温度的影响和对高分子混合溶液的浊点的影响是正相关的。PVCL/P(L-HMPMAm)、PVCL/PHPA和PnPMAm/PHPA三个多层膜在NaCl溶液中都比在水中更稳定，盐酸盐的加入使得薄膜变得更稳定的原因可能是温度响应性的聚合物的盐析。更多还原

【Abstract】 Layer-by-layer (LbL) assembly is a powerful means for fabricating multilayer thin filmswith controlled architecture and composition. Scientists have fabricated multilayer films withvarious kinds of functions by using LbL assembly. In recent years, some groups focused theirresearch interest on fabricating temperature-responsive films through LbL assembly. Suchfilms allow control of surface wettability, adhesion properties and film permeability, etc. bychanges in temperature.Two approaches are usually applied for preparing temperature-responsive multilayerfilms.(1) The second monomer with assembly capability is introduced into atemperature-responsive polymer through copolymerization, and a temperature-responsive LbLfilm is then assembled via covalent bonds or electrostatic interactions. This approach is notconvenient, and a copolymer has to be synthesized.(2) LbL films are assembled usingtemperature-responsive homopolymers via hydrogen bonding. Hydrogen-bonded LbL films ofneutral temperature-responsive homopolymers were usually assembled with poly(carboxylicacid)s at low pH, and this limits the application of the films at physiological conditions. In thisdissertation, we measured the cloud points of mixed solutions of every two polymers amongseveral temperature-responsive polymers. It was found that the cloud point of some mixedsolutions significantly decreased, which indicated interpolymer interaction. Thus, we selectedfive temperature-responsive polymers, poly(N-vinylcaprolactam)(PVCL),poly(2-hydroxypropyl acrylate)(PHPA), poly(N-L-(1-hydroxymethylpropyl)methacrylamide)(P(L-HMPMAm)), poly(N-isopropylmethacrylamide)(PNIPMAm) and poly(N-propyl-methacrylamide)(PnPMAm). Multilayer films were assembled at neutral pH. Dissolution ofthe multilayer film was studied in purified water with step-by-step decrease of temperature.Furthermore, the effects of tetramethylurea and several salts on temperature-responsivedissolution of multilayer films were studied.In Chapter2, the cloud point of some mixed solutions of temperature-responsivepolymers is lower than both cloud points of the corresponding pure polymers, such asPVCL/PHPA, PVCL/P(L-HMPMAm), and PNIPAAm/PHPA. The significant decrease of cloud points of mixed solutions of temperature-responsive polymers suggested that theintermolecular interaction between two polymer chains of different kinds was stronger thanthat between two polymer chains of the same kind. Strong intermolecular interaction betweentwo polymer chains of different kinds is a prerequisite for LbL assembly. Thus, a LbL film oftwo temperature-responsive polymers, PVCL and PHPA, was fabricated at neutral pH at aconstant temperature. The film can be partially dissolved when immersed in purified water at alower temperature. In contrast, the LbL film is relatively stable in buffer solutions nearphysiological pH at the assembly temperature. Additionally, a PVCL/P(L-HMPMAm)multilayer film and a PNIPAAm/PHPA multilayer film were also successfully assembled atneutral pH. Successful fabrication of these LbL films indicates that phase behavior of mixedsolutions of temperature-responsive polymers provides an important guide for the selection ofpolymers suited for hydrogen-bonded LbL assembly at neutral pH. To clarify the effect oftemperature on dissolution of films, the dissolution process of films at a constant temperaturein purified water can be described by a stretched exponential kinetics. As the temperaturedecreased, the dissolution rate increased and final remaining fraction decreased. Watertemperature can be used to control the remaining fraction of the PVCL/PHPA multilayer film.In Chapter3, a LbL film of two neutral temperature-responsive polymers, PnPMAm andPHPA, was fabricated at28°C. The film can be dissolved when immersed in purified water ata lower temperature. The dissolution temperature of the film increased in tetramethylureaaqueous solutions. In tetramethylurea aqueous solutions with different concentration, as thecloud point of mixed solutions of temperature-responsive polymers increased, the dissolutiontemperature of films also increased. In other words, the effect of tetramethylurea ondissolution temperature of films and that on cloud point of mixed solutions are positivelycorrelated. The remaining fraction of temperature-responsive films could be controlled bychanging the concentration of tetramethylurea aqueous solutions.In Chapter4, a LbL film of two neutral temperature-responsive polymers, PVCL andP(L-HMPMAm), was fabricated at a constant temperature. The assembly amount of polymersdecreased with the decrease in assembly temperature. The film can be dissolved when immersed in purified water at a lower temperature. The cloud points of mixed solutions ofPVCL and P(L-HMPMAm) decreased when several chloride salts with different concentrationwere added. The dissolution temperature of multilayer films in chloride salts solutions is lowerthan in purified water. The effect of these chloride salts on dissolution temperature ofmultilayer films and that on cloud point of mixed solutions are positively correlated.PVCL/P(L-HMPMAm), PVCL/PHPA and PnPMAm/PHPA multilayer films in NaCl solutionsare more stable than in purified water. These phenomena could be attributed to salting-out oftemperature-responsive polymers.更多还原