全亲水无规共聚物P(NIPAM-co-AA)的pH和温度双重刺激响应性水相自组装

从N-异丙基丙烯酰胺(NIPAM)和丙烯酸(AA)单体合成了一种全亲水无规共聚物P(NIPAM-co-AA),实验发现该聚合物在水相中可以产生pH或温度双重刺激响应性自组装.采用透射电子显微镜(TEM)观察了自组装体的形貌,采用动态光散射(DLS)和静态光散射(SLS)观察了其粒径及粒径分布.测定了该聚合物水溶液的最低临界溶解温度(LCST)及其zeta电位随pH的变化,通过分析NIPAM和AA两种链节的质子化状态随温度和pH变化的趋势,阐释了其在水相中产生双重响应性自组装的推动力;并结合傅里叶红外(FT-IR)光谱测定自组装体表面富集基团的结果,进一步阐释了不同环境下自组装体的微结构.这类全亲水无规共聚物的合成方法简单,具有pH和温度双重响应性,其全水相中的刺激响应性自组装行为在药物释放等方面具有潜在的应用价值.

Dual pH-and Thermo-Responsive Self-Assembly of the P(NIPAM-co-AA) Hydrophilic Random Copolymer in Pure Aqueous Solution

The random poly(N-isopropylacrylamide-co-acrylic acid) copolymer (P(NIPAM-co-AA)) was synthesized and its stimuli-responsive self-assembly in pure aqueous solution was investigated. P(NIPAMco-AA) is a dual pH-and thermo-responsive hydrophilic random copolymer because it can self-assemble in pure aqueous solution in response to the stimuli of pH and temperature. The morphologies of P(NIPAM-co-AA) assemblies were imaged by transmission electron microscopy, and the radius (R_h) and radius distribution were determined by dynamic and static light scattering. The lower critical solution temperature (LCST) of P(NIPAM-co-AA) and the zeta potential change of the aqueous solution of P(NIPAM-co-AA) with respect to pH were measured. The driving force for pH-and thermo-responsive self-assembly of P(NIPAMco-AA) was deduced from the protonation degrees of two different chain units based on LCST and zeta potential data. The response of the special microstructure of the assemblies to environmental stimulation was confirmed by combining the above results with Fourier-transform infrared spectroscopy, which can provide information about the enriched chain units on the surface of assemblies. The experimental results showed that the P(NIAPM-co-AA) random copolymer can be easily synthesized and is both pH-and thermoresponsive. The stimuli-responsive self-assembly behavior of P(NIAPM-co-AA) in pure aqueous solution can potentially be applied to drug delivery.