部分水解聚丙烯酰胺-羟乙基纤维素的水相pH响应性自组装

pH Responsive Self-Assembly of HPAM-HEC in Aqueous Solution

为考察无规共聚物在全水相环境中的自组装行为,合成了结构类似于无规共聚物的低相对分子质量的部分水解聚丙烯酰胺(HPAM).尝试改变水溶液pH值来诱导HPAM与羟乙基纤维素(HEC)发生自组装,采用透射电子显微镜(TEM)观察到不同pH值时分别获得了100nm的似正方体胶束,200nm×100nm的类椭球胶束,100 nm的串珠状胶束以及500 nmx300 nm×50 nm的半月形胶束等pH响应性核壳型聚合物胶束.建立了金在胶束表面原位还原耦合TEM表征方法,用于检测低衬度聚合物胶束的纳米细节;配合电子探针X射线微区分析(EPMA)和扫描电子显微镜(SEM),证实了半月形聚合物胶束的精致分级构造为亲水性内囊@疏水性连续囊壁@亲水性外壳的多泡囊泡,并证实pH=0.9时多泡囊泡崩解为疏水性内核@亲水性外壳的10 nm类球体小胶束.通过分析链节质子化状态的pH响应性,结合zeta电位和吸光度测定结果,阐释了不同pH值时组成聚合物胶束的核和壳的链段归属,获得了全水相中HPAM自组装驱动力和形貌方面的全新知识.

A low-molecular-weight partially hydrolyzed polyacrylamide （HPAM） was synthesized because of its similar segment distribution to that of the random copolymer of acrylamide and acrylic acid P（AM- co-AA） to investigate the self-assembly of random copolymers in aqueous phase. The pH responsive self-assembly of HPAM with hydroxyethyl cellulose （HEC） in aqueous solution was investigated by transmission electron microscopy （TEM） and various polymeric micelle morphologies were observed in different pH ranges such as 100 nm cube-like micelles, 200 nmx 100 nm pseudo ellipsoidal micelles, 100 nm string beads-like micelles, and 500 nm×300 nm×50 nm half-moon micelles. A method to couple the in situ reduction of gold at＇the polymeric micelle surface and TEM characterization was established and used to detect the nanoscale details of the low contrast polymer micelles. We confirmed by the above method and with the assistance of electron, probe X-ray microanalysis （EPMA） and scanning electron microscopy （SEM） that the delicate conformation of the half-moon polymeric micelle was a multivesicular vesicle （MW） which possessed the following hierarchical structure： hydrophilic inner vesicle @ hydrophobic continuous cystwall @ hydrophilic shell. This structure collapsed at pH 0.9 and it disintegrated into 10 nm pseudo spherical polymeric micelles with the following structure： hydrophobic core @ hydrophilic shell. Therespective compositions of the core and the shell of the micelles were interpreted based on an understanding of the pH responsive degree of protonaUon of the various chain units and the experimentally obtained zeta potential and light absorbance. Therefore, we obtained new information about the driving force and morphology of HPAM self-assembly in the aqueous phase.