原位核磁共振技术考察L-缬氨酸导引下合成花状纳米结构聚苯胺形成机理的研究

利用~1H-NMR原位追踪在L-缬氨酸存在下合成花状纳米聚苯胺的形成过程中发现此结构的形成经历3个阶段:首先在苯胺与缬氨酸构成的类胶束结构内聚合成吩嗪类寡聚物;其次通过p-p重叠作用及胶束融合过程成为片状聚集体;最终通过与缬氨酸形成氢键组装成花瓣状纳米聚苯胺.通过改变反应条件,对比形成过程中核磁共振图谱及产物形貌的变化发现花状纳米聚苯胺的形成有如下特征:反应初期L-缬氨酸作为缓冲试剂可以避免苯胺的骤然质子化,有利于生成具有吩嗪结构的寡聚物;反应前苯胺单体与缬氨酸形成稳定的反应环境保证寡聚物始终在其内聚集生长,有效避免了外部环境的影响.

Formation Mechanism of Flower-like Nanostructured Polyaniline Prepared under Guidance of L-valine

The formation mechanism of flower-like nanostructured polyaniline prepared in the presence of L-valine was explored by a series of in situ 1H-NMR experiments.Depending on the signal evolution of the major species,the flower-like nanostructured polyaniline was observed to be formed through three continuous stages.At first,aniline and L-valine were packed loosely into micelle-like aggregates before the polymerization,and the phenazine-like oligomers were abundantly formed within this kind of micelles;subsequent steady aggregation through π-π stacking interactions rendered the oligomers to arrange into structurally regular polyaniline nanosheets due to their highly conjugated fused rings;further intermolecular packing of these nanosheets under guidance of L-valine through hydrogen bonds generated the desired flower-like architectures.Moreover,a careful comparison between the samples prepared under varied concentration of L-valine and aniline revealed that the formation of the flower-like nanostructure was closely related to the following characters from L-valine:(1) being amphoteric,which could have served as the buffering agent to prevent abrupt protonation of aniline and to induce several aniline molecules to share the charges together so that the electron density at each reactive site on aniline was nearly identical before the polymerization,the formation of phenazine-like oligomers was therefore favored with a steady proton induced aggregation of these oligomers;(2) locating at the outer-most layer of the aggregates upon the formation of L-valine stabilized monomer micelle due to its amphiphilic feature,which could not only stabilize the monomers and the nascent produced oligomers but also would allow the aggregation of the oligomers to form nanosheets and the subsequent formation of the nanoflowers in the micelle or through fusion of the micelles respectively.This way,any irregular structural arrangement induced by the disturbance from the reaction system or the surroundings might be eliminated,leading to the highly thermodynamic stable product to be produced eventually.