结构与制备条件对两亲性偶氮聚合物胶体球尺寸和光响应性的影响

INFLUENCES OF STRUCTURE AND PREPARATION CONDITIONS ON SIZE AND PHOTORESPONSIVE PROPERTIES OF AMPHIPHILIC AZO POLYMER COLLOIDAL SPHERES

合成了3种具有不同官能团或官能化度的双亲性多分散偶氮聚合物.系统研究了它们在选择性溶剂中形成聚合物胶体球时,各种因素对胶体球尺寸和光响应性能的影响规律.结果表明,不仅官能团和官能化度对胶体球的尺寸与光响应性有明显影响,具体的制备条件(如初始浓度、沉淀剂加入速率等)对胶体球尺寸和光响应性能也有重要影响.聚合物胶体球的粒径随官能化度的增加而增大;随初始浓度的增加和沉淀剂加入速率的减小而增大.聚合物PEAPE胶体球的光致异构化速率快于PCNPE胶体球的光致异构化速率.聚合物胶体球的光致异构化速率随官能化度的增加而减小;随初始浓度的增加和沉淀剂加入速率的减小而减小.这些影响表现出了明显的规律性.从双亲性聚合物在选择性溶剂中自组装形成胶体球的热力学与动力学因素出发,讨论了上述现象产生的原因.

Amphiphilic azo polymers with different azo chromophores and degree of functionalization （DF） weresynthesized, and colloidal spheres of the polymers were prepared by gradual hydrophobic aggregation in selective solvents. To obtain suspensions of colloidal spheres, the required amounts of water were added into the THF solutions at a certain stirring rate. As the water content reached ca. 70 vol%, an excess of water was added into the suspensions to ＂quench＂ the formed structures. The obtained suspensions of colloidal spheres were sealed after THF was completely volatilized and were characterized by DLS and UV-Vis spectroscopy. The size and size-distribution ofcolloidal spheres were measured by using a DLS/SLS-5022F laser light scattering apparatus. Before the measurement, the sample was clarified by a 0.45μm Millipore filter to remove dust, and all the DLS measurements were carried out with 90° scattering angle. UV-Vis spectroscopy was used to study the azo chromophore structure variation in the colloid formation process by measuring the parameters such as the trans-to-cis photoisomerizationrate and the isomerization degree at the photostationary state. In the photoresponse experiments, the sample was irradiated by a 365 nm UV light source, and the light intensity was 7000 mV/cm^2 at a distance of 38 cm and 21000 mV/cm^2 at a distance of 5 cm,respectively. In our experiment,the sample was 15 cm away from the UV light, and the temperature of the environment was 30℃. The influences of molecular structure and preparation conditions on the size and photoresponsive properties of the colloidal spheres were studied in some detail. The result shows that the functional group type and DF as well as the preparation conditions （initial polymer concentration, the rate of wateraddition, etc.） have significant effects on the size and photoresponsive properties of the colloidal spheres. The size of colloidal spheres increases with the increase of DF and initial concentration, but decreases with the increase of the rate of water addition. The photoinduced isomerization rate of poly { 2- [ 4- （4-ethoxyphenylazo） phenoxy ] ethyl acrylate-co-acrylic acid } （PEAPE） colloids is higher than that of poly{2-[4-（4-cyanophenylazo）phenoxy] ethyl acrylate-co- acrylic acid } （PCNPE） colloids. The PEAPE colloids with higher DF show a slower photoisomerization rate. Thephotoinduced isomerization rate of the colloids decreases with the increase of initial concentration and the decrease of the rate of water addition. The possible mechanism for the influence is also discussed based on thermodynamics and kinetics consideration. It is believed that the colloidal spheres form through a self-assembling process controlled by the dynamic conditions. For high initial concentration and slow water dropping rate, more polymer chains tend to aggregate on the compact cores formed from the most hydrophobic chains as the water content is above the critical water content （CWC）. Moreover, the polymeric chains had chance to rearrange themselves to form stable andcompact structures due to the slow rate of water addition. On the other hand, as the rate of water addition increased, the polymeric chains attached to the cores were quickly ＂frozen＂ before they could completely adjust their conformations. Also, they could form new less compact cores so as to weaken the continuous aggregation probability. As a result, the formed aggregates had loose structures, and the photoinduced isomerization rate was relatively fast.