【作者】 王小涛；

【导师】 解孝林； 廖永贵；

【作者基本信息】 华中科技大学 ， 材料学， 2011， 博士

【摘要】 近年来,功能化的聚合物微球(如磁性微球、荧光微球、pH响应微球和温度响应微球等)的制备技术日趋成熟,并在生物医药、电子信息、新材料等领域有广泛应用。由于光源具有快捷、可远程操控的优势,光敏性微球的的制备也成为研究的热点。然而,目前报道的光响应微球主要由含光敏基元的嵌段共聚物自组装或层层自组装的方法制得。本论文选用新颖的蒸馏沉淀聚合方法,以不同结构的具有优异的可逆光异构化行为的偶氮苯作为侧链或交联网络骨架,制备含偶氮苯的光响应智能微球,并将之应用于控制释放领域。首先,以Stober方法合成的粒径为250nm的单分散二氧化硅粒子为模板,含一个双键的甲基丙烯酸-6-(4-甲氧基-4’-氧-偶氮苯)已酯(AzoM)为单体,二乙烯苯(DVB)为交联剂,乙腈为溶剂,通过蒸馏沉淀聚合法,在不同的实验条件及配比下制得了一系列的聚偶氮苯包覆的二氧化硅(PAzo@SiO2)杂化微球。选择最优化的聚合条件(DVB含量为20wt%、乙腈用量为200mL、聚合时间为4.5h,乙腈蒸出量为100mL),经氢氟酸刻蚀制得了结构稳定的壳层厚度约20 nm的聚偶氮苯PAzo中空微球。紫外光谱和热失重(TGA)表明PAzo中空微球具有优异的可逆光异构化行为和较好的热稳定性。进一步引入5mol%的甲基丙烯酸甲酯作为共聚单体,在其它条件相同下,合成了窄分散、结构稳定的PAzo中空微球。氮气吸附解吸附测试表明壳层存在中孔通道。由于偶氮苯基元接枝在壳层聚合物网络间,在光异构化作用下,分子尺寸由反式的1.73nm减小为顺式的1.27nm,从而可调节壳层孔径的大小,并成功地应用于荧光分子罗丹明B的控制释放。达到50%释放量时,可见光下需要11.6h；而紫外光下减小为7.8h,扩散系数增加了44.2%。PAzo中空微球的壳层厚度通过蒸馏出不同的溶剂量来调节。接着,以粒径为80、130和180nm的二氧化硅为模板,分别制得不同粒径的聚偶氮苯杂化微球。粒径为80nm的杂化微球粘连程度较大,刻蚀后不能得到明显的中空球形结构,其余两者均为规整的中空微球结构,且具有较好的热稳定性和优异的可逆光异构化行为。选用含两个双键的4,4’-二甲基丙烯酰胺偶氮苯为交联剂,分别以粒径为250、180和130nm的二氧化硅粒子为模板,丙烯酸(AA)为单体,制备含偶氮苯基元的PAA@SiO2杂化微球。经氢氟酸刻蚀后得到含偶氮苯的PAA中空微球。三种中空微球结构稳定、壳层均一、单分散指数较低,并具有较好的热稳定性。对以250nm氧化硅为模板的PAA中空微球进行动态光散射(DLS)和光照下的紫外光谱研究,发现PAA中空微球具有pH和光双重响应性。在紫外光照下,其具有优异的可逆光异构化行为。交联点的偶氮苯基元发生由反式向顺式结构转化,而其它基元发生相应的协同运动,整个壳层网络会发生收缩,而且这种收缩的结构在可见光下可得到回复。动态光散射结果表明,当pH值分别为5、7、9时,其粒径分别为361、481、640nm。将这种双重响应性应用于智能控制释放,pH值为5时,释放量达28.3%；改变释放环境pH值为7,又有一部分罗丹明B分子释放出来,达到平衡时,释放量达38.1%；继续增加pH值为9,累积释放量达64.3%。在光控释放中,紫外光照下,释放320min时,达到平衡态,34.7%的罗丹明B被释放出来；可见光下,880min时,释放达到平衡,63.0%的罗丹明B被释放出来；而交替的紫外光和可见光下,880min达到平衡,释放量高达75.1%。这与交替光照下中空微球处于动态运动的状态有关。最后,对PAA中空微球进行了负载银的探索,有望进一步将之应用于催化、抗菌材料等领域。更多还原

【Abstract】 The fabrication methods of polymer microspheres, such as magnetic microspheres, fluorescent microspheres, microspheres sensitive to pH and temperature, are increasingly mature. These microspheres could be applied in biologic medication, electric information and new materials areas, etc. Light has attracted much attention since it can be localized in time and space and it can also be triggered from outside of the system, so it is of great importance in developing photo-responsive microspheres. At present, photo-responsive microspheres have been normally fabricated through amphiphilic copolymer containing photoresponsive moieties by self-assemble methods and their structures were not robust. In this thesis, photo-responsive azobenzene moieties, as a side group or a backbone unit, have been introduced to fabricate various structures of polyazobenzene microspheres via a novel distillation precipitation polymerization method. The hollow microspheres have been obtained after etching the silica templates by hydrofluoric acid, and their controlled release for fluorescent molecules has been investigated also.Firstly, we synthesized silica particles with diameter of 250 nm through Stober method. A series of PAzo@SiO2 microspheres under different polymerization conditions have been synthesized with 250 nm silica particles as a template, azobenzene containing vinyl chain as a monomer, divinylbenzene as a cross-linker, acetonitrile as a solvent. The optimized condition was chosed:200 mL acetonitrile,20 wt% DVB content relative to monomer, and 100mL acetonitrile was distilled out of the system during 4.5 h of polymerization time. The robust PAzo hollow microspheres with 250 nm core and 20 nm shell have been fabricated. They have excellent reversible photoisomerization behaviors and good thermal stability.Methyl methacrylate (MMA,5 mol%) as a co-monomer was introduced to improve the stiffness of shells. The result of nitrogen adsorption-desorption isotherm indicated the existence of pore channels in the shell. Photo-isomerization behaviors of azobenzene moieties grafted on the network would change the pore diameter within the shell. These photoresponsive pore channels have been successfully applied in photo-controlled release. The half release of Rhodamine B required 11.6 h under visible light and 7.8 h under UV-light, respectively. The diffusion coefficient under UV light was 44.2% larger than that under visible light. PAzo microspheres with different shell thickness could be synthesized by distillation of different amounts of solvent from the reaction system. Silica particles with diameters of 80,130 and 180 nm prepared by Stober method were also used as templates to synthesize PAzo hollow microspheres. PAzo particles prepared with 80 nm core conglutinated each other and didn’t show any hollow structure. The other PAzo particles with uniform hollow structures have been fabricated and showed excellent thermal stability and reversible photoisomerization behaviors.PAA@SiO2 hybrid microspheres have been synthesized with silica diameters of 250, 180 and 130 nm as templates, azobenzene with double vinyl units as a cross-linker, acrylic acid (AA) as a monomer. After etching by hydrofluoric acid, PAA hollow microspheres were obtained. Transmission electron microscopy (TEM) and Scanning electron microscope (SEM) results indicated that all of PAA hollow microspheres had uniform and stable shells, and their dispersion indexes were low. Thermogravimetric analysis (TGA) indicated all of them had excellent thermal stability. PAA hollow microspheres with 250nm core had reversible photoisomerization behaviors which have been proved by UV spectra under both UV and visible irradiation. Under UV irradiation, due to the photo-isomerization behaviors, azobenzene moities transformed from trans- to cis- isomer and other units would have cooperative movement, which would be induced the shrinkage of the shell of the hollow microspheres. Dynamic light scattering (DLS) results indicated the diameters of PAA hollow microspheres were 361,481, and 640 nm when pH values were 5,7, and 9, respectively. These dual-responsive properties have been applied in controlled release. When pH value of the release solution was 5, the total release percent was 28.3%. When the pH changed to 7, some other RhB molecules have been released and the total release percent was 38.1%. When the pH increased to 9, the total release percent was up to 64.3%. For the photo-controlled release, the release of Rhodamine B could reach 34.7% during 320 min under UV-light,63.0% during 880 min under visible-light, and 75.1% during 880 min under alternate UV light and visible light, repectively. At last, the hollow microspheres have been successfully loaded with silver, which could broaden their application on catalyst, antibacterial materials, and so on.更多还原