细乳液聚合法制备聚合物空心球

Preparation of Hollow Nanospheres by Miniemulsion Polymerization

设计、合成了一种两亲性的引发转移终止剂(inifeter),2-(N,N-二羧甲基二硫代氨基甲酸酯基)异丁酸十二酯(DIBDC),通过核磁谱对其结构进行了表征.DIBDC既可引发聚合,又是表面活性剂.以DIBDC作为乳化剂,醋酸铜(Cu(OAc)_2)为催化剂,进行了细乳液聚合法制备聚合物空心球的研究.实验结果表明,通过细乳液聚合,制备了直径为100~200 nm的聚苯乙烯空心球.由于DIBDC中的二硫代氨基甲酸酯基团与卤素在化学行为上相似,因此,DIBDC可作为假卤素引发剂,在Cu(OAc)_2催化作用下产生自由基,从而引发聚合反应.Cu(OAc)_2存在于水相中,可以扩散到油水界面层与DIBDC作用,而活性自由基增长链始终处于油水界面,因此,聚合反应只能在油水界面层的"受限空间"内进行,从原理上避免了实心聚合物球的形成.

An amphiphilic iniferter, 2-（N,N-dicarboxymethyl dithiocarbamate） dodecyl isobutyrate （DIBDC）, was synthesized and characterized by 1H-NMR spectroscopy. Dodecyl 2-bromo-2-methylpropionate was prepared from lauryl alcohol and 2-bromo-2-methylpropionyl bromide in the presence of triethylamine in ice water bath. Sodium N,N-dicarboxymethyl dithiocarbamate was synthesized from iminodiacetic acid, carbon disulfide and sodium hydroxide at room temperature. DIBDC was synthesized by the reaction between dodecyl 2-bromo-2-methylpropionate and sodium N,N-dicarboxymethyl dithiocarbamate at 60℃. Since DIBDC is not only a surfactant, but also used as an initiator, miniemulsion polymerization of styrene was performed in the presence of DIBDC using Cu（OAc）2 as the catalyst. The miniemulsion systemconsisted of distilled water, surfactant, hexadecane and styrene. Stable miniemulsion was obtained after stirring and ultrasonic treatment. After adding copper acetate and heating up to 80℃, the polymerization began.To characterize the hollow spheres, dynamic light scattering （DLS）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM） were used. The results indicated that hollow polystyrene nanospheres with diameters of 100 nm to 200 nm were successfully prepared by the living radical miniemulsion polymerization. The PDI of diameter was below 0.1, showing good monodispersity of the nanospheres. It is well known that dithiocarbamates act as pseudohalogens, therefore, DIBDC can be used to perform a living radical polymerization, which is similar to atom transfer radical polymerization under catalysis of Cu（OAc）2. Due to the amphiphilicity of DIBDC and the reversible equilibrium between the active and the dormant species, thepolymerization was realized in aconfinedspace of the oil-water interface. As a result, hollow nanospheres were formed. And moreover, the formation of solid polymer nanoparticles was avoided. However, when azobisisobutyronitrile （AIBN） was used as the initiator instead of Cu（OAc）2 as a catalyst, solid polystyrene nanospheres were obtained. The reason is that the polymerization is no longer carried out in the confined space, which is similar to suspension polymerization because AIBN is dissolved in the micelles.