原子转移自由基聚合原位合成温敏性微球

以过硫酸钾为引发剂、丙酮-水V(丙酮)∶V(水)＝4∶6]的混合溶剂为反应介质, 在少量二乙烯苯存在的条件下使苯乙烯(St)和对氯甲基苯乙烯(CMSt)进行无皂乳液共聚反应, 得到了粒径大小均匀的交联型聚苯乙烯(PSt)微球, 由X射线光电子能谱对表面组分测定发现: CMSt上的氯原子在聚合过程中富集于交联微球的表面. 以此交联型PSt微球为原子转移自由基聚合(ATRP)的引发剂, 在22 ℃下引发N-异丙基丙烯酰胺(NIPAAm)进行原位ATRP反应, 得到了表面原子转移自由基聚合接枝的交联聚苯乙烯(PNIPAAm-g-PSt)温敏性微球. 借助傅立叶变换红外光谱、差示扫描量热仪、扫描电子显微镜及激光光散射仪等对PNIPAAm-g-PSt的结构、相转变温度、形态及不同温度下的粒径变化进行了测定, 结果表明NIPAAm单体成功地原位ATRP接枝在交联PSt微球的表面, 接枝微球的球形更规整, 在水中的相转变温度约为32 ℃, 具有明显的温度敏感性.

In-situ Synthesis of Thermosensitive Microspheres by Atom Transfer Radical Polymerization

Monodispersed crosslinking polystyrene (PSt) microspheres with chlorine atoms on their surfaces were prepared by emulsifier-free emulsion copolymerization in acetone/water V(acetone)∶V(water)＝4∶6] mixed solvents with potassium persulfate as an initiator, divinylbenzene as a crosslinking agent and p-chloromethylstyrene (CMSt) as a functional monomer. Content of chlorine atoms on the surfaces of the crosslinked PSt microspheres was determined by X-ray photoelectron spectroscopy (XPS). Molar fraction of chlorine was 1.07% on the surfaces of the PSt microspheres based on the XPS analysis when n(CMSt)∶n(St) was 5 to 95 in feed. N-Isopropylacrylamide (NIPAAm) was initiated through in-situ atom transfer radical polymerization (ATRP) using synthesized PSt microspheres as a macroinitiator and the grafted poly(N-isopropylacrylamide) chain was introduced onto the surfaces of the PSt microspheres. The properties of PNIPAAm-g-PSt microspheres, such as structure, morphology and diameter distribution were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, scanning electron microscopy and laser light scattering (LLS) methods. It was shown that the PNIPAAm chains were grafted successfully on the surfaces of the crosslinked PSt microspheres, and its lower critical solution temperature was about 32 ℃ in water. The resulting PNIPAAm-g-PSt microspheres show the temperature sensitivity.