两亲扩展型共聚物的合成及中间极性嵌段对乳化性能的影响

采用聚乙二醇单甲醚(Mn=1 900,5 000)分别引发丙交酯和ε-己内酯开环聚合合成了中间嵌段(PLA)聚合度递增的聚乙二醇-聚丙交酯-聚己内酯(MPEG-PLA-PCL)两亲扩展型共聚物和相应的聚乙二醇-聚己内酯(MPEG-PCL)两嵌段共聚物。用FTIR、1HNMR和GPC对产物结构进行了表征,研究了共聚物和常规低分子表面活性剂的乳化性能,探讨了中间极性嵌段的长度对共聚物乳化性能的影响。结果表明,对于甲苯/水体系,共聚物可用于制备稳定的O/W型乳液,且三嵌段共聚物的乳化性能优于低分子表面活性剂;随着引入PLA嵌段聚合度的增加,共聚物的乳化能力呈先增加后减小的趋势;相对于MPEG1900系列共聚物,MPEG5000系列共聚物中需要引入更长的中间嵌段才能获得最佳乳化性能。

Synthesis of Amphiphilic Extended Copolymers and the Influence of Intermediate Polar Block on Emulsifying Properties

The amphiphilic triblock copolymer poly(ethylene glycol)-co-polylactide-co-poly(ε-caprolactone)(MPEG-PLA-PCL) with increasing PLA block ratio and corresponding diblock copolymer poly(ethylene glycol)-co-poly(ε-caprolactone)(MPEG-PCL)were prepared by ring-opening polymerization of d,l-lactide and ε-caprolactone initiated by monomethoxy poly(ethylene glycol)(Mn=1 900,5 000).The structure of the target copolymers was confirmed by means of FTIR,1HNMR spectra and GPC,and then the emulsifying properties of the copolymers and low molecular surfactants were studied and their relationship with the block ratio of the intermediate polar block PLA in triblock copolymers was discussed in detail.The results indicate that all of the copolymers could emulsify the toluene/water system and the emulsions were oil-in-water type.The copolymers showed better emulsifying properties than the low molecular surfactants,and the emulsifying ability of the copolymers first increased and then decreased with the increase of PLA block ratio.This was due to the enhanced interactions with water and oil phase by inserting intermediate polar block PLA which resulted in a thicker interfacial membrane.To achieve optimum emulsifying performance,longer intermediate polar block was required for MPEG 5000-containing copolymers than that for MPEG 1900-containing copolymers.