折叠链聚酯脲的合成与表征及其自组装行为研究

利用四甲基胍促进二羧酸与二溴代化合物的高效酯化聚合反应,设计、合成了一种新型手风琴式折叠链结构的聚酯脲.具有特殊结构的单体分别是4,4′-二羧基二苯基脲和3,5-二(溴代烷氧基)-苯甲酸酯,因此得到的聚酯脲具有类似接枝共聚物的结构.通过核磁氢谱(~1H-NMR)和傅里叶红外光谱(FTIR)对聚酯脲的结构及分子量进行了表征,结果显示,得到了分子量接近2×10~4的聚酯脲.通过核磁跟踪研究聚合反应动力学,结果表明,聚合反应速度与二溴单体的烷基链长度有关,二溴单体的烷基链较长时,聚合速率较慢.热重分析(TGA)结果显示,这种聚酯脲具有良好的热稳定性;由示差扫描量热(DSC)测试结果获知聚酯脲的熔融温度为57°C,表明它具有结晶性.脲基之间的氢键作用和苯环产生的π-π相互作用驱动这种聚酯脲在溶液中进行自组装.通过透射电子显微镜(TEM)研究聚酯脲的自组装行为,结果表明,该聚酯脲在氯仿和甲醇的混合有机溶剂中,静置4 h后,组装成片层结构;继续静置到3天后,形成了稳定的囊泡结构的聚集体,囊泡壁厚度约7 nm,接近折叠链宽度的预测值;小角X射线(XRD)测试结果表明聚酯脲是有序结构,进一步证实了合成的聚酯脲具有折叠链构象.

Preparation,Characterization and Self-assembly Behavior of Chain-folded Poly(ester urea)

A new kind of accordion-type chain-folded poly(ester urea) was designed and synthesized by polyesterfication of the monomer with dicarboxylic groups,4,4'-(carbonyldiimino) dibenzoic acid and the monomer with dibromo groups,3,5-bis(bromoalkoxyl) benzoate in polar solvents at ambient temperature.The kinetics of the polyesterification reaction was monitored by proton nuclear magnetic resonance (1H-NMR) tracking.It was found that the rate of the polyesterification was highly dependent on the length of the side alkyl chains in the monomer bearing dibromine groups.A shorter alkyl chain was more favorable for the polyestification owing to the different solubility of the monomers,the monomer bearing a long alkyl chain was more soluble.The number average molecular weight and the structure of the obtained poly(ester urea) were characterized by 1H-NMR and Fourier transform infrared spectroscopy (FTIR).The number average molecular weight of the poly(ester urea) was measured to be about 2 x 104.Differential scanning calorimetry (DSC) result showed that the melting point of the poly(ester urea) was 57 ℃,suggesting that the presence of crystallinity in the poly(ester urea).While the result from thermogravimetric analysis (TGA) displayed that the poly(ester urea) was highly thermal-stable with an obvious thermal degradation around 407 ℃.Because of the presence of the hydrogen-bond between the urea groups and π-π interaction between the phenyl units,self-assembly behavior of the poly(ester urea) in a mixed organic solvent of chloroform and methanol was characterized by transmission electron microscope (TEM).The result revealed that lamellar aggregates formed in the poly(ester urea) after self-assemble for 4 h.However,the lamellar aggregates ultimately transformed into thermodynamically stable vesicles after standing for 3 days.The thickness of the vesicle wall was estimated to be about 7 nm,close to the calculated size of the folded chain.Moreover,the result of X-ray diffraction (XRD) confirmed the presence of ordered structure in the polymer,demonstrating further that the poly(ester urea) adopts a chain-folded conformation.