一种光学活性三嵌段共聚物的ATRP合成及表征

以溴代聚砜为大分子引发剂,三(2-二甲氨基乙基)胺(Me6TREN)/CuBr为催化体系,通过原子转移自由基聚合(ATRP)制备了结构预定且分子量分布窄的光学活性三嵌段共聚物,聚(N-甲基丙烯酰-L-亮氨酸甲酯)-嵌-聚砜-嵌-聚(N-甲基丙烯酰-L-亮氨酸甲酯)(PMALM-b-PSF-b-PMALM).通过核磁共振氢谱(1H-NMR)、凝胶渗透色谱(GPC)、端羟基滴定等方法,研究了所合成的三嵌段共聚物的结构.利用差示扫描量热法(DSC)、热失重分析(TGA)以及圆二色谱(CD)研究了嵌段共聚物的热性能和旋光性能.根据TGA计算出的PMALM链段与PSF链段的重复单元数之比,与1H-NMR计算的结果能较好的吻合.共聚物在聚合过程中旋光度发生了反转,且比单体的旋光度的绝对值显著增加,这可能是由于聚合过程中分子主链感应出了手性的二级结构诱导出手性放大效应引起的.在CH3OH/CCl4混合溶剂中,共聚物比旋光度的绝对值随溶剂极性增大呈线性减小趋势,这一结果与CD一起证实了PMALM链段的无规卷曲结构.

SYNTHESIS AND CHARACTERIZATION OF AN OPTICAL ACTIVE TRIBLOCK COPOLYMER via ATOM TRANSFER RADICAL POLYMERIZATION

An optical active triblock copolymer poly(N-methacryloyl-L-leucine methyl ester)-b-polysulfone-b-poly-(N-methacryloyl-L-leucine methey ester)(PMALM-b-PSF-b-PMALM)with predetermined structure and narrow molecular weight distribution was synthesized via atom transfer radical polymerization(ATRP)using polysulfone macroinitiator and CuBr/Me_6TREN complex system.The structure was verified by 1H-NMR,GPC and end group titration techniques.DSC,thermogravimetry analysis(TGA)and circular dichroism(CD)were used to study the thermal and optical properties.The mole ratio of PMALM block to PSF block calculated from TGA has a good agreement with the result calculated from 1H-NMR.Both a reversion and an increase of the absolute value of specific rotation in the transformation from MALM to PMALM-b-PSF-b-PMALM were observed,which were probably caused by some kind of stereostructure of the main chain formed during the polymerization due to the intermolecular hydrogen-bonding.The random conformation of PMALM blocks was verified by CD spectra and the linear relationship between the specific rotation and the polarity of CH_3OH/CCl_4 mixed solvent.