红外光谱法测定聚(乳酸-苯丙氨酸)共聚物的含量

Determination of the Content of Poly(Lactic Acid-co-Phenylalanine) by Infrared Spectroscopy

分别以苯丙氨酸和乳酸为原料合成了3-苯甲基-2,5-吗啉二酮(PMD)与丙交酯(LA),以PMD和LA作为聚合单体经开环聚合分别得到PMD均聚物(PPMD)、丙交酯均聚物(PLA)及聚(乳酸-苯丙氨酸)共聚物。对合成的均聚物进行红外分析,确定1 671.53和870.82 cm-1处的吸收峰分别为PPMD和PLA的特征峰。根据以上两种特征吸收峰并以朗伯-比耳定律为理论依据,建立了利用红外光谱法测定聚(乳酸-苯丙氨酸)共聚物含量的方法。实验测定的标准工作曲线为y=0.055 67x+0.1091,r=0.999 3。利用该标准工作曲线定量测定了共聚物组分含量,其结果与1H NMR测定值一致,相对误差在2%以内,证明红外光谱法可方便、快捷地测定聚(乳酸-苯丙氨酸)共聚物组分含量,且适用于其他聚(乳酸-氨基酸)共聚物的含量测定,具有一定的实用性及推广性。

To improve the thermal stability of poly （lactic acid）, poly （lactic acid-co-phenylalanine） was prepared by introducing the phenyl of phenylalanine to the side chain. 3-phenylmethyl-2,5-morpholinedione （PMD） and lactide （LA） were synthesized using phenylalanine and lactic acid as raw materials, respectively. Subsequently, poly （lactic acid-co-phenylalanine）, homopolymer of PMD （PPMD） and homopolymer of LA （PLA） were obtained by ring-opening polymerization of PMD and LA as monomer. The amount of phenyl had an effect on the thermal stability, so a quantitative analysis by infrared spectroscopy was established in the present paper. Two homopolymers were determined by infrared spectroscopy to find out two characteristic peaks at 1 671.53 and 870. 82 cm^-1 , which were selected for PPMD and PLA, respectively. Choosing the characteristic peaks and according to the Lambert-Beer law, which is the linear relationship between absorbance and concentration of an absorbing species, a standard working curve was calculated： y=0. 055 67x＋0. 109 1 （r=0. 999 3）, where x was the reciprocal of PPMD monomer molar concentration and y was the absorbanee ratio of PLA to PPMD at their characteristic peaks. Collecting the absorbance of poly （lactic aeid-co-phenylalanine） at two characteristic peaks, the contents of copolymer were calculation by the working curve and the results were similar to that of 1HNMR by calculation from the ratio of proton area of PMD and PLA. It was noted that the relative error was below 2%0. It was also confirmed that the content of eopolymer could be determined by infrared spectroscopy conveniently and quickly. Meanwhile, this method could be adopted to determine the other poly （lactic acid-co-amino acid） practicably and widely.