<正>为了制备高光学活性的聚乳酸，以D，L-乳酸为原料，熔融缩聚合成聚乳酸。采用旋光度法、红外光谱、差示扫描量热法、凝胶渗透色谱和核磁共振等方法研究了聚乳酸的结构和性能。结果表明：锡粉催化与自催化的D，L乳酸聚台均可以得到较低分子质量、消旋的聚D，L-乳酸。SnCl2/对甲苯磺酸与Sncl2/邻甲苯磺酸两个催化体系都具有立构选择性，可以催化D，L-乳酸聚合制备L-构型的聚乳酸。立构选择性聚合所得的聚乳酸具有较高相对分子质量（M，>20000）、窄分布（分布指数1.1）、较高光学活性（比旋光度-109，光学纯度70.5%）和熔点（112℃）。

The consumption of cut roses is the first place among all cut flowers in China. It is necessary to develop an economical and innoxious preservation with high applicability and efficiency. With adding spermidine (Spd) and changing bactericide and inorganic salts, we studied the effects of different matching preservative treatments on life of cut rose cultivated in treated liquid, water balance, relative conductance and POD activity of cut roses. The results showed that preservative No.5 (mass fraction of 2% sucrose+200mg/L CA+100mg/L penicillin+0.15%Ca(NO3)2+0.1mmol/L Spd) could remarkably extend the life of cut roses and obviously delay the process of senescence. Each measured parameter of preservative No.5 was better than that of prescriptions and control. The preservative No.5 was suggested to be suitable for cut roses.