D,L-丙交酯的制备及在二甲苯溶液中的开环聚合

PREPARATION AND RING-OPENING POLYMERIZATION IN XYLENE SOLUTION OF D,L-LACTIDE

将乳酸在催化剂存在下脱水环化合成了D,L-丙交酯(D,L-LA)。研究了催化剂用量、脱水温度及稀释剂等对D,L-LA产率的影响,纯D,L-LA的产率最高可达37.3%。将D,L-LA以二甲苯为溶剂、辛酸亚锡为催化剂,经开环聚合得PDLLA。通过正交试验分析了单体浓度、引发剂用量、反应温度和时间等因素对产物分子量的影响,确定了最佳聚合条件为:单体浓度4.62mol/L,n(SnOct2)/n(D,L-LA)=1∶400,聚合温度为120℃,聚合时间为8h。利用最优条件,可制得Mv为76,000的PDLLA。通过同核去偶1H-NMR谱对PDLLA的序列结构进行了表征。结果表明,所合成的丙交酯单体为外消旋型,不含内消旋型丙交酯(meso-LA);且在聚合过程中无消旋化及酯交换反应发生。

The D,L-lactide (D,L-LA) was prepared from D,L-lactic acid with dibutyltin oxide as catalyst. The effects of catalyst quantity, dehydration temperature and diluent on the yield of D,L-LA were discussed. The best yield of pure D,L-LA is (37.3%). Ring-opening polymerization of D,L-LA was carried out in xylene with Sn(Oct)_2 as catalyst. The influences of monomer concentration, catalyst quantity, polymerization temperature and time on the molecular weight of PDLLA were studied by orthogonal experiments. The results show that the optimal polymerization conditions are as follows: is (4.62) mol/L, n(SnOct_2)/n(D,L-LA) is 1∶400, the reaction temperature is 120 ℃ and the reaction time is 8 h. Under the optimal conditions, PDLLA with _v of 76,000 was obtained, and its GPC _n and _w/_n is 48,642, and (1.93) respectively. The chain structure of PDLLA was studied by homonuclear decoupled ()~1H-NMR spectra. No stereosequences of iiiss/ssiii(SSSSRS/RRRRSR) were found. It is concluded that no transesterification and racemization take place in the ring-opening polymerization of D,L-LA under these conditions.