原位制备淀粉接枝聚乳酸

in situ GRAFT COPOLYMERIZATION OF STARCH WITH LACTIC ACID

研究了淀粉与乳酸的原位接枝反应.结果表明,利用乳酸中所含的水先将淀粉糊化,然后在95℃下减压反应,可直接得到淀粉-聚乳酸接枝共聚物.研究发现,上述反应体系中可原位生成丙交酯.该丙交酯的开环聚合是淀粉发生接枝反应的主要原因.利用定量核磁共振等方法对接枝产物的微结构进行了详细的解析.

The biodegradable starch graft copolymer, starch-g-poly （lactic acid） （starch-g-PLA）, was directly produced by in situ graft copolymerization of cornstarch with lactic acid using stannous 2-ethyl hexanoate[Sn（Oct）2 ] as catalyst. The procedure of the grafting reaction was elucidated, based on the HPLC analysis, as the ring-opening polymerization （ROP） from starch surface of the small amounts of lactide produced in situ in the reaction system. Analysis of ^13 C-NMR spectra indicated that ROP of lactide was taken place through acyl-oxygen cleavage co-initiated by hydroxyl group at glucopyranan unit, yielding PLA grafts with a hydroxyl terminus. ^1 H- and ^13 C-NMR spectra were employed to assign the characteristics resonances of the copolymer. The positions of lactyl units at the glucopyranan ring as well as the corresponding distribution are determined. The DS values of the graft copolymer calculated based on ^13 C-NMR spectra of starch ring carbons are indentical to those of carbonyl carbons in LA moieties. The reactivity of hydroxyl groups at glucopyranan rings decreases in the order of C-6 〉 C-3 〉 C-2, while the average length of PLA grafts increases in the order of C-3 〈 C-6 〈 C-2. The phenomena are proposed as a result of the difference of the steric hindrance of hydroxyl groups at glucopyranan units in starch. It was found that the grafted PLA length increased slightly with prolonging the reaction duration. The average length of PLA grafts was 1.33 for 5 h reaction, and that reached to 2.02 when the reaction duration increased to 13 h.