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 stananus 2-ethyl hexanoate[Sn(Oct)2] as catalyst．The procedure of the grafting reaction was ducidated

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 of13C-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．1H-and13C-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 on13C-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