In the first step

3-phenylmethyl-2

5-morpholinedione (PMD) was synthesized by using phenylalanine as the raw material.In the second step

poly(lactic acid-co-3-phenylmethyl-2

5-morpholinedione) was prepared by ring-opening copolymerization of PMD and lactide (LA).Stannous octanoate was used as catalyst in the reaction of second step.The structure of copolymers was analyzed by IR

1H-NMRand DSC.The contents of copolymers were detected by infrared spectroscopy instead of 1H-NMR. Two characteristic peaks at 1671.53 cm-1 and 870.82 cm-1-were selected for PMD and PLA in IR.A standard working curve was established:Y=0.05567X+0.1091(r=0.9993)

where X was the reciprocal of PMD monomer molar concentration

and Y was the absorbance ratio of PLA to PMD at their characteristic peaks.Effects of catalyst content

reaction time and temperature on the concentration of PMD and ［η］ in copolymers were studied.It was found that

with prolonging of reaction time

the ［η］ was first increased then decreased under the condition of low catalyst concentration.Furthermore

under the condition of high catalyst concentration

the ［η］ suspended during 10 h because of the formation of amide linkage products which are more stable.The concentration of PMD in resulting copolymers increases linerly with the increase of PMD in feed.The PMD was less ring-opening reactive than LA

so it was difficult to incorporate the phenyls into the copolymer.However

under the condition of low feed ratio

the contents of PMD can increase when the temperature becomes higher.Moreover

with increasing the concentration of PMD in copolymer

the influence of catalyst content and temperature on copolymer decreased by the stability of phenyl.