Synthesis of poly(lactic acid)-poly(phenyl phosphate) via direct polycondensation and its characterization

Starting from d,l-lactic acid (d,l-LA), ethylene glycol (EG) and phenyl dichlorophosphate (PDP), poly(lactic acid)-poly(phenyl phosphate) was synthesized via direct copolycondensation. The novel poly(lactic acid) (PLA) copolymer containing phosphorus was characterized with FTIR, (1)H NMR, (31)P NMR, GPC, and DSC. The GPC results showed that, after the prepolymerization of d,l-LA and EG, the direct melt copolymerization of oligomer and PDP gave copolymer with higher weight-average molecular (Mw) than the direct solution copolymerization. The optimal synthetic conditions of the direct melt copolymerization, including prepolymerization method, catalyst kinds and quantity, copolymerization temperature and time, were all discussed in detail. When catalyzed by 0.5% (weight percent) ZnO under 160A degrees C and 70 Pa, 8 h's copolymerization gave the copolymer with maximum Mw 9,200 Da. When the feed molar ratio of d, l-LA/EG/PDP was 20/1/1 instead of 20/1/2, the melt polymerization under the above conditions gave the copolymer with maximum Mw 27,700 Da (Mw/Mn 1.07). The novel one-step method could be an alternative route to the synthesis of poly(lactic acid)-poly(phosphate ester) instead of the traditional two-step method using lactide as intermediate. At the same time, the novel PLA copolymer containing phosphorus with phenyl group may give this material more chance for the further structure modification as expected.