Study On The Synthesis Of Poly(l-lactic Acid)

In this paper, poly(L-lactic acid) was synthesized by indirect method.It included the synthesis of L-lactide, the purification of L-lactide, thepolymerization of L-lactide and the polymer's analysis et. al.First the paper studied the synthesis of L-lactide under reducedpressure and N2 atmospheric pressure. It showed that the results underreduced pressure were better than the results under N2 atmosphericpressure.The former', yield was higher than the latter' Its highest yieldwas up to 95.8% and the needed time was shorter. At the same time, thepaper also studied the effects of the pressure, the temperature, the sort ofcatalyst and the catalyst concentration on the result. It showed that highvacuum can give high yield anu in all used catalyst, SnOct₂ was the best. andthe temperature must be below 240℃.Then, the paper studied the purification of crude L-lactide.Recrystallization and filter under reduced pressure were used. But they wereunfit. The method which was based on the different physical properties ofevery component to purify the crude L-lactide was effective. The productwas a colorless needle crystal. Its melting point was 95-96 ℃and itsoptical purity was above 99%.Finally, the purified L-lactide was initiated by SnOct2 to polymerize at110-170℃ in 24-168 hours, and the molar ratio of L-lactide toSnOct₂ was 2000～16000. A polymer with a viscosity average molecularweight of (2^l2.6) × l0⁴, and a melting point of l70^l80℃ wasobtained .When the polymerization temperature was l50℃, thepolymerization time was 48h, and the molar ratio of L-lactide to SnOct₂ was16000, the polymer with the maximum Mv was obtained.