Study an biodegradable polymer materials based on poly(lactic acid). I. Chain extending of low molecular weight poly(lactic acid) with methylenediphenyl diisocyanate
W. Zhong et al., Study an biodegradable polymer materials based on poly(lactic acid). I. Chain extending of low molecular weight poly(lactic acid) with methylenediphenyl diisocyanate, J APPL POLY, 74(10), 1999, pp. 2546-2551
Methylenediphenyl diisocyanate (MDI) was used as the chain extender for low
molecular weight poly(lactic acid) (PLA) to produce high molecular weight
biodegradable polymer material with a better heat resistance. PLA prepolyme
r with a number-average molecular weight (M-n) of 5800 and a weight-average
molecular weight (M-w) of 9800 was produced by direct polycondensation usi
ng stannous octoate as the catalyst. After 40 min of chain extension at 175
degrees C, the resulting polymer had a M-n of 15,000 and a M-w of 57,000.
The glass transition temperature (T-g) of the low molecular weight PLA prep
olymer was 48.6 degrees C. After chain extension, the T-g of the resulting
polymer was raised to 67.9 degrees C, as determined by DSC. DMA results als
o indicate that the heat resistance was improved by the chain extension. Th
e DSC spectrum and X-ray diffraction pattern of annealed samples showed tha
t both the crystallinity and rate of crystallization of PLA were lowered by
chain-extension reaction due to the formation of branched molecular struct
ure. (C) 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2546-2551, 1999.