Study on biodegradable polymer materials based on poly(lactic acid). I. Chain extending of low molecular weight poly(lactic acid) with methylenediphenyl diisocyanate

✍ Scribed by Wei Zhong; Jinjie Ge; Zhenyu Gu; Wenjun Li; Xin Chen; Yi Zang; Yuliang Yang

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 163 KB
• Volume: 74
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(19991205)74:10<2546::aid-app24>3.0.co;2-z

✦ Synopsis

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 prepolymer 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 using stannous octoate as the catalyst. After 40 min of chain extension at 175°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 prepolymer was 48.6°C. After chain extension, the T g of the resulting polymer was raised to 67.9°C, as determined by DSC. DMA results also indicate that the heat resistance was improved by the chain extension. The DSC spectrum and X-ray diffraction pattern of annealed samples showed that both the crystallinity and rate of crystallization of PLA were lowered by chain-extension reaction due to the formation of branched molecular structure.