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Synthesis of polylactides with different molecular weights
S H Hyon1, K Jamshidi, Y Ikada
1Research Center for Biomedical Engineering, Kyoto University, Japan.
Biomaterials
|January 13, 1998
Summary
Ring-opening polymerization of lactides yields high molecular weight poly(lactic acid) (PLA). Optimal catalyst concentration and polymerization time are crucial, as prolonged reactions at high temperatures can cause thermal depolymerization, reducing PLA molecular weight.
Area of Science:
- Polymer Chemistry
- Materials Science
Background:
- Direct polycondensation of lactic acid results in low molecular weight poly(lactic acid) (PLA).
- Ring-opening polymerization (ROP) offers a route to higher molecular weight PLA.
Purpose of the Study:
- To investigate the effect of stannous octoate catalyst concentration and polymerization time on ROP of lactides.
- To determine optimal conditions for achieving high molecular weight PLA via ROP.
Main Methods:
- Ring-opening polymerization of lactides in bulk at 130°C.
- Varying stannous octoate catalyst concentration (0.003–0.8 wt%).
- Monitoring polymerization time and resultant polymer molecular weight (Mv).
Main Results:
- ROP produced polylactides with Mv from 2 x 10^4 to 6.8 x 10^5.
- Maximum monomer conversion and Mv occurred at ~0.05 wt% catalyst.
- Monomer conversion and Mv increased with time up to 80% conversion, then decreased, especially at higher temperatures, due to thermal depolymerization.
Conclusions:
- Stannous octoate catalyzed ROP is effective for synthesizing high molecular weight PLA.
- Careful control of catalyst concentration and polymerization time is necessary to avoid degradation.
- Thermal depolymerization limits achievable molecular weight at prolonged reaction times and elevated temperatures.