Environmental Engineering Reference
In-Depth Information
Figure 10. Types of lactide: Meso-lactide, L-lactide, and D-lactide.
Figure 11. Coordination insertion polymerization of lactide with Sn(Oct)
2
[73].
Polymerization reactions may be performed in bulk or in solution. The type of lactide,
reaction temperature, and catalyst system determine the stereochemistry at each carbon-
carbon bond along the backbone of PLA, in turn determining the properties of the resulting
material. Impurities present in the lactide such as water, lactic acid, and lactyl-lactic acid
decrease the molecular weight of the end polymer [64, 65].
The coordination insertion mechanism is the most common method used to produce high
molecular weight PLA with high optical purity and crystallinity. Many catalytic or initiator
systems have been developed for the coordination insertion polymerization of lactide. Oxides,
halides, and alkoxides of metals possessing free p-, d-, or f- orbitals such as magnesium (Mg)
