Poly(L-lactic acid) is a semicrystalline polyester produced by ring-opening polymerisation of the cyclic lactide, and the L prefix fixes the stereochemistry of the repeat unit. The stereocentre matters, because a random mixture of the two enantiomers gives an amorphous polymer while the pure enantiomer crystallises [1]. The melting point and the crystallinity depend on the content of the opposite enantiomer, and a small amount of it lowers both [2]. Hydrolytic degradation proceeds by random chain scission in the bulk, and the rate is accelerated by the acidic products that accumulate inside a thick part [3]. Blending with a flexible polyester improves the toughness but reduces the strength, and the two phases separate unless a copolymer is formed [4]. Stereocomplexation between the two enantiomers raises the melting point by about fifty degrees and improves the heat resistance [5].
- polylactide
- ring-opening polymerization
- stereochemistry
- crystallinity
- hydrolytic degradation
- stereocomplex
- enantiomer
References
- Chang, L.; Woo, E.; Effects of molten poly(3-hydroxybutyrate) on crystalline morphology in stereocomplex of poly(L-lactic acid) with poly(D-lactic acid). Polymer 2011, 52, 68-76, 10.1016/j.polymer.2010.11.028.
- Tashiro, K.; Kouno, N.; Wang, H.; Tsuji, H.; Crystal Structure of Poly(lactic acid) Stereocomplex: Random Packing Model of PDLA and PLLA Chains As Studied by X-ray Diffraction Analysis. Macromolecules 2017, 50, 8048-8065, 10.1021/acs.macromol.7b01468.
- Macnamara, J.F.; Vallery, R.; Gidley, D.; Auras, R.; Density and Crystallinity Correlations: Enhancing Moisture Barrier Properties in Poly( l ‐Lactic Acid), Poly( d ‐Lactic Acid), and Stereocomplex‐Poly( l,d ‐Lactic Acid) Films. Journal of Applied Polymer Science 2025, 142, e56986, 10.1002/app.56986.
- Cataldo, F.; Optical Rotatory Dispersion of Poly(l-lactic acid) (PLLA) in 19 Solvents and Study of PLLA Complexation with Polyphenylacetylene (PPA) in Solution. Liquids 2026, 6, 20, 10.3390/liquids6020020.
- Zhang, L.Q.; Zhang, Z.Y.; Yang, S.G.; Lei, J.; Stereocomplex crystallization of equimolar Poly(L-lactic acid)/Poly(D-lactic acid) blends from melt with lowered chain entanglements. Polymer 2024, 306, 127229, 10.1016/j.polymer.2024.127229.