Polylactide chemical structure

Polylactic acid (PLA) is the world s most popular synthetic biodegradable polymer and has a widespread use in the biomedical field. It maybe obtained directly from lactic acid by condensation polymerization or, more commonly, by ring-opening polymerization from the cyclic dimer of lactic acid lactide. Lactide is a chiral molecule that exists in three isomeric forms D(-), L(+) and racemic (D,L) lactide. Consequently, the polymerization of this monomer can lead to the formation of three different forms of polylactide poly-L-lactic acid (PLLA), poly-D-lactic acid (PDLA), and poly-D,L-lactic acid (PDLLA). The general representation of the chemical structure of PLA is presented in Figure 16.10. 

In this section, the structure, preparation, miscibility and properties of different polymer blends based on biodegradable polyesters are reviewed. Polylactide-based blends are first revisited and discussed, and the miscibility behaviors of other commercially available biopolymers of great interest such as poly(E-caprolactone) (PCL), poly(3-hydroxybutyrate) (PHB), poly(p-dioxanone) (PPDO) and polyglyco-lide (PGA) are briefly reviewed. Finally, Appendix 2.A provides a brief outline of the investigations used to develop the miscibility study presented here. In this recap, it is possible to find the chemical structures of the polymers and their solubility parameters, and also some brief comments summarizing the research studies. 

Figure 4.5 shows that the chemical structure of poly(lactic acid) (PLA). Poly(lactic acid) or polylactide (PLA) is a biodegradable, thermoplastic. 

The doublet structure of the methyl signal at 17 ppm is caused by the stereochemistry. Polylactides, not yet described in any pharmacopoeias, are rather new biodegradable polyesters derived from the chiral lactic acid and used, e. g., in drug delivery systems. The stereochemistry of the polymer is important to the physical and chemical behavior, especially the polymer properties. Pure tactic polymerization can be differentiated from atactic or mixed polymers by simple comparison of the C NMR spectra (Figure 3-10) [4]. 

PLA is known both as poly(lactic acid) and as polylactide. It is currently the most used packaging plastic that is both biodegradable and biobased. PLA is a member of the polyester family, and is chemically synthesized from lactic acid that is derived from starch by fermentation. PLA has the following structure ... 

Although structurally very similar to PG, the polylactides (PL)s are quite different in chemical, physical and mechanical properties because of the presence of a pendant methyl group on the alpha carbon. This structure causes chirality at the alpha carbon of PL and thus, L, D, and DL isomers are possible. L-PL is made from L(-)-lactide and D-PL is made from D(-i-)-lactide while DL-PL is made from DL-lactide which is a racemic mixture of the L(-) and D(-i-) isomers and the meso form having both the D(-i-) and L(-) configuration on the same dimer molecule. 

Lastly, synthetic varieties of textiles are present primarily in apparel and are either petroleum-based or blends with natural fibers. Polyester fibers, aramid fibers, acrylics, nylon, polyurethane, olefins (hydrophobic), polylactide (hydrophilic), milk protein-based fibers, and carbonization-based fibers all constitute synthetics which require some level of surface-modification. This includes nonwovens, structures bonded together by entangling fiber or filaments mechanically, thermally, or chemically. 

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