Chemical Structure of Poly lactic acid

XuE Jiang, Yan Luo, Xiuzhi Tian, Dan Huang, Narendra Reddy, and Yiqi Yang 

Commercial PLA is a blend of PLLA and PDLA or copolymer PDLLA, obtained by the polymerization of LLA and DLLA, respectively [1]. Many important properties of PLA are controlled by the ratio of d- to L-enantiomers used and the sequence of arrangement of the enantiomers in the polymers. PLLA constitutes the main fraction of PLA derived from renewable sources since the majority of lactic acid obtained from biological sources exists as LLA. PLA with PLLA content higher than 90% tends to be crystalline while that with lower optical purity is amorphous. The melting temperature (Tm), glass transition temperature (Tg), and crystallinity of PLA decrease with decreasing amounts of PLLA [2-5]. 

The properties of PLA such as thermal stability and impact resistance are inferior to those of conventional polymers used for thermoplastic applications. Therefore, PLA is not ideally suited to compete against the conventional polymers [5]. In order to improve the properties of PLA and increase its potential applications, copolymers of lactic acid and other monomers such as derivatives of styrene, acrylate, and poly (ethylene oxide) (PEO) have been developed. PLA has also been formulated and associated with nanosized fillers. Modification of PLA, copolymerization with other monomers, and PLA composites are some approaches that have been used to improve the properties of PLA, such as stiffness, permeabiUty, crystallinity, and thermal stability [1-5]. Considerable research is being done to develop and study modified PLA, PLA-based copolymers, and PLA-based composites. 

The chemical structures of PLA, including the chain structure, configuration, tacticity, conformation, and the frustrated structure, are important parameters that govern 

Polymers that have stereocenters in the repeating unit can exhibit two structures of maximum order, that is, isotactic and syndiotactic. Isotactic polymers contain sequential stereocenters of same relative configuration while syndiotactic polymers contain sequential stereocenters of opposite relative configuration. These stereoregular polymers are typically crystalline and used in a wide variety of applica- 

---

Ihble 2 shows a comparison of physical quantities for three optically active polymers described above. With an increase of polarity in chemical structure, the magnitude of the piezoelectric constant increases remarkably, although the degree of crystallinity and the degree of orientation are not exactly the same for the three polymers. The chemical structure of poly-lactic acid is the simplest form to oou de an asymmetric carbon atom and a polar group CO-O and is most suitable for displaying the piezoelectric effect in this aeries. 

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

Figure 4.5 Chemical structure of poly (lactic acid).

Figure 3 Chemical structure of poly(lactic-co-glycolic) acid polymer. The x component represents lactic acid and y component represents glycolic acid. For other poly(hydroxy acids), the side-chain methyl group is replaced by other alkyl groups.

Figure 14.6 Chemical structure of poly(lactic-co-glycolic acid).

Scheme Chemical structures of poly(e-caprolactone)-b-poly(y-benzyl-L-glutamate) (PCL-PBLG) and poly(L-lactic acid)-b-poly(y-benzyl-L-glutamate) (PLLA-PBLG)...

Carrasco, E., Pages, P., Gamez-Perez, J., Santana, O.O., Maspoch, M.L. Processing of poly (lactic acid) Characterization of chemical structure, thermal stability and mechanical properties. Polym. Degrad. Stab. 95, 116-125 (2010)... 

Fig. 2 Chemical structure of a polyflactic acid), b polyfglycolic acid), c poly(lactic-co-glycolic) acid, d poly(anhydride), and e polyfimide)...

See also PBT degradation structure and properties of, 44-46 synthesis of, 106, 191 Polycaprolactam (PCA), 530, 541 Poly(e-caprolactone) (CAPA, PCL), 28, 42, 86. See also PCL degradation OH-terminated, 98-99 Polycaprolactones, 213 Poly(carbo[dimethyl]silane)s, 450, 451 Polycarbonate glycols, 207 Polycarbonate-polysulfone block copolymer, 360 Polycarbonates, 213 chemical structure of, 5 Polycarbosilanes, 450-456 Poly(chlorocarbosilanes), 454 Polycondensations, 57, 100 Poly(l,4-cyclohexylenedimethylene terephthalate) (PCT), 25 Polydimethyl siloxanes, 4 Poly(dioxanone) (PDO), 27 Poly (4,4 -dipheny lpheny lpho sphine oxide) (PAPO), 347 Polydispersity, 57 Polydispersity index, 444 Poly(D-lactic acid) (PDLA), 41 Poly(DL-lactic acid) (PDLLA), 42 Polyester amides, 18 Polyester-based networks, 58-60 Polyester carbonates, 18 Polyester-ether block copolymers, 20 Polyester-ethers, 26... 

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 ... 

Kawamoto, N., Sakai, A., Horikoshi, T. et al. (2007) Nucleating agent for poly(L-lactic acid)-An optimization of chemical structure of hydrazide compound for advanced nucleation ability. Journal of Applied Polymer Science, 103, 198-203. 

Boudouris et al. also observed microphase-separated structures in poly(3-dodecylthiophene-l7-lactic acid) diblock copolymers 34 after short periods of thermal annealing. The PT blocks retained their crystallinity within the nanos-tructured phases, and chemical etching of the poly(lactic acid) block resulted in the formation of nanoporous PT films. 

Figure 2.8 Chemical structures of a block copolymer poly(alMcyanoacrylate)-block-poly (ethylene glycol) (a), and of a random poly(lactic acid-co-glycolic acid) copolymer (b).

Figure 3.1 Chemical structure of lactic acid (a), glycolic add (b), and the related polymers poly(lactic acid) (c) and poly(glycolic acid) (d).

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. 

Fig. 6 Chemical structure of the aliphatic polyesters poly(glycolic acid) (PGA) and pol(lactic acid) (PLA), sodium alginate, and oxidized sodium alginate...

---