Poly-D-lactic acid

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... 

PDDA polydimethyldiallylammonium PDI protein disulfide isomerase PDLA poly(D-lactic acid)... 

A frequency dependence of complex dielectric permittivity of polar polymer reveals two sets or two branches of relaxation processes (Adachi and Kotaka 1993), which correspond to the two branches of conformational relaxation, described in Section 4.2.4. The available empirical data on the molecular-weight dependencies are consistent with formulae (4.41) and (4.42). It was revealed for undiluted polyisoprene and poly(d, /-lactic acid) that the terminal (slow) dielectric relaxation time depends strongly on molecular weight of polymers (Adachi and Kotaka 1993 Ren et al. 2003). Two relaxation branches were discovered for i.s-polyisoprene melts in experiments by Imanishi et al. (1988) and Fodor and Hill (1994). The fast relaxation times do not depend on the length of the macromolecule, while the slow relaxation times do. For the latter, Imanishi et al. (1988) have found... 

Comparison of the dielectric and viscoelastic relaxation times, which, according to the above speculations, obey a simple relation rn = 3r, has attracted special attention of scholars (Watanabe et al. 1996 Ren et al. 2003). According to Watanabe et al. (1996), the ratio of the two longest relaxation times from alternative measurements is 2-3 for dilute solutions of polyisobu-tilene, while it is close to unity for undiluted (M 10Me) solutions. For undiluted polyisoprene and poly(d,/-lactic acid), it was found (Ren et al. 2003) that the relaxation time for the dielectric normal mode coincides approximately with the terminal viscoelastic relaxation time. This evidence is consistent with the above speculations and confirms that both dielectric and stress relaxation are closely related to motion of separate Kuhn s segments. However, there is a need in a more detailed theory experiment shows the existence of many relaxation times for both dielectric and viscoelastic relaxation, while the relaxation spectrum for the latter is much broader that for the former. 

Li SM, Garreau H, Vert M. Structure-property relationships in the case of the degradation of massive aliphatic poly-(a-hydroxy acids) in aqueous media. Part 1 Poly(d/-lactic acid). / Mater Sci Mater Med 1990 1 130-139. 

In topical formulations, particularly cosmetics, it is used for its softening and conditioning effect on the skin. Lactic acid may also be used in the production of biodegradable polymers and microspheres, such as poly(D-lactic acid), used in drug delivery systems.See also Aliphatic Polyesters. 

Elisseeff, J. et al.. Synthesis and characterization of photo-cross-linked polymers based on poly(D-lactic acidaspartic acid). Macromolecules, 30, 2182,1997. 

Monomers Figure3.8 shows a small selection of cyclic monomers suitable for ROP [43]. Additionally, three different stereoisomers of lactide exist as a consequence of the presence of two stereocenters per monomer unit, namely meso-, L- and d-lactide, see Fig. 3.9. Further, racemic mixture of L- and D-lactide are commercially available. While ROP of either pure l- and D-lactide enables synthesis of highly crystalline poly(L-lactic acid) or poly(D-lactic acid), ROP of rac- or wcj< -lactide with adequate catalysts allows the synthesis of stereoblock copolymers, heterotactic and syndiotactic poly(lactic acid). Notably, stereoregular PLAs display much lower rates of degradation than the amorphous atactic polymer. 

Polylactide (PLA) possesses chiral molecules, polylactides exist in four forms poly(L-lactic acid) (PLLA), poly(D-lactic acid) (PDLA), poly(D,L-lactic acid) (PDLLA)—a racemic mixture of PLLA and PDLA, and mesopoly(lactic acid). Figure 30.4a illustrates the molecular structure of PLA. 

Poly(lactic acid) has three typical optical isomeric forms (i) optically active and crystalliz-able poly(L-lactide) (i.e. poly(L-lactic acid) (PLLA)), (ii) optically active and crystallizable poly(D-lactide) (i.e. poly(D-lactic acid) (PDLA)), and (iii) optically inactive and noncrystal-lizable poly(DL-lactide) [i.e. poly(DL-lactic acid) (PDLLA)]. Of these isomeric polymers, PLLA is most frequently used because its production cost is lower due to its joint mass production of 1.4 X 10 metric tons per year by NatureWorks LLC, which is owned by Cargil... 

Tomita, K., Tsuji, H., Nakajima, T. et al (2003) Degradation of poly(D-lactic acid) by a thermoplule. Polymer Degradation and Stability, 81, 167-171. 

Yamane, H. and Sasai, K. (2003) Effect of the addition of poly(D-lactic acid) on the thermal property of poly(L-lactic acid). Polymer, 44, 2569-2575. 

Fig. 8 Crystallization of stereocomplex PLA by blending poly(D-lactic acid) with poly(L-lactic acid) to form nucleating sites (Tsuji H. 2005)...

Abbreviations l-PLA, poly-L-lactic acid PGA, poly-glycolic acid d-PLA, poly-D-lactic acid PMMA, poly-methyl methacrylate PEMA, poly-ethyl methacrylate PDMS, poly(dimethyl-siloxane) PEHA, poly(2-ethylhexyl acrylate). ... 

The homopolymers obtained with pure l- or pure D-feed are referred to as polyfL-lactic acid) PLLA) and poly(D-lactic acid) (PDLA), respectively. However, commercial PLA grades are usually based on an L-rich mixture as the majority of bacteria used in fermentation processes mainly produce L-lactic acid and typically comprise a minimum of 1-2% D units [14]. The presence of both L-lactic and D-lactic units in the polymer chain makes PLA a random copolymer as such, its properties are affected by the co-unit content [16,17]. 

Fujita, M., Sawayanagi, T., Abe, H., Tanaka, T., Iwata, T., Ito, K. et al. (2008) Stereocomplex formation through reorganization of poly(L-lactic acid) and poly(D-lactic acid) crystals. Macromolecules, 41, 2852-2858. 

Additions of small amounts of poly(D-lactic acid) to poly(L-lactic acid) accelerated overall PLEA crystallization, which was confirmed by the effect of additive on nncleation constant. Similarly addition of 3 wt% UHMWPE to HOPE decreased nncleation constant from 3.04x10 to 2.27x10, indicating that UHMWPE increased nncleation rate in HDPE.20... 

Figure 22. Structure of isomers of PLA (a) poly(D-lactic acid) and (b) poly(D,L-lactic acid)...

Tsuji, H., Hyon, S.-H., Ikada, Y., 1991. Stereocomplex formation between enantiomeric poly(lactic acid)s. 4. Differential scanning calorimetric studies on precipitates from mixed solutions of poly(D-lactic acid) and poly(L-lactic acid). Macromolecules 24, 5657-5662. 

One of the major classes of synthetic bioresorbable polymers is that of aliphatic polyesters or poly(a-hydroxy acids). Poly(a-hydroxy acids) such as PGA, poly(lactic acid) (PLA) stereoisomers poly(L-lactic acid) (PLLA) and poly(D-lactic acid), and pol-y(lactic-co-glycolic acid) (PLGA) copolymers are the most widely used and most popular bioresorbable polymers since they received Food and Drug Administration (FDA) approval for clinical use in humans in different forms (eg, fibers for sutures, injectable forms) (Nair and Laurencin, 2007). These polymers are commonly used in regenerative medicine applications. An example is the InQu Bone Graft Extender Substitute (ISTO Technologies), an osteoconductive biosynthetic product used as bone graft substitute in the skeletal system to support new bone formation. The resorption rate of... 

Another way of generating biopolymers is the fermentation of starch, sugar and other commodities by various microorganisms. Typical examples are poly(hydroxyalkanoates) (especially poly(hydroxybuty-rate) (PHB)) and poly(lactic acid) (PLA). Due to the chirality of lactic acid (D- L-form), two distinct forms of poly(lactic acid) exist (poly(L-lactic acid) and poly(D-lactic acid)). PLA is used, e.g. in biomedical application (sutures, stents, drug-delivery, preparation of bioplastic), in agriculture (mulch-film), packaging, and in blends with synthetic polymers. 

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