Dilactide

Many of the physical properties are not affected by the optical composition, with the important exception of the melting poiat of the crystalline acid, which is estimated to be 52.7—52.8°C for either optically pure isomer, whereas the reported melting poiat of the racemic mixture ranges from 17 to 33°C (6). The boiling poiat of anhydrous lactic acid has been reported by several authors it was primarily obtained duriag fractionation of lactic acid from its self-esterification product, the dimer lactoyUactic acid [26811-96-1]. The difference between the boiling poiats of racemic and optically active isomers of lactic acid is probably very small (6). The uv spectra of lactic acid and dilactide [95-96-5] which is the cycHc anhydride from two lactic acid molecules, as expected show no chromophores at wavelengths above 250 nm, and lactic acid and dilactide have extinction coefficients of 28 and 111 at 215 nm and 225 nm, respectively (9,10). The iafrared spectra of lactic acid and its derivatives have been extensively studied and a summary is available (6). 

Because lactic acid has both hydroxyl and carboxyl functional groups, it undergoes iatramolecular or self-esterificatioa and forms linear polyesters, lactoyUactic acid (4) and higher poly(lactic acid)s, or the cycUc dimer 3,6-dimethyl-/)-dioxane-2,5-dione [95-96-5] (dilactide) (5). Whereas the linear polyesters, lactoyUactic acid and poly(lactic acid)s, are produced under typical condensation conditions such as by removal of water ia the preseace of acidic catalysts, the formation of dilactide with high yield and selectivity requires the use of special catalysts which are primarily weakly basic. The use of tin and ziac oxides and organostaimates and -titanates has been reported (6,21,22). 

DUactide (5) exists as three stereoisomers, depending on the configurations of the lactic acid monomer used. The enantiomeric forms whereia the methyl groups are cis are formed from two identical lactic acid molecules, D- or L-, whereas the dilactide formed from a racemic mixture of lactic acid is the opticaUy iaactive meso form, with methyl groups trans. The physical properties of the enantiomeric dilactide differ from those of the meso form (6), as do the properties of the polymers and copolymers produced from the respective dilactide (23,24). 

Polylactide is the generaUy accepted term for highly polymeric poly(lactic acid)s. Such polymers are usuaUy produced by polymerization of dilactide the polymerization of lactic acid as such does not produce high molecular weight polymers. The polymers produced from the enantiomeric lactides are highly crystalline, whereas those from the meso lactide are generaUy amorphous. UsuaUy dilactide from L-lactic acid is preferred as a polymerization feedstock because of the avaUabUity of L-lactic acid by fermentation and for the desirable properties of the polymers for various appUcations (1,25). 

Reaction of a metal lactate (such as silver lactate) with an alkyl haUde is a classic method of preparation of the ester, but it is too expensive to be of commercial relevance. Lactamide [2043-43-8] is another high yielding condensation product from lactic acid. It can be produced by aminolysis of dilactide or lactate ester such as methyl or ethyl lactate. 

The living nature of PCL obtained in the presence of Zn(OAl-(OPri)2)2 has been used to prepare both di- and triblock copolymers of e-caprolactone and lactic acid (42,43). Treatment of the initial living PCL with dilactide afforded a PCL-PLA diblock with M /Mn = 1.12, with each block length determined by the proportions of the reactants, i.e., the ratio of [monomer]/[Zn]. While the living diblock copolymer continued to initiate dilactide polymerization, it failed to initiate e-caprolactone polymerization. To obtain a PCL-PLA-PCL triblock, it was necessary to treat the living PCL-PLA-OAIR2 intermediate with ethylene oxide, then activate the hydroxy-terminated PCL-PLA-(OCH2CH2)nOH with a modified Teyssie catalyst (Fig. 5). 

Stannous octoate has the advantage of having been used to prepare polymers (Silastic, Capronor) for which substantial toxicological data are now available (6,48). Stannous octoate-initiated polymerization has been used to prepare copolymers of e-caprolactone with other lactones, including diglycolide, dilactide, 6-valerolactone, e-decalactone, and other alkyl-substituted e-caprolactones. Conducting... 

The copolymerization parameters for copolymerization of dilactide and e-caprolactone catalyzed by stannous octoate, stannous chloride, and tetrabutyl titinate have been determined (5). 

For example, the T values of copolymers with dilactide increase in proportion to the dilactide content according to the Fox equation ... 

In addition to solvent uses, esters of lactic acid can be used to recover pure lactic acid via hydrolysis, which in-tum is used to make optically active dilactide and subsequently polylactic acid used for drag delivery system.5 This method of recovery for certain lactic acid applications is critical in synthesis of medicinal grade polymer because only optically active polymers with low Tg are useful for drug delivery systems. Lactic acid esters themselves can also be directly converted into polymers, (Figure 1), although the commercial route proceeds via ring-opening polymerization of dilactide. 

Dilactide, 14 116-117, 122 Diladel, molecular formula and structure, 5 97t, 118t... 

Kowalski A, Duda A, Penczek S (2000) Kinetics and mechanism of cyclic esters polymerization initiated with tin(II) octoate. 3. Polymerization of L,L-dilactide. Macromolecules 33 7359-7370... 

The ring-opening polymerization of dilactide (dimeric cyclic ester of lactic acid) allows the preparation of high molecular weight, optically active polyesters of lactic acid. The configuration of the asymmetric carbon atoms of the monomer is retained when the polymerization is initiated with SnCl4 or Et2Zn, for example ... 

Ring-Opening Polymerization of Dilactide with Cationic Initiators in Solution... 

Monomers like glycolide or lactide are prepared by heating the corresponding acids under controlled conditions [53]. For example, lactide is prepared by heating lactic acid at 120 °C until water ceases to distill. The temperature is then increased to 140 °C and the pressure is reduced to 10 torn After heating for several hours at this temperature, the pressure is reduced further and the temperature increased until lactide begins to distill. Dilactide (3,6-dimethyl-l, 4-dioxan-2,5-dione) contains two asymmetric centers and therefore exists as L-lactide, D-lac-tide, meso-lactide, and the racemic mixture D,L-lactide and gives polymers with different properties. 

Lactic acid 1,2-Propanediol 2,3-Pentanedione, acrylic acid, acrylate polymers, cyclic lactide (dilactide), propylene glycol Acidulant biopolymers, flavourings, pH buffers, preservatives, resins, solvent Polymers Hofvendahl et al., 1999 Hofvendahl and Hahn-Hagerdal, 2000 Datta and Henry, 2006 Bennett and San, 2001... 

C28H50N2O4, Mr 478.72, mp. 121 °C, [0] +21.65° (C2H5OH), monoclinic prisms. C., a macrocyclic symmetrical dilactide, is an alkaloid firom the leaves of the papaya tree (Carica papaya) which causes bradycardia (slowing of heart rate). It is an effective amoebi-cide and exhibits (in vitro) anti-tumor activity even at low concentrations. Derivatives of C. from C. papaya are the 2-epimer (pseudocarpaine), the 1,2-didehydro compound dehydrocarpaine /), and l,l, 2,2 -tetrade-hydrocarpaine (dehydrocarpaine II). 

Another study concerned a sample obtained by ring-opening copolymerization of two cyclic monomers, namely dilactide and depsipeptide of lactic acid and glycine. The MALDI mass spectrum was recorded (Chapter 10), and chain statistics was applied to determine the sequence. The sequence turned out to follow firsf-order Markoff. The composition associated with the P-matrix elements is = 0.77, which compares well with the composition determined by NMR, = 0.76. 

Chisholm, M.H., and Eilerts, N.W., Single Site Metal Alkoxide Catalysts for Ring-Opening Polymerizations. PoIy(dilactide) Synthesis Employing HB93-BuV>z)3 Mg(Oet). 

Kricheldorf, H.R. and Kreiser, 1. (1987) Polylactones. 11. Cationic copolymerization of glycolide with L,L-dilactide. Makromolekulare Chemie, 188, 1861-1873. 

For the production of polymers or their derivatives, the technology for producing the dilactide (the internal diester) is critically important. The processes include a multistage evaporation followed by polymerization to a low molecular weight prepolymer, which is then catalytically converted to the dilactide. The dilactide is purified in a distillation system by partial condensation and recycling. This diester can be used to synthesize high molecular weight polymers and copolymers. " ... 

Synthesis of POE IV materials is similar to POE II reaction, but mono/ dilactide or mono/diglycolide are included in the backbone (Fig. 1.15). These fragments can be considered as latent acids because hydrolysis of POE IV polymers produces lactic acid or glycolic acid which act as catalysts for the hydrolysis of ortho ester linkages. The advantage of these polymers is the... 

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