Lac tides

Lac tides, intermolecular cyclic esters, are named as heterocycles. Lactams and lactims, containing a —CO—NH— and —C(OH)=N— group, respectively, are named as heterocycles, but they may also be named with -lactam or -lactim in place of -olide. For example,... 

H. Tsuji and Y. Ikada, Blends of aliphatic polyesters, i. physical properties and morphologies of solution-cast blends from poly(DL-lac-tide) and poly(f -ca prolactone),. Appl. Polym. Sci., 60(13) 2367-2375, June 1996. 

Noncrystalline aromatic polycarbonates (qv) and polyesters (polyarylates) and alloys of polycarbonate with other thermoplastics are considered elsewhere, as are aliphatic polyesters derived from natural or biological sources such as poly(3-hydroxybutyrate), poly (glyc olide), or poly (lac tide) these, too, are separately covered (see Polymers, environmentally degradable Sutures). Thermoplastic elastomers derived from poly(ester—ether) block copolymers such as PBT/PTMEG-T [82662-36-0] and known by commercial names such as Hytrel and Riteflex are included here in the section on p oly (butylene terephthalate). Specific polymers are dealt with largely in order of volume, which puts PET first by virtue of its enormous market volume in bottle resin. 

Panyam, J., Zhou, W.Z., Prabha, S., et al. Rapid endolysosomal escape of poly(DL-lac-tide-co-glycolide) nanoparticles Implications for drug and gene delivery FASEB. J. 16(10) 1217-1226. 2002. 

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. 

The tacticity of PLA influences the physical properties of the polymer, including the degree of crystallinity which impacts both thermo-mechanical performance and degradation properties. Heterotactic PLA is amorphous, whereas isotactic PLA (poly(AA-lactide) or poly (55-lac tide)) is crystalline with a melting point of 170-180°C [26]. The co-crystallization of poly (RR-lactide) and poly(55-lactide) results in the formation of a stereocomplex of PLA, which actually shows an elevated, and highly desirable, melting point at 220-230°C. Another interesting possibility is the formation of stereoblock PLA, by polymerization of rac-lactide, which can show enhanced properties compared to isotactic PLA and is more easily prepared than stereocomplex PLA [21]. 

Figure 180. DSC curves demonstrating crystallization of poly(/-lac tide) in microspheres following storage, (a) Before storage (b) after 6-month storage at 50°C and 11% RH. (Reproduced from Ref. 713 with permission.)...

Zhang, X., et al.. Controlled release of albumin from biodegradable poly (DL-lac-tide) cylinders. Journal of Controlled Release, 1993, 25, 61-69. 

Cyclodextrins can polymerize cyclic esters such as lactones and lac-tides (67). They can initiate the polymerization of cyclic esters in bulk without any solvents to give products in high yields. 

FuUy biobased poly(L-lactide)-b-poly(ricinoleic acid)-b-poly(L-lac-tide) triblock copolyesters have been described (31). Methyl ri-cinoleate, produced from castor oil, is condensed in the presence of a small amount of 1,3-propanediol. This results in a a, (D-hydroxy-terminated poly(ricinoleic acid) with a molar mass... 

Alternative sheet flooring materials prepared from the poly(lac-tide) based composites have been described (1). The polymeric material can include 30-50% of PVC, polyfethylene glycol) (PEG), poly(glycoUde), ethylene vinyl acetate, polycarbonate, poly(capro-lactone) (PCL), poly(/S-hydroxyalkanoate)s, or ionomer modified polyolefins. 

Xiaoyi, X. Qingbiao, Y Yongzhi, W., et al. Biodegradable electrospun poly(L-lac-tide) fibers containing antibacterial sUver nanoparticles Eur. Polym. J., 2006, 42, 2081-2087. 

Wienforth F, Landrock A, Schindler C, Siegert J and Kirch W (2007), Smart textiles A new drug dehvery system for symptomatic treatment of a common cold , / CZm Pharmacol, 47(5), 653-658. DOI 10.1177/0091270007299927. Bomeman AF (2002), A comparison of poly(L-lactic acid) and poly(D,L-lac-tide co-glycohde) biodegradable fibers as drug delivery devices , MS thesis,The University of Texas, Arhngton. 

Tsuji, H., Tsumno, T., 2010. Accelerated hydrolytic degradation of poly(L-lactide)/poly(D-lac-tide) stereocomplex up to late stage. Polymer Degradation and Stability 95, 477—484. 

Verheyen, C.C.P.M., de Wijn, J., Van Blitterswijk, C.A., Rozing, P.M., de Groot, K. (1993) Examination of efferent lymph nodes after 2 years of transcortical implantation of poly (1-lac tide) containing plug a case report./. Biomed Mater. Res., 27, 1115-1118. 

D-Lactide can be obtained if one has the appropriate biochemistry to produce the D-enantiomer of lactic acid by fermentation of carbohydrates. Copolymeiization of controlled mixtures of l- and D-lactides subsequently offers the advantage of precise control over PLA properties. Moreover, D-lactide is the monomer for the production of poly(D-lac-tide), which is able to form high-melting stereocomplex PLA via 1 1 racemic cocrystallization with P(L)LA, as will be discussed in Chapter 5 [89]. 

W. Hoogsteen, A. R. Postema, A. J. Pennings, Crystal structure, conformation, and morphology of solution-spun poly(L-lac-tide) fibers. Macromolecules 1990, 23, 634-642. 

W.J. Lambert, and K.D. Peck, Development of an in situ forming biodegradable poly-lac-tide-co-glycolide system for the controlled release of proteins, /. Control. Release, 33, 189-195,1995. 

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