A literature review is presented regarding the synthesis, and physicochemical, chemical, and mechanical properties of poly(lactic acid)(PLA). Poly(lactic acid) exists as a polymeric helix, with an orthorhombic unit cell. The tensile properties of PLA can vary widely, depending on whether or not it is annealed or oriented or what its degree of crystallinity is. Also discussed are the effects of processing on PLA. Crystallization and crystallization kinetics of PLA are also investigated. Solution and melt rheology of PLA is also discussed. Four different power-law equations and 14 different Mark–Houwink equations are presented for PLA. Nuclear magnetic resonance, UV–VIS, and FTIR spectroscopy of PLA are briefly discussed. Finally, research conducted on starch–PLA composites is introduced.

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A Literature Review of Poly(Lactic Acid)

4.3. Reaction Mechanism 2373 4.4. Asymmetric Synthesis 2374 4.5. Outlook 2374 5. Alternating Polymerization of Oxiranes and CO2 2374 5.1. Reaction Outlines 2374 5.2. Catalyst 2376 5.3. Asymmetric Polymerization 2377 5.4. Immobilized Catalysts 2377 6. Synthesis of Urea and Urethane Derivatives 2378 7. Synthesis of Carboxylic Acid 2379 8. Synthesis of Esters and Lactones 2380 9. Synthesis of Isocyanates 2382 10. Hydrogenation and Hydroformylation, and Alcohol Homologation 2382

Transformation of carbon dioxide.

Polylactic acid is proving to be a viable alternative to petrochemical-based plastics for many applications It is produced from renewable resources and is biodegradable, decomposing to give H2O, CO2, and humus, the black material in soil In addition, it has unique physical properties that make it useful in diverse applications including paper coating, fibers, films, and packaging (see Figure)

Polylactic Acid Technology

s, and 360 patents, and edited 12 books. He has also received over 80 major awards including the Gairdner Foundation International Award, Lemelson-MIT prize, ACS’s Applied Polymer Science and Polymer Chemistry Awards, AICHE’s Professional Progress, Bioengineering, Walker and Stine Materials Science and Engineering Awards. In 1989, Dr. Langer was elected to the Institute of Medicine of the National Academy of Sciences, and in 1992 he was elected to both the National Academy of Engineering and the National Academy of Sciences. He is the only active member of all three National Academies. Kevin Shakesheff was born in Ashington, Northumberland, U.K., in 1969. He received his Bacheclor of Pharmacy degree from the University of Nottingham in 1991 and a Ph.D. from the same institution in 1995. In 1996 he became a NATO Postdoctoral Fellow at MIT, Department of Chemical Engineering. He is currently an EPSRC Advanced Fellow at the School of Pharmaceutical Sciences, The University of Nottingham. His research group investigates new methods of engineering polymer surfaces and the application of these engineered materials in drug delivery and tissue engineering. 3182 Chemical Reviews, 1999, Vol. 99, No. 11 Uhrich et al.

Polymeric Systems for Controlled Drug Release

RGD modified polymers: biomaterials for stimulated cell adhesion and beyond

Equal amounts of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) were mixed with diphenyl ether (DE) at high temperature in DE-to-polymer composition from 0 to 80 wt.-%. Cooling of the ternary mixtures produced white crystallosolvates without deposition of DE. Various analyses revealed that the crystallosolvates consisted of both homo-chiral (hc) and stereocomplex (sc) crystals of PLLA and PDLA as well as amorphous domains involving DE. The crystallosolvate obtained at a DE content of 80 wt.-%, comprised only the sc crystals. Atomic force microscopy (AFM) revealed that many granules having a size of 20 nm in diameter were formed from rod-like hc crystallites and that the DE was slightly phase-separated to form nano-sized reservoirs. The stronger sc interaction between the PLLA and PDLA chains excluded DE from the polymer matrix.

Formation of Crystallosolvates Comprising Nano-Crystals of Stereocomplex in a Ternary Mixture of Poly(L-lactide)/Poly(D-lactide)/Diphenyl Ether

DNA lesions produced by free radicals are suggested to play an important role in mutagenesis, carcinogenesis, and aging.'V2 The molecular mechanism leading to such biological end points have been extensively studied by a uumber of researchers. In this study, we have focused our attention on a-deoxyadenosine (a-dA, FIG. l), which is a major adenine lesion in DNA y-irradiated under anoxic conditions? The anomerization of the N-glycosidic bond occurs via abstraction of the H1' atom by hydroxyl radicals. Alpha-dA has been site-specifically incorporated into an oligodeoxyribonucleotide template to examine its interaction with DNA polymerase in vitro. Alpha-dA was synthesized by the transglycosylation method? which provides a useful synthesis of a-anomers of purine nucleosides. After protecting groups of the Base (Bz) and sugar (DMT) moieties were introduced, protected a-dA was phosphorylated using 2-cyanoethyl N,N,M,N'-tetraisopropylphosphrodiamidite and purified by flash column chromatography. The structure and purity of the phosphoramidite monomer was confirmed by 'H, 13C, and 31P NMR as well as TLC. An oligodeoxyribonucleotide template containing a single a-dA (abbreviated as template) and two complementary primers (abbreviated as primer 12 and primer 17) were synthesized on a Milligen/Biosearch Cyclone Plus DNA synthesizer. The nucleotide sequences of template and primers 12 and 17 are shown below, where a denotes a-dA.

Interaction of alpha-deoxyadenosine in template DNA with DNA polymerase. A novel mutational spectrum induced by alpha-deoxyadenosine.

PURPOSE:To prepare the titled compsn. with improved antistatic properties, by molding a mixt. of polyethyleneoxydiglycolic acid (alkali metal salt) and polyalkylene terephthalate. CONSTITUTION:0.05-5wt% polyethyleneoxydiglycolic acid (alkali metal salt) of formula (wherein n is 4-300), average MW 300-10,000, is mixed with polyalkylene terephthalate (e.g., polyethylene terephthalate). The mixt. is molded at 260-280 deg.C in fiber, film, or hollow body, and then, if necessary, stretched. EFFECT:No discoloration during melt-molding, exceedingly low cut-off in spinning, no decrease in strength of fiber, and capable of preventing poor bite of pellets into a spinning machine.

Polyalkylene terephthalate composition and preparing same

A new type of copolymerization is presented here, which requires no added initiator. A zwitterion 1 is generated by the interaction between two monomers; one monomer has nucleophilic reactivity (MN) and the other possesses electrophilic reactivity (ME). Two moles of the genetic zwitterion 1 react with each other to produce a dimeric zwitterion 2. The dimeric zwitterion 2 grows by its reaction with 1 to polymeric zwitterion 3. Intermolecular reaction of macro-zwitterions (dimeric 2 and polymeric 3) also occurs, which brings about a sharp increase in molecular weight. In a series of studies, six MN monomers and six ME monomers have been investigated. As the MN monomer, cyclic imino ether, exo-imino cyclic ether, azetidine, Schiff base and cyclic phosphonite have been selected. As the ME monomer, lactone, cyclic anhydride, sultone (sulfolactone), acrylic acid, acrylamide and β-hydroxyethyl acrylate have been successfully used. Thus, thirty-six combinations (six times six) of copolymerization have now become conceivable. The present paper gives a survey of elemental reactions of selected combinations of copolymerization. The emphasis is laid on the discussions of recent results.

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No catalyst copolymerization by spontaneous initiation mechanism

We have recently developed a colon specific drug delivery system by use of an ethanol-soluble segmented polyurethane comprising azo aromatic groups in the main chain. In the present study, two types of model compounds containing the azo aromatic group were synthesized, and their degradation kinetics in an anaerobic culture of intestinal flora was investigated for insight into the degradation mechanism of the polyurethane. A hydrophilic azo compound was readily reduced into its hydrazo form and then to amine form. The reduction rates from azo to hydrazo and from hydrazo to amine were comparable. In the case of a hydrophobic azo compound the reduction was stopped in the first step, and only the hydrazo form was produced. Since the Polyurethane used for the coating is hydrophobic in nature, formation of hydrazo form was found without chain breakage.

Yoshiharu Kimura

Papers

Formation of Crystallosolvates Comprising Nano-Crystals of Stereocomplex in a Ternary Mixture of Poly(L-lactide)/Poly(D-lactide)/Diphenyl Ether

Interaction of alpha-deoxyadenosine in template DNA with DNA polymerase. A novel mutational spectrum induced by alpha-deoxyadenosine.

Polyalkylene terephthalate composition and preparing same

No catalyst copolymerization by spontaneous initiation mechanism

Degradation Mechanism of AZO-Containing Polyurethanes by the Action of Intestinal Flora