The upper bound revisited

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.

/pdf/a-literature-review-of-poly-lactic-acid-559pd7jgnc.pdf

A Literature Review of Poly(Lactic Acid)

Fluorine is the most electronegative element in the periodic table. When bound to carbon it forms the strongest bonds in organic chemistry and this makes fluorine substitution attractive for the development of pharmaceuticals and a wide range of speciality materials. Although highly polarised, the C–F bond gains stability from the resultant electrostatic attraction between the polarised Cδ+ and Fδ– atoms. This polarity suppresses lone pair donation from fluorine and in general fluorine is a weak coordinator. However, the C–F bond has interesting properties which can be understood either in terms of electrostatic/dipole interactions or by considering stereoelectronic interactions with neighbouring bonds or lone pairs. In this tutorial review these fundamental aspects of the C–F bond are explored to rationalise the geometry, conformation and reactivity of individual organofluorine compounds.

Understanding organofluorine chemistry. An introduction to the C–F bond

Polylactide polymers have gained enormous attention as a replacement for conventional synthetic packaging materials in the last decade. By being truly biodegradable, derived from renewable resources and by providing consumers with extra end-use benefits such as avoiding paying the "green tax" in Germany or meeting environmental regulations in Japan, polylactides (PLAs) are a growing alternative as a packaging material for demanding markets. The aim of this paper is to review the production techniques for PLAs, summarize the main properties of PLA and to delineate the main advantages and disadvantages of PLA as a polymeric packaging material. PLA films have better ultraviolet light barrier properties than low density polyethylene (LDPE), but they are slightly worse than those of cellophane, polystyrene (PS) and poly(ethylene terephthalate) (PET). PLA films have mechanical properties comparable to those of PET and better than those of PS. PLA also has lower melting and glass transition temperatures than PET and PS. The glass transition temperature of PLA changes with time. Humidity between 10 and 95% and storage temperatures of 5 to 40 degrees C do not have an effect on the transition temperature of PLA, which can be explained by its low water sorption values (i.e. <100 ppm at Aw = 1). PLA seals well at temperatures below the melting temperature but an appreciable shrinking of the films has been noted when the material is sealed near its melting temperature. Solubility parameter predictions indicate that PLA will interact with nitrogen compounds, anhydrides and some alcohols and that it will not interact with aromatic hydrocarbons, ketones, esters, sulfur compounds or water. The CO2, O2 and water permeability coefficients of PLA are lower than those of PS and higher than those of PET. Its barrier to ethyl acetate and D-limonene is comparable to PET. The amount of lactic acid and its derivatives that migrate to food simulant solutions from PLA is much lower than any of the current average dietary lactic acid intake values allowed by several governmental agencies. Thus, PLA is safe for use in fabricating articles for contact with food.

An Overview of Polylactides as Packaging Materials

https://cmapspublic3.ihmc.us/rid=1266358861321_2027852911_13457/Wound%20Healing%20Dressings%20and%20Drug%20Delivery%20Systems.pdf

Wound healing dressings and drug delivery systems: a review.

Rk. mit silylaziden 10. mitt. synth. alicyclischer beta-aminocarbonsaeuren und ihrer derivate

The (trimethylsiloxy)benzoyl chlorides 1–7 are easily to obtain under mild conditions from silylated hydroxybenzoic acids by means of thionyl chloride. Whereas these acid chlorides are stable at room temperature, they undergo condensation polymerization at temperatures above 100°C. Reactions with various nucleophils, such as thioalcohols, phenols, amines, N,O-bis(silylated) amino acids and N-silylated lactams were investigated. With hexamethyldisilazane and thionyl chloride the (trimethylsiloxy)benzonitriles 21, 22 are accessible, and by means of trimethylsilyl azide the (trimethylsiloxy)phenyl isocyanates 23–25 were obtained. Conversion with phenyl carbazate and subsequent silylation lead to the 2-(trimethylsiloxy)phenyl-1,3,4-oxadiazol-5-ones 27a-c.



Synthesen und Reaktionen von (Trimethylsiloxy)benzoylchloriden.



Die (Trimethylsiloxy)benzoylchloide 1–7 sind unter milden Bedingungen leicht aus silylierten Hydroxybenzoesauren mit Thionylchlorid darzustellen. Obwohl diese Saurechloride bei Raumtemperatur stabil sind, polymerisieren sie bei Temperaturen oberhalb 100°C. Es wurden Reaktionen mit verschiedenen Nukleophilen — wie z. B. Thioalkoholen, Phenolen, Aminen, N,O-bis-(silylierten) Aminosauren und N-silylierten Lactamen — untersucht. Mit Hexamethyldisilazan und Thionylchlorid sind die (Trimethylsiloxy)benzonitrile 21, 22 zu erhalten und mit Trimethylsilylazid die (Trimethylsiloxy)phenylisocyanate 23–25. Umsetzung mit Carbazinsaure-phenylester und nachfolgende Silylierung fuhrt zu den 2-(Trimethylsiloxy)phenyl-1,3,4-oxadiazol-5-onen 27a-c.

Syntheses and reactions of (trimethylsiloxy)benzoyl chlorides

Reversible isomerisierung bei beta-isocyanatocrotonsaeureestern

Synthesis of taurine and sulfanilic acid peptides

Glycolide was polymerized in bulk at 160 °C using various metal acetylacetonates as catalysts. Zirconium acetylacetonate was particularly efficient, enabling rapid polymerization even at 130 °C. The formation of cyclic poly(glycolic acid) (PGA), most likely via a ring-expansion polymerization (REP) mechanism, was proven by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Depending on the polymerization conditions, the formation of even-numbered cycles was favored to varying degrees. Number-average molecular weights (Mn) in the range of 2000–3500 g mol−1 were achieved with dispersities below 2.0. Wide-angle X-ray scattering (WAXS) powder patterns showed that the crystal lattice was the same as that of known linear PGAs, regardless of the Mn values. These patterns enabled a comparison of crystallinities with values derived from DSC measurements.

Cyclic polyglycolide by means of metal acetylacetonates

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