 | |
| Names | |
|---|---|
| IUPAC name Poly[oxy(1-oxo-1,2-ethanediyl)] | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider |
|
| ECHA InfoCard | 100.249.865 |
| UNII | |
| |
| Properties | |
| (C2H2O2)n | |
| Molar mass | (58.04)n |
| Density | 1.530 g/cm3 at 25 °C |
| Melting point | 225 to 230 °C (437 to 446 °F; 498 to 503 K) |
| Boiling point | Decomposes |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Polyglycolide orpoly(glycolic acid) (PGA), also spelled aspolyglycolic acid, is abiodegradable,thermoplasticpolymer and the simplest linear,aliphaticpolyester. It can be prepared starting fromglycolic acid by means ofpolycondensation orring-opening polymerization. PGA has been known since 1954 as a toughfiber-forming polymer. Owing to itshydrolytic instability, however, its use was slow to develop.[1] Polyglycolide and itscopolymers (poly(lactic-co-glycolic acid) withlactic acid, poly(glycolide-co-caprolactone) withε-caprolactone and poly (glycolide-co-trimethylene carbonate) withtrimethylene carbonate) are widely used as a material for the synthesis of absorbablesutures and are being evaluated in thebiomedical field.[2]
Polyglycolide has aglass transition temperature between 35 and 40 °C and amelting point in the range of 225 to 230 °C. PGA also exhibits an elevated degree ofcrystallinity, around 45–55%, thus resulting in insolubility inwater.[2] The highmolecular weight form is insoluble in commonorganic solvents (acetone,dichloromethane, etc.), whereas low molecular weightoligomers are more soluble. Polyglycolide is soluble in highlyfluorinated solvents likehexafluoroisopropanol (HFIP) andhexafluoroacetone sesquihydrate, that can be used to prepare solutions of the high MW polymer formelt spinning and film preparation.[citation needed] Fibers of PGA exhibit high strength andmodulus (7GPa) and are particularly stiff.[2]
Polyglycolide can be obtained through several processes starting with different materials:
Polycondensation of glycolic acid is the simplest process available to prepare PGA, but it is not the most efficient because it yields a low molecular weight product.[citation needed]
The most common synthesis of high molecular weight form of the polymer is ring-opening polymerization of glycolide, the bislactone cyclic dimer of glycolic acid. Glycolide can be prepared by thermalcracking, collecting the diester by means of distillation. Ring-opening polymerization of glycolide can becatalyzed using diversecatalysts, includingantimony compounds, such asantimony trioxide or antimony trihalides,zinc compounds (zinc lactate) andtin compounds likestannous octoate (tin(II) 2-ethylhexanoate) or tin alkoxides. Stannous octoate is the most commonly used initiator, since it is approved by theFDA as a food stabilizer. Usage of other catalysts has been disclosed as well, among these arealuminium isopropoxide,calciumacetylacetonate, and severallanthanide alkoxides (e.g.yttrium isopropoxide).[3][4]
Another procedure consists in the thermally induced solid-state polycondensation of halogenoacetates with general formulaX-—CH2COO−M+ (where M is a monovalent metal likesodium and X is ahalogen likechlorine), resulting in the production of polyglycolide and smallcrystals of asalt. Polycondensation is carried out by heating an halogenoacetate, likesodium chloroacetate, at a temperature between 160 and 180 °C, continuously passing nitrogen through the reaction vessel. During the reaction polyglycolide is formed along withsodium chloride which precipitates within the polymeric matrix; the salt can be conveniently removed by washing the product of the reaction with water.[5]
PGA can also be obtained bycarbonylation (reaction withcarbon monoxide) of formaldehyde or the related compounds likeparaformaldehyde ortrioxane.[citation needed]
The hydrolytic degradation appears to take place in two steps during which the polymer is converted back to its monomer glycolic acid: first water diffuses into the amorphous (non-crystalline) regions of the polymer matrix, cleaving the ester bonds; the second step starts after the amorphous regions have been eroded, leaving the crystalline portion of the polymer susceptible to hydrolytic attack. Upon collapse of the crystalline regions the polymer chain dissolves.
When exposed to physiological conditions, polyglycolide is degraded by random hydrolysis, and apparently it is also broken down by certainenzymes, especially those withesterase activity. The degradation product,glycolic acid, is nontoxic, but likeethylene glycol, it is metabolized tooxalic acid, which could make it dangerous. A part of the glycolic acid is also excreted byurine.[6]
Studies undergone using polyglycolide-made sutures have shown that the material loses half of its strength after two weeks and 100% after four weeks. The polymer is completely resorbed by the organism in a time frame of four to six months.[2] Degradation is fasterin vivo thanin vitro, this phenomenon thought to be due to cellular enzymatic activity.[7]
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While known since 1954, PGA had found little use because of its sensitivity tohydrolysis when compared with other synthetic polymers. However, in 1962 this polymer was used to develop the first synthetic absorbable suture which was marketed under thetradename of Dexon[1] by theDavis & Geck subsidiary of the American Cyanamid Corporation. After its coating with polycaprolactone and calcium stearate it is being sold under the brand name of Assucryl.
PGA suture is classified as a synthetic, absorbable, braided multifilament. It is coated with N-laurin and L-lysine, which render the thread extremely smooth, soft and safe forknotting. It is also coated withmagnesium stearate and finally sterilized withethylene oxide gas. It is naturally degraded in the body byhydrolysis and is absorbed as water-soluble monomers, completed between 60 and 90 days. Elderly,anemic andmalnourished patients may absorb the suture more quickly. Its color is eitherviolet or undyed and it is sold in sizes USP 6-0 (1 metric) to USP 2 (5 metric). It has the advantages of high initial tensile strength, smooth passage through tissue, easy handling, excellent knotting ability, and secure knot tying. It is commonly used forsubcutaneous sutures, intracutaneous closures, abdominal and thoracic surgeries.
The traditional role of PGA as a biodegradable suture material has led to its evaluation in other biomedical fields. Implantable medical devices have been produced with PGA, includinganastomosis rings, pins, rods, plates and screws.[2] It has also been explored fortissue engineering or controlled drug delivery. Tissue engineering scaffolds made with polyglycolide have been produced following different approaches, but generally most of these are obtained throughtextile technologies in the form ofnon-woven felts.
TheKureha Chemical Industries has commercialized high molecular weight polyglycolide for food packaging applications under the tradename of Kuredux.[8] Production is at Belle, West Virginia, with an intended capacity of 4000 annual metric tons.[9] Its attributes as a barrier material result from its high degree of crystallization, the basis for a tortuous path mechanism for low permeability. It is anticipated that the high molecular weight version will have use as an interlayer between layers ofpolyethylene terephthalate to provide improved barrier protection for perishable foods, including carbonated beverages and foods that lose freshness on prolonged exposure to air. Thinner plastic bottles which still retain desirable barrier properties may also be enabled by this polyglycolide interlayer technology. A low molecular weight version (approximately 600 amu) is available fromThe Chemours Company (formerly part ofDuPont) and is purported to be useful in oil and gas applications.[10]
