Abstract:Seit den ersten Untersuchungen yon D u mas, L a ur e n t, R e g n a u l t , Malaguti u. A. uber die sogenannten Substitutionsproducte organischer Verbindungen hat sich die Zahl dieser Harper so aufserordentlich vermehrt und ist uber die Bedingungen ihrer Bildung schon so mancherlei Aufschlufs erhalten worden, dafs es uberflussig erscheinen kiinnte , in dieser Richtung weitere Untersuchungen anzustellen ; allein bei naherer Betrachtung zeigt es sich , dafs selbst bei den am besten untersuchten Verbindungen noch… Show more
“…When certain crystalline metal halogenoacetates (typified by sodium chloroacetate) are heated to sufficiently high temperature, the polymer polyglycolide (poly(oxy-1-oxoethylene)) is formed together with the metal halide: Such elimination of metal halides from salts of halogenoacetic acids has been known since 1857 when Hoffmann and subsequently Kekulé heated potassium chloroacetate to obtain potassium chloride and polyglycolide. , Similar behavior has now been found for many other metal halogenoacetates, of which the most widely studied have been sodium chloroacetate and sodium bromoacetate. …”
It has been known for a long time that, at sufficiently high
temperature, solid sodium chloroacetate undergoes
a polymerization reaction to produce polyglycolide and sodium chloride.
However, an understanding of this
reaction and its mechanism was not previously possible, as sodium
chloroacetate is microcrystalline and
structural information could not be determined from conventional
single-crystal X-ray diffraction methods.
In this paper, we report the structure of sodium chloroacetate;
this advance has been possible through the
application of new methodology, based on Monte Carlo sampling
techniques, that we have developed recently
for crystal structure determination from powder diffraction data.
The reported structure of sodium chloroacetate
provides a direct rationalization, based on topochemical principles, of
the polymerization reaction to produce
polyglycolide.
“…When certain crystalline metal halogenoacetates (typified by sodium chloroacetate) are heated to sufficiently high temperature, the polymer polyglycolide (poly(oxy-1-oxoethylene)) is formed together with the metal halide: Such elimination of metal halides from salts of halogenoacetic acids has been known since 1857 when Hoffmann and subsequently Kekulé heated potassium chloroacetate to obtain potassium chloride and polyglycolide. , Similar behavior has now been found for many other metal halogenoacetates, of which the most widely studied have been sodium chloroacetate and sodium bromoacetate. …”
It has been known for a long time that, at sufficiently high
temperature, solid sodium chloroacetate undergoes
a polymerization reaction to produce polyglycolide and sodium chloride.
However, an understanding of this
reaction and its mechanism was not previously possible, as sodium
chloroacetate is microcrystalline and
structural information could not be determined from conventional
single-crystal X-ray diffraction methods.
In this paper, we report the structure of sodium chloroacetate;
this advance has been possible through the
application of new methodology, based on Monte Carlo sampling
techniques, that we have developed recently
for crystal structure determination from powder diffraction data.
The reported structure of sodium chloroacetate
provides a direct rationalization, based on topochemical principles, of
the polymerization reaction to produce
polyglycolide.
“…For over 140 years it has been known , that alkali-metal salts of halogenoacetic acids eliminate alkali halides upon heating and concomitantly undergo a solid-state polymerizationostensibly without formation of detectable crystalline intermediatesto yield polyglycolide, a polyester that is now of considerable practical value as a biomaterial, especially in medicine. It is used, for example, as a resorbable bone fixation device, , as an intestinal anastomotic device, or as a surgical suture .…”
The solid-state polymerization reaction of sodium bromoacetate has been studied with combined in situ X-ray diffraction and X-ray absorption spectroscopy (XRD-EXAFS). This elimination reaction leads quantitatively to sodium bromide and poly(hydroxyacetic acid), polyglycolide. Both XRD and EXAFS data have been quantitatively analyzed to yield the molar fractions of educt and products during the reaction. Results of both methods confirm that the reaction is occurring without a crystalline, liquid, or amorphous intermediate in one single step. Sodium bromide is precipitated in small crystals in the polymeric matrix. The growth of the microcrystals could be followed by analyzing the XRD line width during the reaction, an observation that is corroborated by scanning electron microscopy. This allows a control of the pore size distribution of the obtained material by variation of the reaction temperature.
The solid-state polymerization of halogenoacetates leads quantitatively to polyglycolide (polyglycolic acid) and an eliminated metal halide. Washing out this salt leaves highly porous polyglycolide (total pore volume about 50%) with pore sizes in the submicron range. Thorough examination of the product with different methods (DSC, IR, and X-ray diffraction) gave no indication of any remaining halogenoacetate. This distinct micromorphology should be advantageous for its application as a biomaterial. Special features of porous polyglycolide are an inherent surface roughness, a high specific surface, a higher gas permeability, and a lower density compared to conventionally prepared polyglycolide. The control over these properties should allow a fine-tuning of the biocompatibility of polyglycolide.
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