Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2000-09-07
2002-01-29
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C528S272000, C528S274000, C528S298000, C528S300000, C528S302000, C528S308600, C528S361000, C428S402200, C428S402240, C428S221000, C424S489000, C424S497000
Reexamination Certificate
active
06342300
ABSTRACT:
The invention relates to biodegradable polycondensates based on dianhydrohexitols, to their preparation, and also to their use.
Biodegradable polycondensates degrade within a certain period of time in a biological medium, losing their original mechanical, physical and chemical properties as a result of breakdown into small fragments, also termed metabolites when the application is in the physiological sector—in particular in humans. An example which may be quoted is a biodegradable surgical suture which initially has the strength to hold together a sutured wound but then in the course of time is degraded by the body. Of course, there must be an appropriate relationship here between the rate of degradation and the healing of the wound.
For the purposes of the present invention, biological media in which biodegradable polymers may be used are media which occur in the natural environment, for example water, air or soil, and also human or animal bodies, and the interior of plants. Biodegradable polymers are frequently used in forms which serve only a single purpose, for example surgical sutures which have solely the function of securing the wound for a particular time, or waste sacks or packaging films, which undergo biodegradation after use, the degradation products themselves not having any particular function.
However, it is also possible to admix active substances with the biodegradable polymers, or as early as during the synthesis of the polymers to give these a chemical form which allows the polymers themselves to develop other active functions besides any mechanical function which they have. For example, it is possible to produce surgical sutures which, besides their mechanical function, have a disinfecting action, for example, or develop a certain medicinal action. Waste sacks may comprise, for example, substances whose odor repels dogs and cats.
Another important factor for biodegradable polymers is that the degradation products are substantially compatible with the medium in which they arise. For example, it is clear that biodegradable polymers can only be used successfully in the medical sector if the fragments (known as metabolites) produced on biodegradation are nonhazardous.
Finally, there is also great interest in obtaining polycondensates substantially from starting materials which occur directly in the natural environment or are obtained from products which occur in the natural environment, that is to say from what are known as renewable raw materials. Particular compounds which are possible molecular building blocks here are those which occur in metabolism in the natural environment, either in humans, in animals or in plants. They also include compounds which can be obtained by hydrolysis, oxidation, reduction or elimination of water from products such as carbohydrates. These compounds also include what are known as dianhydrohexitols, which are obtained by dehydrating the corresponding hexahydric alcohols, specifically isosorbitol, a compound which is obtained by dehydrating sorbitol and is also called 1,4:3,6-dianhydro-D-sorbitol (DAS), 1,4:3,6-dianhydro-D-mannitol (DAM), a compound which is obtained by dehydrating mannitol, and 1,4:3,6-dianhydro-L-iditol (DAI).
There is already extensive literature, especially scientific publications, concerning the preparation of dianhydrohexitols and their use for preparing polycondensates. In this connection it should be pointed out that, especially in German publications, different names are given to one and the same compound. For example, the terms isosorbide, isomannide and isoidide are found in addition to 1,4:3,6-dianhydro-D-sorbitol (DAS) etc.
E. Flèche et al., for example in starch/stärke 38(1), 26-30 (1986) describe the preparation and properties of isosorbitol. J. Thiem et al., in starch/stärke 36 (5) 170-6 (1984) are concerned with the preparation and controlled polycondensation of anhydroalditol units from starch. Storbeck et al., in Makromol. Chem. 194, 53-46, 1993, describe the synthesis of polyesters from DAS, DAM (1,4:3,6-dianhydro-D-mannitol) and DAI (1,4:3,6-dianhydro-L-iditol). Other literature references which may be mentioned are Polymer 34 (23) 5003-6 (1993); Journal of Polymer Science: Part A: Polymer Chemistry 33, 2813-20 (1995); Journal of Applied Polymer Science 59, 1199-1202 (1996); Die Angewandte Makromolekulare Chemie 199 (No. 3530) 191-205 (1992) and 210 (No. 3659) 173-196 (1993).
DE-C 1 263 981 describes modified polyesters in which the glycol component may be composed of up to 20% by weight of isosorbitol, and which may moreover have branching brought about by polyfunctional esters of tri- to pentabasic acids. However, these polycondensates are not biodegradable.
Polycondensates which have amide functions are described in Trends in Polymer Science 2(12)425-36 (1994) and Journal of Polymer Science Part A: Polymer Chemistry 30, 2059-62 (1992), for example.
There are therefore numerous known biodegradable polycondensates, but these have a wide variety of disadvantages. For example, it is often difficult to establish a sufficiently high molecular weight, and other polycondensates release excessive amounts of injurious substances on biodegradation, and others again have limited availability due to high preparation costs. There is moreover a lack of polycondensates whose properties can be quite specifically adapted for particular applications.
Although there is already a wide variety of known biodegradable polycondensates, there is still a need for improved products, for improved preparation processes and for products which are versatile in use.
It is therefore an object of the invention to provide biodegradable polycondensates which have good degradation performance, are simple to produce and can be prepared partially or entirely from renewable raw materials, and which can be modified straightaway during their synthesis to make them suitable for a very wide variety of applications.
This object is achieved by means of biodegradable polycondensates as claimed in patent claim 1. Patent claims 2 to 7 give particularly advantageous embodiments of the novel polycondensates. These novel polycondensates may be prepared by processes as claimed in patent claims 8 to 11. Claims 12 and 13 give particularly advantageous ways of using the novel polycondensates.
a)
The dianhydrohexitols used according to the invention, specifically isosorbitol, isomannitol and isoiditol, may be prepared by processes known per se, by dehydrating the corresponding hexitols, such as sorbitol, mannitol, etc. These compounds, e.g. isosorbitol, can be obtained in relatively large volumes from starch, and are available commercially.
b)
The dibasic organic carboxylic acids used as second component may be aliphatic, cycloaliphatic or aromatic. Examples which may be mentioned here are terephthalic acid, adipic acid, furandicarboxylic acid, and also 3,6,9-trioxaundecanedicarboxylic acid, the use of which is preferred. The dicarboxylic acids may be used as such during the synthesis, but it is also possible to use appropriate derivatives, such as acid chlorides or esters of the carboxylic acids.
c)
Examples which may be mentioned of the polyfunctional organic carboxylic acids which, besides two carboxylic acid functions, have at least one other uncapped or capped function, specifically OH and/or COOH, are tartaric acid, malic acid, hydroxysuccinic acid, citric acid, isocitric acid, aconitic acid and the like. In particular, use may also be made of cholic acid or deoxycholic acid, the biological functions of which make them particular suitable for incorporation in functional biopolymers.
An additional point which should be mentioned for group c) is that these carboxylic acids may be used as such, that is to say with the two or more functions uncapped, i.e. free and accessible for an immediate condensation reaction, or capped, e.g. etherified or esterified. It is fully possible here for all three functions of some trifunctional units to be involved in the polymerization reaction. Partial reactions are also conceivable in which the reaction of o
Bengs Holger
Boehm Gitte
Clauss Joachim
Schoenfeld Alex
Weis Siegfried
Acquah Samuel A.
Celanese Ventures GmbH
Davis Katten Muchin
Pauliquen Corinne M.
Villacorta Gilberto M.
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