Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
1999-09-29
2002-05-28
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C525S419000, C525S420000, C525S421000, C526S064000, C526S066000
Reexamination Certificate
active
06395870
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for preparing biodegradable polymers having repeating succinyl units, especially polyaspartic acid PAA and polysuccinimide (PSI).
BACKGROUND OF THE INVENTION
The preparation and use of polysuccinimide and polyaspartic acid and their derivatives has long been the subject of numerous publications and patents.
U.S. Pat. No. 4,839,461, (EP-A 0 256 366) describes the preparation of PAA from maleic anhydride (MAA), water and ammonia. MAA is reacted in aqueous medium with the addition of concentrated ammonia solution and is subsequently polymerized. During this polymerization, the mass becomes initially highly viscous and then solid-porous, which necessitates complex technical handling.
U.S. Pat. No. 5,296,587, describes the preparation of PSI from MAA, water and ammonia. MAA is hydrolyzed in water to maleic acid and then converted to the ammonium salt with concentrated ammonia solution. In a stirred reactor, the water is evaporated from the solution and subsequently the monoammonium salt is polymerized in bulk at temperatures above 170° C. to PSI. In this case, the mass is reacted in a number of hours by way of highly viscous phase states and on to solid PSI, and is subsequently hydrolyzed to PAA.
U.S. Pat. No. 5,288,783, describes the preparation of PAA from maleic acid or fumaric acid, water and ammonia. MAA is mixed with water in a stirred vessel and is reacted with cooling to give maleic acid. The mono-ammonium salt of maleic acid is prepared by adding concentrated ammonia solution. Subsequently, the water present is evaporated and the dry monoammonium salt is polymerized at temperatures from 190 to 350° C. An alternative proposal is to subject the monoammonium salt, which is present in aqueous solution, to further processing by extrusion at temperatures from 160 to 200° C. to form PSI. The PSI, prepared by one of the two process pathways, is subsequently subjected to alkaline hydrolysis to give PAA.
EP-A 593 187, describes the preparation of PSI by thermal polymerization of maleamic acid at temperatures from 160 to 330° C., in a reaction period of from 2 minutes to 6 hours. Reference is also made to polycondensation in a solvent, using condensation auxiliaries.
DE-A 4 023 463 (U.S. Pat. No. 5,142,062) describes a process for preparing polysuccinimide in the presence of phosphoric acids. DE-A 4 221 875 (WO 94/01486) describes the preparation of so-called modified polyaspartic acids by polycondensation of aspartic acid with further compounds, optionally in the presence of phosphoric acids or derivatives thereof. From WO 95/02007, it is known to prepare polymers of aspartic acid by heating MAA and acid derivatives of ammonia. Phosphoric acid is one of the acids specified. Of the corresponding salts, however, only diamonnium hydrogen phosphate and monoammonium dihydrogen phosphate are mentioned. EP-A 604 813 (DE-A 4 244 031) discloses a process for preparing PSI and PAA from maleamic acid in which MAA and ammonia are reacted to form maleamic acid and the maleamic acid is subjected to a polymerization which can be conducted in the presence of phosphoric acids and polyphosphoric salts.
U.S. Pat. No. 5,919,894, (WO 96/34908), each disclose polymers with repeating succinyl units, in particular, polysuccinimide and polyaspartic acid, that are prepared using triammonium salts, in particular, triammonium phosphates. The patent describes the synthesis of PAA from MAA and triammonium phosphate.
DE 4 322 410, furthermore, shows the synthesis path to PSI or PAA via the reaction of maleic anhydride with ammonium carbonate, which is accompanied by heating.
Disadvantages of the known processes are that they are very complex and in many cases lead to products having unsatisfactory biodegradeability, and also that purification during the production process entails considerable expense. In the case of the condensation of aspartic acid with phosphoric acid, condensation is necessarily followed by laborious separation of the phosphoric acid.
The object of the invention is therefore to provide an improved process for preparing polymers having repeating, fully biodegradable succinyl units, especially PSI and PAA, in which it is no longer necessary to conduct virtually any laborious purification operations after the condensation.
The object of the invention is achieved by—and consequently, the invention provides—a process for preparing biodegradable polymers having repeating succinyl units, characterized in that an 1,4-butanedicarboxylic acid component, e.g., an optionally substituted 1,4-butanedicarboxylic acid or a derivative of 1,4-butanedicarboxylic acid is mixed with an acid anhydride such as acetic anhydride, first of all at room temperature if desired. The resulting mixture is then reacted by polycondensation.
SUMMARY OF THE INVENTION
The process relates to a process for preparing a biodegradable polymer having repeating succinyl units. The process includes the steps of (a) mixing (i) a 1,4-butanedicarboxylic acid component comprising a member selected from the group consisting of unsubstituted 1,4-butanedicarboxylic acid, substituted 1,4-butanedicarboxylic acid, 1,4-butanedicarboxylic acid derivatives, with (ii) an acid anhydride to form a mixture, and (b) reacting the mixture by polycondensation. The polycondensation is brought about by the steps of (i) raising the temperature of the mixture to form a component including a member selected from the group consisting of polysuccinimides and polyaspartic acids, and (ii) simultaneously converting the acid anhydride to the acid corresponding to the acid anhydride by water that is liberated during condensation. The process also involves removing water and the acid corresponding to the acid anhydride from the mixture, preferably with distillation. These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
DESCRIPTION OF THE INVENTION
For the purposes of the present invention, derivatives of optionally substituted 1,4-butanedicarboxylic acid include, for example, salts of and substitution products, such as hydroxy and amino-substituted dicarboxylic acids. In the process of the invention, it is preferred to employ aspartic acid (ASP). It is, of course, also possible to employ monomaleamide. If monoammonium-maleic acid is employed, a preliminary thermal reaction by heating at about 120-150° C. should be carried out first and then the polycondensation to give polysuccinimide should be achieved by addition of acetic anhydride, with further heating.
Where ASP and acetic anhydride are employed, the ratio of ASP to acetic anhydride is preferably 1:1. However, excesses of acetic anhydride of up to 50 mol % can also be used.
Surprisingly, the process of the invention not only gives polymers having repeating succinyl units that are virtually free from substances accompanying the reaction but also gives reaction products which are 100% biodegradable.
The polymers prepared in accordance with the invention preferably feature repeating succinyl units having at least one of the following structures:
Furthermore, depending on the embodiment, it is also possible for iminodisuccinate units to be present, preferably at least one of the following structures:
wherein R represents OH, O—NH
4
+
or NH
2
.
The iminodisuccinate units present can be randomly distributed in the polymer or, preferably, in end-group form. Based on the sum of all repeating units, the iminodisuccinate unit is present optionally in a proportion of at least 0.1 mol %. The molar ratio of the iminodisuccinate units incorporated in the polymer to the sum of all monomer units incorporated in the polymer is preferably from 0.1 mol % to 99 mol %, preferably from 1 mol % to 50 mol % and, with particular preference, from 2 mol % to 25 mol %.
In addition, further repeating units may be present as a result of an appropriate reaction regime and appropriate choice of starting materials, examples of such units being
a) maleic acid units of t
Eyl Diderico van
Gil Joseph C.
Hampton-Hightower P.
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