Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-06-18
2003-12-02
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S361000, C528S363000, C525S418000, C525S419000, C525S420000
Reexamination Certificate
active
06657041
ABSTRACT:
TECHNICAL FIELD
This invention relates to a production process of polysuccinimide, and more specifically to a production process of polysuccinimide, which comprises conducting polymerization of aspartic acid by using an acidic catalyst.
BACKGROUND ART
Technical Background of Polysuccinimide and Its Production Process
Polysuccinimide is used as a suitable precursor or intermediate in the production of polyamino acid derivatives such as polyaspartic acid. Polysuccinimide and polyamino acid derivatives, such as polyaspartic acid, are known to have biodegradability, and are extremely useful as polymers compatible with the environment. Further, crosslinked polyaspartic acid salts which are derivatives of polysuccinimide are equipped with both biodegradability and water absorbency, and are extremely useful polymers.
As techniques for producing polysuccinimide by reacting aspartic acid in the presence of an acidic catalyst, there are, for example, the following conventional techniques (i) to (iii).
(i) U.S. Pat. No. 5,142,062
This patent discloses a technique for producing polysuccinimide having a weight average molecular weight of from 100,000 to 200,000 by the following steps: 1) reacting a mixture of aspartic acid and phosphoric acid or the like at 100 to 250° C. in a vacuum system lower than 1 bar to produce a solid reaction mixture containing polysuccinimide having a weight average molecular weight of from 10,000 to 100,000, and 2) grinding the solid reaction mixture obtained in the first step into particles, the sizes of which ranged from 0.001 to 2 mm, and then conducting polycondensation under conditions selected from the temperature and pressure ranges in the first stage.
In Example 1, a crude product composed of polysuccinimide and phosphoric acid was produced by mixing aspartic acid (50 g, 0.38 mol) and 85% phosphoric acid (25 g, 0.22 mol in terms of phosphoric acid) [phosphoric acid/aspartic acid molar ratio=0.58] and conducting polymerization at 200° C. for 4 hours in a vacuum system. It is disclosed that, when a portion of the crude product was investigated for its molecular weight after washing off phosphoric acid, the crude product was found to have a weight average molecular weight (Mw) of 86,000. In Example 2, polysuccinimide having a weight average molecular weight of 124,000 was obtained by further grinding the crude product of Example 1 into particles, the sizes of which ranged from 001 to 2.0 mm, and conducting polymerization again at 200° C. for 4 hours in a vacuum system of 1 mbar.
It is also disclosed from Example 1 and Example 2 that the reaction product changes, in its form, from a fluid into a solid as the reaction proceeds. This technique features that the inclusion of grinding makes it possible to produce polysuccinimide having a high weight average molecular weight. However, to conduct industrial production while suitably dealing with a reaction in which a reaction product undergoes solidification, a special reactor is generally required, thereby making it difficult to design equipment. Especially when the form of the reaction product continuously changes from a fluid into a solid as the reaction proceeds, it is difficult to design a continuous reactor which can meet such changes.
Incidentally, the molar ratio of phosphoric acid to aspartic acid remains constant from the initiation to the end of the reaction in this conventional technique.
(ii) U.S. Pat. No. 5,457,176 (corres. JP 7-216084 A)
This patent discloses a technique for producing an amino acid polymer by heating a mixture of an amino acid and an acidic catalyst. Specifically, it is clearly indicated in column 2, lines 15-16 that an object of this technique is to produce an amino acid polymer the maximum weight average molecular weight of which is 60,000 or lower.
Further, Example 3 discloses an example in which a reaction mixture in the form of wet tacky white powder, which had been obtained by mixing aspartic acid (800 g, 6.01 mol) and 85% orthophosphoric acid (200 g, 1.73 mol in terms of phosphoric acid), was heated in the form of a layer on a stainless steel pan. It is disclosed in Example 3 that, when heated at 240° C. for 1 hour, the reaction mixture in the form of the wet tacky white powder changed into a solid mass which was hard on an outer side but was tacky in a central part. Polysuccinimide the weight average molecular weight of which was 15,500 was obtained by grinding that solid mass with a pestle in a mortar and heating the resulting powder further at 240° C. for 6 hours.
However, to practice industrial production while suitably dealing with a reaction in which a reaction mixture changes from a tacky form into a solid mass, a special reactor is needed so that the designing of equipment is extremely difficult. In particular, a need arises for a reactor provided with a special mechanism which does not develop a fault or the like in the presence of phosphoric acid at elevated temperatures. It is difficult to design such a reactor.
Among the weight average molecular weights of the polysuccinimide samples disclosed in the Examples, the highest weight average molecular weight is 24,000. This is consistent with the object to produce an amino acid polymer the molecular weight of which is 60,000 or lower.
Incidentally, the molar ratio of phosphoric acid to aspartic acid also remains constant from the initiation to the end of the reaction in this conventional technique.
(iii) U.S. Pat. No. 5,688,903 (corres. JP 8-231710 A)
This patent discloses a process for the production of a polycondensation product of an amino acid or a polypeptide hydrolyzate of the polycondensation product by subjecting the amino acid to bulk polycondensation under heat in the presence of phosphoric acid, phosphorus pentoxide or polyphosphoric acid and optionally, then conducting hydrolysis. This technique features that a fine particulate raw material is prepared with 0.005 to 0.25 mol of the catalyst evenly dispersed therein per molecule of the amino acid and polycondensation is then conducted.
Its Examples disclose illustrative reactions in a vacuum system and illustrative reactions in an atmospheric pressure system. Each of those reactions was conducted after comminuting a raw material, which was composed of a uniform mixture of aspartic acid and phosphoric acid, into a fine particulate raw material in a comminuting machine.
Problems, such as formation of a foam phase during the polymerization and formation of a coherent mass after the polymerization, were overcome by conducting the reaction while using the fine particulate raw material in which the amount of phosphoric acid, phosphorus pentoxide or polyphosphoric acid is controlled in the above-described range. When the viscosity indexes of the polysuccinimide samples as determined in the form of DMF solutions are converted into weight average molecular weights, the weight average molecular weight is, however, about 19,000 in Example 4 and about 28,000 in Example 8. The polysuccinimide samples obtained in the Examples are limited to low molecular weight polysuccinimide samples the weight average molecular weights of which are lower than 30,000. This process is, therefore, not sufficient as a process for the production of high molecular weight polysuccinimide.
In Example 10 (comparative example) in which phosphoric acid was used beyond the above-described range, on the other hand, polysuccinimide the weight average molecular weight was about 76,000 was formed. It is, therefore, appreciated that Example 10 (comparative example) afforded polysuccinimide having a higher weight average molecular weight than the above-described Examples 4 and 9 although formation of a viscous phase and coagulation of the reaction product took place in Example 10. In this conventional technique, the molar ratio of phosphoric acid to aspartic acid also remains constant from the initiation to the end of the reaction.
As mentioned above, polymerization—in which as in the conventional techniques (i) and (ii), solidification of a reaction product takes place and grinding is
Fukawa Susumu
Irizato Yoshihiro
Katoh Toshio
Machida Katsuhiko
Ogawa Shinji
Hampton-Hightower P.
Mitsui Chemicals Inc.
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