Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ion-exchange polymer or process of preparing
Reexamination Certificate
2001-07-03
2003-09-30
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ion-exchange polymer or process of preparing
C521S032000, C528S482000, C528S422000, C528S50200C, C430S642000, C430S643000
Reexamination Certificate
active
06627667
ABSTRACT:
BACKGROUND OF THE INVENTION
The use of gelatin in the art of manufacturing light sensitive materials is well known. Gelatin plays an important role in manufacturing the light sensitive silverhalide emulsions, but also as a matrix in which the silverhalide crystals and, for example, oil-droplets containing colorforming chemicals are dispersed.
It is common practice to chemically modify gelatin to make it better suited for its innate functions (eg. oxidation of methionine groups to influence crystal morphology (U.S. Pat. No. 4,713,320), adjusting hardening properties (U.S. Pat. No. 5,816,902)).
Several methods to link functional groups to gelatin using carboxyl-activators like carbodiimides, carbamoylpyridinium compounds, carbamoyloxypyridinium compounds, di-cation ethers, are described in EP patent 0,576,911 or EP patent 0,487,686. However, the use of N-hydroxy succinimide (NHS) as a carboxyl-activator was not disclosed in these patents.
The use of activated esters of N-hydroxy-succmimide to form peptide linkages between functional groups, like carboxyl groups and primary amines, has been described (Anderson et al., 1964, J.AM.Chem. Soc. 86:1839-1842, U.S. Pat. No. 5,366,958), but was not disclosed in combination with gelatin before.
An activated NHS ester can be made by forming an ester-bond between the activating compound NHS and the functional group which properties should be superimposed onto those of gelatin. Upon addition of the activated NHS-ester, the NHS is substituted by an amino group of gelatin. In the example as shown below, dihydroxybenzoic acid (DHBA) is esterified with NHS. The resulting ester is said to be ‘activated’ since DHBA itself will not bind to the aminogroup of gelatin while the DHBA-NHS ester will. As a result, a chemically modified gelatin is obtained which has now the new scavenger-functionality superimposed onto it, while NHS is liberated:
Besides free NHS, also unreacted NHS-ester remains after the coupling process.
It was found that NHS remaining after gelatin modification increases the hardening speed of gelatin in combination with hardeners such as triazine-compounds. It is well known to an expert in the field of coating photographic emulsions that too high emulsion hardening speeds are undesirable from process point of view in that this may result in the occurrance of defects such as emulsion hardened spots. NHS may also influence photographic properties like sensitivity or fog in adjacent layers by migration after coating of emulsion layers on a substrate.
Also free activated NHS-ester remaining after modification of the gelatin can migrate to adjacent layers causing unwanted effects.
As an example the NHS-ester can be DHBA-NHS. The functional group is a hydrochinon which is capable of scavenging oxidized developer. This functionality is used to prevent migration of oxidized developer between color-forming layers which would otherwise result in a bad color reproducibility. Therefore the modified gelatin is coated between the blue- and green-light sensitive color-forming layers and between the green- and red-light sensitive color-forming layers. It is crucial that this functionality is restricted to these so-called middle layers. Free DHBA-NHS, remaining after gelatin modification, also has scavenging ability. It can migrate to other layers where their scavenging activity will interfere with the normal color-forming reaction.
Contaminants like unreacted NHS-esters or like liberated NHS, should therefor be removed from the reaction mixture.
In manufacturing high quality photographic emulsions there is a demand for reproducible production of essentially impurity- or contaminant-free gelatin batches. Extensive measures are taken to remove impurities or contaminants which can have detrimental effects on silverhalide crystals. It will be obvious to a person skilled in the art that after modification, the modified gelatin is expected to meet the same high standard for purity.
Contaminants like unreacted NHS-esters or like liberated NHS, should therefor be removed from the reaction mixture. A commercially applicable purification method for the process of linking a functional group to gelatin using activated NHS-ester, as described above, has not been disclosed before
Removal of remaining NHS or derivatives thereof from reaction mixtures is not specifically mentioned in literature or patents.
In U.S. Pat. No. 5,316,902 gelatin is modified by linking free carboxyl-groups of the gelatin with an amine using a carboxyl-activator. Unreacted amine and carboxyl activator remaining after modifying gelatin are removed from the gelatin matrix by washing at low temperatures.
Another purification method, of which U.S. Pat. No. 5,362,858 is an example, is precipitation of the polymer by adding a hydrophobic solvent.
Also techniques like dialysis are commonly used to remove contaminants or impurities from solutions of proteins like gelatin.
Purification methods as described above are generally unsuitable for large scale production of modified polymers, because long processing time and/or large quantities of washing liquid are necessary, or they result in a diluted product, which makes an additional concentration step, or longer drying, necessary. Clearly these methods have economical and environmental drawbacks.
SUMMARY OF THE INVENTION
Hence the object of this invention was to provide a method for rapid and effective removal of carboxyl-activators, like N-hydroxy-succinimide, or derivatives thereof.
Also an objective of this invention was to remove carboxyl-activators, like NHS, and derivatives thereof in the same purification step.
The invention relates to a process for modifying a water soluble polymer, said process comprising
modifying a polymer containing amine groups, by reacting at least one of said amine groups with activated ester, said ester being the reaction product of a carboxyl activator and the carboxyl group of a molecule R—COOH, said R-group being a functional group, to produce a reaction mixture containing a polymer, said polymer containing at least one amide group;
subjecting said reaction mixture to at least ion exchange chromatography to purify said reaction mixture, said purification comprising at least partly removing the said reaction product, and/or carboxyl activator.
It was found, surprisingly, that NHS and its derivatives can be removed from polymer solutions fast and effectively in one step by ion exchange chromatography.
The method is especially applicable for removing NHS and/or derivatives thereof from gelatin solutions, and more specifically for removing NHS and DHBA-NHS from gelatin solutions.
The method of this invention has advantage over conventional methods because it is fast, effective and that NHS and DHBA-NHS can be removed in only one purification step.
A further advantage of the method of this invention is that ion-exchange chromatography is a method generally applied in large scale production of gelatin to remove salts, making the need for additional process equipment superfluous.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to a process for modifying a water soluble polymer, said process comprising
modifying a polymer containing amine groups, by reacting at least one of said amine groups with activated ester, said ester being the reaction product of a carboxyl activator and the carboxyl group of a molecule R-COOH, said R-group being a functional group, to produce a reaction mixture containing a polymer, said polymer containing at least one amide group;
subjecting said reaction mixture to at least ion exchange chromatography to purify said reaction mixture, said purification comprising at least partly removing the said reaction product, and/or carboxyl activator.
From the currently available carboxyl activators NHS is of particular interest, since it distinguishes itself from other carboxyl activators in that a stable activated ester can be prepared and purified before the activated ester is added to a polymer solution. This overcomes the problem that, when the carboxyl activator and the molecule consisti
Bouwstra Jan Bastiaan
Kluijtmans Sebastianus Gerardus J. M.
Toda Yuzo
Fuji Photo Film B.V.
Merchant & Gould P.C.
Truong Duc
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