Hydrogels of heterocyclic polymer, method of obtaining them, and

Details Hydrogels of heterocyclic polymer, method of obtaining them, and Hydrogels of heterocyclic polymer, method of obtaining them, and

1993-03-29

1995-02-28

Zitomer, Fred

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

526262, 526306, 5263071, 5263073, 526310, 526312, C08F 2606

Patent

active

053938534

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE ART

Hydrogels of polyvinylimidazole polymers capable of regulating the pH of an aqueous solution without dissolving.


STATE OF THE ART

The buffer concept dates from the beginning of this century [Fernbach and Hubert, Compt. Rend. 131, 293 (1900)]. Since that time, a large number of buffers have been developed.
The buffers marketed at the present time have two major drawbacks. The most important is that they add to the system material which may interfere with measurements carried out on it (for instance, spectroscopic measurements) and which often must then be isolated. The volatile buffers were up to now the only answer to this problem, but they do not represent the absolute solution thereof since the necessity of heating in order to evaporate it also entrains risks for the system and, furthermore, the pH may vary as the buffer evaporates.
Another great inconvenience is that they add ionic strength and, accordingly, decrease the activity of the species of ion in solution and furthermore, once the medium has been buffered, if the system is diluted its pH changes as a result in the change in pK.sub.a with the ionic strength.
A few buffers have a pK.sub.a which varies greatly with the temperature and, accordingly, it is necessary to thermostat the system. The variation of pK.sub.a may be up to 0.03 units per degree.
The references which are cited below contain descriptions of a large number of buffers which attempt to palliate separately for each of the problems which we have commented on:
Eduard J. King, Acid-Base Equilibria, Pergamon Press, Oxford, 1965.
Roger G. Bates, Determination of pH, Theory and Practice., Wiley, New York, 1964.
D. D. Perrin, Boyd Dempsey, Buffers for pH and Metal Ion Control, Chapman and Hall, London, 1974.
Similarly, in the publications of the commercial companies which sell this type of products (Carlo Erba, Fluka, Sigma-Aldrich, Alfa, etc.) a wide range of soluble pH regulators is listed. However, none of these publications, and none of the references cited above, even mentions the existence of insoluble pH regulators such as those described here, or the possibility of regulating the pH by this procedure. Nor have we found any patent which makes reference to solid or pellet buffers. However, these buffers which we present here represent the simultaneous solution for all the abovementioned problems since they do not act by being dissolved or incorporated in the system, but are simply submersed in it.


INTRODUCTION

A pH regulator or buffer is a substance, the presence of which increases the amount of acid or alkali which it is necessary to add in order to produce a change of one unit of pH. Stated in simpler terms, a pH regulator is a substance which, added to a solution, has the result that the pH of the solution scarcely changes even if acids or bases are also added in concentrations below a certain limit.
For example, when 1 mL of a 1N solution of HCl or NaOH is added to one liter of pure water, its pH varies by 4 units; however, if we add it to one liter of an aqueous solution of 0.05 M imidazole hydrochloride and 0.047 M imidazole, the pH changes only by 0.02 units.
Every buffer regulates to a given pH or a certain narrow range of values of pH which are characteristic of the system and are related to the pK.sub.a of its acid-base equilibrium.
The fields of application of buffers are very varied since there are many chemical and biological systems which involve acid-base equilibriums and they therefore depend critically on the pH of the medium. The buffers are used to control the velocity and the yield in organic synthesis reactions. In industrial and analytical chemistry, the control of pH is essential in precipitation reactions and in the control of the electrodeposition of metals. Buffers are also necessary for the stardardisation and control of reactions in laboratory research work, particularly in the field of biology where it is desired to reproduce physiological conditions.
The efficiency of a buffer depends on:
its opposition to the change of pH by addi

REFERENCES:
patent: 3954682 (1976-05-01), Fein
patent: 4058491 (1977-11-01), Steckler
patent: 4066524 (1978-01-01), Phalangas
patent: 4576973 (1986-03-01), Keil
patent: 5232603 (1993-08-01), Denzinger
Fernbach and Hubert, Compt. Rend. 131, 293 (1900).
Eduard J. King, Acid-Base Equilibria, Pergamon Press, Oxford, 1965.
Roger G. Bates, Determination of Ph, Theory and Practice, Wiley, New York, 1964.
D. D. Perrin, Boyd Dempsey, Buffers for Ph and Metal Ion Control, Chapman and Hall, London, 1974.

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