Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins
Patent
1994-09-30
1999-12-28
Tsang, Cecilia J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
524 81, 524115, 524155, C08K 500
Patent
active
060082747
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for stabilizing copolymers of maleic acid or maleic anhydride and vinyl alkyl ethers against a reduction in molecular weight in aqueous solution or in an organic solvent.
Copolymers of maleic acid and vinyl alkyl ethers or copolymers of maleic anhydride and vinyl alkyl ethers are known substances, cf. U.S. Pat. No. 2,047,398 and Ind. Eng. Chem., Volume 41, page 1509 (1949). Copolymers of maleic anhydride and vinyl alkyl ethers are hydrolyzed on dissolution in water, one anhydride group forming two carboxyl groups. The copolymers are then formally built up from maleic acid and vinyl alkyl ether units. The viscosity of the aqueous solutions of copolymers of maleic acid and vinyl alkyl ethers is a logarithmic function of the molecular weight. According to Technical Bulletin 7543-017 published by GAF Corporation in 1965, the maximum handleable concentrations of copolymers of maleic acid and alkyl vinyl ethers at 25.degree. C. for a polymer having a specific viscosity (1 g per 100 ml of methyl ethyl ketone) of from 2.6 to 3.5 is 20% by weight and for copolymers having a specific viscosity of from 0.1 to 0.5 is 35% by weight. At these relatively low polymer concentrations, in particular the high-viscosity and dilute aqueous solutions or solutions of copolymers of maleic acid and alkyl vinyl ethers are susceptible to a reduction in the molecular weight (cf. B. C. Trivedi and B. M. Culbertson, Maleic Anhydride, Plenum Press, New York, 1982, p. 437.
U.S. Pat. No. 2,789,099 discloses that aqueous solutions of polyacrylic acid can be stabilized against gelling during storage by polymerizing acrylic acid in aqueous solution in the presence of sodium hypophosphite as viscosity regulator and in the presence of copper salts.
DE-A-3,030,344 discloses that pulverulent, high-molecular-weight acrylamide polymers can be prepared by drying aqueous solutions of these polymers in the presence of tert-butyl-containing phenols, thioethers or phosphites. These compounds may also be present as early as during the polymerization. They prevent the polymers becoming insoluble during drying.
It is an object of the present invention to stabilize copolymers of maleic acid or maleic anhydride and alkyl vinyl ethers against a reduction in molecular weight, which occurs in particular in aqueous solution or in an organic solvent.
We have found that this object is achieved by a process for stabilizing a copolymer of maleic acid or maleic anhydride and vinyl alkyl ethers against a reduction in molecular weight, which comprises adding from 0.001 to 10% by weight, based on the copolymer, of a reducing agent, selected from the group consisting of sulfurous acid, phosphinic acid, dithionic acid, ascorbic acid and ammonium or alkali metal salts of said acids, to a solution of the copolymer in water or an organic solvent.
Suitable reducing agents are all compounds which have a reducing action, for example sulfurous acid, dithionic acid, hydrogen sulfide, hypophosphorous acid, phosphinic acid, phosphorous acid, diphosphoric acid, hypophosphoric acid and the water-soluble ammonium, alkali metal and alkaline earth metal salts of said acids. Preferred reducing agents are sulfurous acid, phosphinic acid, dithionic acid and ascorbic acid, either as a free acid or in the form of ammonium or alkali metal salts.
The copolymers are stabilized by adding the suitable stabilizers to solutions of the copolymers in water or an organic solvent. The stabilizers are employed in amounts of from 0.001 to 10% by weight, preferably from 0.01 to 5% by weight, usually in amounts of from 0.05 to 2% by weight. They can be added to the copolymer solutions directly after the polymerization or to polymer solutions if they are to be stabilized against a reduction in molecular weight. The stabilizers are usually added to the solution directly after the polymerization so that a reduction in molecular weight is prevented even during work-up of the copolymers.
The copolymers have an essentially alternating structure and contain maleic anhydr
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Frosch Franz
Meyer Harald
Richter Hans
Sanner Axel
BASF - Aktiengesellschaft
Borin Michael
Tsang Cecilia J.
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