Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-07-20
2001-03-06
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S608000, C528S274000, C528S286000, C528S289000
Reexamination Certificate
active
06197897
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for the production of succinimide copolymers by the catalytic co-polymerization of aspartic acid with another monomer.
BACKGROUND OF THE INVENTION
Polysuccinimides, polyaspartates and copolymers thereof are useful as mineral scale inhibiting agents, nutrient absorption enhancers, additives for cosmetics and personal care products, adhesives, anti-redeposition agents for detergents, dispersants, additives for paper making, corrosion inhibitors, metal working fluids, lubricants for conveyor belts, additives for the prevention of encrustation in sugar manufacture, and tartar preventative agents in toothpaste.
Methods are known for the production of polysuccinimide by the polymerization of aspartic acid in the presence of various catalysts, such as phosphoric acid and sulfur-containing dehydrating agents and the like. However, these prior art methods rely on an inefficient process of heat transfer during polymerization, namely the heating of an unstirrable melt. Another disadvantage to these methods is the large amount of catalyst and/or dehydrating agent which is required for polymerization to occur and the subsequent removal of the excess catalyst.
Attempts to perform catalytic polymerizations as stirrable, liquid reactions have been made, but again exceedingly high amounts of catalyst were required to achieve the polymerization of desirable high molecular weight products (U.S. Pat. No. 5,484,945 to Nagatomo et al.).
There is an ongoing need therefore, for a commercially acceptable, convenient method of catalytically polymerizing aspartic acid to polysuccinimide and succinimide copolymers in high yield, purity and of desired, relatively high molecular weight. The present inventive method satisfies this need, provides a useful product and overcomes the disadvantages of the prior art methods.
SUMMARY OF THE INVENTION
An efficient solution-phase method of succinimide copolymer production is disclosed. A liquid reaction mixture containing at least one cyclic carbonate solvent, at least one catalyst, and aspartic acid, optionally together with another polymerizable monomer, is initially prepared. Preferably, the weight ratio of aspartic acid/catalyst is greater than about 1.
The resulting reaction mixture is heated to an elevated temperature which is below the boiling point of the solvent but is sufficient to effect the catalytic polymerization of the aspartic acid in solution. Thereafter, the temperature is maintained for a sufficient time period until a succinimide copolymer with another polymerizable monomer is produced. Succinimide copolymers of relatively high weight average molecular weight and high purity can be produced in relatively high yields even when relatively low ratios of catalyst are employed.
The succinimide copolymers so produced can be recovered by precipitation with a triturating solvent, and hydrolyzed to a polyaspartic acid derivative if desired.
The inventive process requires only a single, stirred, reactor vessel thereby avoiding the problems of prior multi-step methods with handling and recovering the product from semi-solid melts. The inventive method provides a succinimide copolymer in relatively high yields and of relatively high purity.
DETAILED DESCRIPTION OF THE INVENTION
Aspartic acid and at least one catalyst can be dissolved in at least one cyclic carbonate solvent and can be co-polymerized with another monomer, as well as homopolymerized with itself, in solution by the application of heat, the temperature being maintained below the boiling point of the solvent. The aspartic acid can be in any of its L-, D-, and DL-isomer forms. Relatively low catalyst loadings can be used. The term “relatively low catalyst loadings” as used herein means that the ratio of aspartic acid/total catalyst on a solids weight/weight (w/w) basis is greater than about 1.
As presently practiced, the inventive method can produce a succinimide copolymer having a weight average molecular weight (Mw) in the range of about 700 to about 100,000. The molecular weight can be controlled by varying one or more of the following reaction conditions: co-monomer, solvent, concentration of reactants, polymerization temperature, polymerization time, reaction pressure, water removal rate, catalyst, and weight ratio of aspartic acid monomer to catalyst. The term “succinimide copolymer” as used herein and in the appended claims includes polysuccinimide copolymers with another monomer moiety as well as random copolymers constituted by succinimide units with another monomer.
Cyclic carbonate solvents useful in the inventive method preferably have a boiling point in the range of about 150° C. to about 300° C. Cyclic carbonates presently include cyclic organic esters having the formula:
wherein R
1
, R
2
, R
3
and R
4
are independently hydrogen, or alkyl (1 to 20 carbon atoms inclusive), aryl, or hydroxymethyl or chloromethyl.
In a particularly preferred method embodiment, the cyclic carbonate solvent is unreactive with respect to aspartic acid and the monomer to be copolymerized, can solubilize the product succinimide copolymer, and is commercially available at reasonable cost.
Presently preferred solvents are cyclic alkylene carbonates. Examples include ethylene carbonate, propylene carbonate, butylene carbonate, glycerin carbonate, and mixtures thereof. Many such cyclic carbonates are commercially sold under the trademark JEFFSOL® by Huntsman Corporation, Austin, Tex.
The reaction mixture can be formed by combining in a cyclic carbonate solvent, aspartic acid and at least one desired co-polymerizable monomer in the presence of a polymerization catalyst. The copolymerizable monomer has a functionality of at least 2. Suitable monomers for the present purposes are those that are soluble in the cyclic carbonate solvent that is utilized as the reaction medium in any given instance and that possess the desired polyfunctionality. Preferred monomers are poly(carboxylic acids), aminocarboxylic acids, mercaptocarboxylic acids, sulfocarboxylic acids, phosphonocarboxylic acids, phosphinocarboxylic acids, hydroxy-carboxylic acids, diamines and triamines. Mixtures of the aforementioned polyfunctional monomers can also be used to produce succinimide copolymers having properties tailored for a particular purpose.
The order of addition is not important so long as a substantially liquid reaction mixture is obtained with heating. The temperature must be sufficiently high to initiate polymerization of the aspartic acid and will vary with operating conditions. Preferably, the elevated temperature remains below the boiling point of the chosen cyclic carbonate solvent. The elevated temperature is in the range of about 140° C. to about 220° C. Preferably the reactants remain in solution during the whole course of the polymerization reaction. Reaction times can vary in the range of about 5 minutes to about 24 hours, preferably about 30 minutes to about 12 hours.
Succinimide copolymer product is obtained in relatively high yields of about 40% to about 100% and with relatively high purity of about 70% to about 100%.
The reaction pressure can be atmospheric (air or inert gas) or sub-atmospheric. The gas is preferably anhydrous nitrogen, or carbon dioxide and can be passed through the reactor.
The succinimide copolymer product can be linear or branched, can be a random copolymer as well as a block copolymer or a graft linear copolymer, and is recovered by precipitation through the addition of a triturating solvent which is miscible with the cyclic carbonate solvent but is non-solvating for the polysuccinimide product. Useful triturating solvents include, but are not limited to, ketones, alcohols, esters, nitrites, water, and hydrocarbons. Acetone is particularly preferred. The succinimide copolymer product can also be isolated by other solvent separation techniques, such as flash evaporation or distillation.
The succinimide copolymers produced by the present inventive methods can be used directly or can be hydrolyzed to produce corresponding polyaspartate derivat
Kneller James F.
Mazo Grigory Ya.
Mazo Jacob
Ross Robert J.
Donlar Corporation
Olson & Hierl Ltd.
Sellers Robert E. L.
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