NO782126L - WATER-ABSORPING STARCH COPPER POLYMERISAT, AND PROCEDURE FOR THE PREPARATION OF SUCH - Google Patents

Description

"Water-absorbing starch copolymer, as well as method for producing such"

The invention relates to water-absorbing starch copolymers.

During the past few years, certain derivatized starches have been developed which have the ability to absorb and retain large amounts of water. These derivatized starches are often referred to as "water-absorbing starches". In U.S. Patent Nos. 3,935,099 and 3,997,484, starch polymers are described which are said to absorb more than 1000 times their own weight. These water-absorbing starches are generally produced by grafting polyacrylonitrile onto starch molecules and then derivatizing the polyacrylonitrile chains into anions. The grafting is carried out by free radical catalysis (e.g. cerium or irradiation). The starch grafting process is difficult to regulate and is time-consuming. The achievement of a critical grafting level is an essential requirement for a water-absorbing end product. A series of derivatization and neutralization steps are typically used to convert the nitrile group into anions and a water-absorbing starch product. This contaminates the product with salt. The water-absorbing properties of these salt-contaminated starches deteriorate to a large extent when they are used in aqueous solutions containing trace amounts of salts and minerals. It is also difficult to achieve uniform and reproducible water absorbency results. This is apparently due to difficulties in controlling the reaction. These water-absorbing starch products also lack certain other properties that are essential and desirable for many purposes (e.g., they lack adhesiveness, prefabrication and molding properties, film-forming, binding, coating properties, etc.). This generally limits their application to limited areas (eg separately contained in a water-permeable envelope or separately added to or mixed with another substrate). Moreover, these water-absorbing starches cannot be effectively used at high solids coating levels or easily fixed or bonded to a carrier or substrate or easily provided in preformed form.

U.S. Patent No. 3,661,815 also discloses analogous water-absorbing starches prepared by saponification of starch-polyacrylonitrile graft derivatives with certain alkali metal bases. These water-absorbing starch grafts are said to absorb more than 50 times their weight in water. The method according to this U.S. patent and products of the method suffer from similar deficiencies as discussed above with respect to the two previously mentioned U.S. patents.

In this area, there is a need to more easily and efficiently produce water-absorbing starch products under conditions that provide greater uniformity and reproducibility in the end product. Greater tolerance and compatibility with aqueous solutions containing salt and mineral contaminants is also required. What is even more important is the development of a water-absorbing starch that can be easily bonded or fixed to a substrate or pre-formed. Such a water-absorbing starch would significantly expand the limits of applicability and use of water-absorbing starches in this area.

An object of the present invention is to provide a simple and reproducible method for the production of water-absorbing starch products. Another object is to obtain water-absorbing starch products which, in comparison with existing water-absorbing starches, have improved applicability,

utility and functional properties. A further object is to provide a method for applying or fixing water-absorbing starches to supports or substrates or to produce pre-formed products, as well as products from this method.

According to the present invention, a water-absorbing starch copolymer is provided which has the ability to absorb several times its own weight of water, the starch copolymer comprising the copolymer product of ethylenically unsaturated starch molecules and ethylenically unsaturated monomers with the ethylenically unsaturated monomers that form a polymer bonding between the copolymerized starch molecules to provide a non-linear latticework of a plurality of starch chains bonded together by means of polymeric bonds represented by the formula:

(I) -4-starch

starch4~ where "starch" represents a starch chain of D-glucose units, Z represents an organic group that links the -group to the carbon atom in the starch chain by means of a

sulfur atom or an oxygen atom, R is hydrogen or a monovalent organic radical, M represents a plurality of copolymerized ethylenically unsaturated monomers where<*>'p" represents the number of copolymerized monomeric units in the bond, (W) is a water-attracting group or a hydrophilic moiety, e.g., an anion, cation, non-ion, an amphoteric, zwitterionic or amphiphilic moiety or a mixture thereof associated with the polymeric bond, and "n" represents the number of (W) moieties contained in the polymeric bond of the copolymerized monomers, whereby the number of (W) parts is sufficient to impart water-absorbing properties in the copolymer.

The water-absorbing starches or their precursors can be prepared by a copolymerization process comprising queue polymerization of: (a) starch chains containing pendant, terminal ethylenically unsaturated groups represented by the formula: (II) starch"

where "starch", Z and R are as defined above, and "a" represents the degree of substitution of the end-to-end unsaturated groups on the starch chain, and (b) ethylenically unsaturated monomers represented by the formula:

where M* represents an ethylenically unsaturated monomer, "(W)<*>' represents at least one water-attractant

group or a precursor of such, and n<*>is a whole tali,

for providing a cross-linked network of a plurality of starch chains bound together by polymeric bonds represen-

tart by the formula:

where "starch", Z, R, (W) and n are as defined above, M represents a plurality of copolymerized ethylenically unsaturated monomers containing a sufficient number of (W) or {W<*>) precursors within the polymeric bond to give the copolymerized product water absorption capacity, and "P" represen- . ters the number of copolymerized ethylenically unsaturated monomers between juxtaposed starch chains. In the copolymerization process, a large selection of M'-(W*)ft,—monomers can be used for the production of the water-absorbing starch according to the invention. The value of the integer n' and the particular "W" or "W" precursors used in the copolymerization process can vary significantly.

Some of the monolayers will contain "thaw" or "W" precursors (eg n' has a value of 1-3) while others may be free of the "W" or "W" precursor portions (eg n<* > is 0). Likewise, the copolymerized monomers may consist substantially of monomers containing "W" or "W" precursors. In the formula stated above, M' can consist of an ethylenically unsaturated portion of an organic group of the same chemical composition or a mixture of different copolymerized monomers where the M' group differs in composition. Likewise, the "W" or "W* " precursors can be the same or different in type. The amount of W monomers or W monomer precursors copolymerized with the starch is maintained at a level sufficient to give the copolymerized starch product water absorbency. If "W'" precursors are used exclusively, then it is necessary to convert a sufficient number of precursors into the water-attracting form to obtain the desired water-absorbing starch copolymer product.

In comparison with existing water-absorbing starches, the starch copolymers according to the present invention are more applicable and useful. They can be prefabricated from water-soluble or water-dispersible, modified or hydrolysed starches into water-absorbing starch co<p>ol<y>meriates with low molecular weight and which are cross-linked. In general, the ethylenically unsaturated starches used in connection with the present invention are typically provided in a water-soluble form or they can be easily converted into such a form. This makes the present invention particularly applicable to pre-fabrication operations where water or aqueous systems are used

for dispersing, dissolving or piastifying the starch.

The invention is therefore ideally suited to most pre-fabrication operations (e.g. coating, casting, extruding, drying, sheeting, printing, binding, encapsulating, gelling, impregnating, laminating, plasticizing, etc.) where the starch is initially provided in a form most suitable for prefabrication (eg, fluid, pliable, castable, etc.) and then preformed and converted into a solid object.

The starch part of the ethylenically unsaturated starch chains can originate from a selection of starch sources, including grains, legumes, root vegetables. Examples of starches include tapioca, corn, high-amylose, sweet potato, waxy corn, canna, arrowroot, wheat, sorghum, waxy sorghum, waxy rice, soy, rice, pea, amylose or amylopectin fractions, combinations thereof, and the like. The amylose content of starch affects the temperature at which a starch will transform into a water-dispersible or starch-clast form. High amylose starches typically require elevated temperatures and pressures (eg, extrusion, jet cooking, etc.) for uniform distribution in aqueous systems. In contrast, starches with a lower amylose content (eg 3056 amylose or less) are more easily dispersed or pasted in water (eg 50-70°C). Pre-gelled or pre-gelled starches with an amylose content of less than 30% are normally dispersed in water at ambient temperature (e.g.

For many prefabricated products, it is advantageous to modify or change the starch chain so that a more functional and usable starch product is obtained. This can be done by derivatizing the starch chains, so that they contain others

substituents (e.g. esters or ethers which may contain cationic, anionic, nonionic, amphoteric groups, etc.). The ethylenically unsaturated starches can be provided in the pre-

gelled or pre-gelled form or hydrolyzed (eg by chemical or enzymatic hydrolysis of granular or non-granular ethylenically unsaturated starches) to improve their dispersibility in aqueous systems. Ethylenically unsaturated dextrins, maltodextrins and other ethylenically unsaturated hydrolyses that give a low viscosity (e.g. D.E. 0.2-30) are particularly well suited for coating purposes. Such ethylenically unsaturated starch hydrolysates provide an aid to achieving a high solids, low viscosity system which is particularly suitable for aqueous coating and prefabrication purposes. Modification, derivatization or hydrolysis of such starches can be carried out before or after the derivatization to the ethylenically unsaturated form.

Ethylenically unsaturated starches containing hydrophobic substituents can be used, but will typically require a dispersing agent. Water-miscible, organic dispersants, e.g. alkanols (e.g. methyl, ethyl, isopropyl or butyl alcohol), polyhydric alcohols (e.g. glycerol, ethylene glycol), ethers (e.g. methyl, ethyl or propyl ethers, etc.), ketones (raethyl ethyl ketone, ethyl ketone, etc.), as well as conventional anionic, nonionic and cationic surfactants or emulsifiers (see, e.g., McCutcheonj "Detergents and Emulsifiers" - North American edition, 1975) can be used to facilitate their conversion to a more water-dispersible form.

It is usually advantageous to use hydrophilic, ethylenically unsaturated starches which will disperse uniformly in water at temperatures above the starch gelation point without the aid of water-miscible organic dispersants or surfactant systems. Hydrophilic starches which are characterized in that they give a centrifugal starch residue of less than 25% (preferably less than 10%) after immersion in water, (one part ethylenically unsaturated starch/100 parts by weight water) for one hour at temperatures above their gelation point and centrifugation at 10 3 G for 10 minutes is most appropriately used for coating and prefabrication purposes. Hydrophilic, ethylenically unsaturated starches containing pendant ethylenically unsaturated groups with polar moieties or substituents to provide hydrophilicity to the unsaturated portion of the starch molecule (eg, hydroxy, carboxy, amide, carbamyl, sulfoamyl, imido, sulfoamino, ti©, thiolamino, oxy, thiocarbonyl, sulfonyl, carbonyl, sulfamido, quaternary ajsmonium halides, the alkali or ammonium salts) are particularly useful.

The water-dispersible, ethylenically unsaturated starches described herein can be prepared by a variety of starch derivatization processes. Derivatization processes that can be used to produce pendant monoethylenically unsaturated groups include reaction of alkali metal starch or hydroxyethylated starch salts with an allyl propiolate to provide carboxylated vinyl starch ethers, reaction of starch with ethylenically unsaturated organic carboxylic acid hydrides (e.g., methacrylic anhydride, etc.) or organic allyl halides (eg, allyl bromides, allyl chloroformates, etc.), or epoxides (eg, butadiene monoxides, etc.) to provide ethylenically unsaturated starch esters or ethers.

The most suitable monoethylenically unsaturated starches are the starch esters of ".Euethylenically unsaturated carboxylic acids (e.g. acrylate, methacrylate, crotonate, citraconate, itaconate starch^-esters as well as alkali salts and amides thereof, mixtures thereof, etc. );

N-allylcarbaraate starch esters (e.g.

starch

glycidyl methacrylate and glycidyl acrylate starch ethers (see, e.g., XJ.S. Patent No. 3,448,089); allyl starch ethers (eg, allyl, isopropenyl, etc.); allylalkyl starch ethers (e.g. ethyl, propyl, butyl, etc. starch ethers) and allylalkylene oxide starch ethers or allyloxyalkyl starch ethers (e.g. allyloxyethyl, oxypropyl, and oxybutyl, etc. starch ethers)s allyloxyhydroxyalkyl starches (e.g. 3 -allyloxy-2-hydroxypropyl starch, etc.)j starch acrylamides, etc.? combinations thereof, etc. In a more limited embodiment of the invention, the ethylenically unsaturated starches comprise such starches which will easily and uniformly copolymerize with the bridging comonomers. Ethylenically unsaturated starches which contain polar groups immediately adjacent to the unsaturated group and which activate the copolymerizability of the double bonds in the presence of free radical-initiating systems, are particularly well suited for this purpose. Such ethylenically unsaturated starches can be represented by formula III: where starch is a starch chain of D-glucose units, B represents an activating polar group juxtaposed to the ethylenic unsaturation, D is sulfur or oxygen, Q is an organic group linking the D group divalent to the activating polar group, R represents a univalent group and "a" represents D.S. (ie the number of attached ethylenically unsaturated groups per anhydro-glucose unit in the aforementioned starch chain). Typical juxtaposed activating polar groups (ie E) include carbonyl thiocarbonyl and similar groups. The ethylenically unsaturated portion of the starch chains most typically consists of pendant groups that individually have a molecular weight of less than 500, with those having a pendant molecular weight of more than 50 but less than 300 (preferably from 75 to about 150 M.W.) being most typical In a more preferred embodiment of the invention, the group E contains a radical R<*> is a hydrogen atom or a mono-organo group which is linked directly to the nitrogen atom by a monovalent bond. In formula III, Q can be any divalent organic group that connects the activating radical to the starch chain, e.g. linked to D and acrylamide nitrogen atoms via carbon bonds). The starch's oxygen or sulfur atom and activating radical can be directly linked together by means of a single carbon atom or by means of an organic group composed of a plurality of carbon atoms. The group -Q- may consist of substituted or unsubstituted straight-chain or branched aliphatic groups (e.g. alkylene), substituted or unsubstituted aryl groups (e.g. naphthalene, phenylene, etc.) as well as divalent organic groups containing carbon- to non-carbon atom bonds (e.g. organoethers and thioethers, sulphonyl-, N-methylene-substituted secondary and tertiary amines (e.g. a -O^-HdD-Q radical). If desired, the Q -group-linking chain also contain other substituents, e.g. carbonyl, carboxylate, thiocarbonyl, etc. as well as monovalent radicals, e.g. hydroxy, halogen (e.g. Br, F, Cl and I), alkyl, aryl, hydroxyalkyl , hydroxyaryl, alkoxy, aryloxy, carboxyalkyl, carboxy-aryl, amine, combinations of such substituents and the like. The divalent organic Q group will advantageously contain less than 10 carbon atoms and preferably no more than 7 carbon atoms.

In formula III where "E" is an activating group, R' and R can be a mono-organo or hydrogen substituent. The R'- and R-mono-organo groups may also contain an ester, ether, carboxyl-organofree, alcohol, hydrocarbyl (e.g., alkyl, aryl, phenyl, etc.) as well as divalent organic groups containing non-carbon atoms-to -carbon chain bonds (e.g. oxy, sulfonyl, thio, carbonyl groups, etc. as mentioned above with respect to Q). R<*> and R are advantageously either H or a substituted or unsubstituted mono-organo group containing less than 8 carbon atoms, e.g. a lower alkyl or phenyl group. Illustrative substituted mono-organo groups are halogen-substituted alkyl and phenyl, alkoxy, aryl, phenoxy, phenol and alkanol and corresponding thiols, alkane, phenol, tolylibenzoyl, carboxy, sulfoalkyl, sulfophenyl, combinations thereof, etc. In the preferred embodiments of the present invention, R' and R are either hydrogen or a 1-5 carbon alkyl radical (preferably methyl) and "a" has a value of at least 0.002.

The most preferred ethylenically unsaturated starches are those starch acrylamides represented by formula IV:

where D is as defined above (preferably oxy), Q1 represents a divalent organo group, e.g. as Q is defined above, "a" represents the degree of substitution, R and R<*> are monovalent groups as defined herein and<H>n&" is 0 or 1. The starch acrylamides according to the above formula IV can be prepared by reaction of N- methylacrylamides with starch in the presence of an acid or acid-developing catalyst and a polymerization inhibitor, as illustrated by the following etherification equation V: where "an in reactants (A) and (b) represents the number of starch hydroxyl groups in (A) etherified with N The -methylolacrylamide reactants (B), R' and R are mono-organo or hydrogen groups as defined below, and H represents an acid or acid-evolving etherification catalyst. The above N-raethylolacrylamide reaction V can also be used to produce a starch acrylamide reaction product (C) where Q as illustrated in formula XIX Contains an alkyleneoxy or aryleneoxy group, by reacting the corresponding hydroxyaryl or hydroxyalkyl starch ethers (e.g. hydroxypropyl and hydroxyethyl starch ethers) with a H-methyloiacrylamide where R' and R represent a monovalent group. Substituted acrylamides containing a reactive N-methyloyl group attached to the acrylamide nitrogen atoms by intervening divalent organic Q groups and starches containing cationic and anionic or ionic acrylamide substituents can be obtained by etherification of a starch with the relevant N-raethylolacrylamide (e.g. sodium 2-Hr-methylolacrylamido-2-methylpropane sulfonate, an N-methylolacrylamide quaternary aramonium halide, eg 3-(N-methylolacrylamido)-3-methylbutyltrimethylammonium chloride, etc.). Representative R<*>substituents in V above include hydrogen, N-aryl, the H-alkylamines and the N-arylamines, e.g. H-methylol-s N-ethyl-j N-isopropyl-j H-n-butyl-; N-isobutyl-j H-n-dodecyl-j N-n-octadecyl-; N-cyclohexyl-; H-phenyl-j to-(2-hydroxy-1,1-dimethylpropyl)-* H-p-hydroxybenzyl-; N-(3-hydroxybutyl)-i N-(4-hydroxy-3,5-dimethylbenzyl)-j H-(3-hydroxy-1-1-dimethyl)-j N-(2-hydroxy-1,1-dimethylethyl) -» H-(2-hydroxyethyl)-j N-{5-hydroxy-1-naphthyl)~* combinations thereof and the like Illustrative acrylamide reactants (B) include N-methylol and N-thiomethyl acrylamides, e.g. H-(hydroxymethyl)acrylamide; N-(hydroxymethyl)-ff-1(1-hydroxymethyl)propyl]acrylamide t H-(hydroxymethyl)-2-alkyl-acrylamides, e.g. N-(hydroxymethyl)-2-(methylheptyl)acrylamide;

»-1-(1-bydrokaylmethyl)-1-nonyl 1-2-taethyl lacryamide; N-(1-hydroxymethyl)-2-methyl acrylamide; N-(hydroxymethyl)-2-propylacrylamide;

etc*? H-(recaptomethyl)acrylamide; H-methylol-N-isopropylacrylamide;

3* (JJ-methylolacrylamido)-3-methylbutyltrimethylammonium chloride (cationic); sodium 2-&-methylolacrylamido-2-methylpropanesulfonate (anionic -CH2:C(H)C( tO)H(CH2OH)C-l (CH3)2lCH2S05Na+), combinations thereof and the like.

The reaction can conveniently be carried out in the presence of known acid or acid-generating catalysts (eg, ammonium chloride or

-phosphate, mono-ammonium hydrogen phosphate, zinc chloride, etc.), preferably at a temperature of from approx. 70 to approx. 95°C until the desired D.S. level is reached. Conventional polymerization inhibitors (eg, hydroquinone, its derivatives, 2,5-di-t-butyl-> quinone, etc.) prevent homopolymerization of the starch acrylamide and the acrylamide reactants. The starch acrylamides can be produced via solution* slurry, dry, semi-dry or other suitable condensation processes. Por the preparation of a starch acrylamide having a D.S. level of 0.03 or more, it is desirable to disperse

, uniformly generate the acrylamide, the acid or the acid-generating catalyst and polymerization inhibitor in the starch reactant. Uniform dispersion of the H-methylolacrylamide reactant, catalyst, and polymerization inhibitor in the starch can be effectively accomplished by initially forming a starch slurry or by treating the starch with an absorbable dispersing medium (e.g., water) such as the acrylamide, catalyst, and polymerization inhibitor. the inhibitor is soluble in, or placed in mobile form and then permeates or absorbs the dispersant and its solutes into the starch granules.

As explained more fully below, the most suitable ethylenically unsaturated starches for optimum water absorption will depend on the type of starch chain. An ethylenically unsaturated monoglucoside will typically require at least a D.S. value of approx. 2.0 or more, while long chain starch chains (e.g. unhydrolysed starch) typically require a significantly lower D.S. level

(eg 0.0002) to be water absorbent. Furthermore, a direct relationship exists between the D.S. value of any given starch chain and the optimum water absorption capability obtainable from the starch copolymer thereof. An insufficient or excessive ethylenic unsaturation D.S. level will generally result in a copolymer having poor water absorption

properties. Too low a D.S. value will fail to provide the necessary multifunctional polymerization sites for the water absorbency materials. However, for a large proportion of starches, a starch copolymer capable of absorbing several times its own weight can typically be obtained by copolymerizing a starch having an ethylenic unsaturation ranging from approx. 0.002 D.S. to approx. 0.10 D.S. Higher ethylenically unsaturated D*S. levels (eg, 0.2 or more) will generally require more carefully controlled copolymerization conditions with an appropriate proportion of ethylenically unsaturated monomers and type of monomer. Starch copolymers which typically absorb more than 10 times their weight in water are obtained from starches having an ethylenic unsaturation ranging from about* 0.005 D.S. to approx. 0.05 D.S. For applications requiring a stronger water-absorbing starch (eg, more than 100 times the dry weight of the starch), it is advantageous to use starch substrates containing pendent ethylenic unsaturation at a level ranging from about 0.005 D.S. to approx. 0.01 D.S.

The starch copolymer's water-absorbing properties are directly related to its lattice structure (ie, molecular configuration) and its ionic hydrophilicity. The characteristics of the starch chain and the polymeric bonds formed by the interpolymerized ethylenically unsaturated monomers primarily dictate the network structure of the copolymer. Failure to achieve proper polymer bonding or bridging between starch molecules will adversely affect the water absorption properties of the starch copolymer. Too long polymeric monomer bonds tend to result in too open a structure which adversely affects the water absorption character of the starch copolymer network. Conversely, too strong cross-linking (e.g. an ethylenically unsaturated starch with a high D.S. value) or an insufficient amount of copolymerized monomer (e.g. very short bonds between starch molecules) tends to create a closed network and consequent loss in water absorption capacity. The net ionic charge of the copolymer associated with its porous network with respect to water contributes to its water absorption and retention properties. Likewise, achieving the optimal network and an insufficient ion charge impair its water absorption capacity. The combination of a proper network and a sufficient level of ionic charge to attract and absorb water molecules within its porous network provides maximum water absorption capacity.

In the water-absorbing starch copolymer, the copolymerized ethylenically unsaturated monomers (ie, -iMl^, in formula I) contain a sufficient number of hydrophilic substituents (e.g., "(W)a in formula 1) to impart water absorption to

the copolymerized starch product. Illustrative hydrophilic substituents include cationic, anionic, nonionic, arapholytic, zwitterionic, amphoteric moieties, mixtures thereof, and the like. As assumed above, it is not necessary that each copolymerized monomeric unit be a water-extracting group. Thus, a significant part of the polymeric chain units can be

free of ionic substituents whereby the remainder of the units provide a sufficient level of "W" substitution to render the starch copolymer water absorbent. The degree of<H>w" substitution necessary to obtain a water-absorbing starch copolymer will depend on many factors. Such factors as the ionic charge and type of ionic substituents, proportions of ethylenically unsaturated starch relative to raonomers, hydrophilicity and polarity of the copolymerized monomer units, etc., have an effect on the required level of "W" substitution. For most conditions, it is advantageous for the starch copolymer to contain either anionic or cationic substituents.

A selection of conventional ethylenically unsaturated monomers containing either the water-absorbing substituents or their precursors can be used to prepare the starch copolymers described herein. The polymeric bonds may be amphiphilic (ie, contain both polar water-soluble and hydrophobic water-insoluble groups)" Anionic monomers include ethylenically unsaturated monomers containing acid groups or acid salt groups or acid salt precursors. Examples of anionic substituents are carboxylates, oxalates, benzoates, phosphonates, maleates, alates, phthalates, succinates, sulfates, sulfonates, tartrates, fumarates, mixtures thereof and the like. Illustrative ethylenically unsaturated cationic monomers include nitrogen-containing cations, e.g. primary, secondary and tertiary and quaternary ammonium compounds; sulfur-containing cations, e.g. sulfonium salts, halides, etc., phosphorus-containing cations, e.g. phosphonium salts; mixtures thereof and the like. Typical nitrogen-containing cations include monomers represented by the formula

group, and X© is an anion (eg, halide, acetate, CH^SO^, CjHgSO^, etc.). Examples of Ra, R^ and Rc^ mono-organo groups are substituted and unsubstituted alkyl, monoheterocyclic (e.g. piperidine, morpholine, etc.), hydroxyalkyl, aralkyl, cycloalkyl as well as cyclic and heterocyclic groups divalently bonded to the nitrogen atom (eg Ra and R^ form a cyclic structure). The preferred nitrogen-containing ethylenically unsaturated cationic monomers are the water-soluble monomeric salts, e.g. lower alkyl of 1-5 carbon atoms (eg ethyl, methyl*propyl);

polyoxyalkylene (e.g. polyoxyethylene and polyoxypropylene), mixtures thereof and the like; alkoxy (eg, methoxy, ethoxy, propoxy, etc.); hydroxyalkyl and polyhydroxyalkyl (eg, hydroxyethyl, byhydroxypropyl, dihydroxypropyl, dihydroxybutyl); heterocyclic amines (eg, morpholine); amines and amides that carry mono-organic compounds; mixtures thereof, etc. The sulfur- and phosphorus-containing cationic monomers are similar to those mentioned above with the exception that either the phosphorus atom or the sulfur atom replaces the nitrogen atom. The preferred phosphorus and sulfur cations are phosphonium and sulfonium cationic salts. Water-soluble, "w*" ethylenically unsaturated monomers containing an activating group adjacent to the ethylenic unsaturation (e.g., where M* contains a CHj^CR-g radical with the activating group "EM- and

**R™ group as defined above) is preferred.

Representative cationic monomers include the N-ethyl acrylamide reactants discussed above, dimethylaminoethyl methacrylate; t-butylaminoethyl methacrylate; 2-Hydroxy-3-methacryloxypropyltrimethylamranium chloride and allyltrimethylamranium chloride; S-allyl thiuronium bromide, S-methyl(allyl thiuronium)metho-sulphate, diallyldibutyldiaimonium chloride, diallyldimethylammonium met©sulphate, dimetallyldiethylammonium phosphate, diallyldimethylammonium nitrate, s-allyl-(allylthiuronium)bromide, N-raethyl(4-vinylpyrlidinium) )methosulphate, N-methyl(2-vinylpyridinlum)methosulphate, allyldimethyl-/3-methacryloxyethylammonium methosulfate, /S^ethacryloxyinethyltrimethylXammonioinitrate} #-methacryX©ksyetyX-trimethyliammonium-p-toXuensuXf onate, S -acryXoxybutyXtributX-ammonium methosulfate, inetallyldiraethyl-0 -vinylphenylaRimonium chloride, octyldiethyl-m-vinylphenylammonium phosphate-, /J-hydroxyethyldipropyl-p-vinylphenylammonium bromide, benzyldimethyl-2-methyl-5-vinylphenyl-ammonium phosphate; 3-HydroxypropyldiethylvinyphenyXammoniumsuXphate; octadecyldimethylXvinylfsnylaiiBnoaium-p^toluenesulfonate, amyldimethyl-3-^atyX~5-viiiyXphenylaiBmoniuiBtiocyaBat, vinyXoxyetyXtriethyl-ammonium chloride, K-but<y>l-5-Qt<y>l-2-vinylpyridinium iodide, N-propyX-2-vinylquinoiinium methylsulfate , H~butyX-5-ethyX-3-vinypyridinium;r;-. u iodide, II~propyX-2-vinylkiaoXiaivua"-methyXsiiXfat<allyl- ir-myrist-amidopropyldimethylammonium chloride, metallyl- T-caprylamidopropyl-methylethylammonium bromide; allyl- Y-caprylamidopropylmethylbenzyl-ammonium phosphate f at, etallyX- T -myris tamidbpropyimetyX-a-naphthyXmetyX -ammonium chloride, allyl- r -palmitamidopropylethylhexyXammoniura-suXphate; metaXXyX- y -XauraaddopropyXdiaroyXammonitamphos f at, propallyl- T*xauramidopropyldie%yXammonium phosphate, metallyX-capryXamidopropyiæethyl-/?-bydxoxyethylamTaoiU «llyX- T~stearamMopropylmethyldihydKdxypropyXamnumium and XabyX-Xauroamido-Xabydoxyxobarbehxydoxyphosphate metaXXyX-T-abietamidopropyXhexyX-^' -hydroxypropyXaramonium phosphate vinyidiethylmethyXsuXfonium iodide, ethylenically unsaturated nitrogen-containing cations of the formula CHj^CHQN<+>f<R>j<R>gRjJX-" as described, for example, in U.S. Patent No. 3,346. 563 with Q, R^, R^, R3 and 3$T defined as above, mixtures thereof and the like.

Representative anionic monomers include vinyl sulfonic acid and vinyl sulfonates (see, e.g., U.S. Patent Nos. 3,970,604 and 2,859,191); allylsulfuric acid and allylsulfosuccinates (see, e.g., U.S. Patent No. 3,219,608); sulfoesters of o-methylene carboxylic acids and salts thereof (see, e.g., U.S. Patent No. 3,024,221); sulfo-organic esters of fumaric and maleic acids and their salts (see, e.g., U.S. Patent No. 3,147,301); acids and salts of sulfatoalkane acrylates and methacrylates (see, e.g., U.S. Patent Nos. 3,893,393 and 3,7XX,449); acrylamidoalkanesulfonic acid and salts (see, e.g., U.S. Patents 4,008,293 and 3,946,X39), vinyl phosphonic acid and vinyl phosphonates; a,^-ethylenically unsaturated carboxylic acids, their salts (e.g. acrylic acid, raetacrylic acid* ethacrylic acid, propacrylic acid, butacrylic acid, itaconic acid, monoalkyl esters of itaconic acid, crotonic acid and crotonates, fumaric acid and fumarates, etc.), mixtures thereof, etc.

The water-absorbing starches can be prepared by initially copolymerizing the starch with ethylenically unsaturated comonomers containing reactive sites (eg, polar or unpolymerized ethylenic unsaturation) which are then derivatized to "W" moieties. For example, the ethylenically unsaturated starches described here can be copolymerized with unsaturated precursors and converted to the anionic form by e.g. saponification for replacing the alkyl ester group with a metal salt, and known techniques for derivatizing organic compounds to acid or the neutralized acid salt form. The starting monomers preferably contain the hydrophilic structure or one that can be converted directly to the "W<*-> form by neutralization. This will avoid the derivatization step as well as the possibility of contamination of the copolyester with salts and minerals, as well as the need to wash and refine for the removal of such impurities.

The polymeric bonds between copolymerized starch chains can be composed of interpolymerized ionic monomer units and monomer units that are free of "W<*->substituents. The interpolymerized monomer units that are free of "W<**->substituents can be selected from a wide range of ethylenically unsaturated monomers. Hydrophilic and/or hydrophobic comonomers can be used for this purpose. Illustrative interpolymerized comonomers include vinyl aromatic compounds (eg, styrene and styrene derivatives); the alkyl esters of o,^-ethylenically unsaturated acids; ot, 0-ethylenically unsaturated nitriles, α,^-ethylenically unsaturated amides?vinyl halides (e.g. vinyl chloride and -bromide), olefins such as e.g. mono- and di-olefins; vinylidene halide (eg vinylidene chloride and bromide), vinyl esters (eg vinyl acetate and derivatives); diesters of ot,O-ethylenically unsaturated dicarboxylic acids (eg, dimethyl-^illipr diethylitaconate, dimethyl or diethyl maleate, diethyl or dimethyl fumarate, etc.); alkyl vinyl ethers, e.g. methyl or ethyl vinyl ether, etc.; alkyl vinyl ketones (e.g. methyl vinyl ketone, etc.), mixtures thereof, etc.

The polymeric bonds are advantageously predominantly composed of polar or water-soluble monomeric units. Illustrative polar or water-soluble comonomers which are free of "W" substituents that can be copolymerized with the "W" monomers and the starch include the hydroxyalkyl esters of oe,O-ethylenically unsaturated carboxylic acids, e.g. hydroxyethyl, hydroxyethoxyethyl, hydroxymethyl, 2-3-dihydroxypropyl acrylates and methacrylates, di(2,3-dihydroxypropyl) fumarate di(hydroxyethyl)-itaconate, ethyl hydroxyethyl maleate, hydroxyethyl crotonate, mixtures thereof and the like; the lower alkyl esters of ct, /5-ethylenically unsaturated carboxylic acids (e.g. c^-Cj alkyl esters of mono- and di-carboxylic acid, e.g. methyl and ethyl esters of acrylic, methacryl -, furoic, crotonic, maleic, etc.); H-(3-methylamine-^propyl methacrylate;

1-butylamine butyl methacrylate; dimethylaminoethyl methacrylate;

£-(5-Butylamino)ethyl acrylate; 2-(1,1,3,3-tetra-aretylbutylamino)-ethyl methacrylate, etc.); «,^-ethylenically unsaturated amides (e.g. acrylamide and the N-substituted acrylamides, e.g. ST-methyl-, N-ethyl-, H-propyl-, H-N-dimethyl- and N-N-diethyl-, N —butyl- etc. acrylamides or -methacrylamides or -ethacrylamides, H-(#-dimethylamino)ethylacrylamide, N-(0-dimethylamino)ethylmethacrylamide, etc.); wool esters (eg, vinyl acetate, etc.);

vinyl alcohol and vinyl ethers (eg methyl or ethyl vinyl ether, diethylaminoethyl vinyl ether, diethylaminoethyl vinyl sulfide, 5-amino-pentyvinyl ether, 3-aminopropyl vinyl ether, 2-aminoethyl vinyl ether, N-methylaminoethyl vinyl ether); alkyl vinyl ketones (eg, methyl vinyl ketone, etc.); vinylpyridine, vinylpyrrolidone, mixtures thereof, etc. The proportions of ethylenically unsaturated starch copolymerized with the ethylenically unsaturated monomers should typically be sufficient to provide a starch copolymer capable of absorbing at least 10 times its dry weight in water. The type of monomer and type of starch will affect the proportions needed to achieve optimal water absorption capacity. In general, the dry weight of the monomer will usually fall in the range from approx. 5 to approx. 2000 parts by weight for every 100 parts by weight of the ethylenically unsaturated starch. For water absorption that exceeds 50 times the weight of the starch copolymer, approx. 10 to approx. 1000 parts by weight of copolymerizable monomer for every 100 parts by weight of ethylenically unsaturated starch. The amount of "W-monomer e units within the polymeric bond will usually amount from approx.

25 to 100% of the weight of the copolymerized monomer and advantageously at least a major proportion by weight of the polymer bond. Water-absorbing copolymers that have the ability to absorb the least

100 times its dry weight in water, is most conveniently produced from approx. 100 to approx. 750 parts by weight of "W monomer" and from 0 to about 200 parts by weight of ethylenic monomer which is free of "W monomers" for every 100 parts by weight of ethylenically unsaturated starch.

The water-absorbing starch copolymers are advantageously prepared under aqueous polymerization conditions. Homogeneity of the reactants throughout the water phase results in more uniform and reproducible water-absorbing properties. Ethylenically unsaturated starch and ethylenically unsaturated monomer systems that provide homogeneous dispersions that are essentially free of centrifuge residue and/or supernatant Cf*eg* heated to a temperature above the starch's gel point for gelatinization of the starch and centrifuged for 10 minutes at 10 3 G), which is demonstrated by less than 10% by weight centrifuged residue (preferably less than 5%), are particularly well-suited systems for producing the water- absorbent starch copolymers.

In thermal manufacturing processes (e.g. casting, calendering, extrusion, etc.) a high weight ratio between monomer pg starch on the one hand and water on the other (5:1 to 9:1) is typically used. With the reduced water levels and elevated monomer levels, incompatibilities can arise in the ethylenically unsaturated raonora/starch system. Elevated production temperatures and pressures can be used to improve the compatibility of this system. Likewise, water-miscible solvents in which the ethylenically unsaturated monomers are soluble (e.g. glycerol), or emulsifying agents can be effectively used to improve the water-dispersibility of the monomer/starch system in the water phase. In extrusion operations, a sufficient amount of water (with or without conventional starch plasticizers) is used to convert the polymerizable mass into a molten, softened mass at elevated temperatures (eg 80-250°c) and pressure. The molten mass is then extruded through a die into an atmosphere of reduced pressure and temperature maintained below its boiling point to produce void-free extrudates and above its boiling point to produce inflated extrudates.

For coating purposes, it is particularly advantageous to use a gelatinized or pregelatinized starch. Aqueous coating compositions containing the low viscosity ethylenically unsaturated starch hydrolysates are particularly useful when it is desired to coat substrates at binder dry weight levels of at least 40%. Substrates can be moistened evenly and coated at solids levels that vary from approx. SO to 75% by weight with stability against syneresis, separation and viscosity changes. Such coatings dry easily at nominal evaporation costs. Depolymerization of the starch to the appropriate short chain length (e.g., D.E. 0.2-100) for coating purposes can be accomplished by conventional saccharification and/or dilution techniques (e.g., acidic or enzymatic). The starch chains can be depolymerized to the relevant chain length before or after the ethylenically unsaturated derivatives are produced. Starch chains having a degree of polymerization comparable to that obtained by amylase hydrolysis of starch to a D.E. value varying from approx. 0.1 to 32 (advantageously from about 0.25 to about 15

and most preferably below 10), can be used effectively for coating substrates. The reduced starch chain length will not adversely affect the starch coating ratio provided the ethylenically unsaturated D.S. value is sufficiently high to provide chains containing multifunctional unsaturation sites.

For most coating purposes, the water content is typically adjusted to a fluidity that is most suitable for coating the substrate. The viscosity of the starch coating preparation can vary considerably and is largely dependent on the type of coating method used (eg from about 1 to about 40,000 cP or more for extrusion coating). The proportions of water, monomer, and ethylenically unsaturated starch weight ratio can also vary significantly (eg, about 5 to about 10,000 parts by weight of water and about 1 to about 5,000 parts by weight of monomer for every 100 parts by weight of ethylenically unsaturated starch). For coating processes that are carried out under ambient temperatures, it is advantageous to use a homogeneous starch coating preparation with a viscosity higher than approx. 10 cP, but lower than 5,000 cP (most typically between about 20 cP and 1,000 cP) and containing from 25 to about 800 parts by weight water and approx. 10 to approx. 2,000 parts by weight of ethylenically unsaturated monomer for every 100 parts by weight of ethylenically unsaturated starch. Water-miscible organic solvents or surface-active agents are preferably mixed into the coating preparation in order to provide homogeneity and uniform monomer dispersion if the starch coating mixture contains a small amount of water and a high monomer concentration. Starch coating preparations that are adapted

for use in high-speed coating operations, is typically formulated with a viscosity ranging from about 100 cP to about 300 CP (with or without volatile organic solvents or surfactants with about 30 to about SOO parts by weight water and about 25 to about 1,000 parts by weight (preferably between about SO and about 500 parts by weight) ethylenically unsaturated monomer for every 100 parts by weight ethylenically unsaturated starch In mixtures for high speed coating operations, coating homogeneity of the starch is more easily achieved by using less than 3 parts by weight ethylenically unsaturated monomer to 2 parts by weight water and preferably at a ratio by weight of less than one part monomer to each part water.

The copolymers are copolymerized by conventional polymerization initiators. The unpolymerized starch and raonomers can conveniently be prefabricated into the desired configuration and then copolymerized in situ via such conventional polymerization initiation systems. The starch preparations will undergo copolymerization upon exposure to conventional irradiation processes which in situ entangle polymerization initiators in them (eg electron radiation, X-rays, alpha rays, gamma rays, etc. as initiation). Alternatively, free radical catalysts or free radical precursors can be incorporated uniformly into the unpolymerized starch preparation which will then latently copolymerize upon exposure to appropriate initiation conditions (eg photochemical, ultraviolet, heating or microwave techniques, etc.).

Conventional free radical polymerization initiators at levels sufficient to copolymerize the ethylenically unsaturated starch and the monomer (eg, about 0.2 to about 20% on a starch/monomer weight basis) which may be incorporated into the starch preparation , they include organic and inorganic peroxides (e.g., hydrogen peroxide, benzoyl peroxide, tert-butyl hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, caproyl peroxide, methyl ethyl ketone peroxide, etc.), oxidation/reduction initiator esters (ammonium, potassium, or sodium persulfates or hydrogen peroxide with reducing agents such as sodium bisulfites, sulfites, sulfoxylates, thiosulfates, hydrazine, etc.) f azo initiators (e.g. tert-aliphatic azo compounds undergoing homolytic dissociation), e.g. azo-di-isobutyronitrile, snylazotriphenylmethane, 1,1'-azodicyclohexanecarbonitrile, 1,1-dimethylazoethane; diazoamino compounds

(e.g. 3,3~dimethyl-l-phenyltriazene and aryl diazothioethers) and other free radical developing catalysts, e.g. certain aromatic ketones (eg oenzoin methyl ether, benzophenone and its derivatives), chlorinated aromatics as well as other free radical type polymerization initiators. Priradical initiator systems that require externally applied energy (eg, thermal, photochemical, etc.) for free radical generation can be used to provide a latent copolymerized system. The free radical polymerization initiators are advantageously dispersed evenly in the aqueous phase in the starch preparation at levels varying from approx. 0.3 to approx. 10%

(based on the dry weight of polymer is erable starch and monomer).

Polymerization initiation via U.V. - and white light sources (e.g., the 200-430 nanometer (nm) range, e.g., in carbon arc lamps, xenon lamps, high-pressure mercury lamps) are particularly useful in high-speed coating operations. If desired, conventional photosensibilizers (e.g. triethanolamine-soluble benzophenones, eosin sulfonates, methylene blue sulfinate, combinations thereof, etc.) can be incorporated into the starch preparation by transfer of active energy to facilitate the copolymerization initiation reaction. The ultraviolet polymerization initiation processes are generally suitable for coatings or films with a thickness of less than approx.

0.5 mm (preferably below approx. 0.25 mm). Thicker starch polymer articles or films normally require higher penetration irradiation devices (eg, X-rays, electron beams, ganaa development, etc.) or thermal induction. The U.V. copolymerization process is particularly effective for starch coating purposes where high solids (eg, about 55 to about 75% solids) are used because it simultaneously dries and copolymerizes the starch coating in a single step. Water-dispersible, non-volatile free radical initiation systems (e.g. catalysts that volatilize, or leave no catalytic residue in the copolymer solution), e.g. hydrogen peroxide, is preferred.

The water-absorbing starch copolymers have a wide and divergent field of application. A main advantage of the water-absorbing starches 1 according to the invention is based on the possibility of applying the unpolymerized product to a substrate or to prefab it into the desired shape or configuration and then convert it into a water-absorbing starch copolymer. The unpolymerized product can be applied to divergent substrates varying from natural and man-made products, and then polymerized in situ to form an integrated product of uniform construction. This advantage is particularly useful for purposes where it is desired to permanently fix or impregnate a natural or synthetic substrate (eg, films, woven materials, fibers, filaments, etc.) with the water-absorbing starch. Illustrative applications for the water-absorbing starches include sanitary pads, bandages, surgical and catamenial tampons, sanitary napkins, diapers, antiperspirant and deodorant pads, sponges*surgical pads, tampons for dental use, disinfection aids, decorative seedling films, etc. About desired, the water-absorbing starch copolymers can be mixed with natural and man-made products for such divergent applications as cosmetics, water-removal aids, paint removers, solid humectants, pesticides, and further for improving the soil's water-retention capacity, catalysts or chemical carriers, obstacles, etc.

The following examples are only illustrative and should not be taken as limiting the scope of the invention.

Example I

An aqueous acrylamidomethyl starch hydrolyzate (D.S. 0.009) was prepared using the following proportions of reagents.

The ingredients were mixed and filtered on a Bfichner funnel. The starch cake was sucked free of excess water phase, and the unwashed cake (with 63% retention of non-starch reagents) was air-dried to ten percent drying loss. The dried reactant premix had the following ratio of reagents (parts by weight) - 250 starch; 7.95 Kf-methylolacrylamide, 0.025 methylhydroquinone; 29 water. The powdered reaction premix was layered on a stainless steel tray and heated for 2 hours in a forced air drying cabinet at 75.5°C. After resuspension in distilled water, filtration and washing free of unreacted reagent impurities, the dried product contained 0.10 percent nitrogen (on a dry basis), which after correction for the nitrogen in the "STA-TAPE 100" starch (0.022 percent) ;is equivalent to a D.S. value of 0.009. Further information regarding the production of the acrylamidomethyl starches can be found in BRD official document no. 27 18 210.

A portion of the acrylamidomethyl starch (0.77 grams) was homogeneously dispersed in 8.43 grams of water (15 minutes at its boiling point) and cooled to ambient temperature in a 50 ml flask. 0.48 grams of acrylic acid and 0.24 grams of acrylamide were dispersed homogeneously in the acrylamide starch solution, followed by the addition of 0.0169 grams (d.s.b.) of ammonium persulfate (2.28% aqueous solution) and 0.0076 grams (d.s.b.) of sodium bisulfide (1 .04% aqueous solution). Then 0.002 grams (d.s.b.) of ferrous sulfate (0.28% by weight FeSO.sub.7H..0 aqueous solution) was added, which caused an ex ot erm copolymerization of the ethylenic unsaturated substances. Within 1 minute, the entire reaction medium had gelled (12.1/g) into a copolymer that could be agitated with a magnetic stirrer. To convert the acrylic units to the anionic salt, 0.42 grams of solid potassium hydroxide was added. The resulting viscous dispersion (12.53; g total) was then stirred for 15 minutes. The sample contained 15.24% by weight of solids. The gel was then diluted to 5% dry matter by weight with 25.64 g of distilled water and allowed to stand for 24 hours. Then the dispersion (36.84 grams) was further diluted with 55.26 grams of distilled water to provide a 2% gel solids dispersion. The viscosity of the dispersion, respectively, after standing for 6 and 23 hours (spindle no. 4 at 20 rpm) was 500 cP and 3500 cP. The solid was again diluted with 90.52 g of distilled water (1% solids dispersion) which after 29 hours of standing had a viscosity of 700 cP (spindle no. 4 at 20 rpm) and after 58 hours a viscosity of 710 cP. The 1% gel dispersion was air-dried at ambient conditions (intrapping tray i

11 days). A 0.1526 g sample of the resulting gummy

resin was transferred and hydrated with 11.85 grams of distilled water in a 15 ral centrifuge tube. The sample swelled to a volume of 12 ml. The hydrated sample was centrifuged for 15 minutes at 10 3 G. The supernatant liquid was decanted into a tared aluminum dish. 11.38 grams of the swollen gel was transferred to a 50 ml centrifuge tube and was diluted with 11.38 grams of water and allowed to swell for 17 hours followed by centrifugation for 15 minutes at 10<3>G. The supernatant (pH 6.6) together with the above-mentioned supernatant was analyzed for water-soluble starch (0.0423 grams or 27.7% by weight via evaporation.

The weight swelling ratio (WSR) of the copolymer was determined by the equation WSR *^^where I, 0 and S respectively represent the weight of swollen insoluble matter, 9.63 grams; original sample

0.1526 grams and soluble matter, 0.0423 grams (i.e.

Example II

A cationic water-absorbing starch copolymer was prepared by copolymerizing (in 34.6 parts by weight of distilled water) 8.5 parts by weight (0.008 mol) of acrylamidoraethyl starch

0 (dry matter 0.008), 30.9 parts by weight CH2wC(CH3)-C-OCH(OH)CH2lt(GH3)3Cl~

(0.0199 mol) and 11.1 parts by weight of acrylamide (0.0241 mol). The copolymerization reaction was exothermically initiated with 0.1 parts by weight of aramonium persulfate (0.13(NH4)2S2 and é 5 parts by weight of water),

0.07 parts by weight sodium bisulphite (0.07 parts by weight HaHS03.+ 5 parts by weight water) and 0.01 parts by weight FeSO^^&gO (0.01 part by weight FeS0^.7H20 +4.7 parts by weight water). Within 90 seconds, the copolymerization reaction was complete, yielding a water-absorbing, hydrated copolymer gel. This cationic gel was analyzed in accordance with the test method specified in

. i t — a *»p-0_ ,, _. _ « i. _i. i _t, _t Jj- 1 r>~1».»-o/ ., 1 ri**

Example III

A cationic water-absorbing starch copolymer was prepared by copolymerizing 0.008 mol of acrylamide starch (D.S. 0.008 at 8.45 parts by weight), 0.0243 mol of acrylamide 0

M+

(11.25 parts by weight) and 0.01673 mol CH2"C(CH3)-C-OCH2CB2H(CB3)3-CH-jOS<O>^ (30.82 parts by weight) with the exothermic initiation system according to Example II. The resulting copolymer gel (copolymerization was complete within 150 seconds of initiation) was mixed with 2000 mL of water and allowed to swell for 8 days at 25° C. The decanted supernatant thereof contained 20.18% water-soluble material. The insoluble copolymer (79.82% of the total copolymerizable reactants) absorbed 86 times its weight of water at pH 3.6 and 25°C.

Example IV

Using the polymer initiation system of Example II, 10 parts by weight of acrylamidomethyl starch (D.S. 0.008) was copolymerized (about 3 minutes) in 56 parts by weight of distilled water containing 9 parts by weight of potassium hydroxide with 12 parts by weight of acrylic acid and 12 parts by weight of acrylamide. The anionic copolymer gel

(tested using the water absorbency test in Example III)

absorbed 119 times its dry weight of water. This example was again repeated with a starch with a D.S. value of 0.056. The copolymer gel with a D.S. value of 0.056 absorbed only 2? times its dry weight of water. The low water absorption capacity of the acrylamidomethyl starch copolymer with a D.S. value of 0.056 is apparently due to

its higher cross-linked structure.

Example V

This example illustrates a water absorbent copolymerizable starch coating composition that can be copolymerized in situ to provide a substrate (eg, textile, paper, etc.) coated with the water absorbent starch copolymer. The copolymerizable starch preparation (pH 6.0) consisted of 10 parts by weight of acrylamidomethyl starch (0.01D.S*)<2>, 47 parts by weight of distilled water, 12 parts by weight of acrylic acid, 12 parts by weight of acrylamide, 9 parts by weight of potassium hydroxide and 10 parts by weight of aqueous hydrogen peroxide (30 %). 2 — The acrylamidomethyl starch hydrolyzate with a D.S. value of 0.01 contained an average of approximately two acrylamidomethyl groups for each starch molecule.

Five grams of the copolymerizable preparation was placed in an aluminum weighing pan (approximately 5 cm inside diameter) and irradiated 25.4 mm away from a 275 watt solar lamp for 1 minute so that a solid gel was obtained. Another portion of copolymerizable starch preparation was applied with a No. 40 wire-wrapped rod to a glass plate of dimensions 10 cm x 30.5 era and irradiated 6 passes at 6.2. m/min. at 3.8 cm under a Banovia 679fAj lamp. The copolymerizable starch preparation gelled on the first pass (1/6 sec.) and was converted to a dry film after the sixth pass through the irradiator (ie, one second). The WSR of the resulting starch copolymers was 150. An acrylamidomethyl starch of D.S. value 0.056 bie was used instead of the acrylic amidomethyl starch with a D.S. value of 0.01 to provide a copolymer with a WSR of 30.

In another test, an acrylamidomethyl starch with a D.S. value of 0.014 was used in place of the acrylamidomethyl starch reactant with a D.S. value of 0.01 and applied to the glass plates with a No. 40 wire-wrapped rod (pH 6.2$ 25-36 cP in viscosity, spindle no 1

at 20 rev. at 25°C). After 4 passes through the irradiator, a dry, water-absorbing film coating, 83.51% insoluble copolymer solids and a WSR of 120 was obtained. This test was repeated by immersing three pieces of cotton fabric (approximately 45.7 x 15.2 cm) in the copolymerizable starch coating preparations with a D.S. value of 0.014, by passing the coated cotton through the rollers of a Birch Brothers Padder, by placing the coated cotton pieces on glass plates and then irradiating the three samples at 4, 6 and 8 passes .

The dry coating application was 46% by weight. The water-swelling ratios were 120 for 4 irradiation passes, 86 for 8 passes and slightly more than 100 for the fabric sample exposed for 6 passes.

Although the preceding examples primarily illustrate the use of starch chains with a relatively high molecular weight*, the invention applies to a wide range of ethylenically unsaturated glucose-containing monomers such as e.g. such as vary from a fully hydrolysed starch (eg dextrose) to an unhydrolysed starch. The glucose-containing monomers containing multifunctional ethylenically unsaturated groups provide the necessary structure for the porous lyophilic network. The most appropriate D.S. level for a glucose-containing monomer will depend on the number of glucose units present in its starch chain. In order to obtain multifunctional copolymerizable groups for a monosaccharide, disaccharide, trisaccharide or tetrasaccharide monomer, a D.S. value of 2.Q, 1.0, 0.66 and 0.5 with the oligosaccharides (f .eg D.P.4+> and higher starch chains which require a correspondingly smaller D.S. value to achieve multifunctionality In contrast, the higher molecular weight starches (e.g. tihydrolysed starches) will typically have multifunctional copolymerizable groups at a D.S. -value of O.0002 or less.

Since the starch copolymers described here possess a porous structure, their lyophilic properties can be changed via the composition and character of unsaturated starches, monomers and lyophilic groups used in their production. By replacing the polar, water-attracting groups with non-polar and oil- or solvent-attracting groups, it is now possible to "tailor** starch copolymers for absorption of specific solvents, chemicals and/or water-immiscible liquids (f .eg oil).Lyophilic and amphophilic starch copolymers can likewise be obtained by means of starch copolymers containing both polar water-soluble and hydrophobic, water-insoluble substituents.

Claims (14)

1. Water-absorbing starch copolymer, characterized in that it comprises the copolymer product of ethylenically unsaturated starch molecules and ethylenically unsaturated monomers where the ethylenically unsaturated monomers form a polymeric bond between the copolymerized starch molecules to provide a non-linear network of a plurality of starch chains bound together by polymeric bonds represented by the formula: where "starch" represents a starch chain of D-glucose units, Z represents an organic linking group group to the carbon atom in the starch chain by means of a sulfur atom or an oxygen atom, R is hydrogen or a monovalent organic radical, M represents a plurality of copolymerized ethylenically unsaturated monomers where "p" represents the number of copolymerized monomeric units in the bond, (W) is a water-attracting group attached to the polymeric bond and "n" represents the number of groups (W) contained in the polymeric bond of the copolymerized monomers, the number of groups (W) being sufficient to give the copolymer water absorption properties. 2. Water-absorbing starch copolymer as stated in claim 1, characterized in that the organic Z group essentially consists of one group and R' is at least one hydrogen or mono-organo group which is linked directly to the nitrogen atom by means of a monovalent bond. 3. Starch copolymer as stated in claim 1 or 2, characterized in that the ethylenically unsaturated starch molecules essentially consist of starch molecules and attached ethylenically unsaturated groups of a molecular weight that varies from more than 50 to less than 300 and where the degree of substitution for the ethylenically unsaturated pendant groups vary from approx. 0.002 to approx. 0.1, and "W" is at least one anion, cation, nonion or zwitterion. 4. Starch copolymer as stated in any one of claims 1 to 3, characterized in that the weight of ethylenically unsaturated monomer in the copolymer varies from approx. 10 to approx. 1000 parts by weight for every 100 parts by weight of copolymerized ethylenically unsaturated starch and from approx. 25% to approx. 100% of the copolymerized ethylenically unsaturated monomer contains the "W" substituent. 5. Starch copolymer as stated in any of claims 1 to 4, characterized in that the copolymerized ethylenically unsaturated starch essentially consists of amylopectin hydrolyzate with a degree of substitution for the starch ethylenically unsaturated groups varying from approx. 0.005 to approx. 0.05. 6. Starch copolymer as stated in any one of claims 1 to 5, characterized in that the copolymerized ethylenically unsaturated starch essentially consists of an acrylamide starch which has a D .S. value that varies from approx. 0.005 to approx. 0.05 and a D.E. value varying from approx. 0.25 to approx. 15, and in that the copolymer contains 100 parts by weight of copolymerized ethylenically unsaturated starch hydrolyzate, from approx. 100 to approx. 750 parts copolymerized ethylenically unsaturated monomer containing <H> W" groups and from 0 to about 200 parts by weight copolymerized ethylenically unsaturated monomers having no "W" groups. o 7. Process for producing a water-absorbing starch copolymer where the copolymer comprises a plurality of starch chains which are linked together by polymeric bonds represented by the formula: where * st iyelse" represents a starch chain of D-glucose- units, Z represents an organo group which binds the ;group to the carbon atom in the starch chain by means of aV a sulfur atom or an oxygen atom, where R is hydrogen or a monovalent organic radical, where M represents a plurality of copolymerized ethylenically unsaturated monomers containing a sufficient number of (W) groups to provide water-absorbing capability to the copolymerized product, " p"' represents the number of copolymerized ethylenically unsaturated monomers linking together the starch chains, the method comprising copolymerizing: (a) starch chains containing pendant, terminal ethylenically unsaturated groups represented by the formula: ; where "starch", Z and R are as defined above, and "a" represents the degree of substitution for the terminal unsaturated groups on the starch chain, and (b) ethylenically unsaturated monomers represented by the formula: ;where M' represents an ethylenically unsaturated monomer, "(W <*> )" represents at least one water-attracting group or a precursor of a water-attracting group, and n' is an integer under the condition that when the copolymerized M'-(W')nl monomer essentially consists of a precursor for the water-attracting group, a sufficient number of the precursor groups are derivatized to a water-attracting group so that the starch copolymer receives water - absorbent properties. 8. Method as stated in claim 7, characterized in that (W) is at least one water-attracting group or a precursor of a water-attracting group that is an anion, cation, non-ion or zwitterion, and that Z represents an organo -group which links the -CRH- group to the starch chain by means of an oxy moiety. 9. Method as stated in claim 7 or 8, characterized in that Z comprises an organo group represented by the formula: and R' is at least one hydrogen atom or a mono-organo group connected directly to the nitrogen atom via a monovalent bond. 10. Method as stated in any one of claims 7 to 9, characterized in that the attached ethylenically unsaturated groups in the starch chains essentially consist of groups that have a molecular weight that varies from approx. 75 to approx. 150, and "a" represents a degree of substitution varying from approx. 0.002 to approx. 0.1. 11. Method as stated in any of claims 7 to 10, characterized in that from approx. 25 to 100% by weight ethylenically unsaturated monomers contain the "W" group and that the copolymerized weight of ethylenically unsaturated monomer ranges from approx. 10 to approx. lOOO parts by weight of ethylenically unsaturated monomer for every 100 parts by weight of ethylenically unsaturated starch. 12. Method as set forth in any one of claims 7 to 11, characterized in that the ethylenically unsaturated starch essentially consists of an acrylamido starch hydrolyzate which has a D.S. value varying from approx. 0.005 to approx. 0.10 and a D.E. value varying from approx. 0.25 to approx. 15, and that 100 parts by weight of the ethylenically unsaturated starch hydrolyzate is copolymerized with from approx. 100 to approx. 750 parts copolymerized ethylenically unsaturated monomers which are free of "W'" groups and from 0 to about 200 parts by weight of ethylenically unsaturated monomers free of "W'" groups. 13. Method as stated in any one of claims 7 to 12, characterized in that the starch chains essentially consist of an amylopectin hydrolyzate and that "W" represents at least one anion or cation. 14. A method as set forth in any one of claims 7 to 13, characterized in that it includes the additional steps of applying the unpolymerized ethylenically unsaturated starch and the ethylenically unsaturated monomers to a substrate and then copolymerizing the applied starch and the monomers in situ.