Polyacrylamide hydrolysis

Hydrolyzed Polyacrylamide. HPAM (6) can be prepared by a free-radical process ia which acrylamide is copolymerized with incremental amounts of acryUc acid or through homopolymerization of acrylamide followed by hydrolysis of some of the amide groups to carboxylate units. 

Postreactions of polyacrylamide to iatroduce anionic, cationic, or other functional groups are often attractive from a cost standpoiat. This approach can suffer, however, from side reactions resulting ia cross-linking or the iatroduction of unwanted functionahty, such as carboxyl groups from hydrolysis. 

Alkaline hydrolysis of polyacrylamide can be expressed in terms of three rate constants, and where the subscript indicates the number of... 

Hydrolysis of cationic polyacrylamides prepared from copolymeri2ation of acrylamide and cationic ester monomer can occur under very mild conditions. A substantial loss in cationicity can cause a significant loss in performance in many apphcations. Copolymers [69418-26-4] of acrylamide and acryloxyethyltrimethylammonium chloride [44992-01 -0] CgH gN02(Cl), for instance, lose cationicity rapidly at alkaline pH (37). 

Sulfomethylation. The reaction of formaldehyde and sodium bisulfite [7631-90-5] with polyacrylamide under alkaline conditions to produce sulfomethylated polyacrylamides has been known for many years (44—46). A more recent pubHcation (47) suggests, however, that the expected sulfomethyl substitution is not obtained under the previously described strongly alkaline conditions of pH 10—12. This C-nmr study indicates that hydrolysis of polyacrylamide occurs and the resulting ammonia reacts with the NaHSO and formaldehyde. A recent patent claims a new high pressure, high temperature process at slightly acid pH for preparation of sulfomethylated polyacrylamide (48). 

This reaction, conducted in alkaline solution, also produces carboxyl groups by hydrolysis of the amide (54). Recent work on the reaction of polyacrylamide with hydroxylamine indicates that maximum conversion to the hydroxamate fiinctionahty (—CONHOH) takes place at a pH > 12 (57). Apparendy, this reaction of hydroxylamine at high pH, where it is a free base, is faster than the hydrolysis of the amide by hydroxide ion. Previous studies on the reaction of hydroxylamine with low molecular weight amides indicated that a pH about 6.5 was optimum (55). 

Anionic and nonionic polyacrylamides effectively remove suspended soHds such as silt and clay from potable water. SuppHers provide special grades which meet EPA/FDA regulations for residual acrylamides. A recent pubHcation (102) states that hydrolyzed polyacrylamides with narrow interchain charge distributions provide better performance in flocculation of clay. These polymers were prepared by alkaline hydrolysis. (See Flocculating agents.)... 

The principal monomer is acrylamide [79-06-17, where R = H and R = NH2, made by the hydrolysis of acrylonitrile. The homopolymer [9003-05-8] of acrylamide, which in theory has no electrical charge, has some use as a flocculant however, the majority of acrylamide-based flocculants are copolymers with acryHc monomers containing charged functional groups, such as those shown in Figure 1, or polymers containing functional groups formed by modification of acrylamide homopolymers or copolymers (Fig. 2). The chemistry of polyacrylamides has been reviewed by several authors (18—20) (see... 

Fig. 2. Functional groups on modified polyacrylamides (a) formed by reaction with dimethylamine and formaldehyde (Mannich reaction) (b), quatemized Mannich amine (c), carboxylate formed by acid or base-cataly2ed hydrolysis or copolymerization with sodium acrylate and (d), hydroxamate formed by...

If either dry powders or inverse emulsions are not properly mixed with water, large lumps of polymer form that do not dissolve. This not only wastes material, but can also cause downstream problems. This is especially tme for paper where visible defects may be formed. Specialized equipment for dissolving both dry polymers and inverse emulsions on a continuous basis is available (22,23). Some care must be taken with regard to water quaUty when dissolving polyacrylamides. Anionic polymers can degrade rapidly in the presence of ferrous ion sometimes present in well water (24). Some cationic polymers can lose charge by hydrolysis at high pH (25). 

The most commonly used polymers are partially hydrolyzed polyacrylamides (32). The optimum degree of hydrolysis depends on the apphcation, injection water composition, and reservoir conditions (33,34). More salt-tolerant acrylamide copolymers may permit this technology in higher salinity injection water (35). Eield apphcations of cross-linked xanthan gum have also been reported (36). 

Excessive hydrolysis of polyacrylamide in situ can promote undesirable polymer precipitation in the reservoir. The rate of this hydrolysis decreases with increasing level of anionic comonomers such as AMPS (130). 

Anhydrotetracycline oxygenase from Streptomjces aureofaciens which cataly2es the conversion of anhydrotetracycline to dehydrotetracycline, has been isolated and characterized as a flavin-dependent oxygenase (83). It consists of two subunits of mol wt = 57, 500 based on SDS/polyacrylamide—gel electrophoresis. The cosynthetic factor 1 of Streptomjces aureofaciens involved in the reduction of 5a,lla-dehydrochlortetracycline to chlortetracycline, has been identified as 7,8-didemethyl-8-hydroxy-5-deazariboflavin. This work was aided by comparison of spectral data with that of an authentic sample obtained from the hydrolysis of coenzyme F-420 (84). 

Postpolymerization Reactions. Copolymers can also be formed by postpolymetization reactions on polymers. A well-known example is the partial hydrolysis of polyacrjiamide (PAM) to hydrolyzed polyacrylamide (HPAM). The product becomes a random copolymer of acrylamide and acryUc acid (44) (see Acrylamide polya rs). 

Hydrolysis of polyacrylamide under basic conditions is guide rapid and can be used to introduce acrylate groups into macromolecules. 

At hydrolysis of polyacrylamide in 10 M NaCl at I00°C, the degree of hydrolysis becomes —95%, but in this case a degradation of the macromolecules is observed. Various modes of hydrolysis of polyacrylamide under basic conditions have been reviewed [2,12]. 

The polymerization of acrylamide in aqueous solutions in the presence of alkaline agents leads to the ob-tainment of partially hydrolyzed polyacrylamide. The polymerization process under the action of free radicals R (formed on the initiator decomposition) in the presence of OH ion formed on the dissociation of an alkali addition (NaOH, KOH, LiOH), and catalyzing the hydrolysis can be described by a simplified scheme (with Me = Na, K, Li) ... 

Radical copolymerization is used in the manufacturing of random copolymers of acrylamide with vinyl monomers. Anionic copolymers are obtained by copolymerization of acrylamide with acrylic, methacrylic, maleic, fu-maric, styrenesulfonic, 2-acrylamide-2-methylpro-panesulfonic acids and its salts, etc., as well as by hydrolysis and sulfomethylation of polyacrylamide Cationic copolymers are obtained by copolymerization of acrylamide with jV-dialkylaminoalkyl acrylates and methacrylates, l,2-dimethyl-5-vinylpyridinum sulfate, etc. or by postreactions of polyacrylamide (the Mannich reaction and Hofmann degradation). Nonionic copolymers are obtained by copolymerization of acrylamide with acrylates, methacrylates, styrene derivatives, acrylonitrile, etc. Copolymerization methods are the same as the polymerization of acrylamide. 

In semi-cristalline polymers, rate-enhancement under stress has been frequently observed, e.g. in UV-photooxidation of Kapron, natural silk [80], polycaprolactam and polyethylene terephthalate [81]. Quantitative interpretation is, however, difficult in these systems although the overall rate is determined by the level of applied stress, other stress-dependent factors like the rate of oxygen diffusion or change in polymer morphology could occur concurrently and supersede the elementary molecular steps [82, 83], Similar experiments in the fluid state showed unequivocally that flow-induced stresses can accelerate several types of reactions, the best studied being the hydrolysis of DNA [84] and of polyacrylamide [85]. In these examples, hydrolysis involves breaking of the ester O —PO and the amide N —CO bonds. The tensile stress stretches the chain, and therefore, facilitates the... 

Synthetic polymers and natural polymers suitable for drilling muds are listed in Tables 1-7 and 1-8, respectively. Polyacrylamides are eventually hydrolyzed in the course of time and temperature. This leads to a lack of tolerance toward electrolyte contamination and to a rapid degradation inducing a loss of their properties. Modifications of polyacrylamide structures have been proposed to postpone their thermal stability to higher temperatures. Monomers such as AMPS or sulfonated styrene/maleic anhydride can be used to prevent acrylamide comonomer from hydrolysis [92]. 

Unfortunately, the number of systems in which it can be established whether Keller s model is realistic for a particular case is severely limited since the original polymer is usually not soluble in the same medium as the ultimate reaction product. In cases where the entire course of the reaction can be followed, as in the basic hydrolysis of polyacrylamide, investigators have analyzed their results by a computer search for the k, k, k values which fit best their kinetic data (9). This, or course, does not answer the question whether the model using these three rate constants provides a full description of a particular case. 

Figure 1 compares the conversion predicted for any reduced time I = k t with the use of Keller s theory and the above values of k /k and k2/k with experimental results obtained when polyacrylamide was exposed to 0.2N NaOH at 53 C. It may be seen that the reaction slows down at large x much more than predicted by Keller s model. In fact, this decrease of the reaction rate is even more pronounced than predicted by Keller s equations for the case where a single reacted nearest neighbor completely inhibits amide hydrolysis. We believe that this discrepancy is due to the repulsion of the catalyzing hydroxyl ions from amide residues by non-neighboring carboxylate groups. 

Figure 2. Imide formation and hydrolysis from polyacrylamide (2.2 mg/mL) in 0.22 N NaOH at 25 C as monitored by UV absorption at 235 nm.

Production of hydrogels by chemical conversion uses chemical reactions to convert one type of gel to another. This can involve the conversion of a nonhydrogel to a hydrogel or the conversion of one type of hydrogel to another. Examples of the former include the hydrolysis of polyacrylonitrile to polyacrylamide or of poly(vinyl acetate) to poly(vinyl alcohol) an example of the latter... 

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