Acrylamides, reactions with starch

Reaction of starch dialdehyde with urea gave a condensation product.442,2633 Carboxyamides,2624 including acrylamide,524,585 were also allowed to react with starch dialdehyde. Condensation can occur between starch dialdehyde and macromolecules containing amido groups, for instance, epichlorohydrin-crosslinked polyamide resin,598 ammonia-diethylamine-epichlorohydrin copolymer,588 dicyanamide-formaldehyde resins,565,566 quaternary alkylam-monium compounds,596,610,611 amino acids,2634,2635 protein,626,2636-2639 and aminoalkylated starch.2515 The reactions are favored by low pH. The guanidino moieties of proteins entered the condensation the most readily. 

A wide variety of reactions applicable to starch or acrylamide gels have been listed or referenced in a previous section, and these will not be discussed in detail here. The problems associated with using these reactions with large numbers of samples are the following ... 

Many of these reactions are reversible, and for the stronger nucleophiles they usually proceed the fastest. Typical examples are the addition of ammonia, amines, phosphines, and bisulfite. Alkaline conditions permit the addition of mercaptans, sulfides, ketones, nitroalkanes, and alcohols to acrylamide. Good examples of alcohol reactions are those involving polymeric alcohols such as poly(vinyl alcohol), cellulose, and starch. The alkaline conditions employed with these reactions result in partial hydrolysis of the amide, yielding mixed carbamojdethyl and carboxyethyl products. 

A similar procedure was used to prepare starch-j -polyacrylamlde, and 15 g of acrylamide (97%, Polysciences) was used In the polymerization. After irradiation, the reaction mass was extracted several times with water to remove ungrafted polyacrylamide, and the graft copolymer was washed with ethanol and vacuum dried at 60°C. Weight percent polyacrylamide in the graft copolymer (% add-on) was 35%, based on the weight gain of starch. 

Lightly cross-linked polyacrylamide is used to make superabsorbents of water. Astarch-g-polyacryla-mide/clay superabsorbent composite has been synthesized [27] by graft copolymerization reaction of acrylamide, potato starch, and kaolinite micropowder (< 1 pm) followed by hydrolysis with sodium hydroxide. Such a superabsorbent of compositin 20% kaolinite, 20% potato starch, 60% acrylamide, 2% initiator (ceric amonium nitrate), and 0.04% cross-linker (N,N-methylenebisacrylamide) is found to absorb 2250 g H20/g at room temperature at swelling equilibrium. 

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