Starch acrylonitrile graft copolymers

Graft copolymers of starch with acrylonitrile and 2-acrylamido-2-methylpropanesulfonic acid, after saponification, were claimed to be good sorbents.3092 A composite of saponified acrylonitrile-starch-copolymer with vinyl formal polymers showed very good salt-rejection characteristics and served as membranes.3093 The same material prepared with poly(vinyl chloride) has been used in gaskets for concrete pipes.3057 Saponified acrylonitrile-starch graft copolymers blended with C12-C16 alcohols provided excellent water-retention characteristics.3094... 

Although they lack commercial importance, many other poly(vinyl acetal)s have been synthesized. These include acetals made from vinyl acetate copolymerized with ethylene (43—46), propjiene (47), isobutjiene (47), acrylonitrile (48), acrolein (49), acrylates (50,47), aHyl ether (51), divinyl ether (52), maleates (53,54), vinyl chloride (55), diaHyl phthalate (56), and starch (graft copolymer) (47). 

Ihe reaction of starch with oeric salts leads to formation of macroradicals vhich can initiate the polymerization of a wide variety of monomers to yield starch graft copolymers. Graft oopolymers of acrylonitrile and starch are easily prepared Icy technique (Equation 1), and se xxiif ication of starch-g-ipolyacry-lonitrile (Equation 2) yields absorbent polymers that can take jp... 

Acrylonitrile has been grafted onto many polymeric systems. In particular, acrylonitrile grafting has been used to impart hydrophilic behavior to starch (143—145) and polymer fibers (146). Exceptional water absorption capabiUty results from the grafting of acrylonitrile to starch, and the use of 2-acrylamido-2-methylpropanesulfonic acid [15214-89-8] along with acrylonitrile for grafting results in copolymers that can absorb over 5000 times their weight of deionized water (147). 

Etherification and esterification of hydroxyl groups produce derivatives, some of which are produced commercially. Derivatives may also be obtained by graft polymerization wherein free radicals, initiated on the starch backbone by ceric ion or irradiation, react with monomers such as vinyl or acrylyl derivatives. A number of such copolymers have been prepared and evaluated in extmsion processing (49). A starch—acrylonitrile graft copolymer has been patented (50) which rapidly absorbs many hundred times its weight in water and has potential appHcations in disposable diapers and medical suppHes. 

The ozonization method has been extended to the most varied polymer/monomer systems, such as polybutadiene-03 with acrylamide, methyl methacrylate or styrene, cellulose-03 with styrene or acrylonitrile (127), starch-03 with styrene (126). In this last case the formation of some homopolystyrene as side-product has been mentionned by the authors. The starch-styrene graft copolymers are claimed to be good emulsifiers for water-oil suspensions. 

Starch-g-PAN with 40% add-on (M of PAN 35,000) was prepared by ceric initiation as described above, with the exception that only 10 g of acrylonitrile was used. Five grams of this graft copolymer was dispersed in 200 ml of water, and concentrated hydrochloric acid was added to give a pH of 2.0. The mixture was heated under reflux for 15 min, and the polymer was isolated by filtration. The polymer was suspended in water, the pH was adjusted to 6.5 with sodium hydroxide solution, and the polymer was again separated by filtration. The polymer was washed with water and with ethanol and dried under vacuum at 60°C. The yield was 4.357 g of starch-g-PAN, which was 99% soluble in DMSO at 75°C. The % add-on was 46%, as calculated from the original 40% add-on and the loss of 0.643 g of starch by acid hydrolysis. 

Film Formation. Starch-g-PAN samples used for this study were prepared as described above, except that the small amounts of PAN homopolymer were not removed by DMF extraction. For the graft polymerization with gelatinized starch, the starch-water slurry was heated for 30 min at 85°C before reaction at room temperature with acrylonitrile and ceric ammonium nitrate. Saponifications in these experiments were carried out by stirring. 55 g of graft copolymer with 450 ml of 0.711 sodium hydroxide solution in a sigma mixer for 2 hr at 90-100°C. 

In these experiments the number of initiating sites is a set value and cannot be increased. The rate of mutual destruction, the rate of diffusion of the monomer into the starch polymer, and the propagation rate are the controlling factors in the degree of grafting. The diffusion rate would be the critical factor governing the number of starch to acrylonitrile bonds achieved. These factors determine whether a block or a graft copolymer will be obtained. 

Starch polyurethane foams could be converted into sorbents for water when starch-acrylonitrile or starch-methacrylonitrile graft copolymers were crosslinked with diisocyanates.2655 2656 Such polyurethanes have been proposed as occlusive wound dressings,2657 as well as sizes for cotton yams.2658 Starch polyurethanes for reinforced paper were produced in reaction of iV-chlorocarbamoylethyl starch with cresol or thiolignin.2659 The addition of mineral salts to polyurethanes prepared from starch and urea improved their performance as adhesives.570... 

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