Starch graft polymerization

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. 

A large number of SAHs described in the literature combine synthetic and natural macromolecules in the network structure. The natural components are usually starch, cellulose, and their derivatives. It is assumed that introduction of rigid chains can improve mechanical properties (strength, elasticity) of SAH in the swollen state. Radical graft polymerization is one of the ways to obtain such SAH. 

A unique method of formulating delivery systems based on starch/ PLA systems was studied (138). In that approach, the goal was to provide a better matrix for delivery of high molecular weight hydrophilic molecules. A hydrophilic material, starch, was combined through graft polymerization to PLA. The carbolactic polymers were then used to entrap bovine serum albumin in microspheres. 

Schroder, U., Lager, C., and Norrlow, O., Carbo-lactic microspheres Graft polymerization of PLA to starch microspheres, Proc. Int. Control. Rel. Bioact. Mater.. 14, 238,... 

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... 

Gelatinizing starch under milder conditions (30 min at rather than 60 min at 95 C) has little effect on water absorbency. 4) A lower nitric acid concentration in the graft polymerization recipe (O.IH rather than l]f HNQs used to dissolve ceric ammonium nitrate) does not alter absorbency properties. 

AASO3H does not graft polymerize onto starch as readily as acrylonitrile, and Table VI shows that both % add-on and % conversion increase with decreasing percentages of AASO3H in the monomer mixture. Conversion of monomers to polymer is over 90% with monomer mixtures oontcdning about 1 mole % AASO3H or less. 

Superabsorbent polymers are now commonly made from the polymerization of acrylic acid blended with sodium hydroxide in the presence of an initiator to form a polyacrylic acid, sodium salt (sometimes referred to as cross-linked sodium polyacrylate). Some of the polymers include polyacrylamide copolymer, ethylene maleic anhydride copolymer, cross-linked carboxy-methyl-cellulose, polyvinyl alcohol copolymers, cross-linked polyethylene oxide, and starch grafted copolymer of polyacrylonitrile to name a few. The latter is one of the oldest SAP forms created. 

Acrylonitrile graft polymerizes readily with either granular or pasted starch to yield starch-g-polyacrylonitrile (PAN), and reactions are generally carried out in water with ceric ammonium nitrate as the initiating system CL). Reaction of starch-g-PAN with alkali at elevated temperatures converts the nitrile substituents of PAN to a mixture of carboxamide... 

Since the partial insolubility of the starch-ceric ammonium nitrate reaction product complicates the interpretation of solubility data, we ran a second series of graft polymerizations using cobalt-60 as an initiator in an attempt to remove this variable (Table II). If combination of PAN macroradicals is occuring during graft polymerization, it should occur during cobalt-60 initiated polymerizations as well as in those initiated by ceric ammonium nitrate. In the first four reactions of Table II, starch was irradiated as a water slurry under graft polymerization conditions, but in the absence of acrylonitrile, to determine the influence of different doses of irradiation on starch solubility. 

Graft Polymerization. Ceric Initiation. A stirred slurry of 10 g of starch in 200 ml of water was sparged with a slow stream of nitrogen for 1 hr at room temperature 15 g of acrylonitrile was then added, followed after 5 min by a solution of 0.338 g of ceric ammonium nitrate in 3 ml of IN nitric acid. In the reaction run with 1-hexanethiol, ceric ammonium nitrate solution was added first, followed after 5 min by a solution of 1.0 g of mercaptan in 15 g of acrylonitrile. The resulting mixture was allowed to stir for 2 hr at 25-27°C (temperature maintained with ice-water) and then was diluted with 200 ml of ethanol. The pH was adjusted to 6-7 with sodium hydroxide solution, and the polymer was isolated by filtration, washed with water and ethanol, and vacuum dried at 60°C. Ungrafted PAN was removed by repeated extraction of the polymer with dimethylformamide (DMF) at room temperature. 

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. 

Anionic graft-polymerization of paraformaldehyde onto starch and dextrin has been effected in methyl sulfoxide solution, polymerization being initiated by the carbohydrate potassium alcoholate formed from the reaction of the carbohydrate with naphthalene potassium, a metallation procedure not previously described for carbohydrates.220... 

Cerium(IV) salts are used to initiate graft polymerization of starch. In order to graft-copolymerize starch, a complex of Ce(IV) was prepared by blending cornstarch with Ce(NH4)2(N03)6-HN03 reagent in the ratio of 75 glucose residues per Ce(IV) component.648 649... 

Cerium(lV) compounds with suitable reducing agents, readily initiate the redox polymerization of, for example, vinyl monomers [22]. This property is used to initiate graft polymerization of vinyl monomers onto cellulose, wool, starch, cotton, etc. in order to, e.g. improve mechanical strength, resist moisture penetration and reduce micro-organism attack. 

Avery creative application of the system HRP/H202/Acac for graft polymerization of acryl amide on starch was reported recently by Biswas and coworkers [39], Thus, a biocatalytic alternative route to the established cerium( IV)-based routes to poly(acrylate)-grafted starch with applications as superabsorbers [44] or performance additives in paper making [45] or textile sizing [46] was reported. Under non-optimized conditions grafting efficiencies of up to 65% are reported. The... 

General [13,16, 20, 22] Mediator-free [28] Various [i-di kelone mediators [25] Immobilized enzyme [38] Water in SCC02 polymerizations [19] Surfactants [21] Poly acrylamide starch graft polymers[39[. 

Starch thiols can have the SH group directly on the pyranose ring or in a side chain. There are several methods of synthesizing starch thiols of the first type. One of them is based on the pyrolysis of starch xanthates (32), but the reaction proceeds in two parallel routes one producing thionates (35) and the other producing thiols (37).2675,2677 Reduction of starch xanthates with NaBPU in alkali is another approach to thiols. Thiols prepared in this manner were subjected to graft polymerization with vinyl polymers. Nucleophilic substitution of the chlorine... 

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