Graft Copolymers of Polysaccharides

Techniques proved useful in graft-polymerization chemistry include the use of electron-spin resonance spectroscopy for the determination of the initiating radical in gamma-irradiation-induced copolymerization, and of thermogravimetric and infrared analysis for product characteriza-tion. The particular solvent employed for the polymerization may be important in its dispersion of the polysaccharide.  

As already intimated, graft copolymers may be prepared without involvement of free-radical initiation. Graft copolymers of nylon-6,6 on cellulose acetate, such as 30, may be obtained by successive, alternate. 

---

Certain crosslinked graft copolymers of polysaccharides are found to exhibit salt resistant swelling in different concentrations of salts. Swelling decreases with increase in salt concentration and is found to be cationic charge dependent. Depending upon the cations, swelling is found to follow the order Na > NH/> Mg"2> Ca" > Ba"2>Fe"3... 

Superabsorbent polymers were developed in 1974. Initially, they were mostly graft copolymers of polysaccharides such as starch and cellulose. However, the majority of currently used superabsorbent pol3miers are lightly crosslinked acrylic acid polymers. 

Rogovin, Z. A., and U. Zhun-Zhui Structure and properties of cellulose and its esters. LXXXV. Synthesis of new derivatives of cellulose and other polysaccharides. IV. Synthesis of graft copolymers of carboxymethyl cellulose and caprolactam. Vysokomolekulyarnye Soedineniya 1, 1630 (1959). 

The first attempts to produce a graft copolymer of poly(amino acids) onto the natural polymers, such as cellulose, starch, and their derivatives, were carried out by Zilka and Avny in 1965. Sodium methoxide was known to be an initiator of NCA polymerization. Therefore, they proposed to use alkoxide derivatives of polysaccharides as macroinitiators for the graft copolymerization of NCA s of a-amino acids. All known methods for production of alkoxide derivatives of natural polymers, such as the reaction of polyhydroxy polymers with sodium metal in liquid ammonia, or exchange reactions between lower alkoxides and polyhydroxy polymers, - were unsatisfactory for the subsequent graft copolymerization of NCAs, because any residual base would lead to homopolymerization. In addition, alkoxide derivatives of cellulose acetate and nitrocellulose could not be obtained by these conventional methods due to chemical degradation. Zilka et al., finally found that the reaction of alkali metal naphthalenes [20] with polyhydroxy polymers in either... 

Metal ions of transition and other elements of variable valency, e.g. Ce, Co, Fe, V, Mn, etc., are known to oxidize polysaccharides rather selectively, producing macroradicals as intermediates which are capable of adding vinyl monomers and form graft copolymers. These initiators are redox systems which differ from those previously described by not producing free radicals of low molecular weight. Only macroradicals on the substrate are formed in the redox reaction. Some homopolymer may still be formed in the process, e.g. due to oxidation of monomer or other side reactions. ... 

Rogovin, Z. A., T ung Sun, A. D. Virnik, and N. M. Khvostenko CIV. Synthesis of new cellulose and other polysaccharide derivatives. 19. Synthesis of cellulose and carbon-chain graft copolymer withour simultaneous formation of homopolymers. Vysokomolekul. Soedin. 4, 571 (1962). 

The hydroxo-initiator R OH may be a polysaccharide or may be modified by a certain degree of substitution by hydroxyl groups (Scheme lb). Following this scheme, many graft copolymers have been synthesized and characterized ... 

The present review is mainly concerned with the preparation and functionalization of micro compositional materials with cellulosic polysaccharides as the principal component, including four major categories graft copolymers, miscible or compatible polymer blends and networks, polysaccharide/inorganic nanohybrids, and mesomorphic ordered systems. Ultrathin layers of cellulosic... 

Coni I, Ferrero MC, Jimenez-Castellanos RM, Gurruchaga M. Synthesis of hydroxypropyl methacrylate/polysaccharide graft copolymers as matrices for controlled release tablets. Drug Dev Ind Pharm 2002 28(9) 1101-1115. 

Modification of natural polysaccharides through various graft copolymerization techniques is discussed in this chapter. Characterization of graft copolymers using different techniques like FT-IR, C-NMR, SEM, XRD, TGA, DTA and DTG along with their physical, chemical and mechanical properties are discussed as a function of different reaction conditions of their synthesis. Applications for modified polysaccharides include drug delivery devices, controlled release of fungicides, selective water absorption from oil-water emulsions and purification of water. 

Polysaccharides and their graft copolymers find extensive applications in diversified fields. Grafting is known to improve the characteristic properties of backbones. Such properties include water repellancy, thermal stability, flame resistance, dyeability and resistance towards acid-base attack and abrasion. Modification of natural cellulosics through graft copolymerization of methyl methacrylate onto Cannabis indica, rayon, jute, cotton, etc., has resulted in the improvement of their morphology and other physicochemical properties [9-23]. 

---