Natural cationic polymers modifications

This group of cationic polymers includes all those natural polymers that require further modification in order to acquire a cationic character. Therefore, they differ from the biopolymers with inherent cationic properties and those cationic polymers that are produced artificially using polymerization methods. Such polymers often retain their biodegradability, while the introduction of positive charges leads to increased cytotoxicity and therefore decreased biocompatibility. 

Cationic nanocarriers are prepared from natural or synthetic polymers. The most widely used cationic polymers have been reported as PEI, PLL, poly-methacrylates (PMA), chitosan and cationic modifications of other polymers such as cyclodextrin, gelatin and imidazole-containing polymers. ... 

This chapter describes the main properties and methods for the characterization of polyelectrolytes derived from the biomass. The most important sources are plants, with cellulose and starch, which turn to polyelectrolytes after chemical modifications. CarboxymethylceUulose is the main cellulose derivative used in many industrial applications as good thickener and hydrophilic polymer for aqueous media. Cationic starches are mainly used in the paper industry for fiUa- retention or paper wet-strength. Natural polyelectrol5des are produced by algae with anionic alginates and carrageenans as the major representatives, which are used in food applications and for biomedical devices. In this respect, alginates are often associated in an electrostatic complex with a pseudo-natural polyelectrolyte (chitosan), a cationic polymer extracted from crustaceous shells. 

Sulfonation is very useful chemical modification of polymer, as it induces high polarity in the polymer changing its chemical as well as physical properties. Sulfonated polymers are also important precursors for ionomer formation [75]. There are reports of sulfonation of ethylene-propylene diene terpolymer (EPDM) [76, 77], polyarylene-ether-sulfone [78], polyaromatic ether ketone [79], polyether ether ketone (PEEK) [80], styrene-ethylene-butylene-styrene block copolymer, (SEBS) [81]. Poly [bis(3-methyl phenoxy) phosphozene] [82], Sulfonated polymers show a distinct peak at 1176 cm"1 due to stretching vibration of 0=S=0 in the -S03H group. Another peak appears at 881 cm 1 due to stretching vibration of S-OH bond. However, the position of different vibrational bands due to sulfonation depends on the nature of the cations as well as types of solvents [75, 76]. 

Natural, unmodified montmorillonite-Na (MMT-Na) has cation exchange capacity, typically 80-90 mequiv/100 g. Although some polymers, such as polyethylene oxide or polyvinylpyrrolidone, are of sufficient polarity to be able to directly exfoliate unmodified MMT-Na, organic modification of the layered clay is usually required to render the hydrophilic surface of the clay more hydrophobic and thus more compatible with most polymers, thereby improving the wettability and dispersibility of the clay in the polymer matrix. 

The understanding of the mechanisms involved in the polymer synthesis with natural precursors is definitively a key factor for their appropriate exploitation. Taking into account this need, Ronda et al. explained recently different pathways to modify natural resources. These authors proposed three routes to modify vegetable oils to transform them into polymers (1) direct polymerization (cationic, radical, or thermal polymerization) (2) functionalization and polymerization and (3) monomer synthesized, chemical modification and polymerization [32]. 

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