Naturally Derived Cationic Polymers

Natural cationic polymers are generally non-toxic, derived from renewable resources, biocompatible, biodegradable and possess low immunogenicity. Most natural cationic polymers contain reactive sites, which can be easily modified to improve physicochemical properties. 

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In 1956 Brown, in a series of patents(68-75), disclosed that clays could be treated with di-, tri-, or tetra-substituted ammonia derivatives. Later, McLaughlin, et al.(76,77), introduced cationic polymers as permanent clay protective chemicals. A series of published results describing laboratory and field applications soon became available(78-81). Structural details of the cationic polymers appeared in patents(82-85). In general the polymers are polyamine derivatives, mostly quaternary in nature. Theng(86,87) has discussed how the multiple cationic centers in these polymers can interact and permanently protect clays. Callaway(88) et al. has noted that cationic polymers may interfere with the performance of crosslinked fracturing fluids. 

Nagasaki T, Hojo M, Uno A et al (2004) Long-term expression with a cationic polymer derived from a natural polysaccharide schizophyllan. Bioconjug Chem 15 249-259... 

Natural cationic polymers are derived from renewable sources and possess inherent positive charges. They are biodegradable and often possess low immunogenicity and low toxicity. Numerous natural cationic polymers have functional groups like carboxylic acid groups that can be further modified to carry therapeutic molecules. 

Cationic polymers are defined as polyelectrolytes cariying positive charges, and they are either derived from natural sources such as chitosan, or chemically synthesized where the charges have been incorporated on their backbone and/or side chains. They may also exist as block copolymers, where one of the blocks is decorated with positive charges. When these block copolymers consist of a hydrophobic block, they readily undergo self-assembly in aqueous solutions and form micellar structures with a positively charged surface. Similarly, if the block copolymer consists of two hydrophobic blocks, one at each end, the system may self-assemble into network structures called hydrogels, which are water-rich 3D interconnected networks. 

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. 

Chitosan, a copolymer of glucosamine and A -acetylglucosamine units linked by one to four glucosidic bonds, is commerdally obtained from chitin, which is one of the most abundant natural amino polysaccharide. Chitosan could be converted by using proper reagents into a number of 0-alkyl and 0-acyl derivatives. Chitosan also behaves as a moderately basic cationic polyelectrolyte, which readily forms salts with acids. In addition, the presence of the primary amino group in chitosan offers further possibilities for modifications such as Af-acylation, Af-alkylation, and Af-alkyUdenation. Therefore, numerous varieties of chitosan derivatives can be synthesized from this nature s abundant polymer. 

A detailed classification of the chemical compounds usually employed was given by (Dubief et al., 2005). The most important of these are organic acids (carboxylic acids and aromatic sulphonic acids), fatty compounds and their derivatives (fatty acids, fatty alcohols, natural triglycerides, natural waxes, fatty esters, oxyethylenated and oxypropy-lenated waxes, partially sulphated fatty alcohols, lanolin and its derivatives, ceramides), vitamins (A, B and E) (see Section 8.6), protein derivatives (extracts or hydrolysates of keratin, collagen and vegetable proteins), silicones (dimethicone and others), cationic surfactants, cationic polymers, amphoteric and betainic polymers. 

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