Polycarboxylates, biodegradable

Oxidation of polysaccharides is a far more attractive route to polycarboxylates, potentially cleaner and less cosdy than esterification. Selectivity at the 2,3-secondary hydroxyls and the 6-primary is possible. Total biodegradation with acceptable property balance has not yet been achieved. For the most part, oxidations have been with hypochlorite—periodate under alkaline conditions. In the 1990s, catalytic oxidation has appeared as a possibiUty, and chemical oxidations have also been developed that are specific for the 6-hydroxyl oxidation. 

Water-soluble biodegradable polycarboxylates with an acetal or ketal weak link were inventions of Monsanto scientists in the course of their search for biodegradable deteigent polymers. However, the polymers were prevented by economics from reaching commercial status. The polymers are based on the anionic or cationic polymerization of glyoxylic esters at low temperature (molecular weight is inversely proportional to the polymerization temperature) and subsequent hydrolysis to the salt form of the polyacid, which is a hemiacetal (R = H) or ketal (R = CH3) if methylglyoxylic acid is used, and stable under basic conditions. 

Interest in detergent products derived from renewable resources and with better biodegradability has driven evaluation of oxidized sugars and starches as builders or co-builders in detergents.113 Builders and co-builders complex calcium and magnesium ions in hard water to prevent sealing or deposits due to precipitation of insoluble carbonate salts. In current powder detergents, the builders are usually zeolites used in combination with polycarboxylate polymers derived from synthetic acrylic-maleic acid copolymers.114... 

At the same time, the industry embarked on an intensive search for phosphate substitutes. Of a very large number of experimental organic builders, a few substances reached commercialization or near-commercialization, including trisodium nitrilotriaceate (NTA), trisodium carboxymethoxysuccinate (CMOS) (181) and trisodium carboxymethyltartronate (182). As discussed above, sodium citrate ether carboxylates have achieved widespread use as phosphate substitutes. Polymeric builders (polyelectrolytes) proved to be effective calcium sequestrants, but failed to satisfy the criterion of acceptable biodegradability. Interestingly, some monomeric polycarboxylates proved to be even more powerful calcium sequestrants than sodium tripolyphosphate but were not sufficiently biodegradable (183). 

A consistently emerging problem apparently inherent to the use of interferon inducers, even in animal species that do not respond by circulating interferon production, is toxicity. Polycarboxylates owe their toxicity to deposition of the compound in the reticulo-endothelial cells and poor biodegradability. 

The selective oxidation of sucrose is likely to lead to mono-, di-, and polycarboxylic acids (Scheme 21.4). These derivatives have a potential application in detergents, to replace phosphates, thanks to their properties of nontoxicity, biocompatibility, and biodegradability. 

Studies on the aerobic oxidation of sucrose with noble metal catalysts revealed low selectivity and, surprisingly, the involvement of all of the three primary alcoholic functions at Cg, Ci, and Cg while preserving the disaccharide backbone (Figure 21.12). This is not a problem, because mono- and polycarboxylated sugars are both economically attractive as biodegradable calcium sequestering agents ... 

Polycarboxylates Carboxylate derivatives of poly(vinyl alcohol) are biodegradable and functional in detergents as co-builders, although too costly to be practical replacements for polyacrylic acid at this time. Matsumura et al. polymerized vinyloxyacetic acid [69, 70] and Lever has patented polymers based on vinyl carbamates obtained from the reaction of vinyl chloroformates and amino acids such as aspartic and glutamic acids [71]. Both hydrolyze (Scheme 4), to polyvinyl alcohol, which is biodegradable. 

The use of polycarboxylic acids in detergents, particularly poly(acrylic acids), and the search for biodegradable alternatives is well established and has been well reviewed in many articles mentioned earlier [12, 18-21] and by Hunter... 

Mitsubishi [101] claimed a unique biodegradable polycarboxylate (Scheme 8) containing ethylene, carbon monoxide, and maleic anhydride monomers. The initial degradation step is photoactivation to yield low-molecular-weight fragments as indicated in Table 12.2. Unfortunately, no biodegradation data were reported on these fragments. 

Polycarboxylates are generally used as cobuilders in zeolite-based systems. In most cases, their relatively high cost generally precludes their use as a primary builder. Limited biodegradability and high cost are the main reasons that polymers are not used as primary builders. 

Polycarboxylates, also known as polyacrylates, are polymers having a carbon-carbon backbone with attached carboxyl groups. In household consumer products, the anionic polycarboxylates most commonly used are copolymers of acrylic acid and maleic anhydride, copolymers of acrylic acid and methacrylic acid, or polymers of acrylic acid. Polycarboxylates find use as detergent builders and as partial replacements for polyphosphates. However, they are very expensive for use in high concentrations as builders in detergent formulations and also have poor biodegradability [16]. 

Schwamborn, M. (1998) Chemical Synthesis of polyaspartates a biodegradable alternative to currently used polycarboxylate homo- and copolymers. Polym. Degrad. Stab., 59 (1), 39-45. 

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