Low molecular weight chemicals

The thermal degradation of mixtures of the common automotive plastics polypropylene, ABS, PVC, and polyurethane can produce low molecular weight chemicals (57). Composition of the blend affected reaction rates. Sequential thermolysis and gasification of commingled plastics found in other waste streams to produce a syngas containing primarily carbon monoxide and hydrogen has been reported (58). 

In order for a soHd to bum it must be volatilized, because combustion is almost exclusively a gas-phase phenomenon. In the case of a polymer, this means that decomposition must occur. The decomposition begins in the soHd phase and may continue in the Hquid (melt) and gas phases. Decomposition produces low molecular weight chemical compounds that eventually enter the gas phase. Heat from combustion causes further decomposition and volatilization and, therefore, further combustion. Thus the burning of a soHd is like a chain reaction. For a compound to function as a flame retardant it must intermpt this cycle in some way. There are several mechanistic descriptions by which flame retardants modify flammabiUty. Each flame retardant actually functions by a combination of mechanisms. For example, metal hydroxides such as Al(OH)2 decompose endothermically (thermal quenching) to give water (inert gas dilution). In addition, in cases where up to 60 wt % of Al(OH)2 may be used, such as in polyolefins, the physical dilution effect cannot be ignored. 

To improve dimensional stabUity, low molecular weight chemicals are used that penetrate the cell waUs and either bond to the ceU waU polymers or polymerize in the ceU waU. Improvements in dimensional stabUity are measured by antishrink efficiency (ASE) ... 

Sarlo, K. and Clark, E.D., A tier approach for evaluating the respiratory allergenicity of low molecular weight chemicals, Fund. Appl. Toxicol., 18, 107, 1992. 

Arts, J.H.E. et al., Airway morphology and function of rats following dermal sensitization and respiratory challenge with low molecular weight chemicals, Toxicol. Appl. Pharmacol., 152, 66, 1998. 

Sailstad, D.M., et al., A murine model for low molecular weight chemicals Differentiation of respiratory sensitizers (TMA) from contact sensitizers (DNFB), Toxicology, 194, 147, 2003. 

This reaction is truly tempting because it potentially satisfies the need in the search for a way to reclaim the chemical value of a polyurethane recycle foam project [12, 13]. When a polyurethane foam is hydrolyzed, it gives aromatic diamine and polyether polyol, both in very crude forms. The diamine can be purified by regular means, but the crude polyether polyol cannot be easily cleaned up due to its polymeric nature. If this Ganem reaction can work well, the polyether polyol stream can be converted to a low-molecular-weight chemical, which can then be purified by conventional process such as distillation. Indeed, when this reaction was tried on a polyether triol of 3000 molecular weight as a model, the diacetate of propylene glycol was isolated by distillation. Unfortunately, the yield was too low to be of practical interest. 

Arts, J.H.E. and C.E. Kuper. 2007. Animal models to test respiratory allergy of low molecular weight chemicals A guidance. Methods 41 61-71. 

Presently, clinically useful anticancer compounds are low molecular weight chemicals which possess a high pharamacokinetic volume of distribution, which suggests the ubiquitous presence of toxic compounds in the host. It is this total diffusion of drug throughout the body which results in the majority of toxic effects produced by chemotherapeutic regimens. 

Taylor, J.L., and S.E. Grossberg, Chemical induction of interferon caroxymethy-lacridanone and other low molecular weight chemicals. Tex Rep Biol Med, 1982. 41 158-62. 

Xenobiotics can affect allergic disease in one of two ways. They can themselves act as antigens and elicit hypersensitivity responses, or they can enhance the development or expression of allergic responses to commonly encountered allergens, such as dust mite. Chemicals that act as allergens include certain proteins that can by themselves induce an immune response and low molecular weight chemicals (known as haptens) that are too small to induce a specific immune response but may react with a protein to induce an immune response that is then hapten specific. Haptens have been associated with both allergic contact dermatitis (ACD), sometimes called contact hypersensitivity... 

The subsequent deconstruction of biopolymers into single, low-molecular-weight chemicals, allows the identification and definition of catalyst to become clearer. Chemical catalysis has been used to improve many of these... 

Because low-molecular-weight chemicals are haptens and must react with a host protein in order to be allergenic, efforts have also been made to identify chemicals with potential for allergenicity based on the probability that a given chemical structure will react with protein. Two classes of compounds, diisocyanates and acid anhydrides, fit this description and some, but not all, chemicals in these two groups have been identified as respiratory allergens following occupational exposure of humans and/or experimental exposure of laboratory animals. 

Goheen DW (1971) Low molecular weight chemicals In Sarkanen KV, Ludwig CH (eds) Lignins Occurrence, formation, structure and reactions Wiley-Interscience, New York, 818-821... 

Polymers do not normally biodegrade until they are broken down into fairly low molecular weight chemical species that can be assimilated by microorganisms. Aliphatic polyesters degrade in the presence of water by sequential hydrolytic cleavage of the backbone ester bonds leading to production of monomeric hydroxyl carboxylic acids which in turn can be metabolized by bacteria (5). 

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