Degradation monomers

Under aerobic conditions, the conversion of monomers to fully mineralized products is rather simple because 02-respiring bacteria can degrade monomers completely to CO2. However, under anaerobic conditions this process requires... 

Besides coalescence, there is another mechanism by which emulsions degrade (or coarsen) into fewer, larger-sized droplets diffusional degradation. Monomer from smaller droplets diffuses to larger ones as the result of the process of interfacial free energy minimisation. This phenomenon is called Ostwald ripening (224). 

Depending on the point of attack in polymer chain by these enzymes, we distinguish between an exo- and an endo-mechanism [894]. In the case of exo-mechanism (primary degradation), monomers or short-chain oligomers are cleaved successively. 

Fokou PA, Meier MAR. 2009. Use of a Renewable and Degradable Monomer to Study the Temperature-Dependent Olefin Isomerization during ADMET Polymerizations. J Am Chem Soc 131 1664-1665. 

A study of structural units, where a monomer is examined by physicochemical methods to determine its thermostability, its chemical and physical properties, and its sites of degradation. 

Various monomers have been studied for their physicochemical properties and electronic structures (320, 321). For example, a series of monomers can be synthesized following Mulvaney et al. (310) and then theoretical diagrams and degradation sites are studied (Table 111-61) (134). 

The presence of stable free radicals in the final polycondensate is supported by the observation that traces of (11) have a strong inhibiting effect on the thermal polymerization of a number of vinyl monomers. Radical polymerization was inhibited to a larger extent by a furfural resin than by typical polymerization inhibitors (34). Thermal degradative methods have been used to study the stmcture of furfural resinifted to an insoluble and infusible state, leading to proposed stmctural features (35). 

Poly(acrylic acid) and Poly(methacrylic acid). Poly(acryHc acid) (8) (PAA) may be prepared by polymerization of the monomer with conventional free-radical initiators using the monomer either undiluted (36) (with cross-linker for superadsorber appHcations) or in aqueous solution. Photochemical polymerization (sensitized by benzoin) of methyl acrylate in ethanol solution at —78° C provides a syndiotactic form (37) that can be hydrolyzed to syndiotactic PAA. From academic studies, alkaline hydrolysis of the methyl ester requires a lower time than acid hydrolysis of the polymeric ester, and can lead to oxidative degradation of the polymer (38). Po1y(meth acrylic acid) (PMAA) (9) is prepared only by the direct polymerization of the acid monomer it is not readily obtained by the hydrolysis of methyl methacrylate. 

Chemical Properties. Vacuum thermal degradation of PTFE results in monomer formation. The degradation is a first-order reaction (82). Mass spectroscopic analysis shows that degradation begins at ca 440°C, peaks at 540°C, and continues until 590°C (83). 

Because high temperatures are required to decompose diaLkyl peroxides at useful rates, P-scission of the resulting alkoxy radicals is more rapid and more extensive than for most other peroxide types. When methyl radicals are produced from alkoxy radicals, the diaLkyl peroxide precursors are very good initiators for cross-linking, grafting, and degradation reactions. When higher alkyl radicals such as ethyl radicals are produced, the diaLkyl peroxides are useful in vinyl monomer polymerizations. 

Thermal, Thermooxidative, and Photooxidative Degradation. Polymers of a-olefins have at least one tertiary C-H bond in each monomer unit of polymer chains. As a result, these polymers are susceptible to both thermal and thermooxidative degradation. Reactivity in degradation reactions is especially significant in the case of polyolefins with branched alkyl side groups. For example, thermal decomposition of... 

Poly(lactide-coglycolide). Mixtures of lactide and glycolide monomers have been copolymerised in an effort to extend the range of polymer properties and rates of in vivo absorption. Poly(lactide- (9-glycolide) polymers undergo a simple hydrolysis degradation mechanism, which is sensitive to both pH and the presence of ensymes (32). 

The metabohc rate of poly(ester—amide) where x = Q has been studied in rats using carbon-14 labeled polymer. This study indicates that polymer degradation occurs as a result of hydrolysis of the ester linkages whereas the amide linkages remain relatively stable in vivo. Most of the radioactivity is excreted by urine in the form of unchanged amidediol monomer, the polymer hydrolysis product (51). 

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