Depolymerization Subject

A second degradation process is oxidation, often photo-induced especially by exposure to light not filtered for uv. The radicals resulting from this reaction promote depolymerization of the cellulose, as well as yellowing and fa ding of paper and media. Aging causes paper to become more crystalline and fragile, and this can be exacerbated particularly if the paper is subjected to poor conditions. 

A two-step methanolysis-hydrolysis process37 has been developed which involves reaction of PET with superheated methanol vapors at 240-260°C and atmospheric pressure to produce dimethyl terephthalate, monomethyl terephthalate, ethylene glycol, and oligomeric products in the first step. The methanolysis products are fractionally distilled and the remaining residue (oligomers) is subjected to hydrolysis after being fed into the hydrolysis reactor operating at a temperature of ca. 270°C. The TPA precipitates from the aqueous phase while impurities are left behind in the mother liquor. Methanolysis-hydrolysis leads to decreases in the time required for the depolymerization process compared to neutral hydrolysis for example, a neutral hydrolysis process that requires 45 min to produce the monomers is reduced... 

Fig. 5. Kinetics of brain microtubule depolymerization following rapid dilution. (A) Time course of the disassembly reaction with experimental data represented by the data points and the theoretical progress curve indicated by the solid line. (The inset to A shows that the process can be fitted to a simple decaying exponential for part of the depolymerization reaction.) (B) Microtubule length distribution for the sample subjected to rapid dilution in A. (Reproduced from Karr et al. (1980)./. Biol. Chm. 255, 8560-8566.)...

PBS (Figure 30) is an alternating copolymer of sulfur dioxide and 1-butene. It undergoes efficient main chain scission upon exposure to electron beam radiation to produce, as major scission products, sulfur dioxide and the olefin monomer. Exposure results first in scission of the main chain carbon-sulfur bond, followed by depolymerization of the radical (and cationic) fragments to an extent that is temperature dependent and results in evolution of the volatile monomers species. The mechanism of the radiochemical degradation of polyolefin sulfones has been the subject of detailed studies by O Donnell et. al. (.41). 

The solvolytic treatment and the recovery procedures employed yielded about 75% of the original Klason lignin present in the wood. This percentage could be further optimized but was not attempted in the present work. The recovered lignin was subjected to alkaline depolymerization. Yields presented throughout the paper are expressed as percentages of the recovered lignin. 

Gums are tasteless, odorless, colorless, and nontoxic. None, except the starches and starch derivatives, are broken down by human digestive enzymes. All are subject to microbiological attack. All can be depolymerized by acid- and enzyme-catalyzed hydrolysis of the glycosidic (acetal) linkages joining the monomeric (saccharide) units. 

Nitrocellulose with a decreased molecular weight may be obtained as the result of depolymerization (degradation) of the cellulose before nitration, e.g. by keeping it at a temperature of 150-170°C or by treating it with acids. The resultant hydrocellulose, which usually possesses a lower molecular weight than cellulose, is then subjected to nitration to produce a more soluble substance as compared with the nitration product of a non-depolymerized raw material. 

In more recent experiments, Edelmann [95] has followed the depolymerization of nitrocellulose in dilute (0.5%) solution. He reported that nitrocellulose of an average polymerization degree n = 1060, and containing considerably amounts of the n > 2500 fraction, was degraded after being subjected for 1 and 4 hr to the action of ultrasonic waves of 800 kc/sec to an average polymerization degree of n = 910 and 630 respectively. By fractionation, the presence of a small quantity of n = 1400 was established in the latter. 

Jhe distribution of hydrogen types in coals continues to be a subject of considerable interest in coal structure studies. Published data indicate that the fraction of aromatic hydrogens usually increases with increasing rank, but the absolute values depend on the specific analytical method used (7). Hydrogen type analysis of a single coal based on the application of NMR spectroscopy to the soluble fraction from depolymerization with phenol-BFa has been reported by us (3). The conversion of coal to soluble fragments in substantial yields under very mild conditions permits a reliable determination of the hydrogen types by NMR analysis, and these results can be extrapolated to the parent coal with considerable confidence. 

Since the equilibrium constants for the addition of monomer onto the sequence of length 1 or to longer sequences are so different, the following situation must be considered. The living sequences with two monomer units cannot split off a monomer unit, but higher sequences are subject to polymerization-depolymerization equilibria with an equilibrium constant which no longer depends on chain length. We consider the special case in which the equilibrium constant K2 and the constants... 

In Figure 6 Equation 37 combined with Equation 38 was used to evaluate the copolymerization behavior. It is now assumed that the sequence with two monomer units Mi cannot depolymerize, but that longer sequences are subject to the polymerization-depolymerization equilibrium. 

The second soluble starch-g-PAN (No. 3) was prepared by subjecting another starch graft copolymer to a mild acid hydrolysis to partially depolymerize the starch moiety. The ethanol-water solvent system apparently promotes a greater number of starch PAN crosslinks than water, as evidenced by the lower solubilities (45 vs. 71% and 42 vs. 65%) and the higher viscosities for water dispersions (2400 vs. 920 cp and 690 vs. 

Organic insulating materials are generally subject to temperature dependent deterioration during their operational lifetime. The relevant chemical processes are complicated and may be described (with a certain simplification) as slow oxidation which introduces acid groups into the polymeric insulation, the loss of plasticizer, oxygen cross-linking of polymer chains and internally catalysed depolymerization of plastic insulation. 

There has also been considerable additional work by many investigators to Investigate depolymerization and alkylation of coal. In a recently published paper by Larsen (6), the most Interesting results In this subject are assembled and discussed. The investigations to be described In our paper also started from the well-known fact that Lewis acids, such as aluminum chloride, can exert not only a condensing but also a cracking effect on aliphatic-aromatic molecules. We hoped, however, that It would be possible to prevent most of these side reactions by using mild conditions. 

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