Depolymerization residue

NMR Spectra. 13C NMR spectra of the polymers and depolymerization residues were obtained on two instruments an IBM Instruments WP-200 (operating at a 13C resonance frequency of 50.33 MHz, equipped with high-power amplifiers and a Doty Scientific probe for MAS at 5.0 kHz) and a homebuilt solid-state NMR spectrometer operating at 31.94 MHz and a spinning speed of 3.0 kHz. 

Figure 6. 31.94 MHz 13C NMR spectra for suberized cell walls from potatoes, before (bottom) and after (top) depolymerization treatment. The experimental parameters were as in Figure 4. Chemical-shift assignments and relative numbers of carbons for the untreated material are found in Table IV. Delayed-decoupling experiments left some (CH2) signal intensity in the spectrum of intact suberin, but the analogous signals were drastically attenuated in the NMR spectrum of the depolymerization residue.

However, Pacansky and his coworkers77 studied the degradation of poly(2-methyl-l-pentene sulfone) by electron beams and from infrared studies of the products suggest another mechanism. They claim that S02 was exclusively produced at low doses with no concomitant formation of the olefin. The residual polymer was considered to be essentially pure poly(2-methyl-l-pentene) and this polyolefin underwent depolymerization after further irradiation. However, the high yield of S02 requires the assumption of a chain reaction and it is difficult to think of a chain reaction which will form S02 and no olefin. 

In 1976, Meluch and Campbell at General Motors obtained a patent10 for a steam hydrolysis depolymerization of PUR. High-pressure steam hydrolyzes flexible PUR foams rapidly at temperatures of 232-316°C to form diamines and polyols. The diamines are distilled and extracted from the steam and the polyols are obtained from the hydrolysis residue. In 1977, Bayer AG obtained a patent for a continuous PUR hydrolysis process using a specially designed extruder.11... 

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... 

The agitation studies for PET depolymerization were performed in the Atlas Launder-ometer. The Launder-ometer is a device for rotating closed containers in a thermostatically controlled water bath. The procedure used in these experiments was adapted from an American Association of Textile Chemists and Colorists (AATCC) standard test method. The 5% sodium hydroxide solution (250 mL) was preheated to 80°C in a 1-pint stainless steel jar. The catalysts were added in the following amounts in separate experiments TOMAC (0.04 g, 0.0001 mol) TOMAB (0.045 g, 0.0001 mol) and HTMAB (0.045 g, 0.0001 mol). The PET fiber specimens (1.98 g, 0.01 mol) were placed in the containers along with ten -in. stainless steel balls to aid in the agitation process. The jars were sealed in the Launder-ometer, whose bath was at the desired temperature (80°C). The machine was allowed to run for the allowed treatment times (i.e., 30, 60, 90, 150, and 240 min) at 42 rpm. Upon decanting, any residual fibers... 

Glycol groups of nonsulfated D-glucuronic acid or L-iduronic acid residues, or both, have been split by periodate (see Section VIII,3) to give oxyheparins,1,150,151,260,270 reduced oxyheparins,151,152,270 and the corresponding fragments, by depolymerization with base151,270 or acid,137,151,152,155,239,270 respectively. 

The biosynthetic origin of the depolymerization-resistant core of cutin (cutan) remains to be established. The early observation that linoleic acid and linolenic acid were preferentially incorporated into the non-depolymerizable core of cutin in apple skin slices suggested that the ether-linked or C-C-linked core might arise preferentially from the czs-l,4-pentadiene system [31]. The insoluble residue, that contained the label from the incorporated polyunsaturated C18 acids, released the label upon treatment with HI, supporting the notion that some of those aliphatic chains were held together by ether bonds. More recently,... 

Fig. 38.—13C-N.m.r. Spectrum of A, Partly Depolymerized O-Methylcellulose (d.s. 2.8) in CDC13 at 30° (R, signal due to reducing-end residue Me, O-methyl inset lines represent chemical shifts of corresponding carbon atoms in methyl hepta-O-methyl-jS-cellobioside) and of B, O-Methylcellulose (d.s. 0.7), Partially Degraded by Cellulase, in D20 at 30°. (S represents a 13C nucleus bonded to an OMe group inset lines give the chemical shifts of corresponding carbon atoms in methyl /3-cellobioside.)...

Depolymerization of the permethylated carbohydrate is achieved by hydrolysis with acid. Under these conditions, the amino sugar residues are N-deacetylated, and the aminohexosidic linkages become resistant to hydrolysis. Stellner and coworkers29 showed that, when the acid degradation is conducted in 95% acetic acid, the amino sugar residues are also liberated, and can be analyzed by the methylation technique.29 Therefore, acetolysis followed by acid hydrolysis is now commonly used, as it allows the analysis both of hexose and hexosamine residues. 

The partially methylated monosaccharides obtained on depolymerization of the permethylated sample are preferably analyzed as acetates by g.l.c.-m.s., as shown by Bjomdal and coworkers.41,42 The neutral sugars and the amino sugars obtained in acetolysis-acid hydrolysis are reduced, and acetylated for the analysis, and the amino-hexitol and the neuraminic acid residues are acetylated after methanolysis. Identification with the aid of g.l.c.-m.s. has been described for all of the common components of protein- and lipid-linked glycans and oligosaccharides from animal cells, namely, the neutral sugars,41-43 hexitols,44 hexosamines,29,43,45,46 aminohexitols,31,32 and neuraminic acids.33,34,47... 

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