Chain degradation

The cellulose molecule contains three hydroxyl groups which can react and leave the chain backbone intact. These alcohol groups can be esterified with acetic anhydride to form cellulose acetate. This polymer is spun into the fiber acetate rayon. Similarly, the alcohol groups in cellulose react with CS2 in the presence of strong base to produce cellulose xanthates. When extruded into fibers, this material is called viscose rayon, and when extruded into sheets, cellophane. In both the acetate and xanthate formation, some chain degradation also occurs, so the resulting polymer chains are shorter than those in the starting cellulose. 

Yields of sulfonyl fluorides prepared by ECF vary depending on the particular stmcture. Chain degradation becomes more important as the chain length kicreases (6). Yields can vary from 96% for perfluoromethanesulfonyl fluoride (7) to 43—50% for perfluorooctanesulfonyl fluoride (8). Trifluoromethanesulfonic acid can be prepared via trifluoromethanesulfenyl chloride as shown ki equations 5—7 (9). 

BARBIER - WIELAND Degradation A multi-step procedure tor chain degradation ot esters... 

By deactivating the active weak link. For example, commercial polyacetal (polyformaldehyde) resins have their chain ends capped by a stable grouping. (This will, however, be of little use where the initiation of chain degradation is not at the terminal group.)... 

The reaction of carboxylic acids, aldehydes or ketones with hydrazoic acid in the presence of a strong acid is known as the Schmidt reaction A common application is the conversion of a carboxylic acid 1 into an amine 2 with concomitant chain degradation by one carbon atom. The reaction of hydrazoic acid with a ketone 3 does not lead to chain degradation, but rather to formation of an amide 4 by formal insertion of an NH-group. 

It was observed that beyond optimum total dose the percentage of grafting decreased. This may be due to the fact that at higher total doses beyond optimum, chain degradation by /3-scission (reaction 35, 37, 38) occurs. Further at higher doses, hydroxyl radicals arising from... 

First, let us briefly examine the route of side chain degradation in micro-organisms. The pathway is illustrated in Figure 92. 

Figure 9.2 Generalised metabolic sequences of sterol side chain degradation by micro-organisms.

Figure 9.4 Some examples of side chain degradation of 6f) and 19 oxidosterols.

Chain degradation in turbulent flow has been frequently reported in conjunction with drag reduction and in simple shear flow at high Reynolds numbers [187], Using poly(decyl methacrylate) under conditions of turbulent flow in a capillary tube, Muller and Klein observed that the hydrodynamic volume, [r ] M, is the determining factor for the degradation rate in various solvents and at various polymer concentrations [188], The initial MWD of the polymers used in their experiments are, however, too broad (Mw/Iiln = 5 ) to allow for a precise... 

In the semi-dilute regime, the rate of shear degradation was found to decrease with the polymer concentration [132, 170]. By extrapolation to the dilute regime, it is frequently argued that chain scission should be nonexistent in the absence of entanglements under laminar conditions. No definite proof for this statement has been reported yet and the problem of isolated polymer chain degradation in simple shear flow remains open to further investigation. 

Finally, dissolution of non-activated cellulose in LiCl/DMAc, and in ionic liquids has been accelerated by microwave irradiation [72,103,104], although the effect of microwave heating on the DP of the polymer has not been investigated. This last point is relevant in view of the fact that ILs are heated with exceptional efficiency by microwaves [105], so that care must be taken to avoid excessive localized heating that can induce chain degradation of the polymer during its dissolution. 

In this particular instance, u) and m-l hydroxylation, which is then followed by further oxidation and chain degradation, are the principal reactions ( ) In the case of di-n-pro-pylnitrosamine both a- and 3-oxidation occur, with the latter being about 15% of the former (44) The a-hydroxy lation leads to the formation of the n-propyldiazonium ion (22), while the 3-hydroxylation results, at least in part, in oxidation to N-propyl-N-(2-oxopropyl)nitrosamine. Krdger and Bertrum (45) suggested that this product can be cleaved to methyl-... 

Two other series of biodegradable polymers that depend upon chain degradation are the polyanhydrides and the polyorthoesters. Both of these polymers contain hydrophobic units linked together along the polymer chain by functional... 

This reaction has been utilized for side-chain degradation of substituted cholic acids and lanostenoic acid [4],[6]... 

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