Hydrolysis of polymers

Chain scission is the ultimate fate of a stressed bond. At some value below the critical stress for chain rupture, bond angle deformation may result in an increase in reactivity. As stated in Sect. 3.1, mechanically activated hydrolysis of polymers containing ester groups can lead to the scission of the bond this concurrent reaction should be differentiated from homolytic chain scission, for example by looking at any pH-dependence as was found to be the case during shear degradation of DNA [84]. 

Table 1 Monitoring enzymatic surface hydrolysis of polymers...

For all practical purposes, monomeric vinyl alcohol exists only in its tautomeric form as acetaldehyde. Therefore, poly(vinyl alcohol) (PVAlc) is prepared by the hydrolysis of polymers of vinyl esters. For practical reasons, the starting material of choice is poly(vinyl acetate) (PVAc). Although hydrolysis may be carried out under acidic conditions, alkaline conditions in the presence of an alcohol are preferred. The reaction may be represented by... 

Mendez L, Testero SA, Mata EG (2007) For hydrolysis of polymer-supported esters by TMTOH. Tetrahedron Lett 48 1757... 

Polymer-based systems. Pulsatile release of medicaments can be obtained from polymer-based delivery systems. Based on the mechanism of drug release from the polymer, these systems can be divided into various classes and subclasses. Broadly, they can be classified into three classes delivery by hydrolysis of polymers, delivery by osmotic pressure, and delivery by both hydrolytic degradation and osmotic effects. 

Stage I Hydrolysis of polymers to monomeric units (fat---->fatty acids... 

Le Carbone Lorraine Company (France) produces all carbon asymmetric membranes. The support consists of a porous fibre composite tube which is coated on the inner face with one or more porous carbon films obtained by hydrolysis of polymer precursor films. 

The processing of polymers should occur with dry materials and with control of the atmosphere so that oxidative reactions may be either avoided, to maintain the polymer s molar mass, or exploited to maximize scission events (in order to raise the melt-flow index). The previous sections have considered the oxidative degradation of polymers and its control in some detail. What has not been considered are reactions during processing that do not involve oxidation but may lead to scission of the polymer chain. Examples include the thermal scission of aliphatic esters by an intramolecular abstraction (Scheme 1.51) (Billingham et al., 1987) and acid- or base- catalysed hydrolysis of polymers such as polyesters and polyamides (Scheirs, 2000). If a polymer is not dry, the evolution of steam at the processing temperature can lead to physical defects such as voids. However, there can also be chemical changes such as hydrolysis that can occur under these conditions. 

Recently, very high-molecular-weight. polyEI was prepared by acid hydrolysis of polymer formed from 2-phenyl-2-oxazoline. According to viscosity measurements (r)sp/c = 0.15 1 g-1) the authors claim Mw = 350000 68). 

Hydrolysis of polymers derived from 2-substituted monomers requires strong alkaline conditions and the yield does not exceed 90 % 27). However, high-molecular-weight polymer from 2-phenylOXL was converted to linear polyEI using 35% HC1 at 100 °C after 5 days38). 

Table 4-1. Hydrolysis of polymer substrate 9 and monomer substrate...

Many different groups of bacteria, including Bacillus, Pseudomonas, and Thiobacillus, are capable of denitrification. The primary biochemical pathways for organic substrate oxidation by denitri-fiers are similar to that described for aerobic catabolism. Because most of the denitrifiers are facultative anaerobes, they possess a functional TCA cycle that allows them to metabolize substrates completely to carbon dioxide and water. Many denitrifiers do not produce extracellular enzymes required for hydrolysis of polymers thus, they generally rely on hydrolytic enzymes and fermenters to provide readily available substrates (Ljundahl and Erickson, 1985). 

The enzymatic degradation of water-insoluble P(3HB) material by water-soluble PHA depolymerase is a heterogeneous reaction, involving two steps, namely, adsorption and hydrolysis the first step is adsorption of the enzyme on the surface of P(3HB) material by the binding domain of the enzyme, and the second step is hydrolysis of polymer chains by the active site of the enzyme. 

Determination of amino acid composition is, beyond doubt, the most informative method in the analysis of synthetic peptides. The preceding hydrolysis of peptide bonds must of course be complete. This can be achieved by dissolving the sample in constant boiling hydrochloric acid and heating of the solution, preferably in an evacuated and sealed ampoule, at 110°C for 16 hours. Some blocked intermediates, however, are insoluble in the ca 6 N HCl even at its boiling point. In such cases mixtures of HCl with formic acid or acetic acid can solve the problem. For the hydrolysis of polymer-bound peptides often an HCl-propionic acid mixture is applied. The presence of methionine sulfoxide in synthetic peptides deserves special consideration. On hydrolysis with HCl both methionine and its sulfoxide appear on the recordings of the amino acid analyzer, but not necessarily in the ratio they occur in the sample. The sulfoxide is partially reduced ... 

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