Depolymerization hydrolytic

Polyester composition can be determined by hydrolytic depolymerization followed by gas chromatography (28) to analyze for monomers, comonomers, oligomers, and other components including side-reaction products (ie, DEG, vinyl groups, aldehydes), plasticizers, and finishes. Mass spectroscopy and infrared spectroscopy can provide valuable composition information, including end group analysis (47,101,102). X-ray fluorescence is commonly used to determine metals content of polymers, from sources including catalysts, delusterants, or tracer materials added for fiber identification purposes (28,102,103). 

Neutral hydrolysis of PET is usually earned out under pressure (1-4 MPa) at temperatures of 200-300°C.12 High-purity TPA and EG may be obtained by the hydrolytic depolymerization of PET in an autoclave with excess water. PET hydrolysis occurs faster in the molten state than as a solid therefore, it is... 

The hydrolytic depolymerization of PET is followed by obtaining the initial and final weights of die PET and applying die formula ... 

Hie hydrolytic depolymerization of nylon-6 was followed by gel permeation chromatography (GPC), viscometry, and gravimetry. GPC determinations were performed on a Waters 150C chromatography system using benzyl alcohol as die eluant, two Plgel 10-p.m crosslinked polystyrene columns, and a differential refractometer detector. The flow rate was 1 mL/min. The concentration of the polymer solutions was 0.5 wt% and dissolution was accomplished at 130°C. 

Polylactides, 18 Poly lactones, 18, 43 Poly(L-lactic acid) (PLLA), 22, 41, 42 preparation of, 99-100 Polymer age, 1 Polymer architecture, 6-9 Polymer chains, nonmesogenic units in, 52 Polymer Chemistry (Stevens), 5 Polymeric chiral catalysts, 473-474 Polymeric materials, history of, 1-2 Polymeric MDI (PMDI), 201, 210, 238 Polymerizations. See also Copolymerization Depolymerization Polyesterification Polymers Prepolymerization Repolymerization Ring-opening polymerization Solid-state polymerization Solution polymerization Solvent-free polymerization Step-grown polymerization processes Vapor-phase deposition polymerization acid chloride, 155-157 ADMET, 4, 10, 431-461 anionic, 149, 174, 177-178 batch, 167 bulk, 166, 331 chain-growth, 4 continuous, 167, 548 coupling, 467 Friedel-Crafts, 332-334 Hoechst, 548 hydrolytic, 150-153 influence of water content on, 151-152, 154... 

Representative condensation polymers are listed in Table I. The list is by no means exhaustive, but it serves to indicate the variety of condensation reactions which may be employed in the synthesis of polymers. Cellulose and proteins, although their syntheses have not been accomplished by condensation polymerization in the laboratory, nevertheless are included within the definition of condensation polymers on the ground that they can be degraded, hydrolytically, to monomers differing from the structural units by the addition of the elements of a molecule of water. This is denoted by the direction of the arrows in the table, indicating depolymerization. 

Availability of Monomer. Under most solution conditions employed for gel formation, monomer is rapidly consumed to form a distribution of oligomeric species (12). Thereafter the only possible source of monomer is that which is produced by hydrolytic (or alcoholic) depolymerization of siloxane bonds (dissolution). According to Her (241 the dissolution of a-Si02 above pH 2 is catalyzed by OH ions which are able to increase the coordination of silicon above 4... 

Hydrolytic stability hydrolysis promoted by acid or base. Partially hydrolyzed prod gt mo g sensitive to Ca, Mg hydrolytic depolymerization promoted by acid or base esp. at high T... 

When polymerizing A2B monomers there is a possibihty of losing the unique focal point due to intramolecular cyclization. The loss of the focal point in a hyperbranched polyester based on 4,4-(4 -hydroxyphenyl)pentanoic (Fig. 7) acid was closely examined by Hawker et al. [45]. The study showed no significant occurrence of intramolecular cyclization. One disadvantage of polycondensation polymers is that they are sensitive to hydrolysis, that is depolymerization, which might restrict their use. Some hyperbranched polymers are synthesized via substitution reactions which provide less hydrolytically unstable polymers. 

Sources of Proteinases. More than 80 per cent of all industrial enzymes are hydrolytic in action and most are used for the depolymerization of natural substances. Almost 60 per cent of these enzymes are proteolytic, and used by the detergent, dairy and leather industries. 

Figure 4. Comparison of hydrolase and lyase mechanisms from the depolymerization of polygalacturonic acid. Polygalacturonic acid sequences (structure at left) may be depolymerized via hydrolytic cleavage, (indicated by arrows to the left of o-linkages) to yield saturated oligomeric products indicated by the structures at upper right. Alternatively, eliminative depolymerization (indicated by arrows to the right of o-linkages) yields A-4,5-unsaturated oligomers indicated by the structures at lower right.

The thermal depolymerization of polyoxymethylene starts from the unstable hydroxy end groups, but the oxidative and acid-catalyzed hydrolytic degradation takes place within the main chain. Flence, if polyoxymethylene is heated in air or in the presence of strong acids samples with blocked end groups will also degrade. 

Production and Hydrolytic Depolymerization of Ethylene Glycol Lignin... 

This disproportionation offers an insight into the mechanism of hydrolytic degradation of PDMS, especially in the presence of traces of acid. Thus, the siloxane chain may undergo a slow scission in the presence of water to give a silanol ended chain, which then depolymerizes by loss of dimethylsiloxanediol. 

It has been suggested that hydrogen peroxide and iron are the cause of this rapid depolymerization (30). It is possible that the initial attack by micro-organisms is not enzymatic but hydrolytic and oxidative in nature. If this is true, then a preservative system could be based on anti-oxidant properties of the chemical. If the initial attack can be stopped, then the total attack has been stopped. It is also possible that the initial and sustained attacks are caused by a combination of chemical... 

Enzyme activity may be enhanced by a chemical pretreatment, as in the example of alkaline hydrogen peroxide on corn fiber, where the hydrolytic rate was increased by a factor of 1.6 (Leathers, 1993). Some enzymes depolymerize polysaccharides by 3-elimination. 

The variation of TPAOH amount during the synthesis of silica-aluminas has two macroscopic effects the change of the pH and of the relative amount of TPAOH to silico-aluminate oligomers. The textural properties of the final silica-aluminas may result from the different sequence of hydrolysis and condensation reactions (and the reverse reactions esterification and alcoholic or hydrolytic depolymerization) of the Si and A1 alkoxides. Indeed an increase in TPAOH content and therefore of the pH corresponds to an increase of OH" availability that can favor the hydrolysis and depolymerization reactions, giving rise to different gelation rate and to different network formation. 

As a broad generalization the cellulose provides impact resistance and tensile strength, the lignin provides stiffness, and both matrix polymers contribute to hardness and compressive strength. Hydrolytic and oxidative processes that depolymerize and solubilize the wood components will affect the wood properties, often to an extent far greater than might be expected from the limited initial reaction. 

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