Aging depolymerization

On account of its large practical importance, polymer formation in hydrolyzed plutonium(iv) solutions has attracted much interest [203]. This polymer is formed fairly rapidly [204,205]. The reaction is faster, and more extensive, the higher the temperature. As long as ionic plutonium(iv) is present in detectable amounts, the rate of polymerization is proportional to the concentration of this component, and inversely proportional to the square of the acidity. When the ionic plutonium(iv) has been consumed, the rate depends in a rather complicated manner upon the concentration of other oxidation states present [205]. If the polymer is allowed to age, depolymerization becomes very slow even if the concentration of acid is fairly high [204]. The colloid behaves very differently from ionic plutonium(iv) in the extraction and ion-exchange procedures used in the processing of plutonium, and is also apt to transform into a precipitate. The conditions should therefore be chosen so that the formation of the colloid is... 

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. 

This untimely polymer formation is understood to be caused by the very rapid hydrolysis and aggregation of monomeric Pu(IV) species (at the region of condensate reentry into the hot plutonium solution) to produce hydrous polymers that are not readily depolymerized. At high temperatures such as found under reflux conditions, the polymer rapidly ages through the conversion of hydroxyl- to oxo-bridges ... 

Plutonium(IV) polymer is a product of Pu(IV) hydrolysis and is formed in aqueous solutions at low acid concentrations. Depolymerization generally is accomplished by acid reaction to form ionic Pu(IV), but acid degradation of polymer is strongly dependent on the age of the polymer and the conditions under which the polymer was formed (12). Photoenhancement of Pu(IV) depolymerization was first observed with a freshly prepared polymer material in 0.5 HClOh, Fig. 3 (3 ). Depolymerization proceeded in dark conditions until after 140 h, 18% of the polymer remained. Four rather mild 1-h illuminations of identical samples at 5, 25, 52, and 76 h enhanced the depolymerization rates so that only 1% polymer remained after the fourth light exposure (Fig. 3). 

Enhancement of depolymerization rates for aged polymer (polymer with high degree of PuC>2 character (13) were observed... 

The effects of UV irradiation to enhance the degradation of aged Pu(IV) polymer in HClOi. Depolymerization under dark conditions for each experiment is shown by a data point directly above the last light sample point (4). 

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... 

These polycations can be further hydrolyzed or react with each other to give a large number of possible polycations. The olatlon reaction occurs without a change In solution acidity but does change the concentration of hydrolyzed species In solution. Dilution causes the reversal of reaction 2 (I.e., depolymerization) and the Introduction of new hydrolyzed species Into solution. The new species formed can then re-equilibrate through the hydrolysis reaction. The kinetics of aging depend on the relative rates of the olatlon and hydrolysis reactions. 

In Figure 1, the pH of the batch diluted solutions Is plotted against the dilution ratio, C/Co, where C Is the molar concentration of Al In the dilute solution and Co Is the molar concentration of Al In Chlorhydrol (6.43 M). The pH of the most concentrated solution was still Increasing after ten days aging. (The higher viscosity of the concentrated solutions may contribute to the slower equillbriatlon). At higher dilution (lower C/Co values), new equilibria can be Introduced due to depolymerization reactions. For the zero day curve, pH continuously Increases with... 

The surface areas of pillared clays prepared from dilute Chlorhyd-rol solution depend on the extent of dilution and age of the dilute solution. Dilution produces polycations favorable to the production of pillared clays by depolymerizing larger polycations present in the Chlorhydrol solution. Aging is the reequilibration of these depolymerized solutions. 

The oxidation of the film follows first-order kinetics with rates close to those found for decreases in tear strength and depolymerization of cotton and rayon fabrics. The reaction mechanisms appear not to be affected by temperature. The infrared spectra of the film and of the water extract of the aged film are essentially the same as those found for naturally aged linen. 

The mechanism of formation of zeolites is very complex, stemming from the diversity of chemical reactions, including various polymerization and depolymerization equilibria, nucleation and crystal growth processes. The physical and chemical nature of the reactants, which typically involve a source of aluminum and silicon along with hydroxides and salts determine the formation of zeolites. Physical effects such as aging, stirring, and temperature also play an important role. These effects lead to the complexity of zeolite formation, but are also responsible for the large number of frameworks that can be synthesized and the rich chemistry associated with this area. Cl. 21... 

The poor performance of the calcium bicarbonate treated fibers is not so readily understood. However, a very likely explanation is the greatly increased sensitivity of naturally aged (and hence partially degraded) cellulose to alkaline materials. One may speculate that the calcium carbonate that was formed in the fibers was acting as an initiator of depolymerization reactions that are base catalyzed. 

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