Chain-length degradation rate constant

Acid hydrolysis of these samples led to the results to be expected, i.e., a lowering of LODP and residue value by NH3 pretreatment and mercerization as well as by mechanical disintegration prior to the hydrolytic treatment (Table XII). With regard to residue value, an NH3 pretreatment again proved to be more efficient in enhancing accessibility than a mercerization, while the rate constant of chain-length degradation was increased somewhat more by mercerization. 

Ultrasound waves frequency is an important factor that controls the sono-degradation rate. Form this point of view an optimal value was found of about 1 MHz, value at which the cavitation and degradation rate constant reach their maximal values. Table 3.127, and the chains limit length becomes minimal, respectively, Figure 3.387. It can be observed that to a frequency of 1 MHz the value of destruction rate is maximal, 13.0, comparatively with only 0.65 corresponding to a frequency of 20MHz [1135]. 

In flow-induced degradation, K is strongly dependent on the chain length and on the fluid strain-rate (e). According to the rate theory of molecular fracture (Eqs. 70 and 73), the scission rate constant K can be described by the following equation [155]... 

Since the depolymerization process is the opposite of the polymerization process, the kinetic treatment of the degradation process is, in general, the opposite of that for polymerization. Additional considerations result from the way in which radicals interact with a polymer chain. In addition to the previously described initiation, propagation, branching and termination steps, and their associated rate constants, the kinetic treatment requires that chain transfer processes be included. To do this, a term is added to the mathematical rate function. This term describes the probability of a transfer event as a function of how likely initiation is. Also, since a polymer s chain length will affect the kinetics of its degradation, a kinetic chain length is also included in the model. 

Assuming that rate constant is dependent upon chain length, rate constants have been deduced by Jellinek from the initial rate of degradation for fractionated samples. 

These values reveal that the rate of hydrolysis in the alkaline range up to pH < 9 is very small and practically constant, but that it then rises rapidly with decreasing pH. It is also evident that the stability of oligophosphates to hydrolytic degradation decreases in the order diphosphate > triphosphate > tetraphosphate. Degradation experiments with small quantities of oligophosphates with chain lengths n = 4-8 show (858) that stability decreases further up to the octaphosphate (see Fig. 7). (The... 

Table 3.127. Rate constant of degradation polystyrene samples degradation with different initial average chain lengths at different frequencies...

By about 1947 many of the major themes of free radical chemistry had emerged from this war-initiated polymer research data on structure and reactivity and establishment of the utility of competitive kinetics for determining relative rates of chain propagation steps in chain reactions by product analyses as I ve just described th first good rate constants for elementary steps in chain processes - here the first really reliable results were on vinyl acetate polymerization from Paul Bartlett s laboratory ( ) degradative chain transfer, first demonstrated by Bartlett and Altschul and showing how the length of kinetic... 

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