Chain kinetics activation energy

It would be desirable to be able to use data such as that given in Table 12 to predict Dt values for other methyl metallic alkyls and to set a pattern for ethyl and possibly higher alkyls. These dissociation energies should be approximately equal to the kinetic activation energy for the first stage of dissociation in a nonchain decomposition or to the activation energy of the initiation step in a chain decomposition. 

The hydrolytic depolymerisation of PETP in stirred potassium hydroxide solution was investigated. It was found that the depolymerisation reaction rate in a KOH solution was much more rapid than that in a neutral water solution. The correlation between the yield of product and the conversion of PETP showed that the main alkaline hydrolysis of PETP linkages was through a mechanism of chain-end scission. The result of kinetic analysis showed that the reaction rate was first order with respect to the concentration of KOH and to the concentration of PETP solids, respectively. This indicated that the ester linkages in PETP were hydrolysed sequentially. The activation energy for the depolymerisation of solid PETP in a KOH solution was 69 kJ/mol and the Arrhenius constant was 419 L/min/sq cm. 21 refs. 

Nair et al. studied the kinetics of the polymerization of MMA at 60-95 °C using N,1SP-diethyl-NjW-di(hydroxyethyl)thiuram disulfide (30a) as the thermal in-iferter [142]. The dependence of the iniferter concentration on the polymerization rate was examined. The chain transfer constant of the propagating radical of MMA to 30a was determined to be 0.23-0.46 at 60-95 °C, resulting in the activation energy of 37.6 kj/mol for the chain transfer. Other derivatives 30b-30d were also prepared and used to derive telechelic polymers with the terminal phosphorus, amino, and other functional aromatic groups [143-145]. Thermal polymerization was also investigated with the end-functional poly(St) and poly(MMA) which were prepared using the iniferter 13 [146]. 

Most of our knowledge about the kinetics of the homogeneous decomposition has come from shock-tube experiments. These have been performed in several laboratories under a variety of experimental conditions. However, their results are contradictory in some respects especially with regard to activation energy and on the question of the importance of chain reactions. In some cases the experimental conditions are such that consecutive reactions have to be taken into account or at least cannot be safely excluded. Until recently, one reason for the difficulty of reconciling the results of different investigators was that, if they were interpreted in terms of the unimolecular reaction48... 

The bulk polymerization of acrylonitrile in this range of temperatures exhibits kinetic features very similar to those observed with acrylic acid (cf. Table I). The very low over-all activation energies (11.3 and 12.5 Kj.mole-l) found in both systems suggest a high temperature coefficient for the termination step such as would be expected for a diffusion controlled bimolecular reaction involving two polymeric radicals. It follows that for these systems, in which radicals disappear rapidly and where the post-polymerization is strongly reduced, the concepts of nonsteady-state and of occluded polymer chains can hardly explain the observed auto-acceleration. Hence the auto-acceleration of acrylonitrile which persists above 60°C and exhibits the same "autoacceleration index" as at lower temperatures has to be accounted for by another cause. 

Within the temperature range from 10 to 40°C, both PAMAM dendrimers in EDA [5] and PPI dendrimers in water [22] showed a linear relationship between In r and /T, in good agreement with the kinetic rate theory of flow [46]. The apparent activation energies of flow (En) were constant and independent of temperature, and it was shown for PAMAM/EDA systems that the dependence of En on solution concentration was linear for all generations examined [5]. This was considerably different from the typical relationships for the solutions of linear and/or randomly branched chain polymers, where a break in the slope of... 

Fischer-Tropsch synthesis, 28 80, 97, 103, 30 166-168, 34 18, 37 147, 39 221-296 activation energy and kinetics, 39 276 added olefin reactions, 39 251-253 bed residence time effects on chain growth probability and product functionality, 39 246-250... 

Kinetic studies of the unnatural 6-a -epimer of ampicillin, fi-ept-ampicillin (154), have revealed an intramolecular process not undergone by ampicillin (or other natural /3-substituted penicillins) At pH 6-9, intramolecular attack of the jS-lactam carbonyl group by the side-chain amino group of (154) yields a stable piperazine-2,5-dione derivative (155). Theoretical calculations show that the intramolecular aminolysis of 6-epi-ampicillin nucleophilic attack occurs from the a-face of the -lactam ring with an activation energy of 14.4kcalmor In other respects, the hydrolysis of the b-a-epimer is unexceptional. 

The kinetics of the decomposition of PPC has been estimated from several studies. An analysis from TGA shows that the activation energy for end-capped PPC at temperatures over approximately 250°C is in the range of 130 kJ/mol, a relatively low value (for a chain scission process) [19]. The same analysis for uncapped PPC is complicated by non-linear behavior. Results consistently indicate that, at lower temperatures, a different decomposition reaction takes place than at higher temperatures. 

The kinetics and equlibria of the complexation between PAA and PEO or PVPo were studied by Morawetz s group [ 13-15], and it was shown that the complex formation consisted of an initial diffusion-controlled hydrogen-bonding process with a small activation energy and an extensive conformational transition of the two polymer chains which induces additional hydrogen bonding, thus stabilizing the complex. 

Divalent counterions Kinetic measurements using mono- and bifunctional initiators and Ba++ as the counterion in THF were reported by Mathis and Francois (37 ), who applied adiabatic calorimetry. At -7o°C no termination is found and conversion follows first order with respect to monomer concentration. The rate constants do not depend on the concentration of living ends, indicating the absence of free anions. The rate constants are smaller by a factor of 2o as compared with those measured with monovalent counterions. However, they are smaller by a factor of 3 only, compared with those calculated for chains which are intramolecular ly associated (Na+, counterion). The activation energy for PMMA Ba in THF is equal to that for monovalent counterions, but the frequency exponent is smaller by about 1.5 units, reflecting the fact that the transition state for the dianionic ion pair has higher steric requirements. 

Several mechanisms were proposed to interpret bond shift isomerization, each associated with some unique feature of the reacting alkane or the metal. Palladium, for example, is unreactive in the isomerization of neopentane, whereas neopentane readily undergoes isomerization on platinum and iridium. Kinetic studies also revealed that the activation energy for chain branching and the reverse process is higher than that of methyl shift and isomerization of neopentane. 

Figure 23 lists representative acid-labile protecting groups that have been incorporated in positive-tone CA resist systems. These groups can be pendent to the matrix polymer chain, can be attached to a monomeric or polymeric additive that acts as a dissolution inhibitor (64—66), or can even be appended to the PAG structure (67). The kinetics of acid-catalyzed deprotection vary significantly with structure. In particular, the activation energy,... 

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