Activation parameters polymerization

Table VI. Rate Constants and Activation Parameters Polymerization in Nltrobenzenea) in the BCMO...

The three activation parameters, AG, AH, and AS decreased with polyelectrolyte addition. The decrease in AS suggests that the acceleration is due to the enthalpic loss. We recall that the acid hydrolyses of aliphatic esters with polymeric sulfonic acid was accompanied by decreases in AH and AS 97, 98 ... 

Recently samples of TiCl2j active in polymerization without additional activation, were prepared (156-159). The activity of TiClj in ethylene polymerization was practically the same as the activity of a conventional two-component system TiClg + AlEtjCl (see Fig. 3). The polymerization activity of TiClj depends to a large extent on the parameters tempera-... 

The rate of fl-scission of benzoyloxy radicals is such that in most polymerizations initiated by these radicals both phenyl and benzoyloxy end groups will be formed (Scheme 3.4). A reliable value for the rate constant for p-xcission would enable the absolute rates of initiation by benzoyloxy radical to be estimated. Various values for the rale constant for p-scission have appeared. Many of the early estimates are low. The activation parameters (in CCI4 solvent) determined by Chateauneuf et a(.m are log]0 A = 12.6 and Ea = -35.97 kJ mol 1 which corresponds to a rate constant of 9xl06 s 1 at 60 °C. 

The activity of initiators in ATRP is often judged qualitatively from the dispersity of the polymer product, the precision of molecular weight control and the observed rates of polymerization. Rates of initiator consumption are dependent on the value of the activation-deactivation equilibrium constant (A") and not simply on the activation rate constant ( acl). Rate constants and activation parameters are becoming available and some valuable trends for the dependence of these on initiator structure have been established.292"297... 

In addition to chemical reactions, the isokinetic relationship can be applied to various physical processes accompanied by enthalpy change. Correlations of this kind were found between enthalpies and entropies of solution (20, 83-92), vaporization (86, 91), sublimation (93, 94), desorption (95), and diffusion (96, 97) and between the two parameters characterizing the temperature dependence of thermochromic transitions (98). A kind of isokinetic relationship was claimed even for enthalpy and entropy of pure substances when relative values referred to those at 298° K are used (99). Enthalpies and entropies of intermolecular interaction were correlated for solutions, pure liquids, and crystals (6). Quite generally, for any temperature-dependent physical quantity, the activation parameters can be computed in a formal way, and correlations between them have been observed for dielectric absorption (100) and resistance of semiconductors (101-105) or fluidity (40, 106). On the other hand, the isokinetic relationship seems to hold in reactions of widely different kinds, starting from elementary processes in the gas phase (107) and including recombination reactions in the solid phase (108), polymerization reactions (109), and inorganic complex formation (110-112), up to such biochemical reactions as denaturation of proteins (113) and even such biological processes as hemolysis of erythrocytes (114). 

This active site counting methodology has been applied to the determination of initiation, propagation and termination rate laws and activation parameters for the polymerization of 1-hexene [141] catalyzed by 91 in toluene solution. 

In a quest to increase the efficiency of olefin polymerization catalysts and their selectivity in the orientation of the polymerization, the highly effective Group IV metallocene catalysts, M(Cp)2(L)2, have been studied, since they all display high fluxionality. Following methide abstraction, the metallocene catalysts of general formula M(Cp-derivatives)2(CH3)2 (M= Ti, Zr, Hf), were turned into highly reactive M+-CH3 cationic species. The activation parameters for the methide abstraction, derived from variable temperature NMR experiments, establish a correlation between the enthalpies of methide abstraction, the chemical shift in the resulting cation, and the ethylene polymerization activities [149]. 

TABLE 3-14 Activation Parameters for Chain Transfer in Styrene Polymerization (60°C) I... 

The kinetic and activation parameters for the decomposition of dimethylphenylsilyl hydrotrioxide involve large negative activation entropies, a significant substituent effect on the decomposition in ethyl acetate, dependence of the decomposition rate on the solvent polarity (acetone-rfe > methyl acetate > dimethyl ether) and no measurable effect of the radical inhibitor on the rate of decomposition. These features indicate the importance of polar decomposition pathways. Some of the mechanistic possibilities involving solvated dimeric 71 and/or polymeric hydrogen-bonded forms of the hydrotrioxide are shown in Scheme 18. 

Activation parameters for template polymerization were computed from Arrhenius relationship ... 

The presence of a continuous 8 ir- electron ribbon linked through the heteroatom renders the polyenic heteronins (1) and (2) with their tight undelocalizable lone pairs amenable to rapid 6S thermal pericyclization to the general cis- dihydroindene frame shown in (84) experimentally determined activation parameters (72ACR281) for this general transformation are given in Scheme 1. Aromatic and nondescript heteronins, on the other hand, are thermally quite stable (see Scheme 1) but readily darken and polymerize when exposed to air. Photochemically, all three types of heteronin were found to undergo 8S isomerization to the [6.1.0] frames (85). 

Activation parameters for propagation on macroions and on macroion-pairs in polymerization of PL with DBCK+... 

The nature of the active species in the anionic polymerization of non-polar monomers, e. g. styrene, has been disclosed to a high degree. The kinetic measurements showed, that the polymerization proceeds in an ideal way, without side-reactions, and that the active species exist in the form of free ions, solvent-sparated and contact ion pairs, which are in a dynamic equilibrium (l -4). For these three species the rate constants and activation parameters (including the activation volumes), as well as the rate constants and equilibrium constants of interconversion have been determined (4-7.) Moreover, it could be shown by many different methods (e. g. conductivity and spectroscopic methods) that the concept of solvent-separated ion pairs can be applied to many ionic compounds in non-aqueous polar solvents (8). 

Figure 8.16 Reaction coordinate diagram with activation parameters for the copolymerization of oxetane and C02 and for the ring-opening polymerization of TMC.

The oxidation of benzoin with cerium(IV) in perchloric acid solution is proposed to involve an interaction between Ce4+(aq.) ions and the keto alcohol, resulting in the formation of free radicals. The final product is benzoic acid.66 The rate of oxidation of crotyl alcohol with cerium(IV) is independent of the concentration of Ce(IV). The reaction induced polymerization of acrylonitrile indicating the formation of free radicals. The kinetics and activation parameters for the reaction have been determined.67 For the Ir(III)-catalysed oxidation of methyl ketones68 and cyclic ketones69 with Ce(IV) perchlorate, successive formation of complex between the reductant and Ce(IV) and then with the catalyst has been proposed. Results showed that in acidic solutions, iridium(III) is a more efficient catalyst than osmium and ruthenium compounds. 

Singlet phenylnitrene thermally ring expands in the inner phase of a hemicarcerand to the cyclic ketenimine (54), whose polymerization is prevented by the surrounding host.104 This allowed the activation parameters for the ring contraction of (54) to be measured and for the NMR spectroscopic characterization of (53). 

The above type of reaction is characteristic of the so-called polymer reactions . The rate itself and the activation parameters may be quite different from those of the conventional anionic ring-opening reaction of epoxides. In the above reaction of a polymeric epoxide, a polymer consisting of 77% THF. diyl units and 16% epoxide units was isolated in a soluble form. If the opening of the epoxide ring by an alkoxide group had occurred in a random fashion, cross-linking would have taken place to produce an insoluble polymer. 

Table 10. Rate constants of propagation and activation parameters in the polymerization of THF at 0 °C... 

Table 15. Rate constants and activation parameters of internal ionization (ii) and temporary termination (tt) in the polymerization of THF with triflic (CF3SO3 ) and fluorosulfonic (FSOJ) anions lTHF o= 8 mole r25 °C) (Ref. 229)... 

In the polymerization of 2-alkoxy-2-oxo-l, 3,2-dioxaphosphorinanes it Imb been shown that although kp does not depend too much on the structure of the substituent R, the rate constant of termination k, decreases with increasing size of the alkyl group and for the large substituents (e.g. R = ( 113)380 kt becomes eventually so small that it cannot be measured. The corresponding rate constants and activation parameters are given in Table 17. 

Propagation rate coefficients and activation parameters [118, 163] of cyclic ether polymerizations ... 

The RIM process for materials based on PCL requires a stringent control of the many reaction parameters which strongly affect the whole pattern of the activated anionic polymerization. 

---