Polycondensation kinetic rate constants

Reactions (4.6)-(4.9) represent the typical esterification reactions, while reaction (4.10) is the polycondensation reaction, occurring mainly in the second step of polyester formation. Finally, reaction (4.11) is a side reaction resulting in diglycol repeating units, with ether Hnkages in the oligomeric chain. ki(i = 1,6) and k. i = 1,5) representing the kinetic rate constants of the six elementary reactions (lmol min ). 

Kinetic Rate Constants The kinetic rate constants usually depend on temperature, as well as catalyst type and concentration [48]. In literature [49, 50], it has been proposed that the esterification and polycondensation reactions are acid catalyzed and that the corresponding rate constants can be expressed as... 

The kinetics of polycondensation hy nucleophilic aromatic substitution in highly polar solvents and solvent mixtures to yield linear, high molecular weight aromatic polyethers were measured. The basic reaction studied was between a di-phenoxide salt and a dihaloaromatic compound. The role of steric and inductive effects was elucidated on the basis of the kinetics determined for model compounds. The polymerization rate of the dipotassium salt of various bis-phenols with 4,4 -dichlorodiphenylsulfone in methyl sulfoxide solvent follows second-order kinetics. The rate constant at the monomer stage was found to be greater than the rate constant at the dimer and subsequent polymerization stages. 

Repeat Example 2.8 assuming that the polymerization is second order in monomer concentration. This assumption is appropriate for a binary polycondensation with good initial stoichiometry while the pseudo-first-order assumption of Example 2.8 is typical of an addition polymerization. As in Example 2.8, find the rate constant for the reaction assuming that the monomer content is reduced to 20% of its initial value after 2 h, now by second-order kinetics. Also determine the monomer content predicted after 4 h. 

The data for high-temperature polycondensation of different disodium salts of the bisphenols with 4,4 -dichlorodiphenylsulfone (DCDPS) are used [47], The bisphenols denomination, their conventional signs and also the values of poly condensation rate constants k and En are adduced in Table 2. Besides, the kinetic curves conversion degree — reaction duration (Q -1) of polycondensation, adduced in the work [47], were used. 

Thus, the stated above results have shown, thatpolyarylates series high-temperature polycondensation kinetics, characterized by the reaction rate constant pi, at different temperatures and solvents is controlled by three main factors process thermal activation (T), diphenol reactiveness (Z r) and macromolecular coil stmc-ture (Dj.). The obtained generalized dependence Ig allows to perform... 

In paper [67] it has been shown, that high-temperature polycondensation kinetics of polyaiylates and polysnlfones series, characterized by reaction rate constant kr (determined on the first initial part of the kinetic curve Q,) at different temperatures and reactive medinms is described by three main factors. These factors are Process thermal activation, bisphenols reactive ability and macromo-lecular coil structure. The indicated factors can be characterized quantitatively... 

The kinetic treatment of polyreactions is greatly simplified by applying the principle of equal chemical reactivity. This principle assumes that the reactivity of a chemical group is independent of the size of the molecule to which it is attached. This postulated independence of rate constant from molecular size is already achieved at low degrees of polymerization, as can be seen, for example, by comparing the rate constants for the hydrolytic degradation of oligopolysaccharides (Table 15-5). Confirmation of the principle of equal chemical reactivity is also obtained from the polycondensation of dicarboxylic acids with diamines or diols and from free radical polymerizations. 

In modeling the polycondensation kinetics, there is also a question of how we define the reaction rate constants. In the above reaction represented by a functional-group modeling framework, the forward rate constant k is the reaction rate constant for reaction of a methyl ester group with a hydroxyl group, not the reaction rate constant for DMT and ethylene glycol molecules. For example, the above reaction can be represented as follows ... 

The formation of type II metal-containing macromolecules obtained by the reaction of bi/multifunctional low molecular weight metal complexes with another bi/multi-functional ligand can be evaluated by usual rate constants, equilibrium and kinetics as known for polycondensation or polyaddition reactions in macromolecular chemistry. Increasing insolubility results easily in chain termination and formation oligomers. 

Due to the high field strength of the highly nucleophilic hydroxyl ions (OBT) tend to attack silicon ion. The hydrolysis and polycondensation are simultaneous process and their kinetics are affected by several factors including pH, composition, temperature, alkoxide precursor, pressure, and concentration of different ion species. The hydrolysis and condensation rate constants are small for the bulkier alkoxide groups. 

In contrast to template polycondensation or ring-opening polymerization, template radical polymerization kinetics has been a subject of many papers. Tan and Challa proposed to use the relationship between polymerization rate and concentration of monomer or template as a criterion for distinguishing between Type I and Type II template polymerization. The most popular method is to examine the initial rate or relative rate, Rr, as a function of base mole concentration of the template, [T], at a constant monomer concentration, [M]. For Type I, when strong interactions exist between the monomer and the template, Rr vs. [T] shows a maximum at [T] = [M]q. For type II, Rr increases with [T] to the critical concentration of the template c (the concentration in which template macromolecules start to overlap with each other), and then R is stable, c (concentration in mols per volume) depends on the molecular weight of the template. 

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