Polymer equilibria

This compound is sometimes called a nylon salt. The salt polymer equilibrium is more favorable to the production of polymer than in the case of polyesters, so this reaction is often carried out in a sealed tube or autoclave at about 200°C until a fairly high extent of reaction is reached then the temperature is raised and the water driven off to attain the high molecular weight polymer. 

Consequently, AG is defined by Cc coefficient as well as by the change of element deflection, labor over the system, and the number of intermolecular bonds. The value of Cc approaches the A G value observed in similar reactions with the participation of only low-molecular compounds. As intermolecular bonds are distributed in elements according to Gibbs distribution, then chain parts between the molecular bonds and branching points possess different lengths in which the lengths of nonassociated parts are also different. Gibbs distribution is only performed in polymer equilibrium, which usually exists in so-called stationary states. 

This is a typical equilibrium reaction, which proceeds relatively quickly. Next to the water-polymer equilibrium, a ring-chain lactam-polymer equilibrium... 

The critical concentration, that is, the monomer <=> polymer equilibrium dissociation constant for polymerization of ADP-actin, is 25-fold that for polymerization of ATP-actin. However, in both cases the filament is made of F-ADP subunits, and the rate constant for association of ADP-actin to filament ends is only 2.5-fold lower than the rate constant for association of ATP-actin. In the absence of free ATP, the... 

Equilibrium between Monomer and Polymer. A monomer-with-polymer equilibrium is quite different from the polymer-with-condensation-product equilibrium discussed in Section 13.1.1. If the condensation product is removed from the reaction mixture, a condensation polymer increases in molecular weight. If the monomer is removed when it is in equilibrium with the polymer, the polymer depolymerizes to re-form the monomer. At temperatures suitable for long-term use, the equihbrium will be shifted toward stable polymer. However, at fabrication temperatures and at the high temperatures common in devolatilization, the production of monomer and low-molecular-weight ohgomers can be significant. 

The ring expansion mechanism is of course only a special case of the well-known mechanism by which dioxolan reacts with non-cyclic formals e.g., (I) and CH2-(OMe)2 give (MeOCH2OCH2-)2 in this way. It also accounts in a simple manner for the cleanness of the monomer-polymer equilibrium and for the high yields of cyclic dimer (without any detectable linear fragments) which are obtainable from 1,3-dioxane and 1,3-dioxepan [8]. 

The relation between Cp and co is given by a conservation equation (Cp = Co - Cl). At protomer-polymer equilibrium, we have... 

Because the onset of monomer-polymer equilibrium can occur before the filaments achieve their own equilibrium concentration behavior, these filaments will undergo polymer length redistribution. This is a slow process in vitro that in many respects resembles crystallization (See Ostwald Ripening). 

The equilibrium position for the monomer-polymer equilibrium in Eq. 3-174 will be dependent on the temperature with increased temperature, resulting in a shift to the left, since the forward reaction is exothermic. The reaction isotherm... 

Monomer-polymer equilibrium, in more general sense,... 

It was once thought that the Tc of THF was very low, in fact near room temperature (23). However, in recent years, as catalyst systems have been improved and more intensive studies have been carried out, the presumed Tc has risen first to 60—70° (18,24) and finally to 85 2° C (25, 26, 27). The lower values were probably the result of working with systems where a true monomer-polymer equilibrium was not obtained. Possibly also, careful enough techniques were not used in the isolation of the lower molecular weight polymers obtained near the ceiling temperature. Precipitation in water cannot always be used because low molecular weight PTHF s are partially soluble in water. 

These polymerizations depend upon the ability to oxidize the monomer to a radical cation, whose further reactions lead to polymer. Since the oxidation potentials of the polymers are lower than those of the corresponding monomer, the polymer is simultaneously oxidized into a conducting state so that it is non-passivating. Some of the more important electrochemically-synthesised structures are discussed in more detail below and Chandler and Pletcher U4) have reviewed the electrochemical synthesis of conducting polymers. Detailed discussion in terms of thermodynamic parameters is impossible because the polymerizations are irreversible, so that E0 is undefined for the monomer-polymer equilibrium. 

The molecular weight of the polyoxacyclobutane through any one polymerization may rise to a maximum and then decrease (19) but in similar experiments with ethylene oxide the observed maximum was no greater than the experimental error of the weight measurements. This point is of considerable interest and deserves more attention than it has received, for it raises once again the question of monomer-polymer equilibrium and suggests that such an equilibrium may be obscured in the epoxides by the non-equilibrium depolymerization to dioxane. It could also mean however that oxonium ion formation is much slower with oxacyclobutane than with epoxides so that depolymerization becomes important only towards the end of the reaction. 

The fast establishement of the monomer-polymer equilibrium in the presence of basic catalysts makes it possible to arrange depolymerization... 

Tobolsky and Owen (15) extended the Tobolsky-Eisenberg (16) general treatment of homopolymerization equilibria to copolymerization and applied their equations to the copolymerization data of Schenk (14) on selenium and sulfur. In this work the equilibrium degree of polymerization is measured as a function of temperature for total conversion of monomer to polymer. Equilibrium constants for initiation and propagation are derived from homopolymerization experiments. 

The results are not always reliable they depend on the method of measurement (monomer polymer equilibrium, calorimetric data) and mainly on the definition of the initial and final states. 

In most cases, the growth of polymeric chains is accompanied by volume contraction. Therefore external pressure tends to shift the monomer polymer equilibrium in favour of the polymer or, in other words, it increases the ceiling temperature of polymerization (lowers 7 ). This analysis can be refined by means of the known thermodynamic relations. The change in enthalpy with pressure is described by the thermodynamic equation of state... 

Conversion is a very useful quanity for expressing the momentary state of propagation and of the position of the monomer polymer equilibrium. When the mean number average degree of polymerization P is known, then the amount (or concentration) of macromolecules N can be easily calculated from the conversion... 

In some systems, for typical polymerization conditions, indeed kp kc and purely linear polymer is formed by itself. This is, for example, a case of cationic polymerization of THF [90]. After reaching monomer-polymer equilibrium, concentration of cyclic oligomers is undetectably low. Their concentration, however, increases if the living system is kept for a prolonged period of time (cf., Section III. A.3). 

Figure 4.2 Vapor-polymer equilibrium partitioning data for styrene in PS vs temperature and pressure [1]...

Another situation effecting residual levels existing during PS devolatilization is polymer decomposition or unzipping, which limits the devolatilization temperature to <260 °C. If one tries to go to higher temperature to achieve a more favorable vapor-polymer equilibrium concentration, polymer decomposition begins to dominate. The rate of polymer decomposition can be affected by stabilizing the polymer by the addition of phenolic antioxidants, e.g. 2,6-di-tert-butyl-4-methylphenol [17]. Several Asahi patents indicate the superior... 

In the case of MtX unable to react directly with THF (e.g. BF3), Eq. (118) describes a real equilibrium which can be reached either after or before the monomer-polymer equilibrium is established. 

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