Equilibrium polymerization

Polymerization equilibria frequently observed in the polymerization of cyclic monomers may become important in copolymerization systems. The four propagation reactions assumed to be irreversible in the derivation of the Mayo-Lewis equation must be modified to include reversible processes. Lowry114,11S first derived a copolymer composition equation for the case in which some of the propagation reactions are reversible and it was applied to ring-opening copalymerization systems1 16, m. In the case of equilibrium copolymerization with complete reversibility, the following reactions must be considered. 

W. Weltner, Jr., andK. S. Pitzer, Methyl alcohol The entropy, heat capacity and polymerization equilibria in the vapor, and potential barrier to internal rotation. J. Am. Chem. Soc. 73, 2606 2610 (1951). 

Polymerization Equilibria. As mentioned earlier, esters of strong acids, e.g. trifluoromethane sulfonic acid ("triflates"), are excellent initiators for the polymerization of THF. With such initiators, however, a complication arises. In addition to the normal propagation i depropagation equilibria of oxonium ions, Smith and Hubin postulated that the macroion ( ) may also convert into a corresponding nonpolar macroester ( ) by attack of the anion (14). ... 

The concept of the limiting polymerization temperature has been elaborated by Dainton and Ivin. Originally they only considered Tc, and they took the name from previous studies [2] ceilling temperature Tc . In the literature it is still usually designated by this symbol. Eisenberg and Tobolsky [3] are the authors of the broader concept of polymerization equilibria. Due to fluctuations in monomer addition, both kp and kd vary, and Tc is statistical in character. It is rather a temperature interval of some width. Sometimes it is defined as the temperature above which the formation of a high polymer (F > 100) is excluded ... 

It is clear that many solvents interact and produce new H bonding equilibria involving the solvent. These additional equilibria furnish an extraneous and interfering factor in a reference spectrum. On the other hand, a dilute solution of a proton donor in a basic solvent involves well defined species and avoids the usual complication of polymeric equilibria. Consequently, the spectral examination of such systems... 

Polymerization equilibria with laurinlactam (L) and lauric acid (AB) [10] (Concentrations in mole kg )... 

This paper descriBes problems outlined above, methods of determination of the chemical structures in both anionic and cationic ring-opening polymerizations, equilibria between different active species, the corresponding mechanisms of propagation and related rate constants of propagation on these species, and finally the available correlations. 

In order to minimize uncertainties that could arise from variations in polymerization equilibria due to dilution and other sources of error due to unsystematic sampling procedures, we adopted, after some trial and error, the following procedure ... 

Table 16-1. Degrees of Polymerization and Monomer Concentrations for Various Kinds of Polymerization Equilibria...

Consequently, molar masses increase linearly with yield (Figure 18-3). At complete conversion, the achievable degree of polymerization is given by the ratio [A/]o/[/]o alone. The expression ([A/]o - [Af])/([/]o - [/]) applies instead of this to polymerization equilibria. 

The optimum achievable conversion Woo of monomer thus depends on a whole series of different parameters. The appearance of such a limiting value, here, should not be confused with the establishment of a thermodynamic equilibrium. If fresh initiator is given to such dead-end polymerizations, the polymerization continues, which is not the case for polymerization equilibria as long as the initiator concentration is not extremely high. 

If the melt is shock cooled, the polymerization equilibria are frozen in and what is known as plastic sulfur is obtained. Plastic sulfur consists of long sulfur chains that arc plasticized by the cyclic molecules of X-sulfur. If the X-sulfur is extracted, the /x-sulfur crystallizes and becomes brittle. 

In free radical polymerizations, polymerization equilibria can be observed especially well with diradicals. For diradicals, the combination of two monomer radicals leads to a new diradical. Bicyclo[2.2.1]-heptene-2 and SO2, for example, copolymerize spontaneously. In this case, an adduct compound is first formed, and this then rearranges to give a diradical ... 

Chloral, CCI3CHO, can be polymerized cationically or anionically. Phosphine and lithium t-butoxide are especially suitable initiators for anionic polymerization, whereas tertiary amines produce poly(chlorals) of lower thermal stability. The polymerization is first initiated above the ceiling temperature (58°C) and is subsequently allowed to proceed well below the ceiling temperature however, yields of only 75-80% are obtained because of the unfavorable polymerization equilibria. Since the unconverted monomer cannot be removed completely by heating, heating must be supplemented by extraction to remove the residual monomer. 

The polymerization of lactams is distinguished by pronounced polymerization equilibria, i.e., -h M j. The equilibrium position var-... 

Reactions of aluminium(iii) in aqueous media can be complicated by the hydroly-sis/polymerization equilibria involved. The significance of kinetic studies to an understanding of the formation of complexes of analytical importance has been emphasized, and a study of the reactivity of polynuclear hydroxyaluminium(ni) cations has appeared. It is suggested that different processes are involved in the hydrolysis of aluminium(iii) nitrate solution by alkali above and below an [OH] / Al + ratio of 2.5. A theoretical treatment of the hydration of Al + and of the rate of exchange of water molecules between the hydration sphere and the bulk solvent has been published. A study of the kinetics of complex formation between 5-sulpho-salicylic acid, H3L, and Al + has shown the existence of three parallel pathways involving [A10H] +-h [HL] , [A10H] +-f-[H2L]-, and Al +-f [HL] - there is also some evidence for reaction between AP+ and [H2L]". 

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