G. Smets1, Koichiro Hayashi1
1Laboratoire de Chimie Macromoléculaire, Louvain/Belgium
Tóm tắt
AbstractThe kinetics of polymerization of vinylene carbonate have been studied as a function of the concentration of initiator, the concentration of monomer, and the temperature. In acetone solution, the order of reaction with respect to the concentration of initiator is equal to 0.5, independent of the monomer concentration ((M) = 4.15 and 14.7 mole/l.); moreover any thermal polymerization is absent at 70°C. Contrary in ethylbenzoate ((M) = 3.41 mole/l. at 77°C.) the apparent order with respect to the initiator is 0.77; in agreement with the results of Scanlan in the case of vinylacetate. This behavior is interpreted on the basis of an efficiency factor q, corresponding to the fraction of solvent radicals able to reinitiate a growing chain. In ethylbenzoate solution this factor q is equal to 0.45 and 0.80 for vinylene carbonate and vinylacetate, respectively. With respect to the monomer concentration, the order of the reaction is 1 in the presence of ethylene carbonate as solvent over the total range of concentrations. The transfer constant with this solvent is negligible because it results from molecular weight determinations at constant initiator concentration. In acetone and in benzene the apparent order of reaction is 1, only in dilute solutions; in concentrated solutions small amounts of solvent cause a strong decrease of the rates of reactions. This behavior has been interpreted on the basis of a general kinetic scheme, in which the cross‐termination rate constant Φ and the chain transfer constant with the solvent are the predominant factors. In ethylbenzoate the reaction is characterized by a partial degradative chain transfer. The overall activation energy of the polymerization of vinylene carbonate is 22.2 kcal./mole and the coefficient A of the Arrhenius equation is equal to 3.0 × 10−9.
