Kinetic study of the free-radical polymerization of vinyl acetate in the presence of deuterated chloroform by H-1-NMR spectroscopy

摘要

The free-radical polymerization of vinyl acetate was performed in the presence of deuterated chloroform (CDCl3) as a chain-transfer agent (telogen) and 2,2'-azobisisobutyronitrile as an initiator. The effects of the initiator and solvent concentrations (or equivalent monomer concentration) and the reaction temperature on the reaction kinetics were studied by real-time H-1-NMR spectroscopy. Data obtained from analysis of the H-1-NMR spectra were used to calculate some kinetic parameters, such as the initiator decomposition rate constant (k(d)), k(p)(f/k(1))(1/2) ratio (where k(p) is the average rate constant for propagation, f is the initiator efficiency, and k(t) is the average rate constant for termination), and transfer constant to CDCl3 (C-CDCl3). The results show that k(d) and k(p)(f/k(t))(1/2) changed significantly with the solvent concentration and reaction temperature, whereas they remained almost constant with the initiator concentration. C-CDCl3 changed only with the reaction temperature. Attempts were made to explain the dependence of k(p)(f/k(t))(1/2) on the solvent concentration. We concluded from the solvent-independent C-CDCl3 values that the solvent did not have any significant effect on the kp values. As a result, changes in the k(p)(f/k(t))(1/2) values with solvent concentration were attributed to the solvent effect on the f and/or k(t) values. Individual values of f and k(t) were estimated, and we observed that both the f and k(t) values were dependent on the solvent (or equivalent monomer) concentration. (C) 2008 Wiley Periodicals, Inc.