Initiator efficiency of 2,2′-azobis(isobutyronitrile) in bulk dodecyl acrylate free-radical polymerizations over a wide conversion and molecular weight range

The initiator efficiency, f, of 2,2'-azobis(isobutyronitrile) (AIBN) in dodecyl acrylate (DA) bulk free-radical polymerizations has been determined over a wide range of monomer conversion in high-molecular-weight regimes (M-n congruent to 10(6) g mol(-1) [congruent to 4160 units of DA)] with time-dependent conversion data obtained via online Fourier transform near infrared spectroscopy (FTNIR) at 60 degreesC. In addition, the required initiator decomposition rate coefficient, k(d), was determined via online UV spectrometry and was found to be 8.4 (.) 10(-6) s(-1)(+/-0.5 (.) 10(-6) s(-1)) in dodecane, n-butyl acetate, and n-dodecyl acetate at 60 degreesC. The initiator efficiency at low monomer conversions is relatively low (f = 0.13) and decreases with increasing monomer to polymer conversions. The evolution of f with monomer conversion (in high-molecular-weight regimes), x, at 60 degreesC can be summarized by the following functionality: f(60) (degreesC) (x) = 0.13-0.22 (.) x + 0.25 (.) x(2) (for x less than or equal to 0.45). The reported efficiency data are believed to have an error of >50%. The ratio of the initiator efficiency and the average termination rate coefficient, k(t)+/-, (fl<k(t)>) has been determined at various molecular weights for the generated polydodecyl acrylate (Mn = 1900 g mol(-1) (congruent to 8 units of DA) up to M. = 36,500 g mol(-1) (congruent to 152 units of DA). The (f/<k(t)>) data may be indicative of a chain length-dependent termination rate coefficient decreasing with (average) chain length. (C) 2004 Wiley Periodicals, Inc.