KINETIC-ANALYSIS OF LIVING POLYMERIZATION PROCESSES EXHIBITING SLOW EQUILIBRIA .2. MOLECULAR-WEIGHT DISTRIBUTION FOR DEGENERATIVE TRANSFER (DIRECT ACTIVITY EXCHANGE BETWEEN ACTIVE AND DORMANT SPECIES) AT CONSTANT MONOMER CONCENTRATION

The MWD function and moments are derived for a ''living'' polymerizati on process which proceeds via active and ''dormant'' species and where the activity is directly exchanged between these chain ends in a bimo lecular reaction (''degenerative transfer''). Such a mechanism is beli eved to be applicable to many ''living'' polymerizations (e.g., anioni c, group transfer, cationic, and radical). For constant monomer concen tration (slow addition of monomer or low conversion), the polydispersi ty index, <(P)over bar (w)>/<(P)over bar (n)>, depends on the ratio of molar concentrations of monomer and initiator, gamma = M/I-o, the deg ree of polymerization, <(P)over bar (n)>, and the ratio of rate consta nts of exchange and propagation, beta = k(ex)/k(p). In a limiting case (beta > 1, and <(P)over bar (n)> much greater than 1), <(P)over bar ( w)>/<(P)over bar (n)> approximate to 1 + 2 gamma/(beta(P)over bar (n)> ). The molecular weight distributions are always narrower than those o btained for a batch process, where monomer concentration decreases dur ing polymerization.