Simulation of reversible polycondensations with monomer having reactivity different from that of higher homologs

Reversible AB-type polycondensations have been simulated in a batch reactor where the monomer reacts with itself or any higher oligomer with a rate constant R times that for higher mers. Similarly, the rate of reaction of the condensation product with an ? AB? group at the end of a polymer chain has been assumed to be R' times that with an “internal” ? ? AB? ? group. The variation of the number-average chain length μ_n with time (until equilibrium is reached) has been obtained. μ_n is found to be lower and the polydispersity index higher in the presence of the reverse reactions. Where the equilibrium conversions are high enough, a split in the molecular-weight distribution (MWD) curves is observed for even- and odd-order homologs for R < 1, though this effect is considerably diminished as compared with that in similar irreversible polycondensations. It is also found that the most probable distribution does not adequately represent the MWD when the functional groups violate the equal-reactivity hypothesis and number-average chain lengths are relatively small.