|87. Yan, D.Y.; Müller, A.H.E.; Matyjaszewski, K.: Molecular parameters of hyperbranched polymers made by self-condensing vinyl polymerization, 2.Degree of branching, Macromolecules 30, 7024 (1997)|
Using a modified definition, the average degree of branching, , the fraction of branchpoints, , as well as the fractions of various structural units are calculated as a function of conversion of double bonds for hyperbranched polymers formed by self-condensing vinyl polymerization (SCVP) of monomers (or "inimers") with the general structure AB*, where A is a vinyl group and B* is an initiating group. The results are compared to those for the polycondensation of AB2-type monomers. At full conversion, is somewhat smaller for SCVP ( 0.465) than for AB2 systems ( = 0.5). There are two kinds of linear groups in SCVP whereas there is only one kind in AB2 systems. Since there are two different active centers in SCVP, i.e., initiating B* and propagating A* centers, the effect of nonequal reactivities on is also discussed. At a reactivity ratio of the two kinds of active centers, r = kA/kB 2.59, a maximum value of = 0.5 is reached. For the limiting case r << 1, a linear polymer resembling a polycondensate will be formed whereas for r >> 1 a weakly branched vinyl polymer is expected. NMR experiments allow for the determination of reactivity ratio r.