Molecular parameters of hyperbranched polymers made by self-condensing vinyl polymerization .1. Molecular weight distribution

The molecular weight distribution (MWD) and its moments are calculated for hyperbranched polymers formed by self-condensing vinyl polymerization (SCVP) of monomers (''inimers'') with the general structure AB*, where A is a vinyl group and B* is an initiating group. The calculated MWD is extremely broad, the polydispersity index (PDI) being equal to the number-average degree of polymerization: (P) over bar(w)/(P) over bar(n) = (P) over bar(n). It is twice as broad as that for the polycondensation of AB(2) type monomers. If the fraction of unreacted monomer is not taken into account, the MWD becomes somewhat narrower, (P) over bar'(w)/(P) over bar'(n) approximate to 0.40 (P) over bar'(n). The kinetics of the polymerization process are first order with respect to the concentration of vinyl groups; (P) over bar(n), (P) over bar(w), and PDI increase exponentially with time. Comparison of the theoretical results with experimental data indicates that the rate constant of addition of an active center to a vinyl group decreases with increasing degree of polymerization. Since there are two different active centers in SCVP, namely initiating ones, B*, and propagating ones, A*, nonequal reactivities of the two centers (k(A) not equal k(B)) have a strong effect on kinetics and MWD. The MWD narrows down to (P) over bar(w)/(P) over bar(n) = 2 for k(A) much less than k(B) (corresponding to the common polycondensation of AB monomers, but broadens for k(B) > k(A). Several deviations from ideal behavior are discussed.