Molecular Parameters of Hyperbranched Polymers Made by Self-Condensing Vinyl Polymerization. 1. Molecular Weight Distribution

Abstract

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: P̄w/P̄n = P̄n. It is twice as broad as that for the polycondensation of AB2 type monomers. If the fraction of unreacted monomer is not taken into account, the MWD becomes somewhat narrower, P̄‘w/P̄‘n ≈ 0.40P̄‘n. The kinetics of the polymerization process are first order with respect to the concentration of vinyl groups; P̄n, P̄w, 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 (kA ≠ kB) have a strong effect on kinetics and MWD. The MWD narrows down to P̄w/P̄n = 2 for kA ≪ kB (corresponding to the common polycondensation of AB monomers) but broadens for kB > kA. Several deviations from ideal behavior are discussed.