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 polymeriza tion (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 polyco ndensation of AB(2) type monomers. If the fraction of unreacted monome r is not taken into account, the MWD becomes somewhat narrower, (P) ov er 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 theoretica l results with experimental data indicates that the rate constant of a ddition of an active center to a vinyl group decreases with increasing degree of polymerization. Since there are two different active center s in SCVP, namely initiating ones, B, and propagating ones, A*, noneq ual reactivities of the two centers (k(A) not equal k(B)) have a stron g 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.