MOLECULAR-PARAMETERS OF HYPERBRANCHED POLYMERS MADE BY SELF-CONDENSING VINYL POLYMERIZATION .2. DEGREE OF BRANCHING

Using a modified definition, the average degree of branching, <(DB)ove r bar>, the fraction of branchpoints, <(FB)over bar>, as well as the f ractions of various structural units are calculated as a function of c onversion of double bonds for hyperbranched polymers formed by self-co ndensing vinyl polymerization (SCVP) of monomers (or ''inimers'') with the general structure AB, where A is a vinyl group and B* is an init iating group. The results are compared to those for the polycondensati on of AB(2)-type monomers. At full conversion, <(DB)over bar> is somew hat smaller for SCVP (<(DB)over bar>(infinity) approximate to 0.465) t han for AB(2) Systems (<(DB)over bar>(infinity) = 0.5). There are two kinds of linear groups in SCVP whereas there is only one kind in AB(2) systems. Since there are two different active centers in SCVP, i.e., initiating B and propagating A* centers, the effect of nonequal react ivities on <(DB)over bar> is also discussed. At a reactivity ratio of the two kinds of active centers, r = k(A)/k(B) approximate to 2.59, a maximum value of <(DB)over bar>(infinity) = 0.5 is reached. For the li miting case r much less than 1, a linear polymer resembling a polycond ensate will be formed whereas for r much greater than 1 a weakly branc hed vinyl polymer is expected. NMR experiments allow for the determina tion of reactivity ratio r.