Degree of branching in hyperbranched polymers. 2. Enhancement of the db: Scope and limitations

Abstract The degree of branching (DB) as well as the ANB (average number of branches) of polymers obtained from polycondensation of AB 2 and AB m ‐type monomers in general is analyzed in detail on the basis of kinetic considerations. Various possibilities for the enhancement of the DB of hyperbranched polymers beyond the limit for a random AB m polycondensation (0.5 for AB 2 , 0.44 for AB 3 ) are considered, i.e., (i) enhanced reactivity of linear vs. terminal units; (ii) polymerization of prefabricated, perfect dendritic units and (iii) the slow addition technique. For AB 2 monomers, the formation of terminal (T), linear (L) and perfect dendritic (D) units in the course of the random one‐pot polymerization is calculated. Furthermore, the evolution of the DB and ANB with conversion is calculated for AB m monomers. It is shown that the definition of the DB for AB 2 systems (DB = 2 D /(2 D + L )) derived in the first paper on the DB ( Acta Polym. 1997 , 48 , 30) in the case of a random one‐pot polycondensation exhibits the same conversion dependence as the branching parameter α = 1/2 P A , defined by Flory for AB 2 polycondensations. The dilution principle is introduced, which is based on slow addition of AB m monomers to a core molecule B f or an AB m ‐type hyperbranched molecule with an arbitrary DB. It is shown that the maximum DB value obtainable from such a dilution/slow addition process is 0.67 for AB 2 systems. Thus, the DB is considerably higher than in the case of a random one‐step polymerization (0.5). The DB for AB m ‐type hyperbranched polymers prepared according to the dilution principle has been calculated to be m /(2 m –1).