Degree of branching in hyperbranched polymers. 3 Copolymerization of ABm-monomers with AB and ABn-monomers

Abstract

Extending the considerations of previous work (Acta Polym. 1997, 48, 30; Acta Polym. 1997, 48, 298) the degree of branching (DB) and the average number of branches per non-terminal monomer unit (ANB) are defined and calculated for random copolycondensation of ABm with AB monomers as well as ABm with ABn-monomers in general. Copolymerization of linear AB-comonomers can be used to deliberately lower the DB and ANB of hyperbranched polymers. The DB AB/AB 2 for copolycondensation of AB and AB2 monomers in dependence on the monomer ratio r = [AB]/[AB2] and conversion pA is DB AB/AB 2 = 2 pA r + 1/( r + 2)2. The DB AB/AB 2 for copolymerization is compared to the DB for AB2 homopolymerization,showing that a relatively small fraction of AB2 comonomers suffices to obtain considerable degrees of branching. Also, the DB AB/AB 3 and ANB AB/AB 3 for copolycondensation of AB and AB3-monomers are calculated. Finally, a general expression for the DB AB n AB m for copolymerization of ABn and ABm monomers (m ≠ n) is derived. The respective expressions for m, n ⪇ 6 are given. It is demonstrated that the ANB AB n AB m parameter is more useful to describe the extent of branching of complex copolymers of this type.