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 AB_m with AB monomers as well as AB_m with AB_n-monomers in general. Copolymerization of linear AB-comonomers can be used to deliberately lower the DB and ANB of hyperbranched polymers. The DB${}_{\text{AB/AB}{}_{\text{2}}}$ for copolycondensation of AB and AB₂ monomers in dependence on the monomer ratio r = [AB]/[AB₂] and conversion p_A is DB${}_{\text{AB/AB}{}_{\text{2}}}$ = 2 p_A r + 1/( r + 2)². The DB${}_{\text{AB/AB}{}_{\text{2}}}$ 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${}_{\text{AB/AB}{}_{\text{3}}}$ and ANB${}_{\text{AB/AB}{}_{\text{3}}}$ for copolycondensation of AB and AB₃-monomers are calculated. Finally, a general expression for the DB${}_{\text{AB}{}_{\text{n}}\text{AB}{}_{\text{m}}}$ for copolymerization of AB_n and AB_m monomers (m ≠ n) is derived. The respective expressions for m, n ⪇ 6 are given. It is demonstrated that the ANB${}_{\text{AB}{}_{\text{n}}\text{AB}{}_{\text{m}}}$ parameter is more useful to describe the extent of branching of complex copolymers of this type.