Kinetic Evaluation of Hyperbranched A₂ + B₃ Polycondensation Reactions

Abstract

The kinetics of hyperbranched A2 + B3 systems is discussed theoretically with respect to the development of the 7 different structural units, the degree of branching, DB, and the monomer sequences considering the adjacent groups of a structural unit. For A2 + B3 systems, the comonomer ratio, the relative rate constants and the process conditions have an influence on the resulting structure as shown by numerical simulations. With increasing A:B ratios fA/B, the degree of branching will be increased. Also the relative reaction rate constants have a strong impact on the distribution of structural units, especially when the reaction rate constants for the pathway of the B3 monomer are changed. On the other hand, differences in the reaction rate constants for the pathway of the A2 monomer do not have any influence on the degree of branching. The simulation indicates that slow addition of either both monomers or just the B3 monomer has the strongest effect on the resulting DB. In all cases, the conversion is a critical issue to obtain high molecular weight products.Degree of branching (DB) versus conversion of A‐functionalities (pA) for various monomer compositions.imageDegree of branching (DB) versus conversion of A‐functionalities (pA) for various monomer compositions.

Novel Branched Polyphenylenes based on A2/B3 and AB2/AB Monomers via Diels‐Alder Cycloaddition

“…Comparing the B 2 b:Bb 2 ratio of 32:68 for polymer 5a and 5c to a ratio of 42:58 for terminal and linear units evaluated for hyperbranched polymers from A 2 þ B 3 (1:1) polycondensation reactions up to their critical conversion of gelation of 86.6%, [23] our polymer exhibited a lower content of terminal units in favour of more linear subunits. In combination with the small amount of dendritic units, this indicates that the third reaction on a B site, and thus the conversion of Bb 2 to b 3 , is retarded due to the steric bulkiness of the first two reacted B functionalities, so that the linear Bb 2 units accumulate.…”

Degree of Branching of Highly Branched Polyurethanes Synthesized via the Oligomeric A2 Plus B3 Methodology

“…In the earlier literature, it was theoretically predicted that DB would increase with addition of A 2 , which leads to higher molecular weight. [42] However, the oligomeric A 2 plus monomeric B 3 system differs, because the formation of each dendritic unit results in the addition of three oligomeric A 2 units. Therefore, the number of monomeric units, which do not contribute to branching, greatly outweighs the increase in total branching groups and the GDB decreases.…”

Forced Gelation in an Off‐Stoichiometric Copolymerization of A2 and B3 Monomers

“…Among them, the simplest system was the A 2 þ B 3 one. [28][29][30][31] Recently, most of the work has focused on applying the latter systems to prepare hyperbranched polymers rather than gels. [26,32,33] Of interest is to modify the polymerization procedure in order to obtain a product of as highly branched molecular structure as possible.…”