Comparison of irreversible and reversible cluster formation

Abstract

Covalent and reversible cluster molecules were synthesized by an A3B2 type gelation. Crosslinking of three‐arm hydroxyl‐terminated star polymers with 2,4‐toluenediisocyanate gave branched polymers, while the reversible analogue was made by crosslinking of tertiary amine‐terminated star polymers with bis(4‐hydroxy‐3,5‐dinitrophenyl) adipate. Gelation process was followed by static and dynamic light scattering. The extent of reacted groups was measured with UV spectroscopy. Growth of the covalent clusters could be described in terms of percolation scaling laws. The experimental gel point (POH, cr = 0.70) was shifted significantly from the theoretical predicted gel point (POH, cr = 0.50), indicating extensive ring formation during the gelation. The reversible endlinking reaction gave no macroscopic gelation, though increase of the cluster dimensions was observed. Ring formation proved to be an important side reaction in both cases; however, the ring formation ability seems to change in a different manner during the course of a gelation.

Small-angle neutron scattering of arborescent polystyrene-graft-poly(2-vinylpyridine) copolymers

“…Gauthier et al observed that A 2 became close to zero in a good solvent as the branching functionality of arborescent polystyrenes increased which agrees with the results observed in this study [1,24]. The dependence of A 2 on branching functionality can be rationalized by the fact that the dilute solution properties of branched polymers are dominated by their high segment density [26,27]. As the generation number increases the overall segment density inside the polymer coil becomes higher (following scaling relationship which will be discussed later), giving rise to increased numbers of polymer -polymer contacts and the system behaves, from the point of view of A 2 ; equivalently to a linear polymer system at a much higher concentration.…”

“…The high level of branching leads to the molecules having a much smaller average dimension and higher segment density when compared with a linear polymer of the same molecular weight. Studies in the literature have shown a decrease in A 2 with polymer molecular weight for branched polymers compared to equivalent molecular weight linear molecules [26,27] and according to Gauthier et al A 2 for arborescent homopolymer polystyrene in solution is more strongly influenced by branching functionality than by the overall molecular weight of the polymer [24]. Gauthier et al observed that A 2 became close to zero in a good solvent as the branching functionality of arborescent polystyrenes increased which agrees with the results observed in this study [1,24].…”