Modeling of Branching and Gelation in RAFT Copolymerization of Vinyl/Divinyl Systems

Abstract

The reversible addition-fragmentation chain transfer radical polymerization (RAFT) with branching/ cross-linking is theoretically investigated on the basis of the method of moments. The system considered consists of the copolymerization of vinyl monomer in the presence of a small amount of divinyl comonomer. It is found that the gel point is significantly postponed by increasing the RAFT agent concentration. Flory's criterion, Fr w,0 ) 1, is found to be satisfied at the gel point in the RAFT cross-linking process regardless of the unequal reactivities of vinyl/divinyl monomers in the absence of cyclization. The gel conversion can be analytically expressed and is determined by the polymerization recipe and the relative reactivities of various double bonds. The gel point is postponed by the presence of intramolecular cyclization, and its effect becomes significant in a dilute polymerization system. Branching distribution is found to be very broad with a large fraction of linear primary and slightly branched chains. By the introduction of the dependence of the reactivity of the pendant double bond on the local heterogeneity, the branching distribution becomes narrower and can be fine-tuned.

Synthesis and photoresponsive behavior of the high-Tg azobenzene polymers via RAFT polymerization

“…S2; P2, P4, P6 and P8) which became significantly more separated with increasing concentrations of BMI in polymerization system. These results indicated the formation of microgelation or branched polymer structure, in agreement with previous reports which had observed these structures following the addition of divinyl monomer to living free controlled polymerization systems [64][65][66].…”

A rapid crosslinking injectable hydrogel for stem cell delivery, from multifunctional hyperbranched polymers via RAFT homopolymerization of PEGDA

“…We believed this reduction was caused by the increased possibility of the radical chain transfer and termination at the lower monomer/CTA ratio condition due to the higher chain/radicals density in small regions. It has been reported that the increased RAFT agent can significantly postpone the gel point [31][32][33] . Here, with the higher monomer/CTA ratio condition ([M] 0 :[CTA] 0 = 100:1), the molecular weight and distribution dramatically increased at the later reaction phase leading to the earlier gelation; in contrast this trend was significantly delayed with the lower monomer/CTA ratio (or in other words, with higher concentration of the RAFT agent) ( Figure 2C-D), which was consistent with the former studies.…”

PEG Molecular Net-Cloth Grafted on Polymeric Substrates and Its Bio-Merits

“…Controlled/living radical polymerization (CLRP) techniques have been demonstrated to be advantageous in developing homogeneous polymer networks with controlled microstructure171819. However, since the CLRP methods generally require tedious pretreatment process prior to the immobilization of initiators on surface, it is difficult to directly apply them to inert polymeric substrates.…”