Gelation in ATRP Using Structurally Different Branching Reagents: Comparison of Inimer, Divinyl and Trivinyl Cross-Linkers

Abstract

Inimer and multivinyl cross-linkers were used as branching reagents for gelation in atom transfer radical (co)polymerization (ATRP) with methyl acrylate (MA). A fully reacted 2-((2-bromopropionyl)oxy)ethyl acrylate (BrA) inimer produced a “T” shaped cross-linkage, from which three chains emanated out. In contrast, the reactions of divinyl cross-linker, ethylene glycol diacrylate (2A), and trivinyl cross-linker, 1,1,1,-trimethylolpropane triacrylate (3A), generated “X” shaped and “x̵” shaped cross-linkages, respectively, from which 4 and 6 chains radiated out. The ATRP of MA and BrA produced soluble branched polymers, but the addition of a small amount of 2A into the reaction induced gelation and produced gels containing both “T” shaped and “X” shaped cross-linkages (“T&X” reaction). Three types of ATRP reactions, “T&X”, “X” and “x̵” reactions, were performed to study the effect of cross-linkage structure on the experimental gel points and the properties of gels. Under the same molar ratio of [vinylbranch]0/[R−Br]0, the “T&X” reactions had an experimental gelation occurred at lower MA conversions (earlier gelation) than the “X” reactions because of the faster intermolecular reactions in the “T&X” reactions. The earlier gelation in the “x̵” reaction, with respect to a comparable “X” reaction, was ascribed to the higher cross-linking efficiency and less required cross-linker amount for gelation when using trivinyl cross-linker. At complete conversion gels obtained in these comparable reactions showed an order of gel fraction: “T&X” ∼ “x̵” > “X” and of gel swelling ratio: “T&X” > “X” > “x̵”, due to the difference in the structure of branching reagents.