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

Immer 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-bromoptopionyl) oxy)ethyl acrylate (BrA) immer 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 "X" 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" and "X" shaped cross-linkages ("T&X" reaction) Three types of ATrP reactions, "T&X", "X" and "X" 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 [vinyl(branch)](0)/[R-Bi](0) the "T&x" reactions had an experimental gelation occurred at lower MA conversions (earlier gelation) than the "X" reactions because of the laster intermolecular reactions in the "T&X" reactions. The earlier gelation m the "X" reaction, with respect to a comparable "X" reaction, was asubed 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" similar to "X" > "X" and of gel swelling ratio. "T&X" > "X" > "X", due to the differnce in the structure of branching reagents.