Novel cross-linking mechanism for producing PAA microgels synthesized by precipitation polymerization method

A series of new cross-linkers, ethylene glycol diglycidyl ether (EGDGE), with new cross-linking mechanism, was utilized to prepare cross-linked poly(acrylic acid) microgels by precipitation polymerization method. All of the epoxy rings do not react with –COOH groups of PAA chains during polymerization stage; therefore, the unreacted epoxy rings would be reacted after polymerization stage (during sample drying time), which was named as “post curing stage.” The effect of cross-linker concentration, time, and temperature of post curing stage on the samples behaviors (i.e., swelling capacity, gel content, glass transition temperature, and rheological properties) were investigated. A new relationship between gelation rate in the post curing stage and epoxy content was defined. Also a relationship between average molecular weight of two successive cross-links (Mc), epoxy concentration ([epoxy]), and temperature of post curing stage (T _pc ) was suggested. The microgel properties such as the rotational viscosity and rheological properties (that was synthesized by this novel cross-linking method) were compared to that of microgels that were synthesized by divinyl-type cross-linkers (trimethylol propane triacrylate (TMPTA)). The results show that the microgel properties which were synthesized by novel cross-linking mechanism are better than that of microgel properties by conventional cross-linking method.