Preparation of poly (acrylic acid) microgels by alcohol type cross-linkers and a comparison with other cross-linking methods

Herein, poly (acrylic acid) (PAA) microgels were synthesized via alcohol type cross-linked by a free radical precipitation polymerization approach. At the first time, 1,6-hexanediol (1-6 diol), trimethylolpropane (TMP), and pentaerythritol (PEN) were selected as multifunctional cross- linking agent to synthesize crosslinked poly(acrylic acid) microgels. Alcohol type cross-linking agents can connect the PAA chains. The cross-linking reaction takes place due to reaction between hydroxyl groups of various cross-linkers and carboxyl groups of PAA chains. All of the hydroxyl groups do not participate in the reaction with acid groups of polymer chains through the polymerization stage; therefore, unreacted hydroxyl groups will react through sample drying (post-curing stage). The influence of cross-linker functionality and its concentration on various properties like swelling capacity, gel content, Tg (glass transition temperature), and rheological behavior were examined. The PAA microgels prepared via this cross-linking approach were compared to properties of microgels synthesized by epoxy type and vinyl type cross-linking agents in the previous studies. As a result, synthesized microgels via novel mechanisms have higher properties (for example, rheological and thermal properties) than that of PAA microgels prepared via the conventional mechanism. These behaviors can be due to decreasing (Mc) over bar (average molecular weight of two successive cross-links) in the polymeric network by utilizing new cross-linkers.

Automated summary

In this study, poly(acrylic acid) microgels were synthesized using alcohol type cross-linking agents, and the effects of different cross-linkers on properties were investigated. Microgels prepared via novel mechanisms showed higher properties, possibly due to a decrease in the average molecular weight of the polymer network.