Rheological Properties of (Meth)acrylic Cross-Linked Polymer Microparticles, 2. Role of Interactions in Non-Reactive and in Reactive Diluents. Copolymerization Studies

Abstract

The rheological properties of (meth)acrylic cross-linked polymer microparticle solutions have been studied regarding the influence of physical interactions. Cross-linked polymer microparticles (CPM) were synthesized with different functionalities: epoxy, acrylic, carboxyl, hydroxyl, octadecyl and methyl. The viscosities of either dilute or concentrated solutions in non-reactive solvent (xylene) and in reactive solvents (styrene and isobornyl acrylate monomer) have been measured for each type of CPM. A very weak effect of functionality was noticed on the intrinsic viscosity of CPM, whatever the solvent. Only carboxyl groups had a significant influence by increasing the viscosity because of hydrogen bonding. Greater effects were shown on the rheological properties of concentrated solutions. All solutions exhibited shear-thinning behavior when the solvent was xylene or styrene. Carboxyl functionalized CPM still led to higher viscosity, while octadecyl groups reduced the low shear limiting viscosity. The recovery time was strongly increased for CPM with epoxy and acrylic functionalities when styrene was used instead of xylene, whereas it remained the same for all other CPM solutions. In isobornyl acrylate monomer, only CPM functionalized epoxy and acrylic showed shear-thinning behavior, the other solutions being Newtonian. Finally a copolymerization study has been done on three solutions, containing either non-reactive CPM in reactive diluent, or reactive CPM in non-reactive diluent, or reactive CPM in reactive diluent. This study confirmed the cross-linking mechanism of acrylic systems. First, intramolecular reaction took place within the CPM and small aggregates were formed. Then these aggregates interconnected leading to a viscoelastic solid.