Preparation and properties of novel plastisols based on acrylic core-shell lattices

Abstract

A series of core-shell lattices comprising a core portion of rubbery acrylic homo- or copolymers and a surrounding shell portion of glassy methyl methacrylate (MMA) homo- or copolymers were designed as plastisols for automotive underbody coatings. The lattices were synthesized by a semi-continuous seeded emulsion polymerization and characterized by using differential scanning calorimetry (DSC) and scanning electronic microscopy (SEM). DSC investigations demonstrated that the incorporation of a hard segment of MMA into the core portion and strongly polar monomer methyl acrylic acid (MAA) or cross-linker allyl methacrylate (ALMA) into the shell portion resulted in an improvement of the glass transition temperatures. SEM micrographs verified that the latex particles were always spherical with regular structure throughout the polymerization stage. Novel plastisols were developed based on the abovementioned core-shell polymers with dioctyl phthalate (DOP) or tricresyl phosphate (TCP) plasticizers, whose core portions were compatible with the employed plasticizer and whose shell portions were incompatible with the plasticizer. Evaluation of the viscosity as a function of the storage time revealed that the storage stability of the plastisols could be obtained through incorporation of the strongly polar monomer MAA or the cross-linker ALMA into the shell portions. The mechanical properties of the plastigels were improved by incorporating MMA into the core portion or by incorporating MAA or ALMA into the shell portion of the lattices. A balance between the mechanical properties of plastigels and the storage stability of plastisols should be considered during selection of the monomers both for the core and shell.