Diffusion of oligomers in latex systems — A route to low volatile organic compound (VOC) coatings

Abstract

We synthesize specially designed latex polymer systems by an in situ emulsion polymerization process that yields latex particles with both a high molecular weight polymer phase and a low molecular weight oligomer phase. The oligomer functions as a plasticizer by lowering the glass transition temperature (Tg) of the polymer. A polymer system is prepared by blending soft latex and a hard latex where the hard mode consists of a hard, high molecular weight polymer and an oligomer, allowing for facile film formation at ambient conditions. Upon the soft and hard particles coming into contact during the film formation process, the oligomer preferentially diffuses from the hard polymer to the soft polymer, thus recovering the natural Tg of the hard polymer as described in a recent patent application. Oligomer diffusion allows a hard coalesced phase to be incorporated into a latex film without using a coalescing solvent, which would contribute to the volatile organic compound (VOC) content. A well-coalesced hard phase in a latex film contributes to a variety of desirable coatings properties, such as tack, print, block, and scrub resistance properties.