Film Formation of Two-Stage Acrylic Latexes: Toward Soft-Core/Hard-Shell Systems

Abstract

Controlling the colloidal structure of multiphase latex particles offers a route to significant improvements in the mechanical properties of dried films for use in coatings. However, there is often conflict between the morphology that leads to optimum mechanical properties and the morphology that ensures good film formation at reduced temperatures. In this work, the case of two-stage latex particles in which the second-stage polymer has a high glass transition temperature (Tg) is considered. First, a number of different core/shell-like particles with different polymer compositions and particle structures are synthesized by seeded semi-batch emulsion polymerization. Using these latexes, the importance of phase mixing, particle morphology, and polymer composition with respect to film formation behavior and mechanical performance is discussed. The results highlight that in multiphase latex systems, the film formation behavior is dictated by the interplay between various colloidal and polymeric features of the samples. It is shown that understanding these features offers a route to systems that can match the film formation properties of a low Tg latex, whilst also approaching the mechanical properties of a high Tg polymer.