An overview is presented of the progress in understanding polymer heterogeneity over the last 20 years and how this has contributed to the improvement of coatings. Solvent-based polymers are homogeneous in nature, since all polymeric materials tend to be dissolved in the same solvent mixture. This is different for most waterborne polymers, which tend to be present in a compartmentalized way. Most polymeric materials are present in particles, which are separated by the continuous aqueous phase. This gives excellent opportunities to create particle morphologies that form the basis for the film morphology after drying of the coating. This article gives an overview of the various types of heterogeneity which are accessible in waterborne polymers and will show how heterogeneity in the polymer can contribute to the solution of several persistent problems of the coating industry.

The development of a waterborne acrylic binder that can be formulated into zero VOC paints requires the tuning of film formation under difficult conditions, hardness, and flexibility properties. To meet these requirements, a model of the 'ideal' film was developed and polymers were synthezised to comply with this model. The choice of particle size and glass transition temperature (T g ) of the polymer phases were the key parameters in producing the desired film morphology. However, to ensure good mechanical properties, it was also crucial to optimize the interaction between the polymer phases by varying both the polymer composition and the stabilization of the latex.

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Using self‐consistent field (SCF) theory, we studied the self‐assembly characteristics of polyurethane pre‐polymer dispersions in aqueous solutions. With a molecularly detailed model implementing the Scheutjens–Fleer discretization scheme, it is shown how the stability, equilibrium size, and internal structure of the (swollen) micelles in polyurethane (PU) dispersions depend on the chemical structure and the molecular composition of the charged pre‐polymer mixtures. The stability region of these micelles is found to increase when acid groups become deprotonated and when the ionic strength is lowered. Insight into the physical–chemical behavior of PU pre‐polymer dispersions is important for the subsequent process of film formation from the PU dispersions for the final coating properties.

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