Well-defined Polymer-based Particles and Films: Controlled Morphologies trough Polymerization Processes in Heterogeneous Systems

Aim of the work The general objective of this research was the exploration of various different approaches to the development of water-borne polymer-based particles and latex films having a well-defined structure, morphology and surface. Free radical emulsion polymerization, if necessary combined with sol-gel chemistry, was selected as the key synthetic procedure for the preparation of nanostructured materials mainly aimed at coating applications. This dissertation is divided in four parts: - In Chapter 2 the evolution of the main colloidal parameters in the seeded starved-feed semi-continuous emulsion polymerization of a methacrylic monomer (butyl methacrylate) was investigated, with the main purpose of defining the key parameters necessary to achieve latex colloidal stability and control over the final particle size. Both the role of the latex seed and the effect of the type and amount of surfactant (anionic or non-ionic) added during the semicontinuous stage were considered. The results of such preliminary investigation represent the common ground for the following sections, in which an accurate control of size, composition and morphology of the produced polymer particles were critical factors for the successful development of more complex hybrid nanostructured latex-based materials. - In Chapter 3 is described the synthesis of reactive acrylic latex particles based on copolymers of trimetoxysilylpropyl methacrylate (TSPMA) by means of seeded starved-feed semi-continuous emulsion polymerization. The effects of polymerization conditions, pH, copolymer composition, and thermal annealing of the latex films were studied and related to the bulk polymer properties (Tg, swelling, dynamic-mechanical properties) and to self-crosslinking behavior. - In Chapter 4 the behavior of asymmetric blends of fluorinated and non-fluorinated acrylic copolymer latexes was studied with particular attention to the role of particle size, particle size asymmetry, and volume fraction of the two polymers in determining specific surface morphologies and generating low free energy surfaces. The surface behavior and the bulk properties of the films cast from the latex blends were investigated and the percolation phenomenon was taken into account in order to explain the observed results. - At last, in Chapter 5 hybrid nanostructured latex particles were prepared by combined emulsion polymerization and sol-gel processes. TSPMA-containing latexes were used as precursors for hybrid acrylic/silica core-shell particles. The key reaction parameters during the sol-gel stage were investigated with regard to the effectiveness of the sol-gel coprecipitation of silica onto the surface of pre-formed polymer latex particles, with particular attention to the colloidal stability and morphology of the resulting core-shell hybrid particles.