Study On Synthesis Of Well-Defined Fluorinated Acrylate Polymer Latex Particles And Their Film Formation

Fluoropolymers are an important class of high performance materials on account of their high chemical and thermal stability, low refractive index and dielectric constant, low surface energy leading to low friction coefficient and outstanding water- and oil-repellent properties. Because of the insolubility of fluorinated polymers in common solvents, aqueous emulsion polymerization with added fluorinated surfactants is a preferred method for industrial fluoropolymer production. However, such technology is not versatile and inadequate for many end user applications. Incorporation of fluorinated monomers into polymeric materials through copolymerization or blending is a common strategy to bypass the processing limitations determined by the incompatibility of most fluorinated polymers with unfluorinated polymers and solvents. In addition, the unfluorinated components may convey improved adhesivity and cohesivity, both important for coating applications, and reduce the cost of the final polymeric material.The general objective of this research was the exploration of various approaches to the development of water-borne fluorinated acrylate 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. The major study of the work is as follows:Aqueous dispersions of fluorinated particles (PBF) based on copolymers of butyl acrylate (BA) with 2-(perfluorononenyloxyl)ethyl methacrylate (FNEMA), were synthesized by emulsion polymerization in the presence of unfluorinated and fluorinated anionic surfactant binary mixtures. These fluorinated dispersions showed good to excellent colloidal stability, as determined by freeze-thaw, centrifugation, and critical coagulation concentration measurements. Latex films from the FNEMA copolymers stabilized with APFO, a perfluorocarboxylate surfactant, were highly hydrophobic as opposed to those in which AFPO was replaced by the branched perfluorosulphonate SFNBS.Well-defined core-shell semifluorinated particles containing the copolymer of slightly fluorinated 2,2,2-trifluoroethyl methacrylate (TFEMA) and reactive trimetoxy -silylpropyl methacrylate (TSPMA) as shell was synthesized by seeded semicontinuous monomer-starved emulsion polymeriozation. The non-fluorinated core particles were formulated to become the film-forming matrix of the heterophasic, nanostructured films, which were composed of the copolymer of butyl acrylate, methyl methacrylate and TSPMA (BMT).Stable colloidal dispersions of nanostructured semifluorinated acrylic particles with an unfluorinated core and an outer layer consisting of copolymers of the highly hydrophobic and lipophobic heptadecafluorodecyl methacrylate (FMA) were successfully synthesized with the assistance of three different cyclodextrins as phase transfer catalysts:β-cyclodextrin (β-CD), hydroxypropylβ-cyclodextrin (HpCD) and methylβ-cyclodextrin (MeCD). While all the cyclodextrins form a stable inclusion complex (IC) with FMA, only the ICs with the more hydrophilic HpCD and MeCD are soluble in water. Nevertheless, incorporation of FMA in the particle shell copolymer could be achieved also when usingβ-CD. On the other hand, the morphology of the nanostructured particles was dependent on the cyclodextrin used, the best results being obtained with MeCD. A monomer-starved semicontinuous emulsion polymerization procedure was essential to favor the CD-mediated incorporation of FMA into the copolymer structure, and to achieve a stable colloidal dispersion even in the presence of small amounts of mixed anionic-nonionic surfactants. The thermal and surface properties of the latex films showed a good correlation with the shell composition and nanostructured morphology of the particles.A series of water borne fluorinated acrylic copolymer particles with nanostructured core-shell morphology, narrow size dispersity and different controlled sizes and compositions were prepared by multi-stage emulsion polymerization. The latex particles had a common unfluorinated soft core copolymer containing the reactive trimetoxysilylpropyl methacrylate (TSPMA) and a thin, hard shell copolymer of either the slightly fluorinated 2,2,2-trifluoroethyl methacrylate (TFEMA) or the highly fluorinated 1H,1H,2H,2H-heptadecafluorodecyl methacrylate (FMA). In particular, the FMA-based particles were characterized by a range of either reactive (by TSPMA) or unreactive shell copolymer compositions and"patchy"morphologies dictated by the type ofβ-cyclodextrin used in the synthesis as FMA phase carrier. Corresponding differences of thermal and surface properties of the respective latex films were determined by differential scanning calorimetry, static and dynamic contact angle with water and hexadecane. Four series of binary blends of either TFEMA or FMA copolymer particles with large (3-4 diameters) particle size ratios and covering the whole range of compositions were prepared with the ultimate goal of producing super-hydrophobic film surfaces. The hexagonal compact packed 3D organization of the large particles in the single component films observed by AFM and electron microscopy was disrupted already at very low content of small particles, seemingly due to the insufficiently large particle size ratio. As a result, only moderate correlation between blend composition, film nano-roughness and contact angle of the highly hydrophobic films was found. Nevertheless, the results confirmed the proposed architecture as a promising tool for the simple fabrication of nanoheterogeneous highly hydrophobic and lipophobic films.