Comb-like acrylic-based polymer latexes containing nano-sized crystalline or liquid crystalline domains
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Conventional (meth)acrylate polymer latexes have been widely used for coatings, adhesives, paper and textile finishes, cement additives and other applications. These polymers exhibit useful properties such as adhesion to relatively polar substrates (steel, aluminum, tin, glass and wood), durability, weather resistance, flexibility in composition and glass transition temperature, and compatibility with many polar polymers and inorganic components. However, since these polymers are generally amorphous, they cannot compete in demanding applications where polymers with some degree of crystallinity performed well; e.g., they do not adhere well to most non-polar substrates such as polyolefins, they do not exhibit good mechanical properties (toughness) and they are inferior to olefins in terms of water resistance, barrier properties and durability. Therefore, there is a need of polymer compositions which provide better mechanical and barrier properties, adhesion to polar and non-polar substrates, water and weather resistances and durability. Crystalline and liquid crystalline domains are known to impart improved mechanical and barrier properties of polymers; therefore, the introduction of crystalline and/or liquid crystalline domains in amorphous (meth)acrylate polymer matrix may be a good solution for the above mentioned purpose.This work focus on both coating and adhesive applications of waterborne (meth)acrylic-based copolymer latexes containing crystalline domains and liquid crystalline polymers. The polymer latexes were synthesized via 2-step seeded miniemulsion copolymerization of a crystallizable long side chain acrylate monomer (stearyl acrylste, SA) (first method) or side chain liquid crystalline monomer (SCLCM) (second method) with short side chain (meth)acrylates. Thermal characterization of the films prepared from these latexes indicated that the heat of fusion and crystallinity of the copolymer latexes increased with SA or SCLCM content. The performance of coating films showed that the presence of poly(SA) crystalline and/or liquid crystalline domains reinforced the mechanical properties of polymer films. Conversely, the amorphous domains of poly(SA) and side chain liquid crystalline polymers had plasticizing effects and decreased the mechanical properties of the copolymers. Moreover, the presence of poly(SA) and side chain liquid crystalline polymers improved the barrier and water sensivity of the polymer films. Additionally, for pressure sensitive adhesives (PSAs) it was found that shear resistance, peel resistance and loop tack of soft acrylic-based PSAs increased with crystalline content. Moreover, the PSAs containing crystalline domains showed thermo-responsive behavior.