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ABSTRACT:The design of a semicontinuous emulsion polymerization process, primarily based on theoretical calculations, has been carried out with the objective of achieving overall independent control over the latex particle size, the monodispersity in the particle size distribution, the homogeneous copolymer composition, the concentration of functional groups (e.g., carboxyl groups), and the glasstransition temperature with n-butyl methacrylate/n-butyl acrylate/methacrylic acid as a model system. The surfactant coverage on the latex particles is very important for maintaining a constant particle number throughout the feed process, and this results in the formation of monodisperse latex particles. A model has been set up to calculate the surfactant coverage from the monomer feed rate, surfactant feed rate, desired solid content, and particle size. This model also leads to an equation correlating the polymerization rate to the instantaneous conversion of the monomer or comonomer mixture. This equation can be used to determine the maximum polymerization rate, only below or at which monomer-starved conditions can be achieved. The maximum polymerization rate provides guidance for selecting the monomer feed rate in the semicontinuous emulsion polymerization process. The glass-transition temperature of the resulting carboxylated poly(n-butyl methacrylate-co-nbutyl acrylate) copolymer can be adjusted through variations in the compositions of the copolymers with the linear Pochan equation.

Poly(n-butyl methacylate-co-n-butyl acylate) [P(BMA/BA)] soft latexes (carboxylated and noncarboxylated) were synthesized using a semicontinuous emulsion polymerization process that was designed on the basis of a theoretical calculation to determine the suitable surfactant [i.e., sodium dodecyl sulfate (SDS)], monomer, and water feed rates to maintain a constant particle number throughout the polymerization (guaranteeing monodispersity in the particle size), to obtain a homogeneous copolymer composition, and to independently control the particle size and carboxyl group concentration. The experimental results support the theoretical calculation. The surface coverage of the carboxyl groups present on the soft latex particles ranges from 7.6 to 21.9% for a series of latexes with particle sizes around 120 nm. In another series of latexes, the particle size was varied over a range from 120 to 450 nm. Monodisperse carboxylated polystyrene hard latexes were synthesized by shot growth (batch) and semicontinuous processes. The shot growth method is somewhat inflexible in providing more choices in surfactant, particle size, and surface carboxyl coverage. A semicontinuous process designed using a similar method used for the synthesis of P(BMA/BA) latexes successfully eliminated the drawbacks of the shot growth process. In this way, the changes in the surface carboxyl coverage (varies from 0 to 77.2%) was independent of the particle size, which was precisely controlled by the amount of styrene fed under suitable styrene and SDS feed rates.

ABSTRACT:The mechanical properties of films prepared from model high-glass-transition-temperature (T g )/low-T g latex blends were investigated with tensile testing and dynamic mechanical analysis. Polystyrene (PS; carboxylated and noncarboxylated) and poly(n-butyl methacrylate-co-nbutyl acrylate) [P(BMA/BA); noncarboxylated] were used as the model high-T g and low-T g latexes, respectively. Carboxyl groups were incorporated into the PS latex particles to alter their surface properties. It was found that the presence of carboxyl groups on the high-T g latex particles enhanced the Young's moduli and the yield strength of the PS/ P(BMA/BA) latex blend films but did not influence ultimate properties, such as the stress at break and maximum elongation. These phenomena could be explained by the maximum packing density of the PS latex particles, the particleparticle interfacial adhesion, and the formation of a "glassy" interphase. The dynamic mechanical properties of the latex blend films were also investigated in terms of the carboxyl group coverage on the PS latex particles; these results confirmed that the carboxyl groups significantly influenced the modulus through the mechanism of a glassy interphase formation.

ABSTRACT:The surface properties of films prepared from a blend of precipitated calcium carbonate pigment (PCC) and poly(n-butyl methacrylate-co-n-butyl acrylate) [P(BMA/BA); T g ϭ 0°C] latex were investigated in terms of the surface characteristics of the PCC and P(BMA/BA) latex particles. It was found that the presence of carboxyl groups on the P(BMA/BA) latex particles significantly improved the uniformity of the distribution of the PCC particles within the P(BMA/BA) copolymer matrix and the gloss of the resulting films. This phenomenon could be explained by an acid-base reaction between the PCC particles and the carboxylated P(BMA/BA) latex particles. Studies on the influence of the composition of PCC/P(BMA/BA) latex blends on the gloss and transparency of the films were also performed, which led to the determination of the critical pigment volume concentration (CPVC) of this system, which was found to be 42 vol %.