Colloidal Properties Of Latexes Research Articles

Synthesis of sulfonated poly(styrene‐co‐methyl methacrylate) by semicontinuous heterophase polymerization for filtration membranes

AbstractIn this study, styrene (St) and methyl methacrylate (MMA) were copolymerized in semicontinuous heterophase using Hitenol‐BC10 (HBC10) as polymerizable surfactant and ammonium persulfate as initiator to obtain copolymers of poly(St‐co‐MMA). The effects of St/MMA weight ratio and surfactant concentration on kinetics, and colloidal properties of latexes were studied. Copolymers and latexes were characterized by scanning electron microscopy, thermogravimetric analysis (TGA), gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, and X‐ray diffraction analysis. Fast reaction rates under monomer starved conditions and high conversions (>85%) were observed in all cases, with a weight‐average molecular weight in the range of 2.10 × 106 to 0.96 × 106 g mol−1, decreasing with the HBC10 concentration due to an effect of chain transference to surfactant. Stable latexes with spherical particles with average diameter in the interval of 65–41 nm and Z‐potential in the interval of −68.24 to −38.44 mV were obtained. Copolymers were sulfonated using acetyl sulfate as sulfonating agents and subsequently used for filtration membrane fabrication through the phase inversion method. Membranes were tested in simulated seawater filtration (3.5% NaCl) under constant pressure. At a pressure of 20 psia, permeated flux (J) of pure water and salt rejection (R) varied from 13.8 to 20.5 L m−2 h−1 and 37.8%–50.7%, respectively. It was concluded that membrane's performance is dependent on copolymer composition, the crystallinity of copolymers, and the ionic exchange capacity of membranes, being the best membrane composed of 90/10 of St‐to‐MMA weight ratio and using a monomer‐to‐surfactant weight ratio of 29.9.

Synthesis and characterization of water-based poly(vinyl acetate-co-butyl acrylate) latexes containing oligomeric protective colloid

Poly(vinyl acetate-co-butyl acrylate) latexes having oligomeric N-methylol acrylamide were prepared by semi-continuous emulsion polymerization. The effects of new protective colloid and comonomer ratios on the physicochemical and colloidal properties of latexes were investigated. The changes in homopolymer and copolymer latexes were determined by measuring viscosity, particle size, molecular weight (MW), molecular weight distribution (MWD), and surface tension. \( \bar{M}_{n} \) values of copolymer latexes were found to be lower than the MWs of the poly(vinyl acetate) and poly(butyl acrylate) homopolymers. In general, \( \bar{M}_{n} \) and \( \bar{M}_{\text{w}} \) values of copolymer latexes changed irregularly with increasing BuA ratio in the copolymer composition.

Batch and semicontinuous emulsion copolymerization of vinyl acetat–butyl acrylate. I. Bulk, surface, and colloidal properties of copolymer latexes

AbstractVinyl acetate (VAc)–butyl acrylate (BuA) comonomer mixtures with various composition were polymerized by batch and semicontinuous emulsion polymerization processes. PVAc and PBuA homopolymer latexes as well as the (VAc‐BuA) copolymer latexes were characterized with respect to particle size, molecular weight, acid end groups on particle surfaces, and colloidal stability against electrolytes. The surface and colloidal properties of these latexes were also compared before and after aging and acid hydrolysis. The average particle size of batch latexes was independent of copolymer composition, whereas for semicontinuous latexes it decreased with increasing BuA content and was always lower than that of the corresponding batch latex. The molecular weight distribution (MWD) for batch latexes was narrower and much less dependent on composition than that of the semicontinuous latexes; bimodal MWD was found in most semicontinuous latexes with a substantial amount of low MW fraction. The total weak and strong acid end groups on particle surfaces for semicontinuous latexes is higher, and more dependent on composition, than the batch latexes. Acid‐induced hydrolysis results in a drastic change in the type and concentration of the surface groups of the semicontinuous latex particles. Colloidal stability against electrolytes showed that both electrostatic (due to surface acid groups) and steric [due to surface poly(vinyl alcohol)] mechanisms are contributing. However, for semicontinuous latexes, increasing PVAc content above 50 mol % resulted in a proportional increase and ultimately dominant role of steric stabilization. The results were interpreted in terms of differences in reactivity ratios and water solubilities of the two monomers and their effects on the locus of initiation and growth in the two polymerization processes, as well as the monomer sequence within the polymer chain and degree of homogeniety of the copolymer composition within the particle.