The preparation and characterisation of polymer latices formed in the absence of surface active agents

Abstract

Methods have been devised for the formation of monodisperse polystyrene latices in the absence of added surface active agents. The particles are stabilised, as a colloidal dispersion, by surface groupings which are an integral part of the particle and are not removed by dialysis. By suitable variation of the ionic strength of the aqueous phase, the initiator concentration and the polymerisation temperature, the final particle size obtained in single‐stage reactions was varied between c. 0.15 and 1.0 μm. The coefficient of variation on particle diameters was usually less than 5%. The ionic strength of the aqueous phase was found to play an important part in determining particle size; this was explained in terms of a limited coagulation process occurring at the stage involving the nucleation of polymer particles. Conductometric titration experiments revealed the presence of sulphate, carboxyl and hydroxyl groups on the particle surfaces. Molecular weight determination of the polystyrene formed showed that this was lower than that formed in conventional emulsion polymerisation.

Emulsifier-free emulsion copolymerization of styrene with quaternary ammonium cationic monomers

“…After that, the particle size increased with monomer conversion whereas the particle number remained constant (two-stage mechanism). 2 In the case of emulsifier-free emulsion copolymerization of styrene with an ionic monomer, the presence of the ionic monomer repeat-unit along the copolymer chains could make the mechanism for particle formation more complicated. Firstly, the incorporation of ionic monomer into the growing oligomeric radicals must have an influence on nucleation process.…”

“…Once they reach a critical chain length, the oligomeric radicals would precipitate to form nuclei (homogeneous nucleation) 19 or become surface active to form micelles (micellar nucleation). 2,20 These nuclei or micelles could be swollen by styrene molecules and consequently grow by three possible ways: 1) coagulation; 2) capture of newly formed oligomers or of dead polymer molecules from the aqueous phase; and 3) polymerization of absorbed styrene inside them. The particle stabilization is solely attributed to the electrostatic forces of the ionic end-groups that originated from the ionic initiator fragments and were located at the particle surface.…”

“…Emulsifier-free emulsion polymerization is especially suitable for the generation of particles free of added contaminating surfaceactive agents. The surface ionic groups can be easily introduced by using ionic initiators, as pioneered by Goodwin et al 2 For tailored synthesis of ionic polymer microparticles, however, emulsifier-free emulsion copolymerization of a sparingly water-soluble basic monomer (e.g., styrene) with an ionic comonomer is more versatile. The copolymerization can be conducted by using a batch process.…”

Formation of highly monodispersed emulsifier-free cationic poly(methylstyrene) latex particles

“…The most studied emulsifier-free system is styrene/persulfate/water. Goodwin et al 10,11 described the effect of initiator type and its concentration, ionic strength, and reaction temperature as well as monomer concentration on the particle size and surface charge density. Rudin et al…”

pH‐Responsive Microrods Produced by Electric‐Field‐Induced Aggregation of Colloidal Particles

“…Particle Synthesis: Anionic and cationic polystyrene lattices were prepared using a surfactant-free free-radical polymerization technique [27]. Poly(2-vinylpyridine) microgel particles containing 1 wt % divinylbenzene crosslinker were synthesized by using the same technique [25].…”