High Ionic Strength Promotes the Formation of Spherical Copolymer Particles

Abstract

A comprehensive experimental study of thermally initiated styrene‐styrene sulfonate emulsion copolymerization in the presence of 15 different low‐molecular‐weight electrolytes clarifies the enormous influence of both the concentration and nature of the added salt on the outcome of the polymerization. The ionic strength (IS) has a direct influence on the styrene sulfonate content in the final copolymer and determines whether the physical state of the final reaction product is a solution or dispersion. Stable latexes have been obtained for IS as high as 18 M. Electron microscopy images show irregularly shaped clusters at low and spherical particles at high IS. The properties of the copolymer molecules and dispersion can be additionally modified by the chemical properties of the counter‐ and coions introduced with the salt.magnified image

“Schizomorphic” Emulsion Copolymerization Particles

“…[ 17 ] The PSS-PS copolymer particles were produced via self-initiating aqueous emulsion copolymerization of styrene and sodium styrene sulfonate. [ 18 ] This polymerization scenario favors the formation of copolymers with a block-like or gradient structure rather than statistical copolymers as discussed in. [ 18 ] The blockiness of the PSS-PS copolymer molecules is clearly supported by differential scanning calorimetry results showing only a single glass transition at 107.9 ° C, which is in the typical range for PS.…”

“…[ 18 ] This polymerization scenario favors the formation of copolymers with a block-like or gradient structure rather than statistical copolymers as discussed in. [ 18 ] The blockiness of the PSS-PS copolymer molecules is clearly supported by differential scanning calorimetry results showing only a single glass transition at 107.9 ° C, which is in the typical range for PS. Poly(styrene sulfonate) homopolymer shows no glass transition between -50 and 300 ° C.…”

“…The morphology as shown on image d of Figure 1 and image b of Figure 2 is observed at high and low concentration as well as on images of the solids after freeze-drying. [ 18 ] The lower the concentration of the particles in the dispersion, the farther the buds stretch away from the particle cores (Figure 1 image b). Further lowering of the particles concentration nearly causes their complete disintegration and aggregates of various morphologies appear ( Figure 1 , Figure 2 ).…”

“…Moreover, this behavior explains the huge difference of about 1000 nm in the average particle size estimated from electron microscopy images and determined by dynamic light scattering. [ 18 ] With the results presented here, this information must certainly be called into question as the routine evaluation of the dynamic light scattering data relies on solid spherical particle shape. to change shape and morphology in dependence on the particle concentration in the dispersion.…”

“…Modulation of the energetics happens via the particular conditions regarding ionic strength, valency of the counterions, and nature of the coions. [ 18 ] The fi nal form of such copolymer particle is the result of the various forces acting on it. It should be mentioned that the morphological features of the block This observation led us to the conclusion that the buds originate from the hydrophilic stabilizing blocks.…”