Influence of the geometric factors of the experimental device used in suspension polymerization on the properties of poly(styrene‐co‐divinylbenzene) microparticles

Abstract

The prediction of the final particle size for reactive systems such as the reactions of suspension polymerization is a complex matter. Thus, the preparation of very small microparticles is specially challenging, probably because of the coalescence of the polymeric beads taking place during the later stages of the polymerization. In this work, very small gel-type styrene-co-divinylbenzene beads were synthesized by using a previously determined set of experimental synthesis conditions in which the stabilization of the dispersion of the monomeric droplets was ensured, and, under these conditions, the factors related to the geometry of the experimental device were modified to determine their actual effect on the final size of the microparticles. From the experimental results, a very simple and useful model was obtained that was able to predict the final size of the microparticles as a function of the values of the geometric factors of the reactor. This model indicates that the most influential factors in the final size of the microparticles are the liquid depth inside the reactor and the stirrer diameter; thus, an increase in the liquid depth produces larger particles, and, conversely, the particle size decreases when using larger stirrer diameters. Additionally, the model permits the design of polymerization experiments aimed at obtaining microparticles with a diameter smaller than 50 lm.

Functionalizable hydrogel microparticles of tunable size and stiffness for soft-tissue filler applications

“…The relative span represents the breadth of size distribution, with a smaller span suggesting a lower polydispersity. Unless otherwise noted the MP prepared in this study had a relative span of ~1.5, which being lower than 2, suggests a low polydispersity [30]. The gelatin MP, the semi-IPN MP of HA methacrylate–gelatin and the PEG MP prepared at twice the normal PI concentration or UV intensity were visibly “sticky”.…”

“…While the method is generally applicable to acrylated (bio)polymers and was used to prepare MP of acrylated HA, gelatin and their semi-IPNs, PEG MP were used for detailed characterization. The D90 and relative span value were used to report the particle size distribution (PSD) in this study because they are commonly used to report size data of particles with a non-symmetric PSD and have been used for other suspension-polymerized systems [30]. The relative span represents the breadth of size distribution, with a smaller span suggesting a lower polydispersity.…”

“…As with suspension or emulsion polymerization systems used to prepare PLGA MS or polystyrene MP [30,46], increasing stirring speed or surfactant concentration decreased the size of PEG50 MP. The droplet size and eventually the MP size in suspension polymerization systems are decided by the competition between the rate of droplet break-up and coalescence.…”

“…Upon filtering an MP suspension through a metallic sieve 115 μm in size, we found that the D90 decreased from 135 to 61 μm and, importantly, the relative span decreased from 1.54 to 0.74. Experimental variables such as the geometry of the vessel, the stirrer size and the experimental conditions, which are known significantly affect the size, polydispersity and yield of the MP [30,58], may be systematically optimized to obtain the desired MP. Changing the identity, concentration and functional groups of the non-crosslinked (bio)polymers can also be used to prepare MP with desired characteristics, such as pH sensitivity or surface charge.…”

“…Photocrosslinking was chosen because it can be carried out in ambient conditions, is efficient and affords precise spatiotemporal control over the crosslinking. The size distribution of suspension-polymerized MP can change as the reaction proceeds and, unlike chemical or thermal crosslinking, light-based crosslinking provides better control over the termination of the reaction [30]. Irgacure 2959 (I2959) was chosen as the photoinitiator (PI) because of its better cytocompatibility relative to other commercially available photoinitiators and its extensive use in preparing biomaterials, including those that encapsulate mammalian cells [31–34].…”