Non-equilibrium particle morphology in dispersion-polymerized polystyrene particles

Abstract

Abstract:The interior particle morphology of dispersion-polymerized polystyrene particles was investigated by freeze fracture TEM (FFTEM) in order to compare the morphology of particles formed under two extreme mechanistic conditions: (a) particle growth by scavenging of dead polymer chains formed in solution (which gives rise to large particles of 5-10 pm) and (b) particle growth by oligomeric radical capture and polymerization inside the particle (giving rise to small particles of 1 pm or less). Although not generally recognized in the literature, ascribing mechanistic significance to an observed morphology requires a demonstration that the morphology is of the non-equilibrium type, i.e., the morphology depends upon how the particle was formed. An equilibrium morphology, by definition, must be independent of the particle formation route, and therefore cames no mechanistic information. In this case, large PS particles of 6.5 pm were found to have a nodular morphology that was unchanged on heating well above Tg, indicating an equilibrium structure (the nodularity of amorphous polymers is briefly rationalized by comparison with literature results over the past 20 years). On the other hand, small PS particles of 1.3 pm had a pronounced radial structure that could be converted into the nodular morphology by the same heat treatment, or by dissolving and precipitating from a suitable solvent combination. This means that the small particles have a non-equilibrium morphology, from which we may attempt to draw mechanistic inferences consistent with the suspected growth mechanism.Key words: dispersion-polymerized polystyrene, non-equilibrium polystyrene particle morphology, freeze fracture transmission electron microscopy.RCsumC : On a Ctudik la morphologie de la particule intkrieure d'une dispersion de particules de polystyrkne (PS) par la technique de FFTEM dans le but de comparer la morphologie des particules formkes sous deux conditions mkcanistiques extr&mes : (a) croissance des particules par pikgeage des chaines mortes de polymkre formCes en solution (qui donnent lieu & de grosses particules de 5-10 pm) et (b) croissance des particules par une capture d'un radical oligomCrique et une polymkrisation & l'inttrieur de la particule (donnant lieu 2 de petites particules de I pm ou moins). M&me si ce fait n'est gtnkralement pas reconnu dans la littkrature, l'attribution d'une signification mkcanistique i une morphologie observCe ntcessite une demonstration que la morphologie est d'un type non Cquilibrk, c'est-&-dire que la morphologie dkpend de la faqon dont la particule s'est forrnCe. Par definition, une morphologie d'equilibre doit &tre indkpendante de la voie de formation de la particule; elle n'a donc aucune signification mkcanistique. Dans ce cas, on a trouvk que de grosses particules de PS de 6,5 pm posskdent une morphologie nodulaire qui ne change pas par chauffage & des tempkratures bien supkrieures & la T,; ceci suggkre l'existence d'une structure en tquilibre (on rationalise brikvement le caractkre nodulaire d...

Synthesis of highly crosslinked monodisperse polymer particles: Effect of reaction parameters on the size and size distribution

“…A combination of the multiple wavelengths and the two polarizations provided information about the differences between the particle sizes. With this instrument, the geometric standard deviation was directly defined with d 16 and d 84 from the cumulative volume distribution, which is used by many researchers because of the insensitivity to the size range selected for the calculation 5, 23–27…”

“…With this instrument, the geometric standard deviation was directly defined with d 16 and d 84 from the cumulative volume distribution, which is used by many researchers because of the insensitivity to the size range selected for the calculation. 5,[23][24][25][26][27] The size, shape, and size distributions of the polystyrene particles were also characterized by a Hitachi S-2500 C scanning electron microscope (SEM) operated at 10 kV. The glass-transition temperatures (T g 's) of the noncrosslinked and crosslinked monodisperse polystyrene particles EFFECT OF REACTION PARAMETERS were measured with a differential scanning calorimeter (DSC, PerkinElmer DSC7) at a heating rate of 10°C/min.…”