The dispersion polymerization of methyl methacrylate (MMA) has been studied in a nonpolar hydrocarbon solvent at low temperature using N,N‐dimethylaniline (DMA) and lauroyl peroxide (LPO) as redox initiation system. To explain the heterogeneous kinetic characteristics of the polymerization process, the reaction locus has been experimentally and theoretically investigated. The evolutions of monomer conversion, polymer molecular weight distribution (MWD), and particle morphology were measured throughout the polymerization. It was found that the significant preferences of LPO and DMA to accumulate in the polymer‐rich phase after the system phase separation are mainly responsible for both the uniformity of particle sizes and the broad polymer MWDs. It was observed that particle agglomeration and breakup mechanisms were enhanced under agitation, thus promoting the formation of broader particle size distributions. The observed kinetics and thermodynamics of the low‐temperature polymerization were also examined through a mathematical model where the distributions of initiators, solvent, and monomer between phases were considered. A good agreement between the experimental and theoretical results was observed and the model was used to estimate the conditions that promote bimodal MWDs. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

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Cover: A highly porous silica particle used as a support for metallocene catalyst is emulated on two geometrically well‐defined support structures for the study of ethylene polymerization kinetics and nano‐ and micron‐scale polymer growth morphologies. Further details can be found in the article by Kyu Yong Choi and co‐workers http://doi.wiley.com/10.1002/mren.201400018.

Spherical silica particles with pseudo‐inverse opal structure are synthesized by using pomegranate‐like polymer microparticles as templates. A micro‐dispersion polymerization occurring in the suspended monomer droplets in the presence of a silica precursor leads to the formation of nearly monodisperse polymer sub‐particles of about 1 µm size, randomly‐packed within a 30–100 µm polymer particle. The polymerization is followed by an acid‐catalyzed reaction that induces formation of silica in the interstices between the sub‐particles within a polymer particle. Spherical PIOS particles are eventually produced by selectively removing the polymer template by pyrolysis. The PIOS particles show large specific surface areas with unique pore geometry and pore size distribution.magnified image

The kinetics of ethylene polymerization and the growth of polymer nanofibrils for the racEt(indenyl) 2 ZrCl 2 /MAO catalyst supported on flat-surface silica and nonporous silica nanoparticles are presented. The polymerization rate per mol of Zr is highest for the flatsilica supported catalyst due to maximum exposure of catalyst sites to cocatalyst and monomer. The SEM and AFM analysis show that large clusters of oxidized form of MAO are present at the surface, while nano-silica supported catalyst show less of such effects. The polyethylene grows as nanofibrils of 30-50 nm in diameter from the silica surface. No particle fragmentation is observed with nano-silica supported catalyst where polymer nanofibrils grow only from the external surface. Polymer properties are little affected by the support type.