PMMA particle size distribution

Although a majority of these composite thermistors are based upon carbon black as the conductive filler, it is difficult to control in terms of particle size, distribution, and morphology. One alternative is to use transition metal oxides such as TiO, VO2, and V2O3 as the filler. An advantage of using a ceramic material is that it is possible to easily control critical parameters such as particle size and shape. Typical polymer matrix materials include poly(methyl methacrylate) PMMA, epoxy, silicone elastomer, polyurethane, polycarbonate, and polystyrene. 

It was also found that the polystyrene-b-PDMS block copolymers were not only effective at stabilizing styrene polymerizations in C02, but also in stabilizing MMA polymerizations. When using a polystyrene-b-PDMS block copolymer as the stabilizer the resulting PMMA was recovered in 94.1% yield with a Mn = 1.8 x 10 g/mol and a PDI = 2.8. The particles obtained are much smaller and more polydisperse than the particles obtained when using poly(FOA) homopolymer as the stabilizer (particle size = 1.55 - 2.86 pm vs. 0.23 pm and particle size distribution = 1.05 vs. 1.46). 

The data on particle size distributions for both PVA and PMMA emulsions suggest that small particles could be quite important in the kinetic scheme, and that the larger particles probably grow by internal polymerization and by flocculation with smaller particles. The experiments with the tubular reactor installed upstream of the CSTR demonstrate a practical way to eliminate uncontrolled transients with continuous systems. We believe that the particles generated in the tube prevent CSTR oscillations by avoiding the unstable particle formation reactions in the CSTR. Berrens (8 ) accomplished the same results by using a particle seed in the feed stream to a CSTR with PVC emulsion polymerizations. 

PMMA is also commonly used In dentistry applications for teeth and dentures. In most cases, several types of particulate filler are used to achieve a multimodal particle size distribution (for a higher particle content) and desired properties like wear resistance, processability, color, and gloss. Under physiological conditions, dental composites take up a certain amount of water. Repeated drying and wetting cycles can result in microcrack formation and accumulation at the interface between the polymer matrix and the inorganic filler (see Figs. 8.32-8.34). 

The particle size distribution after polymerizing a 5% Si02 particle in monomer suspension in water is depicted in Figure 5.11. Particles range in the size of 100 nm and distributions are rather narrow. As can be seen in the transmission electron microscopy (TEM) picture, the silica nanopartides are encapsulated in PMMA. As the particle content of the suspension was low, some polymer particles remain nonfilled. 

Figure 5.11 Particle size distribution measured with static laser light diffraction of PMMA particles filled with SiOi nanoparticles and TEM picture of the core-shell nanoparticles.

The adsorption of HMI on solid particles was investigated [11] using two different latex dispersions, namely polystyrene (PS) and polymethylmethacrylate (PMMA). Both lattices have a narrow particle size distribution with PS having a diameter of 321 nm and polydispersity index of 0.03 and PMMA having a diameter of 273 nm and polydisper-sity index of 0.05. The results are shown in Figure 15.5, which shows the amount of adsorption F in pmol/m versus HMI concentration (pmol/dm ). 

The product of the innovated polymerization procedure described above shows a uniform size distribution of spherical particles, with spheres size of 8 pm, contrary to polydispersed MWCNT/PMMA particles 1—12 pm in diameter. The polydispersity may originate from the presence of MWCNT particles (48), and the size of final MWCNT/PMMA spheres depends on MWCNT concentration and size and also on the level of MWCNT aggregation and the number of individual MWCNTs involved in the formation of composite particles. The presence of nanotubes in PMMA/MWCNT composites was confirmed by SEM analysis, which identified a large amount of MWCNTs at the surface of the composite spheres. Some of them are just adhered on PMMA spheres surface but others come into bulk of PMMA matrix. It was also confirmed by TEM analysis that nanotubes are well embedded in the surface of PMMA particles and even more, they are present inside individual PMMA/MWCNT particles. 

The above cited authors further modified the procedure (57) by applying ultrasonication during the whole polymerization time the resulting pure PMMA and composite particles are presented in Figure 8.10. Figure 8.10(a) represents PMMA microparticles prepared under mechanical stirring. As can be seen, the particles pose uniform size distribution, with a slightly smaller diameter ( 6 pm) than in the previous paper (48). The other two pictures present... 

It was discovered that sonication of the mixture during reaction results in PMMA/MWCNT particles with a uniform size distribution, which indicates that size distribution of composite spheres is strongly dependent on proper dispersion of the nanotubes in the reaction mixture, in this case caused by permanent sonication. Again, SEM analysis proved the presence of MWCNT on the surface of MWCNT/PMMA particles (nanotubes strongly and thickly adhered to the surface). 

The potential of SAXS for a precise analysis of the radial structure of latexes can be discussed best when considering model particles consisting of a well-defined core and a closed shell of a second polymer. The particles analyzed by SAXS [45-49] have been prepared recently [45] by a seeded emulsion polymerization [97] of PMMA onto a polystyrene core having a narrow size distribution. The alteration effected by seeded emulsion polymerization can be seen directly in the analysis of the size distribution by ultracentrifugation [87], the resulting distributions are shown in Fig. 17. Besides the increase in radius when going from the... 

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