PMMA particles

Yamamoto and Minamizaki [159] disclose the use of a curable silicone based release agent blended with resin particles which swell or are soluble in organic solvent. Coatings made with such blends can be written on with solvent based inks. For example, an addition cure silicone network containing 20 wt% 0.1 p,m diameter PMMA particles exhibited both good writeability (no ink dewetting and smear free) and a low release force of 10 g/cm for a PSA tape. 

Suppose we have a physical system with small rigid particles immersed in an atomic solvent. We assume that the densities of the solvent and the colloid material are roughly equal. Then the particles will not settle to the bottom of their container due to gravity. As theorists, we have to model the interactions present in the system. The obvious interaction is the excluded-volume effect caused by the finite volume of the particles. Experimental realizations are suspensions of sterically stabilized PMMA particles, (Fig. 4). Formally, the interaction potential can be written as... 

In-column solvent Column size (mm) Theoretical plate number Exclusion limit PMMA - Particle size (/ttn) Pore size (A) Flow Rate (ml/min) Maximum pressure (kgf/cm ) Maximum temperature (°C)... 

Fig. 2. Scatmu electron micrographs (JNM-ECP400-JEOL) of PMMA particles produced with different surfectaats (A) PDMS- OH (5.0 wt %), (B) PDMS-itiA (5.0 wt %). (C) PDMS-h-P(MMA(l.lK)-eo-MA(0.5K)) (5.0 wt %), (D) PDMS4b-P(MMA(l.lK)-co-MA(0.5K)) (10.0 wt %), (E) PDMS-co-PMA (5.0wt %), and (F) PDMS-co-PMA (10.0 wt %). Parameters in the paranthrais are wt % of surfactant with respect to monomer.

Fig. 7. Scanning electron micrographs of PMMA particles produced by dispersion polymerization in supercritical C02. Stabilized by PFOA homopolymer (top) [103] stabilized by PDMS macromonomer (bottom) [121]... 

Figure 2. Scattering intensity from PS(D) blocks in PS particles (a) and PMMA particles (b) (+, x, A, o) different PS(D)/PS(H) ratios between 1/2 and 1/12 in the particles ...

Flocculation studies (6) indicated that the mechanism of steric stabilization operates for the PMMA dispersions. The stability of PMMA dispersions was examined further by redispersion of the particles in cyclohexane at 333 K. Above 307 K, cyclohexane is a good solvent for PS and PDMS, and if the PS-PDMS block copolymer was not firmly anchored, desorption of stabilizer by dissolution should occur at 333 K followed by flocculation of the PMMA dispersion. However, little change in dispersion stability was observed over a period of 60 h. Consequently, we may conclude that the PS blocks are firmly anchored within the hard PMMA matrix. However, the indication from neutron scattering of aggregates of PS(D) blocks in PMMA particles may be explained by the observation that two different polymers are often not very compatible on mixing (10) so that the PS(D) blocks are tending to... 

Figure U. Plot according to Equation U for PMMA particles containing PS(D) blocks with undeuterated particle signal subtracted (reproduced from Higgins, J.S., Dawkins, J.V., and Taylor, G. Polymer 1980, 21, 627 by permission of the publishers Butterworth and Co. (Publishers) Ltd. ).

The combinational contribution to AG,n for PMMA particles stabilized by PIB in 2-methylbutane is shown plotted as a function of temperature in Figure 3(a). The values of the parameters used in Equations 2 and 3 were u = 8 x 10- g cm-, a = 300 nm, >2 = 1.09 cm g- and V = 116.4 cnr mole- . The thickness of the steric barrier,L, was taken to be 25 nm and the particle separation, do, was fixed at 30 nm. It can be seen from Figure 3(a) that AGj (comb) is a positive quantity that becomes more positive as the temperature increases, indicating that in the absence of other contributions to AG, the particle would become more stable with increasing temperature. In the above calculation, we have assumed that the S function, Equation 3, remains invariant with temperature, which is incorrect. 

Kreuter and Speiser [77] developed a dispersion polymerization producing adjuvant nanospheres of polymethylmethacrylate) (PMMA). The monomer is dissolved in phosphate buffered saline and initiated by gamma radiation in the presence and absence of influenza virions. These systems showed enhanced adjuvant effect over aluminum hydroxide and prolonged antibody response. PMMA particles could be distinguished by TEM studies and the particle size was reported elsewhere to be 130 nm by photon correlation spectroscopy [75], The particle size could be reduced, producing monodisperse particles by inclusion of protective colloids, such as proteins or casein [40], Poly(methylmethacrylate) nanoparticles are also prepared... 

Figure 6.6 The limiting high shear viscosity for quasi-hard sphere for PMMA particles in dodecane. (The particle has a different effective radii, HK3 = 419nm, HK4 = 281 nm, HK5 = 184 nm, HK7 = 120nm, HK8 = 162 nm.) The solid line is given by the Krieger equation (6.6) for a packing of (pm( oo) = 0.605...

Fig. 23. Variation of surface layer thickness with molecular weight of the stabilizing polydimethylsiloxane (PDMS) chain. Hydrodynamic thickness <5109) PMMA particles (O), PS particles ( ), micellar dispersions (A) from viscosity data x, thickness h from surface coverage data of PMMA particles assuming a prolate ellipsoid model for the...

Figure L Dependence of surface coverage on M (PDMS) (%) PMMA particles with Mn (PS] < 20000 PMMA particles with Mn (PS) > 30000 (O) PS particles (6)...

Figure 2. Dependence of surface layer thickness on Mn (PDMS) (O) PMMA particles ( , A) particles (6)...

In an effort to estimate the magnitude of the decrease in sedimentation rate due to interparticle interactions, several poly (methyl methacrylate) latexes (PMMA) were prepared since PMMA particles are too hard for expansion to occur at low acid levels. Thus surface charge can be adjusted in the absence of expansion. 

Furthermore, such monomers can be readily emulsified by dissolving in volatile solvents such as methylene chloride and chloroform. Uniform polylactide particles, and composite polystyrene (PST) and polymethyl methacrylate (PMMA) particles were produced by solvent evaporation [84-86]. 

Fig. 5.10 A monolayer of 700 pm. diameter Polymethyl methacrylate (PMMA) beads during a sintering process at 203°C, x 50. (a) After 25 min (b) after 55 min. [Reprinted by permission from M. Narkis, D. Cohen, and R. Kleinberger, Sintering Behavior and Characterization of PMMA Particles, Department of Chemical Engineering, Technion Israel Institute of Technology, Haifa.]...

The copolymer composition in miniemulsion copolymerization of vinyl acetate and butyl acrylate during the initial 70% conversion was found to be less rich in vinyl acetate monomer units [34]. Miniemulsion polymerization also allowed the synthesis of particles in which butyl acrylate and a PMMA macromonomer [83, 84] or styrene and a PMMA macromonomer [85] were copolymerized. The macromonomer acts as compatibilizing agent for the preparation of core/shell PBA/PMMA particles. The degree of phase separation between the two polymers in the composite particles is affected by the amount of macromonomer used in the seed latex preparation. 

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. 

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 same experimental group continued the research (61) by adsorption of carbon nanotubes onto both PS and PMMA particles in the same method, with four different surfactants. Finally, the prepared PS microspheres with adsorbed nanotubes were sonicated in deionised water to test the durability of their association. It was found that individual tubes remain strongly adhered to the PS microspheres surfaces even after exposition to ultrasound. 

Fig. 3 Changes in PMMA particle size during long term storage at 60 °C for microlatexes stabilized by different surfactants (filled triangles) TTAB (filled squares) TTAC (filled circles) CTAB (empty triangles) OTAC...

Dispersion polymerization in the presence of reactive surfactants including surfmers, inisurfs and transurfs is also a versatile method for producing functional microspheres [26]. For example, the macromonomeric azoinitiator 26 is an effective inisurf in the preparation of PS and PMMA particles [155]. 

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