Polymer phase porous

Experiments pertaining to a new system for the application of bromine to flame retardant polypropylene and foamed polystyrene are described. The FR compound, ammonium bromide, is formed in the amorphous regions of the polymer phase by the interaction of bromine sorbed on the polymer and ammonia, sorbed subsequently. Gaseous nitrogen which is also produced, expands and brings about the rearrangement of the chains to produce a porous structure. The ammonium bromide produced is finely divided and imparts FR properties to the polymer. 

Up to now, a variety of non-zeolite/polymer mixed-matrix membranes have been developed comprising either nonporous or porous non-zeolitic materials as the dispersed phase in the continuous polymer phase. For example, non-porous and porous silica nanoparticles, alumina, activated carbon, poly(ethylene glycol) impregnated activated carbon, carbon molecular sieves, Ti02 nanoparticles, layered materials, metal-organic frameworks and mesoporous molecular sieves have been studied as the dispersed non-zeolitic materials in the mixed-matrix membranes in the literature [23-35]. This chapter does not focus on these non-zeoUte/polymer mixed-matrix membranes. Instead we describe recent progress in molecular sieve/ polymer mixed-matrix membranes, as much of the research conducted to date on mixed-matrix membranes has focused on the combination of a dispersed zeolite phase with an easily processed continuous polymer matrix. The molecular sieve/ polymer mixed-matrix membranes covered in this chapter include zeolite/polymer and non-zeolitic molecular sieve/polymer mixed-matrix membranes, such as alu-minophosphate molecular sieve (AlPO)/polymer and silicoaluminophosphate molecular sieve (SAPO)/polymer mixed-matrix membranes. 

Similar to Chromosorb 102 condition at 250°C most popular of all porous polymer phases... 

The limiting case of porous plastics are the so-called reticular porous plastics which lack cell walls, and the entire polymer phase is concentrated in the cell struts ... 

Supercritical pSFC applications can be defined as those in which the mobile phase is a single substance heated and pressurized above its critical point. Carbon dioxide has overwhelmingly been the compound of choice for these mobile phases. Stationary phases typically used for these applications have been polymeric materials or polymer-coated porous silica. Chromatography on uncoated silica-based stationary phases with CO2 has, in general, been unsuccessful. 

Continuous polymer rods, however, usually exhibit higher back pressure than conventional stationary phases. Therefore, a choice among polymerization solvents known to behave as pore formers has to be carefully made so that the resultant polymers are porous enough to give good flow properties of the eluent. To date, the most successful pore... 

The gases are assumed to be in equilibrium with the polymer phase on both sides of the skin layer. The composition of the gas in the pores next to the skin is generally not the same as the bulk composition of the permeate at that point The bulk composition depends on the flow arrangement of the separator, and the bulk gas could have either more A or less A than the gas in the porous layer. The diagram in Fig 26.4 shows a case where the bulk permeate is about 70 percent A, and the gas leaving the skin layer is about 90 percent A. 

The effective diffusion coefficient accounts for the rate of diffusion of the protein through the complex, porous polymer matrix. Incorporation of an effective diffusion coefficient is necessary because protein molecules do not diffuse through the pure polymer phase, but must find a path out of the slab by diffusing through a tortuous, water-filled network of pores. Z>eff is assumed to be independent of position in the slab Equation 9-14 is justified in this case by local averaging over a volume that is large compared to a single pore. Characteristic desorption or protein release curves are represented by Equation 9-18, with substitution of Dgn- for Z),.p ... 

FIGURE 28-28 Applications of size-exclusion chromatography, (a) Separation of fatty acids. Column polystyrene based, 7.5 x 600 nm, with exclusion limit of t x t0 Mobile phase telrahydrofuran. Flow rale 1.2 mL/min. Deteclor refractive index, (b) Analysis of a commercial epoxy resin n - number of monomeric units in the polymer). Column porous silica 6.2 > 250 mm. Mobile phase letrahydrofuran, Flow rate t.3 mL/min. Deteclor UV absorption. (Courtesy of BTR Separations.)... 

The (weak) opposition to silica gel consists of non porous materials, polymer phases, mixed phases (differing surface coverage within one column), titanium dioxide Ti02, aluminum oxide AI2O, graphite and micro cellulose. 

Stable polymer phases (e.g. molecularly imprinted gels) and non-porous materials have the best chances for a broader use. However, especially for non-porous materials the high price is an issue. 

Porous polymeric adsorbing resins, particularly styrene—DVB copolymers, have a complex texture which is well known to result from the microphase separation of an inert diluent from the polymer phase during the polymerization of the initially homogeneous solution composed of the comonomers and the diluent. Two types of diluents and, correspondingly, two reasons have been recognized for the phase separation. 

Molecularly imprinted polymers are highly cross-linked thermosets, and therefore porosity has been a necessary feature of their morphology to allow permeability and transport of template molecules to the bulk polymer phase. A high internal surface area ensures that the vast majority of the polymer mass is within several molecular layers of the surface and allows access of the template molecules to the majority of the polymer mass. A broad distribution of pore sizes is desirable for the use of these materials in chromatographic applications. Mesoporosity of amorphous porous materials is most commonly evaluated using a porosimeter by analyzing the N2 adsorption/desorption isotherms. Parameters that can be obtained from the measurements include surface area, average pore size, and pore size distribution. 

In this type of system, a matrix with a more or less continuous pore system is filled with a second component. The pore system is, however, fixed during the formation of the matrix itself. Thus one might expect some differences between polymer-impregnated concretes and the latex-modified concretes discussed above for example, the latter are inherently more porous because porosity will always develop during curing, regardless of the presence of polymer. In both cases, however, the cement and polymer phases appear to form continuous and intertwined networks. 

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