Polystyrene solvent/nonsolvent

Ogawa et al. (23) used a HFIP/toluene (20 80) mixture as the eluant for nylon 12. Column fractionation of the same polymer was also performed using benzyl alcohol/decalin as the solvent/nonsolvent pair. They were able to demonstrate that in the HFIP/toluene mixture, polystyrene narrow standards and nylon 12 narrow fractions were in compliance with the universal calibration... 

Phase Separation. Microporous polymer systems consisting of essentially spherical, intercoimected voids, with a narrow range of pore and ceU-size distribution have been produced from a variety of thermoplastic resins by the phase-separation technique (127). If a polyolefin or polystyrene is insoluble in a solvent at low temperature but soluble at high temperatures, the solvent can be used to prepare a microporous polymer. When the solutions, containing 10—70% polymer, are cooled to ambient temperatures, the polymer separates as a second phase. The remaining nonsolvent can then be extracted from the solid material with common organic solvents. These microporous polymers may be useful in microfiltrations or as controlled-release carriers for a variety of chemicals. 

In addition to monomers and the initiator, an inert liquid (diluent) must be added to the monomer phase to influence the pore structure and swelling behavior of the beaded resin. The monomer diluent is usually a hydrophobic liquid such as toluene, heptane, or pentanol. It is noteworthy that the namre and the percentage of the monomer diluent also influence the rate of polymerization. This may be mainly a concentration or precipitation effect, depending on whether the diluent is a solvent or precipitant for the polymer. For example, when the diluent is a good solvent such as toluene to polystyrene, the polymerizations proceed at a correspondingly slow rate, whereas with a nonsolvent such as pentanol to polystyrene the opposite is true. 

Producing a polystyrene (PS)-DVB copolymer of increasing porosity has been accomplished by dissolving 50-80% styrene, 10-50% divinylbenzene, and 30-70% of an inert organic liquid. Toluene is a solvent for the monomer but is a nonsolvent for the polymerized polymer. The monomer solution is then incorporated into water to form a dispersion of oil droplets followed by the polymerization of the suspended oil droplets from the aqueous medium into the polymer (21). 

To follow up this reasoning, we subjected reprecipitated polystyrene to spectrographic analysis. Emulsion polymer at its unadjusted pH was precipitated in 10-fold excess of methanol (a solvent for Triton X-405), dried, dissolved in toluene (a nonsolvent for the Triton), filtered, and the toluene solution was added to a 10-fold excess of methanol. About 1.5% of the polymer remained as a fine dispersion which could not be precipitated or separated by the addition of water or by centrifugation, thus exhibiting characteristics to be expected of a polystyrene graft to Triton X-405. [The value of 1.5% is completely consistent with the calculated value of about 18% by weight of Triton X-405 which could be associated... 

The solution was diluted with cyclohexane, a solvent for polystyrene and a nonsolvent for polymethylmethacrylate, and the product thereafter precipitated by addition to methanol THF/cyclohexane/methanol = 1 2 10 (by volume). The product was finally dried to constant weight. 

Cross-linked polystyrene porous particles (with 21 mol% DVB) have been prepared by the concentrated emulsion polymerization method, using either toluene or decane as the porogen and an aqueous solution of SDS as the continuous phase. Since toluene is a good solvent for polystyrene while decane is a nonsolvent , the morphologies obtained in the two cases were different. The particles based on toluene (with a volume fraction of dispersed phase of 78%) have very small pores which could not be detected in the SEM pictures. The pore size distribution, which has sizes between 20 and 50 A and was determined with an adsorption analyzer, almost coincides with that in a previous study [49] in which porous polystyrene beads have been prepared by suspension polymerization. In contrast, the porous particles based on decane have pore sizes as large as 0.1-0.3 pm, which could be detected in the SEM pictures [44a], and also larger surface areas (47 m2 g ) than those based on toluene (25 m2 g ). The main difference between the concentrated emulsion polymerization and the suspension polymerization consists of the much smaller volume fraction of continuous phase used in the former procedure. The gel-like emulsion that constitutes the precursor in the former case contains polyhedral cells separated by thin films of continuous phase. The polymerization of the cells does not... 

Sederal and De Jong propose a further novel modification in controlling the porosity of SDVB matrices by using a solvating or a nonsolvating diluent along with a linear polymer such as polystyrene. The modified polymeric materials PMS (porous by macromolecular material and solvent) and PMP (porous by macromolecular material and precipitant) differ in their pore structure from the polymeric matrix... 

As shown In Figure 4, the rate of polymerization of styrene was retarded by good nonvlscous solvents such as benzene, cyclohexane, and octane whose solubility parameters (6) were within 1.5H of that of polystyrene at styrene to additive ratios of 3 to 1. The absolute rates were slightly Increased In poorer nonvlscous solvents such as heptane and hexane and were fastest In viscous nonsolvents such as dllsoctyl phthalate and Nujol. Rate studies Indicated a Rp dependency on [E] substantially greater than unity for the styrene emulsion systems modified with viscous poor solvents. 

It is noteworthy that highly porous resins may also swell in certain nonsolvents (e.g. polystyrene in methanol). Swelling of highly porous resins by nonsolvents is the result of liquid storage within the pore structure of the resin matrix whereas general solvent compatibility of copoly(styrene-... 

Rotational diffusion rates of 2,2,6,6-tetramethyl-4-piperidinol-l-oxyl, bound to 2% cross-linked polystyrene with DF 0.02, arc slower than those of the soluble nit-roxyl (331. The rates (as the inverse rotational correlation time v ) increase with increased swelling of the polymer, from 3 x 10 s with no solvent or with the nonsolvents ethanol and 2-propanol, to 3 x 10 s i with benzene, to >10 s for a benzene solution of the corresponding soluble polystyrene. Increased cross-linking (4% and 12% DVB) gives decreased swelling a decreased rotational diffusion rates. 

Because of its solubility in both THE and more polar solvents, PVAc has also been used to calibrate systems employing mobile phases that are nonsolvents for polystyrene. Gilding et al. (9) describes a technique for calibrating an SEC system in hexafluoroisopropanol (HPIP) using broad molecular weight distribution (MWD) PVAc standards. HPIP, a nonsolvent for polystyrene, is an excellent solvent for polyamides, polyesters, polyurethanes, and polyglycolic acid. 

In addition, polymer micelles have been demonstrated to be more stable and also have a significantly lower cmc than surfactant micelles. Further discussion of surfactant micelles is beyond the scope of this review, and, instead, the reader is directed to a recent review article by Armes. In fact, the polymer building blocks need not be amphiphilic and such phase-separated nanostructures can be formed from completely hydrophobic or lipophilic diblock copolymers that contain two segments with differing solubility (such as polystyrene- -polyisoprene) and hence can undergo phase separation in selective solvents. One example of such completely hydrophobic phase-separated micelles are those reported by Wooley and coworkers, which can be obtained from toluene and acetone solutions of a [polystyrene-a/f-poly(maleic anhydride)]-fc-polyisoprene Iriblock. Conversely, inverse structures are also accessible and are known as reverse micelles. These can be formed by adding a nonsolvent for the hydrophilic block to afford the opposite of a conventional micelle, for which the hydrophilic core is surrounded by a hydrophobic shell in a hydrophobic surrounding media. There have been a handful of reports on the application of these reverse micelles, for example, as nanoreactors and for the extraction of water-soluble molecules. ... 

The dye adsorbed on the spectrophotometer cell wall from a solution containing PSCOO D can be washed out by methanol, a nonsolvent for polystyrene. The adsorbed dye is, therefore, unlikely to have PSCOO" as its counter ion. In all probability the co-ex-tracted water in the organic solvent caused a reversal of the equilibrium (l) as follows ... 

If a nonsolvent such as methanol is gradually added to a homogeneous solution of a polymer in a good solvent (such as polystyrene in chloroform) the negative value of AG wiU decrease correspondingly, until the special situation of AG = 0 (i.e., = TA mix). called the (theta) 0-condition,... 

Instead of using benzene or toluene as a solvent for styrene/DVB in the grafting solution, polar solvents, such as methanol, 2-propanol, and 2-propanol/water mixtures, brought about substantially enhanced grafting kinetics, because these nonsolvents do not swell the grafted polystyrene and thereby result in extended radical lifetimes. 

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