Polymers, removal from purified

In the 1970s, Solvay iatroduced an advanced TiCl catalyst with high activity and stereoregulahty (6). When this catalyst was utilized ia Hquid monomer processes, the level of atactic polymer was sufftciendy low so that its removal from the product was not required. Catalyst residues were also reduced so that simplified systems for post-reactor treatment were acceptable. Sumitomo has developed a Hquid monomer process, used by Exxon (United States), ia which polymer slurry is washed ia a countercurrent column with fresh monomer and alcohol to provide highly purified polymer (128). 

To a 50-mL three-necked flask (Fig. 3.18b) equipped with a stirrer (comprised of a stainless steel shaft and paddle), a head for the distillation of water, and a nitrogen inlet is added 20 g of purified 11-aminoundecanoic acid. The flask is then purged with nitrogen for 5 min. The flask is warmed in a silicon oil bath to 220° C and maintained at this temperature for 10 h. After raising the stirrer from the molten mass, the reaction is cooled under nitrogen and the resultant polymer removed by breaking the glass. The Tm of the polymer is 185—190° C and the rjmh in m-cresol (0.5% at 35°C) is 0.6—0.7. 

Adipic acid and HMDA are obtained from nylon-6,6 by die hydrolysis of die polymer in concentrated sulfuric acid (Fig. 10.7). The AA is purified by recrystallization and the HMDA is recovered by distillation after neutralizing die acid. This process is inefficient for treating large amounts of waste because of die required recrystallization of AA after repeated batch hydrolyses of nylon-6,6 waste. In a continuous process,5 nylon-6,6 waste is hydrolyzed with an aqueous mineral acid of 30-70% concentration and the resulting hydrolysate is fed to a crystallization zone. The AA crystallizes and the crystals are continuously removed from the hydrolysate. Calcium hydroxide is added to neutralize the modier liquor and liberate the HMDA for subsequent distillation. 

Since better selectivity was obtained when the ligands were removed from the dihydropyran-derivatized polymer support, after synthesis they were cleaved from the polymer and used in catalysis without purification. Comparable selectivities were obtained with ligands that were used directly without purification and selected examples where the ligands were purified prior to use. For such an approach to be useful in catalyst development, it is critical that the material from the synthesis be of sufficient purity to be used without purification. 

A 25-ml scintillation vial was charged with the step 1 product (7 g), tin(II)-2-ethyl-hexanoate, and ethylene glycol (7.507 mmol) and then thoroughly shaken using a KEM-Lab vortex mixer at 35 rpm. This mixture was then treated with 4,4 -methylene-bis(cyclohexylisocyanate) (11.262 mmol) and then further shaken by the vortex mixer for 1 minute. The vial was then placed into a heat shaker for 15 minutes and stirred to ensure its consistency and then returned to the heat shaker for 3.45 hours. Half of the hot mixture was removed from the vial and placed into a second vial, which was treated with 15 ml of /V, V-d i met h I ace tam i de and put onto the shaker until the biodegradable elastomer was dissolved. This solution was then precipitated in 1000 ml of water, the dissolution/precipitation process being repeated twice. Thereafter the precipitated polymer was isolated and purified by lyophilization. 

As mentioned earlier, the ease of isolation of the product is the major advantage of the solid phase method. However, this is also a disadvantage because the product, the growing polypeptide attached to the polymer, is never purified until it is finally cleaved from the polymer. Each time a coupling reaction does not proceed in 100% yield, a small amount of the final product will be missing one of the amino acids. These impurities build up with the number of steps in the synthesis and become more and more difficult to remove as the polypeptide becomes larger. For this reason the yield of each step must be as high as possible. Current methods provide yields of 99.5% or better in each step. 

Interesting peculiarities of mass transfer processes are observed in fine membranes permeable to ions but impermeable to colloidal particles (semipermeable membranes, e.g. collodium film). If such a membrane separates colloidal system or polyelectrolyte solution from pure dispersion medium, some ions pass through the membrane into the dispersion medium. Under the steady-state conditions the so-called Donnan equilibrium is established. By repeatedly replacing the dispersion medium behind the membrane, one can remove electrolytes from a disperse system. This method of purifying disperse systems and polymer solutions from dissolved electrolytes is referred to as the dialysis. 

Thus, practically, a concentrated solution of purified D4 in CH2C12 solvent is polymerized by CF3S03H. Traces of water should carefully be removed. The ratio [D4.]o/[CF3S03H]o yields the required polymerization degree. The polymer is precipitated in CH3OH and the solvent is removed from the oily or solid polymer under vacuum. Monofunctional chain-stoppers (like hexamethyldisoloxane) can also be used to control the polymer Mn. 

Low-pressure Processes. Three processes for the polymerization of ethylene have recently been developed. The commercial process of the Phillips Petroleum Company for the polymerization of ethylene is carried out at relatively low pressures (100-500 psi) in either fixed-bed or slurry-type operations. The catalyst consists of 2-3 weight per cent chromium as oxide on silica alumina, and the reaction temperature varies from 90— 180°C. In fixed-bed operation, purified ethylene and hydrocarbon solvent streams are passed downflow, liquid phase over the catalsrst bpd. Solvent and polymer are collected, and the solvent is flashed overhead. Unreacted gases are removed from the solvent, taken overhead, and metered the solvent is recycled to the reactor. The solvent and polymer in the first receiver are cooled to room temperature to precipitate the polymer, which is then filtered and dried in a vacuum oven. In the slurry-type operation (indicated in Fig. 15-33 by a proposed flow diagram), solvent and a small... 

Merrifield succeeded in doing exactly what he described. The basic steps are in Scheme 1 (i) 1) An N-protected amino acid is attached as an ester to a cross-linked polystyrene support. 2) The protecting group is removed. 3) An N-protected, activated amino acid is coupled to the amino group of the polymer-bound amino acid. Steps 2 and 3 are repeated with different amino acids to produce the desired peptide sequence. 4) The completed peptide is cleaved from the polymer, deprotected, and purified. 

After less than 10% conversion the reaction tubes were cooled and the vacuum was released. The viscous solution was then precipitated in excess of dry hexane. The polymers were further purified by repeated dissolution and precipitation from THF into n-hexane so as to remove the unreacted comonomers and initiator species. 

In fact, the Eriedel-Crafts polymerization is a polycondensation, however, the term polymerization is more common. The Friedel-Crafts polymerization is notorious in producing an intractable reaction product, which is difficult to remove from the reaction vessel and to purify. Further, polymers with undesirably low molecular weights or poor thermal stahihty are obtained, if the reaction conditions are not appropriately chosen. ... 

Residual solvent and reactants were removed from the dough. Initial attempts to purify the polymer included one vacuum oven drying step (4 h at 80 C), used to drive off the residual solvent, followed by up to three supercritical CO2 extraction steps (8-h soak at room temperature and 2,000 psig), used to remove unreacted monomers, oligomers, and residual solvent. 

Poly(2,5-furandiylcarbonylimino-l,4 cyclohexylenemethylene-l,4 cyclo hexyleneiminocarbonyl). Following the procedure of Kelly, 1.200 g (0.0062 mole) of 2,5-furan dicarbonyl chloride (recrystallized in a dry box from purified hexane immediately before use) was dissolved in 20 ml of purified chloroform in a dry box. To this solution was added 1.320 g (0.0060 mole) of bis(4-aminocyclohexyl) methane and 1.200 g (0.012 mole) of purified triethylamine in 20 ml of purified chloroform, dropwise with magnetic stirring. The addition was made over approximately 0.5 hr. after which the solution was left to stir in the dry box overnight. After 16 hrs. the solution was removed from the dry box and poured into 350 ml of petroleum ether-F, with magnetic stirring. The white solid formed was collected by suction filtration, washed in 300 ml of technical ethanol, and dried vacuo (0.10 torr) at 40 over phosphorous pentoxide for 48 hrs. The polymer, 1.34 g, 67% yield, was found to have [n] = 0.33 (m-cresol, 29.6°) IR (KBr) 3350, 3000, 2700, 2540, 1670, 1570, 1500, 1275, 1210,... 

The adsorption section contains one or more beds of polymer particles maintained in a fluidized state by the flow of gas being purified. Regenerated polymer particles are continuously added to the top bed, and saturated particles are continuously removed from the bottom. The saturated adsorbent is pneumatically transported to the top of the desorber. The particles flow down through the desorber where they are heated, stripped by contact with a small stream of air or inert gas, and cooled. The cooled and regenerated adsorbent is transported back to the adsorber. 

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