Weighting for solutes

Fig. 3. Cabannes factor as a function of molecular weight for solutions of polyethylene glycol in methanol33) at T = 25 °C and X0 = 546 nm. [Inset - refer to Section IV.2 Dependence of Cabannes factor on concentration for solutions indicated in Fig. 59)...

In order to cover the whole range of molecular weights for solutes in a polymer matrix we can start with Eq. (6-21) and introduce a supplementary positive term, aMrB ... 

FIGURE 6.5 Dependence of diffusion coefficient on molecular weight for solutes in water and polymer. [Graph reconstructed from data by Haglund et al.,./. Chem. Ed., 73, 889 (1996)]. 

The logarithm of intrinsic viscosity of polybutylenes plotted against the logarithm of molecular weight, for solutions in diisobutene at 20 C. 

Properties.—Carbon-13 and field-dependent proton spin-lattice relaxation times have been measured as a function of temperature and molecular weight for solutions of polycarbonates in CDCI3. The spin-lattice relaxation times were interpreted in terms of segmental motion, characterized by the sharp cut-off model of Jones and Stockmayer, for phenyl group rotation and methyl group rotation. ... 

Figure C2.1.8. Reduced osmotic pressure V l(RTc as a function of the polymer weight concentration for solutions of poly(a-metliylstyrene) in toluene at 25 °C. The molecular weight of poly(a-metliylstyrene) varies...

Calculate Apj, ATf, ATj, and n for solutions which are 1% by weight in benzene of solutes for which M = 10 and 10 . Assume that these solutions are adequately described by dilute ideal solution expressions. Consult a handbook for the physical properties of benzene. Comment on the significance of the results with respect to the feasibility of these various methods for the determination of M for solutes of high and low molecular weight. 

In these unit conversions on H, we have used the facts that 1 atm = 760 Torr and the ratio of densities PHg/ soin - /Psoin t onverts from Torr to millimeters of solution. These numerical examples show that experiments in which Apj, ATf, or ATj, are measured are perfectly feasible for solutes of molecular weight 100, but call for unattainable sensitivity for polymeric solutes of M = 10 . By contrast, osmometry produces so much larger an effect that this method is awkward (at least for 1% concentration) for a low molecular weight solute, but is entirely feasible with the polymer. 

Using the original Hc2/r values, recalculate M using the various refractive index gradients. On the basis of self-consistency, estimate the molecular weight of this polymer and select the best value of dn/dc2 in each solvent. Criticize or defend the following proposition Since the extension of the Debye theory to large particles requires that the difference between n for solute and solvent be small, this difference should routinely be minimized for best results. 

Chain transfer is an important consideration in solution polymerizations. Chain transfer to solvent may reduce the rate of polymerization as well as the molecular weight of the polymer. Other chain-transfer reactions may iatroduce dye sites, branching, chromophoric groups, and stmctural defects which reduce thermal stabiUty. Many of the solvents used for acrylonitrile polymerization are very active in chain transfer. DMAC and DME have chain-transfer constants of 4.95-5.1 x lO " and 2.7-2.8 x lO " respectively, very high when compared to a value of only 0.05 x lO " for acrylonitrile itself DMSO (0.1-0.8 X lO " ) and aqueous zinc chloride (0.006 x lO " ), in contrast, have relatively low transfer constants hence, the relative desirabiUty of these two solvents over the former. DME, however, is used by several acryhc fiber producers as a solvent for solution polymerization. 

Concentration and Molecular Weight Effects. The viscosity of aqueous solutions of poly(ethylene oxide) depends on the concentration of the polymer solute, the molecular weight, the solution temperature, concentration of dissolved inorganic salts, and the shear rate. Viscosity increases with concentration and this dependence becomes more pronounced with increasing molecular weight. This combined effect is shown in Figure 3, in which solution viscosity is presented as a function of concentration for various molecular weight polymers. 

Effect of Shear. Concentrated aqueous solutions of poly(ethylene oxide) are pseudoplastic. The degree of pseudoplasticity increases as the molecular weight increases. Therefore, the viscosity of a given aqueous solution is a function of the shear rate used for the measurement. This relationship between viscosity and shear rate for solutions of various molecular weight poly(ethylene oxide) resins is presented in Figure 8. 

The solubihty of the ammonium haUdes in water also increases with increasing formula weight. For ammonium chloride, the integral heat of solution to saturation is 15.7 kj /mol (3.75 kcal/mol) at saturation, the differential heat of solution is 15.2 kj /mol (3.63 kcal/mol). The solubihty of all three salts is given in Table 1 (7). 

In two proposed alternative processes, the chlorine is replaced in the hypochlorination reaction by hypochlorous acid [7790-92-3] HOCl, or tert-huty hypochlorite. In the first, a concentrated (>10% by weight) aqueous solution of hypochlorous acid, substantially free of chloride, chlorate, and alkah metal ions, is contacted with propylene to produce propylene chlorohydrin (113). The likely mechanism of reaction is the same as that for chlorine, as chlorine is generated in situ through the equiUbrium of chlorine and hypochlorous acid (109). 

Ternary-phase equilibrium data can be tabulated as in Table 15-1 and then worked into an electronic spreadsheet as in Table 15-2 to be presented as a right-triangular diagram as shown in Fig. 15-7. The weight-fraction solute is on the horizontal axis and the weight-fraciion extraciion-solvent is on the veriical axis. The tie-lines connect the points that are in equilibrium. For low-solute concentrations the horizontal scale can be expanded. The water-acetic acid-methylisobutylketone ternary is a Type I system where only one of the binary pairs, water-MIBK, is immiscible. In a Type II system two of the binary pairs are immiscible, i.e. the solute is not totally miscible in one of the liquids. 

Component A = feed solvent, component B = solute, and component S = extraction solvent. K is the partition ratio in weight-fraction solute if/x for the tie line of lowest solute concentration reported. Ordinarily, K will approach unity as the solute concentration is increased. 

Molecular weights for fully hydrolyzed and partially hydrolyzed grades of PVA (expressed in terms of 4% solution viscosity) from aqueous SEC-MALLS are summarized in Table 20.6. M values range from less than 20,000 Da for a 3 centipoise (cP) viscosity grade to over 230,000 Da for a super-high viscosity... 

About 250 ml of a reaction mixture obtained by the electrolytic reduction of nitrobenzene in sulfuric acid solution and containing about 23 grams of p-aminophenol by assay is neutralized while at a temperature of 60° to 65°C, to a pH of 4.5 with calcium carbonate. The calcium sulfate precipitate which forms is filtered off, the precipitate washed with hot water at about 65°C and the filtrate and wash water then combined. The solution is then extracted twice with 25 ml portions of benzene and the aqueous phase is treated with 0.5 part by weight, for each part of p-aminophenol present, of activated carbon and the latter filtered off. The activated carbon is regenerated by treatment with hot dilute caustic followed by a hot dilute acid wash, and reused a minimum of three times. 

D) 4 -[N-Ethyi-1 "-Methyl-2 -(4" -Methoxyphenyl)Ethylamino]Butyi-3,4-Dimethoxybenzoate Hydrochloride 10.3 g of 4 -iodobutyl-3,4-dimethoxybenzoate and 11.0 g of N-ethyl-p-methoxyphenylisopropylamine (obtained by catalytic reduction of an alcoholic solution of an excess quantity (60%) of p-methoxy-phenyl-acetone, to which was added a 33% (weight-for-weight) aqueous solution of ethylamine, with Pt as a catalyst), were boiled in 200 ml of methyl ethyl ketone for 20 hours, cooled and the iodine ion was determined the reaction was found to be complete. Then the methyl ethyl ketone was evaporated in vacuo and the residue was dissolved in 300 ml of water and 30 ml of ether the layers were separated and the water layer was extracted twice more with 20 ml portions of ether. 

The analysis of the main properties of aqueous solutions of polyacrylamide and copolymers of acrylamide has been reviewed [4,5]. The main characteristics of aqueous solutions of polyacrylamide is viscosity. The viscosity of aqueous solutions increases with concentration and molecular weight of polyacrylamide and decreases with increasing temperature. The relationship between the intrinsic viscosity [q]) in cmVg and the molecular weight for polyacrylamide follows the Mark-Houwink equations ... 

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