Solvents intrinsic

Riseman (139) or Kuhn and Kuhn (153 , 153"). For the sake of comparison, Fig. 12 also shows the theta-solvent intrinsic viscosities of polystyrene in cyclohexane [experimental valuesofKRiGBAUMandFuoRY (149), small black points theoretical values, broken line] and the theoretical intrinsic viscosities of rigid ellipsoids with axial ratios p = M/500 (chain curve). As a matter of course, the chain curve reduces to the Einstein value of [rf in the range of M below500 [see, for example, Petehlin (16) ]z. 

The broken line gives the hypothetical theta-solvent intrinsic viscosity, Me = KMand the gap between the solid and broken curves, therefore, represents the expansion or swelling factor a . The end effect is again seen in the deviation of the four lowest open circles from the line. It is interesting to note that if no measurements in dichloroacetic acid existed above a molecular weight of about 50,000 the viscosity exponent v would have to be chosen in the neighborhood of 0.5, even though it is clear from the complete body of data that the system is very far from the theta point ... 

Analysis of the C z and C e olefin mixtures by gas chromatography and/or NMR indicated that in both cases the internal isomers were the predominant product. With all the alkylaluminum coinitiators the ratio of internal to terminal olefin was 3 1. Product characterization data are shown in Table 1. Number average molecular weights of polyisobutylenes were determined using a Hewlett-Packard 503 high speed membrane osmometer at 37° C and toluene solvent. Intrinsic viscosities were obtained with a Ubbelohde capillary viscometer at 30° C in cyclohexane solvent. The viscosity average molecular weights were calculated... 

Branched polymers in good solvents Intrinsic viscosity of polyelectrolyte solutions... 

Bhanushali et al. [22] showed differences between porous UF polymer membranes and dense reverse osmosis/NF membranes. According to these authors, permeability can be correlated with the inverse of the solvent viscosity for UF membranes whatever the nature of the solvent. For reverse osmosis/NF membranes, a permeation model is proposed in which the flux relates to a solvent permeability coefficient, accounting for a number of solvent intrinsic parameters, like molar volume V , the viscosity p, the sorption value O, and to an intrinsic parameter of the membrane (the solid-vapor surface tension ysv). 

Intrinsic Viscosity in- ltrin-zik- n (limiting viscosity number) In measurements of dilute-solution viscosity, intrinsic viscosity is the limit of the reduced and inherent viscosities as the concentration of polymer solute approaches zero. It represents the capacity of the polymer to increase viscosity. Interactions between solvent and polymer molecules give rise to different intrinsic viscosities for a given polymer in different solvents. Intrinsic viscosity is related to polymer molecular weight by the equation [77] = K -M, where the exponent a lies between 0.5 and 1.0, and, for many systems, between 0.6 and 0.8. Also known as Limiting Viscosity Number. See also... 

Saltiel J and Sun Y-P 1989 Intrinsic potential energy barrier for twisting in the f/ a/rs-stilbene SI State in hydrocarbon solvents J. Phys. Chem. 93 6246-50... 

Anotlier simple way to obtain the molecular weight consists of measuring tire viscosity of a dilute polymer solution. The intrinsic viscosity [q] is defined as tire excess viscosity of tire solution compared to tliat of tire pure solvent at tire vanishing weight concentration of tire polymer [40] ... 

The influence of solvent can be incorporated in an implicit fashion to yield so-called langevin modes. Although NMA has been applied to allosteric proteins previously, the predictive power of normal mode analysis is intrinsically limited to the regime of fast structural fluctuations. Slow conformational transitions are dominantly found in the regime of anharmonic protein motion. 

It can be seen from Table 2 that the intrinsic values of the pK s are close to the model compound value that we use for Cys(8.3), and that interactions with surrounding titratable residues are responsible for the final apparent values of the ionization constants. It can also be seen that the best agreement with the experimental value is obtained for the YPT structure suplemented with the 27 N-terminal amino acids, although both the original YPT structure and the one with the crystal water molecule give values close to the experimentally determined one. Minimization, however, makes the agreement worse, probably because it w s done without the presence of any solvent molecules, which are important for the residues on the surface of the protein. For the YTS structure, which refers to the protein crystallized with an SO4 ion, the results with and without the ion included in the calculations, arc far from the experimental value. This may indicate that con-... 

Fox and Floryf used experimental molecular weights, intrinsic viscosities, and rms end-to-end distances from light scattering to evaluate the constant in Eq. (9.55). For polystyrene in the solvents and at the temperatures noted, the following results were assembled ... 

The polymers dissolve in l,l,l,3,3,3-hexafluoro-2-propanol [920-66-1/, hot phenols, and /V, /V- dim ethyl form am i de [68-12-2] near its boiling point. The excellent solvent resistance notwithstanding, solvents suitable for measurement of intrinsic viscosity, useflil for estimation of molecular weight, are known (13,15). 

Solution Polymers. Acryflc solution polymers are usually characterized by their composition, solids content, viscosity, molecular weight, glass-transition temperature, and solvent. The compositions of acryflc polymers are most readily determined by physicochemical methods such as spectroscopy, pyrolytic gas—liquid chromatography, and refractive index measurements (97,158). The solids content of acryflc polymers is determined by dilution followed by solvent evaporation to constant weight. Viscosities are most conveniently determined with a Brookfield viscometer, molecular weight by intrinsic viscosity (158), and glass-transition temperature by calorimetry. 

SAN resins show considerable resistance to solvents and are insoluble in carbon tetrachloride, ethyl alcohol, gasoline, and hydrocarbon solvents. They are swelled by solvents such as ben2ene, ether, and toluene. Polar solvents such as acetone, chloroform, dioxane, methyl ethyl ketone, and pyridine will dissolve SAN (14). The interactions of various solvents and SAN copolymers containing up to 52% acrylonitrile have been studied along with their thermodynamic parameters, ie, the second virial coefficient, free-energy parameter, expansion factor, and intrinsic viscosity (15). 

Analytical and test methods for the characterization of polyethylene and PP are also used for PB, PMP, and polymers of other higher a-olefins. The C-nmr method as well as k and Raman spectroscopic methods are all used to study the chemical stmcture and stereoregularity of polyolefin resins. In industry, polyolefin stereoregularity is usually estimated by the solvent—extraction method similar to that used for isotactic PP. Intrinsic viscosity measurements of dilute solutions in decahn and tetraHn at elevated temperatures can provide the basis for the molecular weight estimation of PB and PMP with the Mark-Houwiok equation, [rj] = KM. The constants K and d for several polyolefins are given in Table 8. 

Intrinsic viscosity is often used to characterize tetrahydrofuran polymers. Intrinsic viscosities in a variety of solvents and Mark-Houwink constants for the equation [rj] = Khave been deterrnined for a wide variety of solvents (39—45),where [Tj] is the intrinsic viscosity, M is molecular weight, and K and a are constants many of the constants have been summarized and tabulated (6). 

Dilute Polymer Solutions. The measurement of dilute solution viscosities of polymers is widely used for polymer characterization. Very low concentrations reduce intermolecular interactions and allow measurement of polymer—solvent interactions. These measurements ate usually made in capillary viscometers, some of which have provisions for direct dilution of the polymer solution. The key viscosity parameter for polymer characterization is the limiting viscosity number or intrinsic viscosity, [Tj]. It is calculated by extrapolation of the viscosity number (reduced viscosity) or the logarithmic viscosity number (inherent viscosity) to zero concentration. 

The viscosity ratio or relative viscosity, Tj p is the ratio of the viscosity of the polymer solution to the viscosity of the pure solvent. In capillary viscometer measurements, the relative viscosity (dimensionless) is the ratio of the flow time for the solution t to the flow time for the solvent /q (Table 2). The specific (sp) viscosity (dimensionless) is also defined in Table 2, as is the viscosity number or reduced (red) viscosity, which has the units of cubic meters per kilogram (m /kg) or deciUters per gram (dL/g). The logarithmic viscosity number or inherent (inh) viscosity likewise has the units m /kg or dL/g. For Tj g and Tj p, the concentration of polymer, is expressed in convenient units, traditionally g/100 cm but kg/m in SI units. The viscosity number and logarithmic viscosity number vary with concentration, but each can be extrapolated (Fig. 9) to zero concentration to give the limiting viscosity number (intrinsic viscosity) (Table 2). 

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