Viscosity intrinsic solvent

The experimental determination of polymer intrinsic viscosity is done through the measurement of polymer solution viscosity. The connotation of intrinsic viscosity [hi/ however, is very different from the usual sense of fluid viscosity. Intrinsic viscosity, or sometimes called the limiting viscosity number, carries a far more reaching significance of providing the size and MW information of the polymer molecule. Unlike the fluid viscosity, vdiich is commonly reported in the poise or centipoise units, the [h] value is reported in the dimension of inverse concentration xinits of dl/g, for exanple. The value of [hi for a linear polymer in a specific solvent is related to the polymer molecular weight (M) through the Mark-Houwink equation ... 

A viscometer has been constructed using membrane pores as capillary viscometers and can be readily adapted to conventional SEC equipment. The viscometer has been shown to give reasonable values of viscosities for solvent flow and intrinsic viscosities for moderate molecular weight polymers of MW approximately 100,000. 

Figure 4.2. Determination of intrinsic viscosity. Intrinsic viscosity is determined by extrapolation of the reduced specific viscosity (r sr) to zero concentration. The reduced specific viscosity is calculated by taking the difference between the flow time in a capillary for polymer in a solvent and that of the pure solvent and dividing the difference by the flow time of the pure solvent times the polymer weight concentration. Data are shown for hyaluronan for various fractions isolated from bovine vitreous.

A.3.1.1 Dependence of Viscosity on Solvent. The intrinsic viscosity of randomly coiled polymers such as polystyrene and polyisobutylene is strongly dependent on the nature of the solvent used. There is a decrease in the viscosity of such a flexible... 

Here the subscript i refers to the solvent, whereas the superscript (A or B) refers to the component homopolymer. For example, ai is the thermal diffusion coefficient of a homopolymer consisting of component B in solvent 1. Parameters [rj]i and Xi are the intrinsic viscosity and retention parameter measured on the copolymer in solvent i T g in equation 9c is the temperature at the center of gravity of the retained polymer zone in solvent i, while rjo is the viscosity of solvent i at Teg- Equations 7 through 9 are applicable to copolymers with only two components similar equations could be derived for n-component copolymers, in which case My and Xa are determined from retention and viscosity data in n separate solvents. 

The intrinsic viscosity of a polymer is obtained from the viscosities 17 and no of solution and solvent, respectively, through the following transformations. The relative viscosity is the ratio nrei = v Vo- By assuming that the viscosity n of a dilute solution is given by the sum of viscosities from solvent and solute molecules, the specific viscosity, Tjsp, represents the polymer contribution to viscosity ... 

The intrinsic viscosity [n] is obtained by plotting the reduced viscosity versus concentration and extrapolating to infinite dilution. Reduced viscosity is given by the expression r -r o/r oC where iq is the viscosity of solution, iq is the viscosity of solvent, and C is the concentration in g/dL. 

The grouping in the parenthesis of Equation 10.10 can be related to the characteristic ratio and is nearly independent of the polymer molecular weight the dependence of intrinsic viscosity on solvent quality is therefore proportional to the product aM. In theta solvents, a is unity (the intrinsic viscosity scales with and in good solvents a is proportional to (the intrinsic viscosity scales with M ). Comparison with Equation 10.1 suggests that the Mark-Houwink parameter should lie in the range 0.5 expansion factor if theta conditions for the polymer solution are known. 

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... 

A monodisperse polymer with a molecular weight of 133,000 has an intrinsic viscosity in a theta solvent at 35°C of 2.10 dl/g and a melt viscosity at 200°C of 250 kPa-s. What will be the value of the intrinsic viscosity (same solvent and temperature as earlier) for a new sample made from the same monomer but with a melt viscosity (at 200°C) of 835 kPa-s ... 

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] ... 

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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