Polymers intrinsic viscosity

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). 

Solution viscosity is empirically related to molecular weight for linear polymers. Intrinsic viscosity ([17]) is (risp/Qc-a< where is (rj, - 1) and C is a concentration of the polymer in solution. The quantity Vr represents J7/170, where rj and tjq are the viscosity of the polymer solution and pure solvent, respectively. Inherent viscosity (T i h) is ln(VQ-... 

For polymer-solvent systems with known Mark-Houwink coefficients, K and a, the polymer intrinsic viscosity value [n] can be estimated from the SEC-MW data using the following equation ... 

B. Direct SEC-[n] Calibration. Because the SEC separation process is directly related to the size of the solvated molecules, and for a homopolymer series the molecular size is directly related to MW as well as [n]/ it is not necessary to proceed through MW calculations to study polymer intrinsic viscosity. Since... 

A new direct method for using size exclusion chromatography (SEC) to evaluate polymer intrinsic viscosity [n] is discussed. Sample viscosity information is obtained by combining SEC elution curve data and calibration data using direct SEC-[n] calibration procedures without involving polymer molecular weight calculations. The practical utility, convenience and the expected precision of the proposed method are illustrated. 

In some cases the relationship between polymer intrinsic viscosity ([n]) and molecular weight (M) has been established for the SEC solvent and temperature conditions i.e., the empirical Mark-Houwink coefficients (2)(K,a) in the equation... 

Once a value for M[ is assumed, this leaves one unknown b which can be determined from the SEC chromatogram and the measured whole polymer intrinsic viscosity in the following manner. First, one estimates a value for b, and calculates M CV) and [n](V) across the chromatogram using the universal calibration curve and equation (3). Then the whole polymer intrinsic viscosity is obtained from... 

For a statistical coil, the product of polymer intrinsic viscosity and molecular weight is directly proportional to the cube of the root-mean-square radius of gyration RG 77137... 

Kim, O.K., Little, R.C., and Ting, R.Y. "The Correlation of Drag-Reduction Effects with Polymer Intrinsic Viscosity," J. Colloid Interface Sci.. 1974, 47(2). 

The sample fluid could be any neat liquid or a sample of polymer solution. Under favorable conditions, a single viscosity determination on a polymer solution at high dilution can provide a direct measure of the polymer intrinsic viscosity, without the need of polymer concentration extrapolation. With this viscometer used as a continuous viscosity detector for SEC, it is possible to achieve SEC molecluar weight calibration by way of the universal SEC calibration methodology without the need of molecular weight standards for the unknown polymers. 

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 ... 

Figure 16.5. In-plane and out-of-plane refractive indexes and birefringence of 6FDA-PFMB films as a function of the polymer intrinsic viscosity.

Another very useful approach to molar mass information of complex polymers is the coupling of SEC to a viscosity detector [55-60]. The viscosity of a polymer solution is closely related to the molar mass (and architecture) of the polymer molecules. The product of polymer intrinsic viscosity [r ] times molar mass is proportional to the size of the polymer molecule (the hydrodynamic volume). Viscosity measurements in SEC can be performed by measuring the pressure drop AP across a capillary, which is proportional to the viscosity r of the flowing liquid (the viscosity of the pure mobile phase is denoted as r 0). The relevant parameter [r ] is defined as the limiting value of the ratio of specific viscosity (qsp= (n-noVflo) and concentration c for c—> 0 ... 

If a concentration-selective detector, such as a DRI, is connected on-line with the viscosity detector, the ratio of the two signals yields the intrinsic viscosity distribution of the polymer sample. In polymer characterization, the intrinsic viscosity can be a property just as important as the molecular-weight distribution. Furthermore, polymer intrinsic viscosity follows the Mark-Houwink relation to the molecular weight, M, where K and a are Mark-Houwink viscosity constants ... 

It is important to note that synthesized polymers PAG and PMAG are insoluble and even don t swell in any of investigated by us organic solvents - methanol, ethanol, dioxane, DMSO, DMFA. At the same time we established that when the values of synthesized polymers intrinsic viscosity were high enough - 2.5 dl g 1 for PMAG and 0.9 dl g1 for PAG they were easily solved in water that indicated on their linearity. The data of element analysis and NMR1H spectroscopy of polymers confirmed that their structure corresponds to theoretical. 

How well do predicted and observed non-Newtonian intrinsic viscosity agree for a wormlike model of xanthan Fixman (Ref. J2 Fig. 4) gives the non-Newtonian intrinsic viscosity for a flexible chain model at various values of the excluded volume parameter a, as a function of the normalized shear rate parameter The parameter Kn, which incorporates the effects of molecular weight and chain stiffness, equals 1.71[n]oMnog/RT where [nJo is the polymer intrinsic viscosity at zero shear stress, o is the solvent viscosity, g is the shear rate in sec"i and the other symbols have their usual meaning. 

PET chip or representative samples of CP spin-draw polymer are conveniently characterized as by their molecular weight, cleanliness, and thermal behavior. Molecular weight is characterized by the polymer intrinsic viscosity [tj], usually in halogenated solvents the best halogenated solvents are hexafluoroisopropanol/pentafluorophenol mixtures. Intrinsic viscosity is related to molecular weight by the Mark-Houwink equation, i.e.,... 

In its turn, the value a is connected with polymer intrinsic viscosity in aibi-traiy [q] and ideal [q]0 solvents as follows [22] ... 

A second major problem that causes error in EOR polymer intrinsic viscosity measurements concerns the uncertainty that dilute solution conditions exist during viscosity measurements. As shown by Figure 1, dilute solution conditions exist only when the overlap parameter is less than one. Extrapolation to "zero concentration reduced viscosity is linear only if viscosity data is taken in the dilute region. However, a polymer solution having an intrinsic viscosity of 30 dl/g is dilute only if the concentration is less than 1/30 g/dl (33 ppm). At concentrations higher than this, excessive coil overlap may exist. Solution reduced viscosities determined above the dilute solution region can not be easily extrapolated to zero concentration. When linear extrapolation is done, the apparent intrinsic viscosities which are obtained are larger than the true intrinsic viscosity. 

Solubility Swelling of cross-linked polymer Intrinsic viscosity [n]... 

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