Mark-Houwink-Sakurada parameters

TABLE VIII Mark-Houwink-Sakurada Parameters for Viscosity Molecular Weight of Poly(vinyl acetate)... 

REPORTED VALUES OF THE MARK-HOUWINK-SAKURADA PARAMETERS RELATING INTRINSIC VISCOSITY TO MOLECULAR WEIGHT FOR PHB... 

The properties of the linear and cyclic polymers are compared in Figure 3.24 (92). As one might expect, the more compact cyclic polymers possessed smaller hydrodynamic volumes (i.e., they eluted later via GPC in Figure 3.24A). They had lower intrinsic viscosities than their linear analogs, with [r7]cyciic/[r7]iinear = 0.4 (Figurc 3.24B). The Mark-Houwink-Sakurada parameter a was 0.7 in both cases. 

Isopropanol Glass transition temp., Rheological properties of aqueous solution Mark-Houwink-Sakurada parameters ... 

Tatro SR, Baker GR, Fleming R, Harmon JP. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry determining Mark-Houwink-Sakurada parameters and analyzing the breadth of polymer molecular weight distributions. Polymer 2002 43 2329-2335. 

Solution Establish Mark Houwink Sakurada parameters. 

Molecular weight calibration from a monomer to several million daltons can be carried out by a variety of techniques. Because narrow standards of p(methyl methacrylate) (pMMA) are available, these are often used. Narrow standards of p(styrene) (pSty) are also available and can be used. Using the Mark-Houwink-Sakurada equation and the parameters for pSty and pMMA, a system calibrated with pSty can give pMMA-equivalent values, and vice versa. 

Benoit and co-workers [18] proposed that the hydrodynamic volume, Vr which is proportional to the product of [17] and M, where [17] is the intrinsic viscosity of the polymer in the SEC eluent, may be used as the universal calibration parameter (Fig. 18.3). For linear polymers, interpretation in terms of molecular weight is straightforward. If the Mark-Houwink-Sakurada constants K and a are known, log [t7]M can be written log M1+ + log K, and VT can be directly related to M. The size-average molecular weight, Mz, is defined by this process ... 

Here K and a are the parameters of the Mark-Houwink-Sakurada viscosity law ... 

The sodium and ammonium salts of PVSA are soluble in water but insoluble in organic solvents (6). The calcium salt is insoluble. Potentiometric titration studies indicate that PVSA is a strong acid that ionizes completely in water. Ion binding selectivity with alkali metals has been observed in viscosity and phase separation studies. Mark-Houwink-Sakurada (MHS) parameters ofK = 2.22 and a = 0.65 have been obtained for sodium PVSA in 0.5 M NaCl at 25°C. 

Much of the above discussion indicates that, to study excluded volume effects, an accurate determination of unperturbed dimensions is required. For this, a common procedure is to extrapolate intrinsic viscosity of known molecular weight samples to zero molecular weight. Several extrapolations have been used, notably the Stockmayer-Fixman plot. Dondos and Benoit have now introduced a modified version of this, which appears to be linear over a wider range of molecular weights. It introduces a parameter D, which is shown to be linearly related to the exponent of the Mark-Houwink-Sakurada equation. 

In Table II, the large variations in the parameters for the Mark-Houwink-Sakurada equation [Eq. (I)] relating intrinsic viscosity [/y] to molecular weight M (AT and a are parameters which have to be determined for each polymer-solvent system). 

The Mark-Houwink-Sakurada (MHS) equation (eqn (5.5)) offers a convenient means of determining the molecular weight of a polymer which is soluble in a solvent. It has been experimentally confirmed that the parameters Km and a in the MHS equation are constant over a wide range of molecular weights under the constraints of zero shear rate at given temperature for a... 

Another of SEC s serious imperfections is that it relies on calibration. However there are really only a handful of polymers for which monodisperse standards are available, and all of these are common polymers. A way around this is to use universal calibration, but this firstly relies on Mark-Houwink-Kuhn-Sakurada (MHKS) parameters being known, and secondly it requires that workers are aware of the need for this procedure - many evidently are not. Further, given that the aim of much research in polymer synthesis is to make new polymers for which, by definition, MHKS parameters will not be available, it follows that in many cases universal calibration will not be possible anyway. 

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