Assessment of errors in the determination of Mark-Houwink-Sakurada and Stockmayer-Fixman constants using size-exclusion chromatography with on-line viscometric detection: Analyses of poly(p-substituted styrenes) in tetrahydrofuran

Critically Evaluated Rate Coefficients for Free‐Radical Polymerization, 4

“…A detailed discussion has been given by Jackson et al [15] An extensive study on the error structure of MH parameters and their influence on PLP experiments was published by Coote and Davis. [16] Two important observations were made. Firstly, sampledependent errors dominated the MH analyses and therefore multiple samples are required to minimize (or at least quantify) error, and secondly the MH constants should only be used for exactly the same molecularweight range for which they were determined.…”

Studies on the propagation reaction in the free radical polymerization of ethylα-hydroxymethacrylate

“…The Mark-Houwink-Kuhn-Sakurada (MHKS) constants were determined in THF according to a previously published procedure [8] utilising SEC with on-line viscometry. The analysis was based on the on-line viscosity measurement of 96 independent PEHMA samples (50 567 individual data points) and subsequent statistical treatment that provides an estimate of the upper and lower bounds to the errors as discussed previously.…”

Effect of the copolymer composition on the K and α constants of the Mark–Houwink equation: Comments on a recent article by Songkhla and Wootthikanokkhan

“…The following are recommended: It is preferable to use narrow distribution polymers in Mark–Houwink or Stockmayer–Fixman constant determinations—particularly where fractionation techniques are not used before analyses. A broad range of molecular weight coverage is advised with multiple samples to allow accurate assignment of precision and accuracy (this is a recommendation even when GPC with online viscometry is used19). It should be evident that the derived molecular weights (if not polystyrene samples) are not absolute where GPC is used with PS calibration. GPC separation is affected by copolymer composition in addition to molecular weight; therefore, it is an invalid technique for heterogeneous copolymer samples. Copolymer composition measurements are not always trivial and are subject to error—as pointed out recently this leads to significant uncertainties in reactivity ratios even for established systems such as methyl methacrylate and styrene. Graphical methods for analyses of copolymer composition data are generally obsolete, and nonlinear least‐squares regression is a facile method for analysis that allows for the correct assignment of errors. High‐conversion copolymer data should be analyzed with the integrated version of the copolymer composition equation. …”