Correction and Reassessment of Intrinsic Viscosity and The Universal Calibration Method - A Bridge from Polymers to Small Molecules

The current definition of intrinsic viscosity ([riD, and its application in the universal calibration method, applies to polymeric materials with molecular weight (MW) >>1,000. However, there have been numerous discussions regarding the [11]of low MW oligomers. Difficulties can be encountered at very low MW, because the [1"1] in some cases becomes negative, which in theory is impossible. A new model is proposed in this paper to refine the calculation of [rl]. The new model is based on the fact that [ri] is a polymer volume expansion coefficient; i.e., [11]times the polymer density is the expansion ratio of the hydrodynamic volume in solution to the polymer volume in the solid state. In the calculation of [rl], as in measuring the density of a low-density material in air, the volume of solvent should be added. For a polymer with MW greater than 10,000, this correction can be neglected. However, the correction becomes important for small oligomers. With this correction, the Mark-Houwink curve of n-alkane and polystyrene in the low MW region become linear. The universal calibration curve, calculated with corrected [rl], is also linear across the range from polymer to small molecules.