【国外标准】 Standard Test Method for Molecular Weight Averages and Molecular Weight Distribution of Polystyrene by High Performance Size-Exclusion Chromatography

5.1 General Utility—The molecular weight (MW) and molecular weight distribution (MWD) are fundamental characteristics of a polymer sample. They are used for a wide variety of correlations for fundamental studies, processing, or product applications. For example, the observed MWD is compared to one predicted from assumed kinetics or mechanisms for a polymerization reaction. Differences between the values will allow alteration of theory or experimental design. Similarly, the strength, melt flow, and other properties of a polymer sample usually are dependent on MW and MWD. Determinations of MW and MWD are used for quality control of polymers.5.2 Limitations—Because of the need for specific calibration of the polymer type under study, and because of the specific nature of polymer/solvent/column-packing interactions, this test method is valid only for polystyrene and non-exclusion effects are to be avoided. However, many of the principles of the method have been applied in generating HPSEC methods for other polymer systems, for example, using the principles of universal calibration. (see Practice D3016).1.1 This test method covers the determination of molecular weight (MW) averages and the distribution of molecular weights for linear, soluble polystyrene by high-performance size-exclusion chromatography (HPSEC). This test method is not absolute and requires the use of commercially available narrow molecular weight distribution (MWD) polystyrene standards for calibration. This test method is applicable for samples containing molecular weight components that have elution volumes falling within the elution volume range defined by polystyrene standards (that is, molecular weights generally from 2000 to 2 000 000 g·mol−1).1.2 The HPSEC is differentiated from traditional size-exclusion chromatography SEC (also referred to as gel permeation chromatography (GPC)) in that the number of theoretical plates per metre with an HPSEC system is at least ten times greater than that for traditional SEC (see Terminology D883 and Practice D3016).2 The HPSEC systems employ low-volume liquid chromatography components and columns packed with relatively small (generally 3 to 20 μm) microporous particles. High-performance liquid chromatography instrumentation and automated data handling systems for data acquisition and processing are required.1.3 The values stated in SI units are to be regarded as the standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 9.NOTE 1: There is no known ISO equivalent to this standard.1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.