At present, the average molecular weight (Mn and Mw) and molecular weight distribution (MWD) of synthetic polymers are basically measured by gel permeation chromatography (GPC). The principle of GPC is based on the volume exclusion effect between the polymer compounds in the mobile phase and the porous gel column bed in the chromatographic column [7]. Conventional GPC equipped with differential refractive detector (RID) is a typical commonly used gel permeation chromatography system, which is widely used in many physical and chemical components of polymerizationIn the laboratory analysis. Due to its simplicity, excellent precision, and low cost of use, it has become the first choice for analytical laboratories in the industry. GPC-RID is not only suitable for measuring the average molecular weight and molecular weight distribution of polymer samples with narrow and wide distributions, but also for quantitative analysis by separating a single component from a mixture. However, the limitation of GPC-RID is that it must establish a calibration curve to calculate the average molecular weight and molecular weight distribution of the polymer. In organic phase GPC applications, the standard used to establish calibration curves is usually polystyrene (PS), and the commonly used mobile phase is tetrahydrofuran (THF). However, due to the differences in chemical structure between polystyrene and most of the currently tested polymers, the average molecular weight obtained through GPC-RID is generally a relative value, known as the relative average molecular weight. If the chemical structure of the standard is similar or identical to that of the analyte, the average molecular weight calculated by GPC-RID will be closer to the theoretical value. However, in most cases, standard samples with chemical structures similar or identical to the tested substance are difficult to obtain or do not exist at all. Fortunately, for GPC-RID analysis of polyether polyols, we can find a commercial standard with a similar structure, namely polyethylene glycol. This article confirms through experimental comparison that using polyethylene glycol to establish a calibration curve can obtain more accurate relative average molecular weight compared to selecting polystyrene as the standard; And further discussions were conducted from the perspective of fluid mechanics volume. Different from the speculation of chemical structure similarity theory, based on real experimental data, we clearly and intuitively reveal the reasons for the differences in measurement results obtained when using polyethylene glycol and polystyrene as standards.

However, any technology has its limitations, and using polyethylene glycol to establish a calibration curve to calculate the average molecular weight of polyether polyols is no exception [8]. Compared with the calibration curve of polystyrene, it is difficult to achieve a completely consistent molecular weight measurement range for polyethylene glycol in tetrahydrofuran system. Therefore, for high molecular weight polyether polyols (Mn greater than 10000 g/mol), choosing polyethylene glycol as the standard is not suitable. Therefore, this article uses Agilent 1260 Infinity III GPC combined with Agilent 1260 MDS multi detector system, which can not only perform the conventional GPC-RID analysis mentioned in the article, but also achieve absolute molecular weight measurement (DALLS) and universal calibration curve measurement (Viscosity Detector, abbreviated as VD) of polyether polyols. The use of GPC combined with DALLS or VD technology can effectively solve the problem of traditional GPC data accuracy relying on the chemical structure similarity between standards and samples. Therefore, for the measurement of average molecular weight of polyether polyols or MWD analysis of polymers, the 1260 Infinity III GPC combined with the 1260 MDS multi detector system is a complete solution. This scheme can not only help analysts obtain accurate average molecular weight information, but also further analyze the specificity of samples by characterizing the configuration/conformation information of polymers, providing reliable experimental data support and technical support for the study of polymerization reaction processes.