Refractive index, its chromatic dispersion, and thermal coefficients of four less common glycols

We report comprehensive measurements of the refractive index as a function of wavelength and temperature for four less commonly studied glycols: pentaethylene glycol, hexaethylene glycol, dipropylene glycol (mixture of isomers), and tripropylene glycol. The measurements cover the spectral range of 0.39–1.07 μm and temperatures from 1 °C to 45 °C. The data were modeled using a two-pole Sellmeier equation, with temperature dependence expressed through wavelength-dependent thermal coefficients. Four fitting models (Sellmeier and Cauchy) with different numbers of parameters were tested; for pentaethylene glycol, results from all models are shown, while for the remaining glycols, only the two-pole Sellmeier fits are presented in tabulated form. Thermal coefficient values for six wavelengths of practical importance are also tabulated. Experimental uncertainties in refractive index, wavelength, and temperature were rigorously evaluated and incorporated into the analysis. The influence of sample purity – including residual water content and manufacturer-reported impurities – was assessed and accounted for in the uncertainty estimates. To our knowledge, this is the first dataset to systematically characterize both chromatic dispersion and thermal variation of the refractive index for these glycols over such a broad spectral and temperature range. The validated fitting equations and parameters are suitable for use in optical modeling, materials characterization, and related applications. All raw data are available in a publicly accessible repository.