Determination of Hydroxyl Number in Polymers by Infrared Spectroscopy: Comparison of Near-IR and Mid-IR

Abstract

A comparison of near-infrared (NIR) and mid-infrared (mid-IR) techniques for the determination of hydroxyl number in polyesters was made. Both of these analyses are faster and involve less exposure to irritating, highly toxic, and corrosive chemicals than the chemical analysis, although both techniques rely on developing calibration files. The mid-IR procedure consisted of making thin films of polymer on IR crystals by spin coating and taking transmission spectra. The program used for the analysis, Nicolet PLS Quant, compensated for the resulting indeterminate pathlength. The NIR procedure consisted of taking transmission spectra of the clear, viscous polymers in 4-mm cuvettes and using standard regression analysis of the spectra.

Multivariate near infrared spectroscopy models to monitor polycondensation production process reactions

“…The application of NIR spectroscopy to determine the main analytical properties during polycondensation is reported in the literature [5][6][7][8][9], but few have used an inline fiber-optic probe. Robbins et al [5] determined, using NIR spectroscopy at 1415 nm and applying univariate linear regression, the average molecular weight based on the disappearance of the hydroxyl group.…”

“…Robbins et al [5] determined, using NIR spectroscopy at 1415 nm and applying univariate linear regression, the average molecular weight based on the disappearance of the hydroxyl group. Likewise, Lee et al [6], using univariate linear regression, related the hydroxyl value with the second derivative of the NIR spectra. Blanco et al [7] developed multivariate models for different stages of the production process.…”

In Situ Monitoring of an Escherichia coli Fermentation Using a Diamond Composition ATR Probe and Mid-infrared Spectroscopy

“…The relative qualitative and quantitative merits of both near‐ and mid‐infrared spectroscopy have been considered for a variety of systems (Cooper et al, 1997; Doyle, 1995; Lee et al, 1993; Stallard, 1997; Yu and Phillips, 1992). Mid‐infrared spectroscopy measures the fundamental vibrational modes of molecules (Colthup et al, 1990; Peters et al, 1974; Robinson, 1995; Smith, 1979).…”