Monitoring Polymerization Reactions by Near-IR Spectroscopy

Abstract

The following overview is an investigative survey on the feasibility of near-infrared (NIR) spectroscopy as an on-line process analytical technique for control and optimization. The review focuses on current developments in the field of polymerization monitoring. A brief background description on instrumentation and methods of data analysis leads to suggestions for further investigation. After NIR's introduction in the early 1950s, it remained unnoticed by polymer chemists and engineers through the 1960s and 1970s. MR recaptured chemical engineers' attention in the late 1980s for two major reasons:(1) the development of advanced optical fiber materials and solid state detectors and (2) the incorporation of recent progress on multivariate data analysis algorithms. A review of the current trends in reactor monitoring strategies comprises the last section.

A New Approach to Near-Infrared Spectral Data Analysis Using Independent Component Analysis

“…It is now widely used in agricultural, food, and beverage industries. , Because the NIR technique is noninvasive and safe, it is also increasingly used in the medical field . The widespread use of the NIR technology is also found in pharmaceutical, biomedical, textile, and petrochemical industries. − …”

“…The NIR spectrum range is 780−2500 nm (12 820−4000 cm -1 ). Most NIR spectra are the result of overtones or combinations of fundamental vibrations involving hydrogenic stretching modes in the mid-infrared region of the spectrum (4000−600 cm -1 ). ,, For a given molecule, many active overtone and combination bands are typically present in a narrow NIR region and force the peaks to overlap significantly, and other fundamental vibrations manifest in the NIR region only as high-order overtones that are generally too weak to provide useful analytical information. Because of the difficulties in dealing with the highly overlapping peaks and the weak absorption in the NIR region, it had remained unnoticed for almost the next two decades since it was first introduced in the early 1950s.…”

“…Because of the difficulties in dealing with the highly overlapping peaks and the weak absorption in the NIR region, it had remained unnoticed for almost the next two decades since it was first introduced in the early 1950s. In late 1980s NIR began to emerge as an important technique, mainly due to the development in advanced optical fiber materials and solid detectors as well as the progress in multivariate data analysis. , The multivariate techniques used for NIR spectra analysis include multiple linear regression (MLR), principal component regression (PCR), and partial least squares (PLS) regression, as reviewed by Bouveresse and Massart, Hildrum et al, and Williams and Norris . Fourier, , and more recently wavelet transforms − have also been studied for NIR spectral data analysis.…”

Monitoring of the Thickness of Ultraviolet-Cured Pigmented Coatings and Printed Layers by Near-Infrared Spectroscopy

“…In this way, the application range of NIR spectroscopy was also extended for the monitoring of polymerization reactions. [3][4][5][6][7] For instance, batch, 3,6 solution, 5,7 and emulsion polymerization reactions as well as thermal curing processes 8,9 of (meth)acrylates and epoxy formulations have been monitored by near-infrared spectroscopy. Besides thermal polymerization of monomers, photochemically induced curing has become a technology of growing importance.…”

Process Control in Ultraviolet Curing with in-line near Infrared Reflection Spectroscopy

“…a wide range of polymer reactions have already been followed in the laboratory or under production conditions. [3][4][5][6][7] as well as bulk, solution and emulsion polymerisation reactions, this also comprises thermal curing reactions 8,9 as well as converting and compounding processes such as reactive and non-reactive extrusion of polymers. 7,10 In contrast, very few attempts have been made so far to mo nitor photochemically-induced curing reactions, [11][12][13][14] although uV photopolymerisation of thin polymer coatings has become an established and rapidly increasing technology.…”