Dual physicochemical analysis

There has been recent interest in developing dual spectroscopic-rheological techniques for characterizing polymer solutions and melts. Primarily this is because of the advantage of being able to obtain chemical and physical information simultaneously from the system to be monitored. Obviously, this is of extra relevance for curing systems that have time-dependent chemical and physical properties. 

A review of rheo-optical techniques by Sherman et al. (1996) notes that there has been an increase in the use of rheo-optic set-ups both for FT-IR dichroism and for dynamic IR dichroism spectroscopies for polymer melts and polymer blends. Skytt et al. (1996) highlight the use of simultaneous measurement of the transient or steady-state rheological properties and IR dichroism to characterize orientation in polymer melts. However, there is little reference to dual spectroscopic-rheological techniques for reactive polymer systems in the literature. 

Chemoviscosity profiles may also be correlated to chemical rate parameters. Simultaneous acquisition of the NIR spectrum and low-shear dynamic rheology may also be undertaken from prior to gelation to beyond vitrification for various epoxy-resin systems for selected isothermal profiles to provide network information from rheological power-law indices, fractal dimensions and network rheological structure parameters. 

Recently Benali et al. (2004) reported the development of a new laboratory-made system that allows the combination of rheometric (Alessi et al, 2005) and spectroscopic (Fourier-transform-near infrared (FT-NIR) spectroscopy) measurements for reactive polyurethane materials along the lines of these principles. 

There are also more recent developments of other dual physio-chemical experimental methods. For example Durand et al (2006) presented a laboratory-made system that allows the coupling of dielectric analysis and Fourier-transform near-infrared spectroscopy (FT-NIR) to follow the cure of polyepoxy reactive systems. Complementary data are provided by the simultaneous dielectric analysis (the vitrification phenomenon) and near-infrared spectroscopic analysis (the extent of the reaction). 

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The Hammett-type correlation for the rate constants of 5-allyl-5-R-barbiturates has been reported by Carstensen et al. and suggested for use in stability predictions.569 Similar correlations were also found for the hydrolysis of 5-arylidenebarbituric acids.363,567 Linear free energy relationships have also been reported for dissociation constants,45,51 polarographic half-wave potentials,570 fluorescence70 and luminescence phenomena,71 and 13C-NMR chemical shifts129 for different classes of barbituric acid derivatives. Application of the dual substituent parameters method in LFER analysis of barbiturates, using Taft s polar and steric constants for various chemical and physicochemical properties, was also evaluated.571... 

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