Polymerization reactions simultaneous monitoring

This chapter will concentrate on monitoring techniques applied to polymerization reactions in supercritical fluids. Different available techniques will be discussed, ending with the coupling of analytical and calorimetric measurements. This kind of coupling could be one solution to the problem of simultaneous evaluation of physicochemical properties, kinetic data, and engineering information such as heat transfer and thermicity. 

Alb AM, Drenski ME, Reed WF. Simultaneous continuous, non-chromatographic monitoring and discrete chromatographic monitoring of polymerization reactions. J Appl Polym Sci 2009 13 190-198. 

Simultaneous monitoring by in situ NIR spectroscopy and ACOMP was reported in the case of methyl methaaylate (MMA) polymerization reaction [6]. 

A new advance with regard to the instrumentation and methods available for online monitoring of heterogeneous polymerization reactions was made by using ACOMP for monitoring the evolution of multiple characteristics during polymerization. The information-rich data collected simultaneously by multiple detectors provide absolute, model-independent determination of quantities such as conversion, composition, and molar mass distribution and avoid potentially damaging effects of the reactor environment. 

Monitoring polymerization reactions has both fundamental and applied motivations. At the basic level, simultaneous monitoring of the various reaction characteristics, such as the evolution of copolymer composition and molecular weight, can reveal the underlying kinetics and mechanisms involved in reactions and also illuminate ways in which the reaction may deviate from what is ideally thought to occur. The ability to monitor reactions will become increasingly important as new, stimuli-responsive, and intelligent polymers are developed at the frontiers of twenty-first century materials science. 

Perhaps the most obvious chemical application is the monitoring of polymerization reactions involved in the production of polymers. Like most chemical reactions, the polymerization process shows up very well in vibrational spectra as the simultaneous disappearance and appearance of spectral bands. For example, in the polymerization of a typical vinyl monomer, carbon-carbon double bonds are broken and carbon-carbon single bonds are formed. This... 

Any chemical reaction that is accompanied by enthalpy changes can be followed by calorimetric methods [3,24,29], DSC is widely used to study polymerizing systems, especially epoxides [55-57]. Both the rate and the extent of reaction can be monitored using either isothermal or scanning modes of operation [3,24,29]. If volatile products are formed, the reaction must be carried out in sealed pans or under pressure [58] to conserve mass and avoid an uncertain correction for vaporization or to pressure-shift simultaneous vaporization events. 

While hydrolyzation uses water as a reactant, polymerization regenerates water as a product. The kinetics of this process are very complex. In fact, the mechanism for reactions catalyzed by acid is different from that catalyzed by base (5, 12). To monitor the extent of these reactions, an experiment was devised to simultaneously measure ethanol and water content in the reaction flask (7). An increase in ethanol content would indicate progress in hydrolyzation. A minimum in water with a subsequent rise would indicate progress in polymerization. 

Real-time infrared spectroscopy (RTIR) (21). The basic principle of this analytical technique consists of exposing the sample simultaneously to the polymerizing UV beam and to the analyzing IR beam, and monitoring on a high speed recorder the sharp decrease of the acrylic absorbance at 812 cm l. Conversion versus time curves have thus been recorded for the first time for photopolymerizations that develop extensively in a fraction of a second (211. If the reaction time drops into the millisecond range, a transient memory recorder (221 or an oscilloscope with storage function can be used to shorter the time resolution further. 

To control the heating cycles of polymerizations, we have found that electrically actuated pnemnatic jacks are very useful. In conjunction with temperature controller that monitors the temperature inside the reaction flask, the heating mantle for the flask is raised or lowered as required with such jacks. The temperature history may be recorded simultaneously with a suitable flat-bed recorder. There is also equipment to monitor and record the stirring speed [44]. 

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