Polymerization reactions monitoring viscosity

In ultrasound-induced polymerization reactions, the viscosity has a large influence on the radical formation rate. Therefore, it is important to monitor the viscosity during these reactions. By coupling the overall heat transfer coefficient U to the viscosity of the reaction mixture, the influence of the C02-concentration on the viscosity of polymer solutions has been deter-... 

The fluorescence quantum yields of certain compounds exhibit a strong dependence on the viscosity of the medium. As early as 1913, Stark (5) noticed that some dyes which do not fluoresce in ordinary solvents will, however, fluoresce strongly in highly viscous media such as glycerol at low temperatures. A number of studies on the viscosity-dependence of the fluorescence quantum yields of various compounds have appeared (6-12). Particularly noteworthy among these are the work of Oster and Nishijima (6), Forster and Hoffman (7), and Sharafy and Muszkat (8). However, Loutfy (13,14) was the first to exploit this effect for monitoring polymerization reactions. He applied the viscosity-dependent fluorescence probe approach for study of polymerization of vinyl monomers and discussed the potential of such probes for the study of polymeric systems... 

Viscosities are of interest in polymer technology in order to fohow the course of a polymerization reaction or to monitor continuously the quality of a product. Viscosity fi is the constant of proportionality between applied shear stress t and the resulting shear rate y according to Newton s Law of viscosity [Eq. (29)] [11, 13]. 

Spectroscopic techniques have been employed extensively for monitoring and control of processes in different fields. Since a detailed review of the applications of spectroscopic techniques in distinct areas is certainly beyond the objectives of the chapter, the interested reader should refer to textbooks and surveys for additional details [ 10,27,30,33,43,44]. It is also important to emphasize that most publications available in the field of polymer and polymerization reactions make use of spectrometers for off-line characterization of polymer properties. Typical applications include identification of polymer materials [82], evaluation of copolymer and polymer blend compositions [83, 84], evaluation of monomer and polymer compositions during polymerizations [85], determination of additive content in polymer samples [86, 87], and estimation of end-use properties of polymer materials. End-use properties analyzed include the degree of crystallinity of polymer samples [88], the degree of orientation of polymer films [85], the hydroxyl number of polyols [89], the melt flow index of polymer pellets [90], and the intrinsic viscosity of polymer powders [91], the morphology of... 

During a homogenous (bulk or solution) polymerization reaction, both the concentration of polymer and molar mass change and hence viscosity should also change. Therefore, online monitoring of the viscosity could give... 

Rotational (torque measurements) or capillary process viscometers, as well as ultrasound and tube oscillations [58] can be used to measure viscosity online during a polymerization reaction. The first two techniques have been widely applied in the monitoring of both chain growth polymerizations and step-growth polymerizations. 

Torque measurements have been used for online monitoring of the viscosity of polymerization reactions. The advantage of the torque measurement as compared with that of the capillary is that no treatment (dilution and flow) of the reaction medium is needed. Several examples of monitoring chain-growth polymerization reactions [62, 63] and step-growth polymerization reactions (specially curing reactions) can be found in the hterature [64]. 

Dietrich T, Ereitag A, Schlecht U. New micro viscosity sensor—A novel analytical tool for online monitoring of polymerization reactions in a micro reaction plant. Chem Eng J 2010 160 823-826. 

Mignard E, Guerret O, Berlin D, Reed WF. Automatic Continuous Online Monitoring of Polymerization reactions (ACOMP) of high viscosity reactions. Polym Mat Sci Eng 2003 88 314-316. 

FIGURE 12.7 Automatic Continuous Online Monitoring of Polymerization Reactions detectors response (LS90 ° and viscosity) to the different components of the diluted, phase inverted polyacrylamide emulsion (top) determination of dissolution time, from RI data for polyacrylamide in emulsion and in dry form. Reprinted (adapted) with permission from Alb AM, Farinato F, Calbick J, Reed WF. Online monitoring of polymerization reactions in inverse emulsions. Langmuir 2006 22 831-840. 2006 American Chemical Society. 

Monitoring polymerization reactions with detectors that make fundamental measurements of polymer properties allows a virtually model-free set of primary data concerning conversion, composition drift, and evolution of molecular weight and intrinsic viscosity. Unusual or unexpected events, such as microgelation or phase separation, can also be monitored directly. 

Advancement Process. In the advancement process, sometimes referred to as the fusion method, Hquid epoxy resin (cmde diglycidyl ether of bisphenol A) is chain-extended with bisphenol A in the presence of a catalyst to yield higher polymerized products. The advancement reaction is conducted at elevated temperatures (175—200°C) and is monitored for epoxy value and viscosity specifications. The finished product is isolated by cooling and cmshing or flaking the molten resin or by allowing it to soHdify in containers. 

Striking support of this contention is found in recent data of Castro (16) shown in Figure 14. In this experiment, the polymerization (60-156) has been carried out in a cone-and-plate viscometer (Rheometrics Mechanical Spectrometer) and viscosity of the reaction medium monitored continuously as a function of reaction time. As can be seen, the viscosity appears to become infinite at a reaction time corresponding to about 60% conversion. This suggests network formation, but the chemistry precludes non-linear polymerization. Also observed in the same conversion range is very striking transition of the reaction medium from clear to opaque. 

A technique is described [228] for solving a set of dynamic material/energy balances every few seconds in real time through the use of a minicomputer. This dynamic thermal analysis technique is particular useful in batch and semi-batch operations. The extent of the chemical reaction is monitored along with the measurement of heat transfer data versus time, which can be particularly useful in reactions such as polymerizations, where there is a significant change in viscosity of the reaction mixture with time. 

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