On the importance of accurate internal temperature measurements in the microwave dielectric heating of viscous systems and polymer synthesis

摘要

The relationship among viscosity and microwave absorptivity of organic solvents/polymers, the stirring rate, and the resulting errors in temperature measurement upon microwave dielectric heating is investigated. For a set of common solvents and polymers covering a broad range of viscosities and microwave absorptivities significant variations in the temperatures simultaneously recorded by external infrared sensors and internal fiber-optic probes are experienced. The implications of these apparent difficulties in establishing the genuine reaction temperature for microwave-heated viscous reaction systems are evaluated for a ring-opening polymerization and for the synthesis of a surfactant. Stirring is Everything: If reaction mixtures under microwave conditions cannot be stirred properly, monitoring of reaction temperature is troublesome and can lead to erroneous conclusions. This is of particular importance for the synthesis of polymers, which often involves highly viscous reaction mixtures that cannot easily be stirred/agitated.