This paper presents a comparative study of two commercial calorimeters, RC1 (Mettler-Toledo GmbH, Schwerzenbach, Switzerland) [1] and CPA202 (ChemiSens International AB, Lund, Sweden) [2], which provide calorimetric data using two different heat-transfer principles. The capabilities of the two calorimeters are evaluated and compared using highly exothermic free-radical polymerization reactions of methyl methacrylate (MMA) and n-butyl acrylate (nBA) initiated by Vazo 52 or 67 in xylene at 60, 70 and 80 C.The comparison is in terms of the reaction heat generation profile, calorimetric conversion, monomer conversion, and molecular weight distribution. Analytical measurements of final polymer sample properties, as well as model predictions are also used in this study.

The CPA202 has a glass or steel reactor of total volume 250 ml. The reaction volume can vary between 10 and 180 ml. The pressure operating range of the reactor is between 0 to 10 Mpa, and the temperature range is from -50 to 200 C. The reactor can be operated in various thermal modes such as isothermal, isoperibolic, adiabatic, constant heat flow, and low power. It can measure a rate of heat release as low as 2 Joules with a precision standard deviation of less than 1%. The power measurements can be made in the range of -30 to +30 Watts. CPA202 has a compact size, has diverse thermal modes for various applications, permits direct measurement of heat of reaction from a true heat flow curve, and has an easy-to-use computer interface software, ChemiCall [2].

The Mettler-Toledo RC1 Reaction Calorimeter is an automatic lab reactor with heat balancing [3]. The temperature control modes include “Tj mode”, “Tr mode”, “distillation mode”, and “adiabatic mode”. In polymerization experiments, the overall polymerization rate can be inferred from the instantaneous heat of reaction. An additional IR probe can be used for on-line concentration measurements [4].

MMA, nBA, xylene, Vazo 67, and Vazo 52 were used as received. Homo-polymerization was carried out in the 1-liter RC1 and the 250 ml CPA202 calorimeter reactors. Each experiment was started with loading the reactor with xylene and the monomer. The initiator, Vazo 67 or Vazo 52, dissolved in xylene, was injected in one dose using a syringe after the reactor temperature had reached steady state conditions. CPA202 was operated isothermally. Samples were drawn from the reaction mass at the end of each batch. Polymer and residual monomer concentrations were obtained by gravimetric and Gas Chromatographic (GC) analysis. GC analysis was done using Hewlett-Packard (HP), HP-FID system with a DB-5 column. Molecular weight distributions were obtained by performing High Performance Liquid Chromatography (HPLC) using a HP HPLC system with an RI detector and a four column set configuration (105, 104, 103, 102 A 30 cm X 7.8 mm id microstyragel columns) [5, 6].

References

[1] www.us.mt.com

[2] www.chemisens.com

[3] WinRC Online Help, April 2001.

[4] De La Rosa, V.L., Sudol, E.D., El-Aasser, M.S., Klein, A., Details of the Emulsion Polymerization of Styrene Using a Reaction Calorimeter, Journal of Polymer Science Part A: Polymer Chemistry, 34(3), p.461, 1996.

[5] Quan, C., Soroush, M., Grady, M.C., Hansen, J.E., Simonsick, W.J., Characterization of Thermally Polymerized n-Butyl Acrylate and Ethyl Acrylate, Macromolecules, 2005, 38(18), p. 7619.

[6] Rantow, F.S., Soroush, M., Grady, M.C., Kalfas, G.A., Spontaneous Polymerization and Chain Microstructure Evolution in High-Temperature Solution Polymerization of n Butyl Acrylate, polymer, 47, p.1423, 2006.