In an attempt to reduce the emission of hazardous VOCs, SCFs have been intensively investigated as alternative solvents during the last two decades. In this study, the application of reaction calorimetry, an efficient tool to obtain kinetic and safety data, is presented on the free radical dispersion polymerization of MMA in scCO2. The effect of three major parameters with respect to the reaction evolution are studied, namely of stirrer type and stirring speed, the monomer and CO2 concentration and the stabilizer concentration. The effective formation of the dispersion as well as the balance between the polymer formed in the continuous phase or inside the particles are key features of this analysis.

Summary: Experiments of methyl methacrylate dispersion polymerization are carried out in a reaction calorimeter using PDMS-mMA as surfactant. Different stabilizer concentrations from 0 to 10 wt% with respect to monomer have been considered in order to control particle morphology. The analysis by scanning electron microscopy reveals a definite decrease of the total particle surface area at decreasing stabilizer concentration. At the same time, the analysis of the polymer microstructure by gel permeation chromatography shows a trend of the average molecular weight towards smaller values. In particular, a second mode at low molecular weights has been observed leading to bimodal molecular weight distributions. The experimental results are compared with simulation results obtained through a detailed kinetic model developed in previous studies.[1] The key role of the radical exchange between continuous and dispersed phases is confirmed.

No abstract

No abstract

in Wiley InterScience (www.interscience.wiley.com).The free-radical dispersion polymerization of methyl methacrylate was studied using the reaction calorimetry technique. An especially developed calorimeter for use with supercritical fluids was employed and a set of experiments was explicitly designed to isolate the effect of the pressure. It was found that, under marginal dispersion stability conditions, small pressure changes can have significant effects on the reaction evolution. The pressure was also found to affect the partitioning of the monomer between the two reaction phases. The heat released during the nucleation stage of the reaction was measured for the first time and permitted the discussion on the polymerization locus during this stage.

in Wiley InterScience (www.interscience.wiley.com).Supercritical carbon dioxide (scCO 2 ) is a promising foaming agent for the production of polymeric foams, representing an environmentally friendly alternative for the foaming agents currently used. During the expansion phase of the scCO 2 -foaming process, temperature plays an essential role. This study focuses on relating the effects of temperature and pressure profiles on the foaming process and the resulting foam morphology. Therefore, several experiments have been performed in a high pressure reaction calorimeter (RC1e) that can be set to three different modes: isothermal, adiabatic, and isoperibolic. It has been observed that the foaming could be divided into four stages: nucleation, slow cell growth, fast cell growth, and shrinkage. The degree of shrinking that occurs is for a great deal dependent on the exposure to higher temperatures at the end of the foaming process. Since shrinkage does not occur in the adiabatic mode, this mode gives the best control on the foam morphology.

The heat flow reaction calorimetry technique was developed for reactions with supercritical fluids and was applied to monitor the free-radical dispersion polymerization of methyl methacrylate in supercritical carbon dioxide (scCO 2 ). The main mathematical equation for the calorimetric calculations was modified to take into account the particularities linked to the supercritical nature of the solvent. As a result, important heat transfer variables, such as the overall heat transfer coefficient, can be measured at the actual reaction conditions. This information is later used to calculate the heat released by the reaction and thus monitor its evolution. The robustness and accuracy of the technique allowed also investigating the effects of several reaction parameters. Finally, the obtained data were used to illustrate the importance of pressure as far as the safety of the reaction is concerned.

The technique of reaction calorimetry adapted for use with reactions in supercritical fluids was used to study some safety aspects of the free‐radical dispersion polymerization of methyl methacrylate in scCO2. The reaction heat rate profile was found to change very little once the dispersion was well formed. Furthermore, it provided valuable information for the calculation of the maximum temperature attainable by the synthesis reaction (MTSR) in the case of a hypothetical cooling system failure. Finally, a series of failure scenarios demonstrated the importance of the pressure as far as the safety of the process is concerned, due to the particularity of the supercritical state of the solvent. It was found that the acceleration phase of the reaction is the most critical period, since a cooling system failure during this phase leaves very little time before the pressure overcomes the operational limit of the equipment and results in an accident. Hence, the utility and the importance of defining the reaction heat rate profile become obvious and several safety features have to be taken into consideration when designing a SCF process. © 2009 American Institute of Chemical Engineers Process Saf Prog 2009