Continuous flow microwave catalytic chain transfer polymerisation of methyl methacrylate oligomers

The aim of this project was to develop and compare microwave at 2.45 GHz and conventional heating processes to produce low molecular weight methyl methacrylate oligomers. The required level of conversion for this process to be successful was 40 %. Batch and flow processes were investigated for both heating methods, and conversions of up to 70 % in batch and 55 % in flow were achieved.\ud \ud A large number of publications conclude that microwave heating can lead to significant improvements in conversion, rate and product quality when compared to conventionally heated reactions. In many cases this has been attributed to a non-specific thermal effect due to material interactions with the electric field component of the microwave. In many cases these conclusions stem from inaccurate temperature measurement in a microwave environment, and comparisons with conventional heating being carried out under different conditions. In this work a robust methodology was developed to compare microwave and conventional heating for oligomer production.\ud \ud Initial work was carried out at 30-50 cm³ using a CEM Discover SP (300 W) microwave, a conventionally heated stirred oil bath and a single mode cavity. Investigation into the effects of temperature, heating rate and reaction time on conversion were carried out, and it was found that the target material could be produced to 70% conversion in less than 5 minutes. From the understanding gained using small scale batch reactions a set of design requirements were produced for larger scale flow systems using microwave and conventional heating, and these systems were constructed as part of this project. This apparatus allowed for repeatable production of the target material at flow rates of up to 36 kg/hour when operated using a 2 kW microwave generator with automated tuning. Conventional comparisons were carried out at in flow with the use of apparatus of the same physical geometry under the same conditions.\ud \ud This is the first work published to carry out direct comparisons between conventionally heated and microwave reactions under the same conditions. It was found that at all scales and under all the conditions investigated that there were no quantifiable benefits in conversion or product quality offered by the use of microwave heating. It was concluded that such benefits concluded elsewhere are likely to result from poor control and rigour in experimental comparisons