Abstract
It has been shown by previous workers that ultrasound is capable of both reducing the molecular weight of polymers and narrowing their molecular weight distribution. Further, ultrasonically induced cavitation has been shown to be capable of initiating polymerisation in bulk vinyl monomers. However, the rate of polymerisation is slow and the yield of polymer low. The present study may be divided into four parts. Firstly, the effect of ultrasound on solutions of diphenyl picrylhydrozyl (DPPH) dissolved in benzene. Secondly, the effect of ultrasound on the rate of decomposition of the initiator azo-bis-isobutyronitrile (AZBN). Thirdly, the effect of ultrasound on the kinetics of polymerisation of N-vinyl carbazole (NVC) monomer dissolved in benzene initiated by AZBN. Finally the structure and physical properties of the polymers resulting from the irradiated polymerisations were studied.The loss of DPPH from both solutions at elevated temperatures and from solutions irradiated at a number of ultrasonic intensities, was found to be first order. This observation has been rationalised as resulting from a first order. This observation has been rationalised as resulting from a first order abstraction reaction between DPPH and the solvent and not from the expected zero order free radical reaction.
Ultrasonic irradiation was shown to be capable of accelerating the decomposition of AZBN at low intensities and retarding it at high intensities. This observation was rationalised as resulting from the combined effects of the temperature and pressure maxima resulting from cavitation. Thus allowing a means of predicting the decomposition rate constant in the presence of ultrasound to be successfully developed.
During the polymerisation, ultrasound was shown to increase the rate of polymerisation at low intensities and inhibit the polymerisation at high intensities. It has been further shown that although ultrasound can increase the rate of decomposition of AZBN, the initiator efficiency is greatly reduced. Ultrasound was also shown to increase the termination rate constant at a greater rate than the propagation rate. Finally ultrasound has been shown to reduce main chain branching, the degree of branching being lower in polymerisations irradiated at the higher intensities and hence producing a more linear polymer.
| Date of Award | 1992 |
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| Original language | English |
| Supervisor | Timothy Mason (Supervisor) & John P Lorimer (Supervisor) |