Abstract
The ultrasound techniques are widely useful to study the physical properties of solid, liquid and gas. The chain dynamics in polymer solutions and the interaction between polymer chains and solvents have been investigated by measuring the sound absorption and velocity. It is well known that irradiation of the ultrasound with the high intensity in the frequency range from 20 kHz to a few MHz produces cavitation bubbles in liquids and solutions. The local reaction field at the high temperature and pressure (the hot spot) is formed when the bubbles collapse. Application of the power ultrasound to polymer solution has been examined by many workers. The session of polymer chains under sonication is of interest in connection with controlling the molecular weight. The degradation has been studied by the viscosity measurement and gel permeation chromatograph. These results revealed that the ultrasonic irradiation to polymer solutions results in the decrease of the solution viscosity and the molecular weight. The long time ultrasonic irradiation gives rise to the low molecular weight(a few thousands) and the narrow polydispersity samples. The results of the ultrasonic degradation of water-soluble polymers are given in this paper. The degradation mechanism is well interpreted by the Glynn's model. They indicated that ultrasonic degradation proceeded with a certain degradation probability. The water-soluble polymers degrade with a Gaussian probability and the degradation rate depends on the molecular structure and flexibility of the polymers. At the local reaction field in monomer and polymer solutions produced by the ultrasound, monomer and polymer radicals (or others) are formed, and polymerization is initiated. Up to date, ultrasonic polymerization has been studied for various systems, such as monomer, monomer and polymer, and polymer and polymer systems. One of useful advantages in ultrasonic polymerization is that polymerization proceeds without the initiators. Recent results are reported here concerning the frequency effect on polymerization of styrene under sonication which was carried out at a constant ultrasonic intensity measured by chemical dosimeter. It is indicated that there is an optimum frequency in the range from 92 to 518kHz for effective polymerization. Effect of sonication on autopolymerization of styrene in the presence of 2,2,6,6-tetramethylpiperidinyl-1-oxy(TEMPO) as the mediating radical will be reported. The thermal polymerization under sonication proceeds in the manner of a "living" radical polymerization to afford well-defined polystyrene.
