Ooi SK, Biggs S
Department of Chemistry, University of Newcastle, Callaghan, NSW, Australia.
Ultrason Sonochem. 2000 Jul;7(3):125-33. doi: 10.1016/s1350-4177(99)00040-1.
Polystyrene latex samples have been synthesised from an oil-in-water (o/w) emulsion of the monomer using ultrasonic irradiation as the initiation source. No added chemical initiators were used in any of the reactions. The free radicals formed from the cavitation process under the action of the ultrasound are sufficient to initiate the polymerisation. In the current study, the effects of varying the input intensity of the ultrasound were investigated. A marked increase in the monomer conversion rate as a function of time was seen as the power was increased. Despite this increase in conversion rate, the increasing intensity did not affect the resultant latex particle sizes. In all cases, the particle diameters at the conclusion of a polymerisation were seen to be in the range of 40 to 50 nm. The effects of changing the concentration of surfactant in the polymerisation medium and of changing the temperature were also probed. Increases in both were seen to lead to an increased rate of conversion at a fixed input intensity. Again, the particle diameters were invariant as a function of changing conditions. The small particle sizes and high conversion rates are thought to be due to a continuous nucleation process that is caused by the scavenging of free radicals throughout the polymerisation by freshly formed small oil droplets.
聚苯乙烯胶乳样品是通过超声辐照作为引发源，由单体的水包油（o/w）乳液合成的。所有反应均未使用添加的化学引发剂。超声作用下空化过程产生的自由基足以引发聚合反应。在本研究中，研究了改变超声输入强度的影响。随着功率增加，单体转化率随时间显著增加。尽管转化率有所提高，但强度增加并未影响所得胶乳颗粒的大小。在所有情况下，聚合结束时的粒径均在40至50纳米范围内。还探讨了改变聚合介质中表面活性剂浓度和改变温度的影响。在固定输入强度下，两者的增加均导致转化率提高。同样，粒径不随条件变化而改变。小粒径和高转化率被认为是由于在整个聚合过程中，新形成的小油滴对自由基的清除导致的连续成核过程。
