Synthesis and Characterization of Poly-(Methyl Methacrylate) Nanoparticles with Ultrasound Assistance

Abstract

Nano-sized poly-(methyl methacrylate) (PMMA) is synthesized by employing three different methods with various techniques of emulsifying. This research is aimed at finding more effective and simpler ways to synthesize PMMA nano particles with acceptable particle size and conversion rate. Because of this, particle size and conversion rate are two main indicies for every sample of every different combination of synthesis methods and ways of emulsifying, and those two indicies are tested and calculated most commonly among all experiments. For certain experiments, other aspects of the polymerization process like temperature, initiator type, length of reaction time, and monomer/water ratio are also changed to study their influence on the polymerization. Ultrasound, one type of powerful emulsifying methods, is widely used among most of the experiments, and the intensity of ultrasound is different for every specific experiment. Three main methods are the batch reaction method, pre-mixing separation method, and differential addition method. There are also five main emulsifying techniques, magnetic stirring, bath ultrasound, probe ultrasonic dismembrator, combination of magnetic stirring and probe ultrasonic dismembrator, and combination of bath ultrasound and probe ultrasonic dismembrator. For the batch reaction method, results have shown that appropriate intensity of ultrasound can help to lower the particle size to 20nm with narrow distribution. At the same, the traditional magnetic stirring method cannot even convert all monomers into nano particles, which means there is always a part of MMA monomers being consumed to form rigid floating subjects during the reaction. However, experiments also reveal that a too powerful emulsifying force will lead to implosion, which significantly increases the reaction rate and the particle size. The combined emulsifying methods are much easier to cause implosion than an individual emulsifying method. The increase of particle size should be avoided, but the increase of reaction rate may have advantages in massive production. The pre-mixing separation method can help to make particle size even smaller and the distribution even narrower than the batch reaction method, but a too-powerful emulsifying method will have greater side effects on this type of reaction method. Experiments of the differential addition method are designed to synthesize fine polymer particles with narrow distribution, and to achieve a high conversion rate.