Free radical polymerization mediated by nitroxides in emulsion and miniemulsion at low temperatures

Abstract

One of the most important processes for producing polymers is free radical polymerization. This process is easy to perform, can be applied to the most of monomers under mild reaction conditions, allows working in a wide temperature range, is tolerant to impurities and water, besides the possibility of being used in copolymerization reactions.Despite all the advantages offered by this technique, there are some limitations to control some key elements such as the polymer molecular weight, polydispersity and chain architecture. Polymers with well-defined structures have been obtained by controlled free radical polymerization, which is capable of producing polymers with narrow molecular weight distributions and polydispersities close to unity.Among the techniques of controlled radical polymerization, nitroxide mediated polymerization (MRP), using TEMPO (2,2,6,6-Tetramethyl-1-piperidinyloxy) as controller has become effective, versatile, safe, inexpensive and simple techniques, and will be used in this work. In the literature, the vast majority of articles presents the application of this technique in homogeneous media (bulk polymerization), and a few papers deal with heterogeneous polymerization (emulsion and miniemulsion). There is still much to be explored in the area of NMRP polymerization in heterogeneous media, until to get the production of controlled polymers in industrial scale. One of the major disadvantages of NMP polymerization in heterogeneous systems is the need of using high temperatures, around 115 to 125 ° C, which are temperatures above the boiling point of water, which may destabilize the system. To overcome this problem, the literature proposes the use of SG1 agent (N-tert-butyl-N-[1-diethylphosphono (2,2-dimethylpropyl)]) and their derivatives, in substitution of TEMPO controler however, these controllers are more expensive and less comercial available, one disadvantage of its application to produce controlled polymers in large scale.In our research group, it was possible to successfully perform the controlled polymerization in emulsion using TEMPO at temperatures lower than 100 ° C (90 and 95 º C). This work concerns a dissertation defended by the German Giovanny Chaparro Montezuma (FAPESP process 2009/04006-8). The methodology used to achieve this goal was patented (protocol number 018110045780). As long as we know, this was the first time that NMRP polymerization using TEMPO was successfully obtained at temperatures below those typically used in the processes NMRP with TEMPO (around 115 to 125°C).In this project, the work of Montezuma (2011) will be continuated. More experiments will be carried out in emulsion in order to better understand the factors affecting the reaction. The methodology used for the emulsion process will be tested for the miniemulsion process, with the goal of trying to achieve a synthesis in miniemulsion at temperatures below 100 º C, which is a big advantage for the industrial point of view.The monomer to be used is styrene and the polymerization is conducted in stirred tank reactor of 1 liter of capacity. Important properties of the polymer will be investigated, for example, molecular weights, polidisersities and particle size.