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| Author(s): |
Telma Regina Nogueira
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Química |
| Defense date: | 2008-10-11 |
| Examining board members: |
Liliane Maria Ferrareso Lona;
Domingos Savio Giordani;
Leila Peres
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| Advisor: | Liliane Maria Ferrareso Lona |
| Abstract | |
Living free radical polymerization, also known as "pseudo-living radical polymerization" has received more and more attention as a technique for the production of polymers with micro structure highly controlled (narrow molecular weights distributions and polydispersity index close to one). Conventional routes to obtain polymer like this have been ionic polymerizations, however, they are extremely sensitive to impurities and solvents. Free radical polymerizations, which are more versatile and robust to impurities, for the production of polymers with controlled structures by "controlled" or "pseudo-living" process, have become an important alternative. As a disadvantage of the controlled process can be pointed the low reaction rate when compared to the conventional process. Most of the published papers about nitroxide mediated living free radical polymerization consider the homopolymerization of styrene as case study. In this research, the co-polymerization of styrene and divinylbenzene (DVB) by living free radical polymerization (NMRP) is investigated in experimental level. The stable radical used was 2,2,6,6-tetramethyl-1-piperidinoxyl (TEMPO). The initiators used in this work were tertbutylperoxy- 2-ethylhexyl carbonate (TBEC) and benzoyl peroxide (BPO). DVB acts as a branching generator, improving the properties of the styrene as the solvent and impact resistance. TBEC was used in substitution to conventional initiators as 2, 2-Azo-bisisobutyronitrile (AIBN) and BPO, with the aim of accelerating the reaction rate, trying to keep a controlled/living system. All the experiments were performed in ampoules. To better understand this system, many experiments were performed at different temperatures, divinylbenzene concentrations, initiator concentrations and molar ratios between controller and initiator. Conversion was obtained by gravimetric method and the polymer was characterized by Gel Permeation Chromatograph (GPC). It was observed that, at certain operating conditions, the TBEC initiator was able to produce copolymers with polydispersity close to unity in a much faster velocity when compared to BPO. (AU) | |