Electrically conductive polymeric materials through polymerization and compatibilization

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Minna Annala Name of the doctoral dissertation Electrically conductive polymeric materials through polymerization and compatibilization Publisher School of Chemical Technology Unit Department of Biotechnology and Chemical Technology Series Aalto University publication series DOCTORAL DISSERTATIONS 116/2012 Field of research Polymer Technology Manuscript submitted 7 March 2012 Date of the defence 2 November 2012 Permission to publish granted (date) 29 August 2012 Language English Monograph Article dissertation (summary + original articles) Abstract Three different electrically conductive polymeric materials were studied. In the first part, carbon nanotube (CNT) composites were prepared by using in situ polymerization of styrene and methyl methacrylate. Emulsion polymerization and combined emulsion/suspension polymerization methods were used. The mechanical properties of composites were improved directly due to the addition of the CNTs, but also indirectly due to the effect of CNTs on molecular weight and molecular weight distribution. The molecular weights increased and distribution narrowed, if CNTs were present in the polymerization reaction. The composites were conductive if the amount of CNTs was over 1.5 wt.% in polystyrene composites and over 3 wt.% in poly(methyl methacrylate) composites. As the stable dispersion of CNTs in the composites was obtained, these composites were tested as masterbatches.Three different electrically conductive polymeric materials were studied. In the first part, carbon nanotube (CNT) composites were prepared by using in situ polymerization of styrene and methyl methacrylate. Emulsion polymerization and combined emulsion/suspension polymerization methods were used. The mechanical properties of composites were improved directly due to the addition of the CNTs, but also indirectly due to the effect of CNTs on molecular weight and molecular weight distribution. The molecular weights increased and distribution narrowed, if CNTs were present in the polymerization reaction. The composites were conductive if the amount of CNTs was over 1.5 wt.% in polystyrene composites and over 3 wt.% in poly(methyl methacrylate) composites. As the stable dispersion of CNTs in the composites was obtained, these composites were tested as masterbatches. In the second part, polyaniline (PANI) complex and polyethylene were blended to create an electrically conductive polymer blend. The PANI complex was plasticized in order to use melt blending and processing, and metallocene polymerization was utilized to prepare carboxyl acid and hydroxyl functionalized polyethylenes for compatibilization of the blend components. Compatibilization was based on hydrogen bonds, which do not decrease the conductivity of PANI to the same extent as covalent bonds. The polyethylene contained only 0.2 mol-% of functionalities. Therefore the number of formed hydrogen bonds was small. Conductivity above 10-4 S/cm was obtained with 15 wt.% of the camphorsulfonic acid doped PANI complex. The mechanical properties of the blend were clearly improved with addition of 18 wt.% of functionalized polyethylene. In the third part, metallocene polymerization was utilized to prepare an ethylene/styrene copolymer, which was sulfonated in order to get a proton conductive polymer membrane. With the alternating structure of the copolymer with nearly 1:1 molar ratio of ethylene/styrene, sulfonic groups were evenly distributed along the membrane that was hot pressed from the copolymer. A high sulfonation degree with styrene content of 50 mol-% caused high water uptake and ion exchange capacity, thereby achieving high proton conductivity, above 70 mS/cm. Mechanical stability of highly sulfonated proton conductive membranes was improved by using a glassfiber tissue as reinforcement and by adjusting sulfonation conditions for crosslinking.