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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 applications yet it is necessary to develop low cost and more efficient PEMFCs. The heart of the PEMFC is the membrane electrode assembly composed of a proton exchange membrane sandwiched between two porous gas diffusion electrodes. These electrodes are made up of a catalyst support material or gas diffusion layer and a catalyst layer. Catalyst support materials have significant effect on the cost, performance and the durability of PEMFCs. The ideal support materials should provide high dispersion, utilization, activity, and stability for the catalyst especially platinum (Pt) (1-3). Carbon black has been extensively used as a catalyst support for Pt in PEMFC. However, alternatives to carbon black are still needed to enhance catalyst utilization and reduce the cost.Novel nanostructured carbon materials (carbon nanofibers, carbon nanotubes and graphene) have generated intense interest as catalyst supports in PEMFCs due to their unique structures and properties (4, 5). However, the main drawbacks of these materials are high production cost and mass production. At this point, graphene nanosheets can serve as the promising catalyst support because of its low-cost and large-scale production. In addition, free standing graphene sheets have large surface area, high thermal and electrical conductivity, and high mobility of charge carriers (6). According to Saner et al. (7) a few graphene layers provide effective surface area to improve metal-support interaction. Authors proposed a mild chemical exfoliation method for the reduction of layer number in graphitic structure and the production in large quantities of 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Ruoff et al. (9) showed that chemically modified graphene was incorporated into ultracapacitor test electrodes in order to increase the energy density of the packaged ultracapacitor by increasing the electrode thickness and eliminating additives.Conducting polymers have high conductivity, are lightweight, inexpensive, flexible, airstable, and environmentally friendly but the major obstacle of conducting polymers as an electrode material is the degradation during cycling because of the volume change of the polymer due to the insertion/deinsertion of counter ions (10).Therefore, nanocomposites based on conducting polymers and carbon nanomaterials can be used as a potential catalyst support to improve the properties of supports and extend life cycle of fuel cells. There have been several attempts for the synthesis of these type of nanocomposites. Previously, Wang et al. (11) reported that the remarkable electrical conductivity and specific capacitance of graphene/polya...

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Pentablock poly(L-lactide-co-∊-caprolactone) (PLLA/PCL), with a central fluorinated segment and four PLLA/PCL side chains was synthesized by sequential ring-opening polymerization (ROP) with stannous octoate catalyst in an environmentally benign and clean medium, scCO2. Copolymers of PLLA and PCL are extensively researched for biomedical applications. Fluorinated hydrocarbons are similarly promising for biomedicine, and especially for oxygen-carrying substitute applications. Initially, a fluorinated reactive triblock stabilizer (prepolymer, PCL-FLKT-PCL) with inner fluorinated segment and PCL side chains was synthesized in bulk from a tetraol fluorinated alcohol (FLKT) with a 99% conversion. The prepolymer was then utilized for the synthesis of copolymers in scCO2, where PLLA segments were successively incorporated to the ends of the prepolymer, forming a pentablock structure with four polyester side chains. Reactions were carried out at 75°C and 4000-4500 psi. Solubility studies of the prepolymer and the pentablock copolymer in scCO2 showed effective solubilization at the reaction temperature and pressure. The molecular weights of the products were measured with the aid of gel permeation chromatography; the prepolymer and the copolymer possessed average number molecular weights (Mn) in the range of 13 000 and 24 000 (for 96% conversion of LLA), respectively. Low poly-dispersity indexes were obtained: 1.34 for the prepolymer and 1.08-1.34 for the pentablock copolymer. Material characterization was carried out by 1H NMR, 13C NMR, 19F NMR, differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and scanning electron microscopy (SEM).