In this study, we have functionalized graphene oxide (GO) by growing polymer chains on its surface and then utilized the polymer-g-GO as a nanofiller with oxypolybenzimidazole (OPBI) to make a highly efficient nanocomposite-based proton exchange membrane (PEM). Three different monomers, namely, acrylamide (AAM), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and 3-sulfopropyl acrylate potassium salt (SPAK), were polymerized on the activated GO surface via surface-initiated reversible addition fragmentation chain-transfer polymerization to obtain three different types of polymer-g-GO, namely, pAAM-g-GO, pAMPS-g-GO, and pSPAK-g-GO. Furthermore, the chain length of grafted polymers in each case was altered in order to study the effects of the grafted polymer structure and chain length on the properties of nanocomposite PEMs. The exfoliation of GO nanosheets after polymer grafting was confirmed by studying the surface morphology using various microscopic techniques. Gel permeation chromatography and thermogravimetric analysis helped in measuring the chain length of grafted polymers and grafting density on the GO surface. Furthermore, we have impregnated polymer-g-GO as nanofillers by varying loading wt % into the OPBI to fabricate a mixed matrix membrane which upon doping with phosphoric acid (PA) converted into a mixed matrix PEM. The prepared nanocomposite PEM displayed exceptionally good thermal stability, significantly improved tensile properties, improved PA loading followed by superior proton conductivity, and remarkable PA retention when exposed to saturated water vapor. When the 2.5 wt % pSPAK-g-GO (where the pSPAK chain length is 19.6 kDa) mixed with OPBI, the resulting PEM showed a remarkably high proton conductivity value of 0.327 S cm −1 at 160 °C, a significant 5-fold increment compared to the pristine OPBI membrane (0.067 S cm −1 at 160 °C). To the best of our knowledge, this will be the first report on utilization of polymer-g-GO in polybenzimidazole membranes for hightemperature PEM application.

No abstract

Carbon nanotubes (CNTs) are of particular interest because of their ability to enhance the mechanical strength in the material; however, processing difficulties of CNTs often restrict utilization up to its full potential. To resolve this, in the current study, we have developed a simple and efficient method to functionalize the surface of a multiwalled carbon nanotube (MWCNT) with precise functional polymer chains, which were covalently graf ted on the surface of the MWCNT, and delved into an application to demonstrate this material as an efficient nanofiller in developing a proton conducting membrane (PEM) from polybenzimidazole (PBI). At first, the MWCNT surface was converted to a polymerizable surface by attaching a trithiocarbonate based chain transfer agent (CTA). Then, a N-heterocyclic block copolymer, namely poly-N-vinyl-1,2,4-triazole-b-poly-N-vinyl imidazole (pNVT-b-pNVI), was grown from the CTA anchored surface with a one-pot surface initiated reversible addition−fragmentation chain transfer (SI-RAFT) technique. Graf ting of block copolymer chain was confirmed by GPC, NMR, TGA, TEM, FESEM, and EDX studies. To the best of our knowledge, this will be the first report of a growing block copolymer structure graf ted covalently on the surface of the MWCNT. The novelty of the work was further enhanced by incorporating pNVT-b-pNVI-g-MWCNT as a nanofiller into the oxypolybenzimidazole (OPBI) membrane to obtain homogeneous nanocomposite membranes with excellent thermomechanical and tensile properties, thermal stability, superior proton conduction when doped with phosphoric acid (PA), and PA holding capacity. The nanocomposite membrane with 2.5 wt % nanofiller loading displayed a tensile stress of 1.8 MPa and a strain of 176% at break. The basic N-heterocyclic rings dangling from the block copolymer chains graf ted on the MWCNT surface allowed formation of strong H-bonding, acid−base interaction with PA, which is responsible for high acid uptake and superior PA retention, and also exhibited proton conductivity as high as 0.164 S cm −1 at 180 °C, which is a 2.6-fold increment when compared with a pristine OPBI membrane. This significant increase in conductivity is attributed to the proton conducting nanochannel pathway generated along the polymer-g-MWCNT surface.

Hollow polymer nanocapsules (HPN) consist of ferrocenyl shell have been developed by crosslinking the polymer chains grafted over silica nanoparticles (SiNP) which were synthesized via one pot grafting from surface...