Tunable uptake of poly(ethylene oxide) by graphite-oxide-based materials

We investigate the role of structure and chemical composition on the uptake of poly(ethylene oxide) by a series of graphite oxides (GOs) and thermally reduced GOs, leading to the formation of polymer-intercalated GO and polymer-adsorbed graphene nanostructures. To this end, a series of poly(ethylene oxide) (PEO) - GO hybrid materials exhibiting a variable degree of GO oxidation and exfoliation has been investigated in detail using a combination of techniques including X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetry, scanning-electron microscopy, and nitrogen adsorption. Intercalation of the polymer phase into well-defined GO galleries is found to correlate well with both the degree of GO oxidation and with the presence of hydroxyl groups. The latter feature is an essential prerequisite to optimize polymer uptake owing to the predominance of hydrogen-bonding interactions between intercalant and host. Unlike the bulk polymer, these intercalation compounds show neither crystallisation nor glass-transition associated with the polymer phase. Exfoliation and reduction of GO result in high-surface-area graphene layers exhibiting the highest polymer uptake in these GO-based materials. In this case, PEO undergoes surface adsorption, where we observe the recovery of glass and melting transitions associated with the polymer phase albeit at significantly lower temperatures than the bulk

Dielectric relaxations in poly(glycidyl phenyl ether): Effects of microstructure and cyclic topology

Cyclic and linear, isoregic and aregic, and isotactic and atactic poly(glycidyl phenyl ether) (PGPE) with molecular weights up to Mw = 5.5 kg/mol are synthesized by ring-opening polymerization of glycidyl phenyl ether. Initiation with tetrabutylammonium fluoride leads to isoregic linear polymers with ~95% regular linkages, and initiation with B(C6F5)3 and B(C6F5)3/water leads to aregic cyclic and linear polymers, respectively, with ~50% regular linkages as quantified by 13C NMR. Local, segmental, and chain dynamics in PGPE is investigated by broadband dielectric spectroscopy (10–2–106 Hz). The ß-relaxation for linear PGPE is separated into two contributions arising from the motions of side groups and end groups with activation energies of 35.4 and 23.8 kJ/mol, respectively. The ß-relaxation process for cyclic PGPE shows the same activation energy as that shown by the side-group contribution in linear PGPE, indicating that topology does not play a key role on the side-group local dynamics. Moreover, cyclic PGPE samples show higher calorimetric and dynamic glass transition temperatures as well as lower dynamic fragility compared to linear chains. Unexpectedly from topological considerations, cyclic PGPE shows low frequency dielectric contributions that can be attributed to short wavelength internal ring motions and that are detectable by dielectric relaxation due to the aregic nature of the rings.Peer ReviewedPostprint (author's final draft

Polymers under Extreme Two-dimensional Confinement : Poly(ethylene oxide) in Graphite Oxide

4 páginas, 4 figuras.The confinement of poly(ethylene oxide) in graphite oxide is studied using a combination of diffraction, calorimetric, and spectroscopic methods. Polymer intercalation into subnanometer graphite oxide layers leads to the complete suppression of crystallization phenomena and dielectric α-relaxation processes, as well as a slowdown of β-relaxation modes. For the first time, high-resolution inelastic neutron scattering shows that poly(ethylene oxide) under these extreme confinement conditions adopts a planar zig-zag conformation, in no way resembling the characteristic 72 helical structure of the bulk crystal. The neutron data also shows a strong suppression of the COC and OCC bending modes and a distinct broadening of C–O torsional bands.The authors gratefully acknowledge the support of the Spanish Ministry of Education (MAT2007-63681), the European Union (502235-2, SOFTCOMP), the Basque Government (IT-436-07), and the UK Science and Technology Facilities Council for beam time on the TOSCA spectrometer. FBB acknowledges a JAE-Doc contract from CSIC. FFA and SFP acknowledge financial support from the UK Science and Technology Facilities Council.Peer reviewe