Cyclic polyethers by zwitterionic ring-opening polymerization

Resumen del trabajo presentado al International Symposium on Ionic Polymerization, celebrado en Bordeaux (Francia) del 5 al 10 de julio de 2015.Peer Reviewe

Dynamics of cyclic polyethers by broadband dielectric spectroscopy

Resumen del trabajo presentado al International Chemical Congress of Pacific Basin Societies, celebrado en Honolulu, Hawai (USA) del 15 al 20 de diciembre de 2015.Peer Reviewe

Neutron spectroscopy as a probe of macromolecular structure and dynamics under extreme spatial confinement

6th Meeting of the Spanish Neutron Scattering Association (SETN2012).We illustrate the use of high-resolution neutron spectroscopy to explore the extreme spatial confinement of soft matter in nanostructured materials. Two well-defined limits are considered, involving either intercalation or interfacial adsorption of the ubiquitous polymer poly(ethylene oxide) in graphite-oxide-based hosts. Vibrational modes associated with the confined macromolecular phase undergo dramatic changes over a broad range of energy transfers, from those associated with intermolecular modes in the Terahertz frequency range (1 THz = 33 cm−1), to those characteristic of strong chemical bonds above 2000 cm−1. We also consider the effects of polymer chain size and chemical composition of the host material. Variation of the degree of oxidation and exfoliation of graphite oxide leads to two distinct cases, namely: (i) subnanometer two-dimensional confinement; and (ii) surface immobilization. Case (i) is characterised by significant changes to conformational and collective vibrational modes of the polymer as a consequence of a preferentially planar trans-trans-trans chain conformation, whereas case (ii) leads to a substantial increase in the population of gauche conformers. Macroscopically, case (i) translates into the complete suppression of crystallization and glassy behaviour. In contrast, case (ii) exhibits well-defined glass and melting transitions associated with the confined phase, yet at significantly lower temperatures than those of the bulk.The authors gratefully acknowledge the continued support from the Spanish Ministry of Education (MAT2007-63681), Basque Government (IT-436-07), Gipuzkoako Foru Aldundia (2011-CIEN-000085-01), and the UK Science and Technology Facilities Council. F.B.-B. acknowledges financial support from BERC-MPC.Peer Reviewe

Zwitterionic polymerization of glycidyl monomers to cyclic polyethers with B(C6F5)3

A new method of generating cyclic polyethers is reported. Glycidyl monomers react with B(C6F5)3 to generate cyclic polyethers under anhydrous conditions. In the presence of water, linear chains are formed. A zwitterionic ring-opening polymerization mechanism is postulated based on experimental evidence and DFT calculations. The obtained cyclic polyethers can be considered a new family of crown ethers, where peripheral functional groups such as phenyls, fluorinated aliphatic chains or hydroxyls decorate the rings.Peer reviewe

Easy-dispersible poly(glycidyl phenyl ether)-functionalized graphene sheets obtained by reaction of ‘‘living’’ anionic polymer chains

3 páginas, 2 figuras.Excellent dispersion of functionalized graphene (FG) sheets in polystyrene was achieved relying on the reaction of “living” poly(glycidyl phenyl ether) chains onto graphene sheets. The physical aging of polystyrene was substantially accelerated by the presence of FG sheets at low filler content, retaining film transparency and increasing the electrical conductivity.The authors acknowledge the support of the Spanish Ministry of Education (CSD2006-00053), the Basque Government (IT-436-07), and SGIker UPV/EHU for TEM and NMR facilities. FBB and VB acknowledge the JAE-Doc contract from CSIC.Peer reviewe

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

Intercalation and confinement of poly(ethylene oxide) in porous carbon nanoparticles with controlled morphologies

Polymers confined at the nanometer scale often exhibit a distinct structural and dynamical response compared to their bulk counterparts. In this study, we observe that the confinement of poly(ethylene oxide) (PEO) in the nanopores of carbon nanoparticles (CNPs) leads to the suppression of crystallization and to a significant reduction of the Cp at the glass transition. We ask whether these changes are dominated by interfacial interactions (van der Waals type) or by geometrical constraints. For pore diameters below 2 nm (micropores following IUPAC nomenclature), we find that the larger the pore surface, the higher the amount of PEO intercalated in the micropores and, consequently, the larger the reduction of the Cp at the glass transition (up to 50%). For pore diameters in the range 2-50 nm (mesopores), larger pore surfaces lead to a higher amount of PEO adsorbed on the mesopore walls and the smaller the reduction of the Cp at the glass transition. Under these conditions of spatial confinement at the nanoscale, PEO chains cannot arrange themselves into large crystalline domains, as evidenced by a negligible degree of crystallization of at most 1.8%. High-resolution inelastic neutron scattering data show that the PEO chains confined in the pores of CNP adopt a planar zigzag conformation, which is distinctly different from those characteristic of the 7/2 helical structure of the bulk crystal.The authors gratefully acknowledge the support of the Spanish MEC (MAT2012-39199-C02-02 and MAT2012-31088), the Basque Government (IT-654-13), and the UK Science and Technology Facilities Council for the provision of beam time on the TOSCA spectrometer. P.P. acknowledges a PhD research contract from UCM (BE45/10). F.F.A. and S.R. acknowledge financial support from the UK Science and Technology Facilities Council.Peer Reviewe

End-to-end vector dynamics of nonentangled polymers in lamellar block copolymer melts: The role of junction point motion

By using dielectric spectroscopy, we investigate the chain dynamics of nonentangled polyisoprene (PI) under soft confinement in lamellar domains of block copolymer melts with polydimethylsiloxane (PDMS). The data show a dramatic difference in the end-to-end vector dynamics of the PI blocks as compared not only with that of the corresponding homopolymer PI chains but also with respect to previous results for the same blocks under soft confinement in cylindrical domains. Two contributions to the dielectric normal mode relaxation are detected. The data are analyzed by means of a model including contributions from internal chain modes (accounting for the fastest component) and a slow component attributed to the junction point dynamics. The contribution of the internal chain modes is modeled according to the analysis of the Rouse modes obtained from simulations of a generic bead-spring model for strongly segregated symmetric diblock copolymers. In this way it is shown that the internal chain modes of the blocks have time scales close to those expected from the homopolymer chain independently of the structural details. In contrast, the contribution attributed to the junction point dynamics depends critically on minor structural differences. We interpret these findings as a result of the presence of fast moving defects and/or grain boundaries in the lamellar structures formed by these relatively short, nonentangled diblock copolymers. © 2013 American Chemical Society.We acknowledge the financial support from Projects MAT2012-31088 (Spanish Government) and IT654-13 (Basque Government).Peer Reviewe

Synthesis of water-soluble copolymers carrying long-chain (C12 to C30) aliphatic moieties

6 páginas, 5 figuras, 2 tablas, 3 esquemas.-- et al.Water-soluble copolymers from mono-1-alkyl itaconates and N-vinyl-2-pyrrolidone are synthesized and characterized. The mono-1-alkyl itaconates are prepared from itaconic anhydride and the related alcohol: 1-dodecanol, 1-octadecanol, 1-docosanol, and 1-triacontanol. The mono-1-triacontyl itaconate is synthesized from plant growth regulator policosanols extracted from Agave fourcrouydes, where 1-triacontanol is the major product. The reactivity ratios, calculated according to the Mao-Huglin method for copolymerizations conducted to medium-high conversions, indicate a tendency toward alternation for all copolymerization reactions. Water solubility of copolymers is provided as a function of copolymer composition and aliphatic chain length.FBB thanks the Deutscher Akademischer Austauschdienst (DAAD) for a PhD grant and the Departamento de Postgrado y Postítulo, Universidad de Chile, Beca PG/86/02.Peer reviewe

Structure and dynamics of poly (ethylene oxide) confined in the interlayer space of graphite oxide

Resumen del trabajo presentado al 7th International Discussion Meeting on Relaxations in Complex Systems: "New results, Directions and Opportunities", celebrado en Barcelona (España) del 21 al 26 de julio de 2013.We explore the effects of chain size on the structure and dynamics of poly(ethylene oxide) (PEO) confined in the interlayer space of graphite oxide (GO). To this end, a PEO series of increasing chain length have been studied by means of high-resolution inelastic neutron spectroscopy (INS) on the TOSCA spectrometer, ISIS, UK, and broad band dielectric spectroscopy (BDS). PEO chains are accommodated in a layer of thickness 3.0–3.4 Å characterized by planar zigzag (trans–trans–trans) conformations. Moreover, we observe a strong reduction of vibrational motions for the confined polymer phase, as clearly evidenced by the disappearance, shift, and/or broadening of mode-specific INS spectral features, as well as by the complete suppression of crystallization and glass transition. All of these effects are surprisingly insensitive to the length of the PEO chains. BDS experiments of confined PEO show two relaxations: the faster one is independent of the chain length in agreement with INS results, whereas the slower one is dependent on the chain length and it could be associated to interfacial effects, typical of heterogeneous systems.Peer Reviewe