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  • 1.
    Limé, Fredrik
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Irgum, Knut
    Umeå University, Faculty of Science and Technology, Chemistry.
    Monodisperse Polymeric Particles by Photoinitiated Precipitation Polymerization2007In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Macromolecules, Vol. 40, no 6, p. 1962-1968Article in journal (Refereed)
    Abstract [en]

    Monodisperse polymer particles consisting of DVB and styrene-copoly-DVB were successfully synthesized by photoinitiated precipitation polymerization with 2,2'-azobis(2-methylpropionitrile) (AIBN) as initiator. A focused 150 W xenon short arc lamp was used to radiate the sample mixtures. The size of the particles ranged from 1.5 to 4 m and could be varied by changing the monomer concentration between 2 and 10% (v/v) and by means of the time of polymerization. By using photoinitiation instead of thermal initiation, it was possible to avoid coagulum and arrive at spherical particles with an exceptionally high monodispersity for particles of this size range (polydispersity index < 1.02) and with monomer loadings well above 5%.

  • 2.
    Tonpheng, Bounphanh
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Britt M
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tensile strength and young's modulus of polyisoprene/single-wall carbon nanotube composites increased by high pressure cross-linking2010In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 43, no 18, p. 7680-7688Article in journal (Refereed)
    Abstract [en]

    High-viscosity liquid cis-1,4 polyisoprene (PI), with up to 20 wt % single-wall carbon nanotubes (SWCNTs), has been cross-linked by high pressure and high temperature (HP&HT) treatment at 513 K and pressures in the range 0.5 to 1.5 GPa to yield densified network polymer composites. A composite with 5 wt % SWCNTs showed 2.2 times higher tensile strength σUTSUTS = 17 MPa), 2.3 times higher Young’s modulus E (E = 220 MPa) and longer extension at break than pure PI. The improvement is attributed to SWCNT reinforcement and improved SWCNT−PI interfacial contact as a result of the HP&HT cross-linking process, and reduced brittleness despite a higher measured cross-link density than that of pure PI. The latter may originate from an effect similar to crazing, i.e., bridging of microcracks by polymer fibrils. We surmise that the higher cross-link densities of the composites are due mainly to physical cross-links/constraints caused by the SWCNT−PI interaction, which also reflects the improved interfacial contact, and that the CNTs promote material flow by disrupting an otherwise chemically cross-linked network. We also deduce that the PI density increase at HP&HT cross-linking is augmented by the presence of CNTs.

  • 3.
    Tonpheng, Bounphanh
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Yu, Junchun
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Thermal conductivity, heat capacity, and cross-linking of polyisoprene/single-wall carbon nanotube composites under high pressure2009In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 42, no 23, p. 9295-9301Article in journal (Refereed)
    Abstract [en]

    Polyisoprene (PI)/single-wall carbon nanotube (SWCNT) composites and pure PI have been cross-linked by high-pressure treatment to yield densified elastomeric states. Simultaneously, the SWCNT and cross-linked-induced changes of the thermal conductivity, heat capacity per unit volume, and glass transition were investigated by in situ measurements. The thermal conductivity of both the elastomeric and liquid PI improves ≈120% by the addition of 5 wt % SWCNT filler. The SWCNT filler (5 wt %) increases the glass-transition temperature of liquid PI by ≈7 K and that of the elastomeric state by as much as 12 K, which is due to a filler-induced increase in the cross-link density. Moreover, the 5 wt% filler yields a heat capacity decrease by ≈30% in both the glassy and liquid/elastomeric states, which indicates that SWCNTs cause a remarkably large reduction of both the vibrational and configurational heat capacity of PI. Finally, the consequences of high-pressure densification and the possibilities this provides to help elucidating the nature of the heat conduction in polymer/carbon nanotube composites are discussed.

  • 4. Vestberg, Robert
    et al.
    Westlund, Robert
    Eriksson, Anders
    Lopes, Cesar
    Carlsson, Marcus
    Umeå University, Faculty of Science and Technology, Chemistry.
    Eliasson, Bertil
    Umeå University, Faculty of Science and Technology, Chemistry.
    Glimsdal, Eirik
    Lindgren, Mikael
    Malmström, Eva
    Dendron Decorated Platinum(II) Acetylides for Optical Power Limiting2006In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 39, no 6, p. 2238-2246Article in journal (Refereed)
    Abstract [en]

    The effect of dendritic substituents on a nonlinear optical chromophore for optical power limiting (OPL) has been investigated. Synthesis and characterization of bis((4-(phenylethynyl)phenyl)ethynyl)bis(tributylphosphine)platinum(II) with dendritic end groups are described. Polyester dendrimers up to the fourth generation were grown divergently using the anhydride of 2,2-bis(methylol)propionic acid (bis-MPA). The introduction of the dendritic moieties onto the NLO chromophore enables further processing of the materials using polymeric and related techniques. OPL measurements performed at 532, 580, and 630 nm show that the OPL properties improve with increasing size of the dendritic substituent. It is also shown that the addition of the dendrons increase the OPL as compared to the nondecorated bis((4-(phenylethynyl)phenyl)ethynyl)bis(tributylphosphine)platinum(II). By use of femtosecond z-scan measurements carried out at different pulse-repetition frequencies, it is shown that the two-photon absorption cross section is ~10 GM. Using pulse repetition frequencies (100 kHz-4.75 MHz) so that the time between the pulses is comparable with the triplet excited lifetime, the z-scans become dominated by excited-state absorption of excited triplet states.

  • 5.
    Yu, Junchun
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tonpheng, Bounphanh
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    High-pressure-induced microstructural evolution and enhancement of thermal properties of nylon-62010In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 43, no 24, p. 10512-10520Article in journal (Refereed)
    Abstract [en]

    The transition behavior and thermal properties of nylon-6 at elevated pressure, p, have been established by in-situ thermal conductivity, κ, and heat capacity measurements. The glass transition temperature, Tg, of virgin nylon-6 is described well by the empirical equation Tg(p) = 319.60(1 + 1.90 p)0.24 (p in GPa and Tg in K). Moreover, isobaric heating in the 1−1.2 GPa range causes a cold-crystallization transition near 500 K. As a result, κ increased 15% whereas the heat capacity per unit volume decreased 7% slowly with time during 4 h annealing at 530 K. The transformation is associated with a significantly increased crystallinity, from 35% to 55−60%, and a pressure-induced preferred orientation and increased size for the lamellae of monoclinic α crystalline structure. This state has 8−10 K higher melting temperature and better formic acid resistance than that of virgin nylon-6. However, the results show no indication of cross-linking, as reported for similarly treated nylon-1010 and nylon-11, but instead chain scissoring.

  • 6.
    Yu, Junchun
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tonpheng, Bounphanh
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gröbner, Gerhard
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    A MWCNT/Polyisoprene Composite Reinforced by an Effective Load Transfer Reflected in the Extent of Polymer Coating2012In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 45, no 6, p. 2841-2849Article in journal (Refereed)
    Abstract [en]

    Tensile and microstructural properties of multiwall carbon nanotube (MWCNT)/polyisoprene (PI) composites have been investigated after cross-linking achieved purely by simultaneous high-pressure high-temperature treatment. The method enables gradual increase of the cross-link density without interference of vulcanization chemicals, and the results suggest a link between an interfacial PI layer wrapped/coated on the MWCNTs and reinforcement in carbon nanotube (CNT)/PI composites. The interfacial layer, which is augmented by high-pressure treatment, was detected indirectly in swelling experiments and also reflected in results of atomic force microscopy. The results imply more efficient load transfer and mechanical reinforcement by CNTs with improved interfacial layer and that changes in the layer can be probed by swelling measurements.

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