Search results for "Copolymer"
showing 10 items of 1003 documents
Ethylene-vinyl Acetate Thermoplastic Copolymers Filled with Multiwall Carbon Nanotubes: Effect of Hydrothermal Ageing on Mechanical, Thermal, and Ele…
2013
A range of properties of two commercial thermoplastic ethylene-vinyl acetate (EVA) copolymers, Elvax 420 and Elvax 450, neat and as melt-mixed composite filled with 15 wt.-% of multi-wall carbon nanotubes (MWCNTs), are studied in the “as produced” state and after hydrothermal ageing. Addition of MWCNTs into the neat copolymers introduces the functionality of electrical conductivity and significantly improves their mechanical properties, while thermal characteristics are slightly affected by the presence of carbon nanotubes. A remarkable increase of the elastic modulus (150%) and stress at failure (50%) in stress–strain experiments as well as creep resistance (40%) of the nanocomposites in c…
Living Light-Induced Crystallization-Driven Self-Assembly for Rapid Preparation of Semiconducting Nanofibers.
2018
Well-defined nanostructures composed of conjugated polymers have attracted significant attention due to their intriguing electronic and optical properties. However, precise control of the size and uniformity of these semiconducting nanostructures is still rare and challenging, despite recent advances in strategies to obtain self-assembled nanostructures with narrow dispersions. Herein, we demonstrate the preparation of fluorescent conjugated block copolymers by one-shot polymerization and rapid formation of nanofibers in a few minutes via light-induced crystallization-driven self-assembly, driven by facile cis-to- trans photoisomerization of its poly( p-phenylenevinylene) blocks. Furthermor…
Nanotube Friendly Poly(N-isopropylacrylamide).
2010
Poly(N-ispropylacrylamide) [PNIPAM] is a widely studied polymer for use in biological applications due to its lower critical solution temperature (LCST) being so close to the human body temperature. Unfortunately, attempts to combine carbon nanotubes (CNTs) with PNIPAM have been unsuccessful due to poor interactions between these two materials. In this work, a PNIPAM copolymer with 1 mol-% pyrene side group [p-PNIPAM] was used to produce a thermoresponsive polymer capable of stabilizing both single and multi-walled carbon nanotubes (MWNTs) in water. The presence of pyrene in the polymer chain lowers the LCST less than 4 °C and the interaction with nanotubes does not show any influence on LC…
Organolanthanides, catalysts for specific olefin-diene copolymerization: access to new materials
2001
Abstract Non-hindered ansa dicyclopentadienylallyl complexes of samarium, [(CMe2C5H4)2Sm(allyl)]n, and (CMe2C5H4)2Sm(allyl)L (L=THF or allylLi) polymerize isoprene without an aluminum cocatalyst. The polymerizations are highly stereospecific, affording nearly quantitatively 1–4 trans polyisoprene. In the presence of linear 1-olefins, copolymers are formed, with 6–10% of olefin inserted; the 1–4 trans structure of the polyisoprene chain is not altered, and only one olefin molecule is inserted between two polyisoprene fragments. In the common initiator of these three catalytic systems, the (CMe2C5H4)2Sm(allyl) moiety, only one vacant site would be available. As a consequence of the presence o…
Diene/olefin/polar monomer copolymerisation: unprecedented functional polymers from a rare earth catalyst
2002
An ansasamarocene allyl system is an efficient initiator which polymerises 1,3-dienes, copolymerises dienes and long-chain α-olefins or α,ω-dienes to give functionalisable polymers. It also polymerises caprolactone and allows the controlled diblock copolymerisation of isoprene or isoprene/ α-olefin copolymer and caprolactone.
Linear-dendritic nonionic poly(propylene oxide)–polyglycerol surfactants
2003
Abstract A new type of linear-hyperbranched surfactant has been prepared by anionic ring-opening multibranching polymerization of glycidol onto an end-functional poly(propylene oxide) (PPO) macroinitiator. A hyperbranched, highly hydrophilic polyglycerol block is obtained as the polar segment of the structure. Molecular weights of the nonionic amphiphiles obtained were in the range of 390 to 8,600 g/mol. For comparison, initiators bearing a C16 alkyl chain have also been employed. Furthermore, hyperbranched polyglycerol homopolymers were investigated with respect to amphiphilic properties. All linear-dendritic amphiphiles have been characterized by SEC, DSC, 13 C and 1 H NMR spectroscopy. A…
Neutron scattering characterization of homopolymers and graft-copolymer micelles in supercritical carbon dioxide
1996
Abstract Superficial fluids (SCF) are becoming an attractive alternative to the liquid solvents traditionally used as polymerization media [1]. As the synthesis proceeds, a wide range of colloidal aggregates form, but there has hitherto been no way to measure such structures directly. We have applied small-angle neutron scattering (SANS) to characterize such systems, and although SCF polymerizations are carried out at high pressures, the penetrating power of the neutron beam means that typical cell windows are virtually transparent. Systems studied include polymers soluble in CO 2 such as poly(1,1-dihydroperfluorooctyl acrylate) (PFOA), poly(hexafluoropropylene oxide) (PHFPO) and poly(dimet…
Shear induced mixing/demixing: blends of homopolymers, of homopolymers plus copolymers, and blends in solution
2000
Shear may shift the phase boundary towards the homogeneous state (shear induced mixing, SIM), or in the opposite direction (shear induced demixing, SID). SIM is the typical behavior of mixtures of components of low molar mass and polymer solutions, SID can be observed with solutions of high molar mass polymers and polymer blends at higher shear rates. The typical sequence with increasing shear rate is SIM, then occurrence of an isolated additional immiscible area (SLD), melting of this island into the main miscibility gap, and finally SIM again. A three phase line originates and ends in two critical end points. Raising pressure increases the shear effects. For copolymer containing systems S…
Freely-Suspended and Transferred Freely-Suspended Films of Polymeric Liquid Crystals
1993
Freely-suspended (FS) liquid-crystal (LC) films of a polymethylsiloxane homo- and a copolymer with different mesogenic side groups have been prepared and investigated. For both substances the preparation of the films succeeded only in the isotropic phase but the higher ordered phases were reached after cooling. The films of the homopolymer have only been obtained with thicknesses estimated to be in the pm-range and with an unusual “Book-Shelf” orientation of the smectic layers. In contrast, the films of the copolymer were thinner and showed a homeotropic orientation of the mesogens in the smectic A phase. Interestingly, this material exhibited a different layer spacing in film and bulk, alt…
Temperature triggered self-assembly of polypeptides into multivalent spherical micelles.
2007
We report herein thermally responsive elastin-like polypeptides (ELPs) in a linear AB diblock architecture with an N-terminal peptide ligand that self-assemble into spherical micelles when heated slightly above body temperature. A series of 10 ELP block copolymers (ELP(BC)'s ) with different molecular weights and hydrophilic-to-hydrophobic block ratios were genetically synthesized by recursive directional ligation. The self-assembly of these polymers from unimers into micelles was investigated by light scattering, fluorescence spectroscopy, and cryo-TEM. These ELP(BC)'s undergo two phase transitions as a function of solution temperature: a unimer-to-spherical micelle transition at an interm…