Summary: Poly(cis‐norbornene‐exo‐2,3‐dicarboxylic acid dialkyl esters) (alkyl = Me, Et, Pr, Bu, Pen, and Hex) are synthesized as a vinyl‐type with a palladium(II ) catalyst in high yield from easily prepared, pure exo‐monomers. The polymers show good solubility in common organic solvents and excellent thermal stability up to 330 °C. The polymers with alkyl groups larger than methyl exhibit a two‐step thermal degradation profile of an initial thermal degradation of side‐chains starting at 350 °C, followed by thermal degradation of the norbornene backbone starting at ca. 430 °C. The glass transition temperature decreases and the mechanical flexibility increases as the alkyl length of the side‐chain increases.
Normalized loss shear modulus (G″) versus temperature for polynorbornene dicarboxylic acid dialkyl esters. 相似文献
Several series of fluorene-based light-emitting polymers with the emphasis on achieving efficient and stable bluelight emission are reported. Spiro-functionalization may narrow the emission spectra (with smaller tail at Ionger wavelengths)of fluorene homopolymers to provide purer blue emission. The thermal spectral stability of the polymers could also beimproved because of the elevation of the glass transition temperature caused by the spiro-functionalization. However, theexcimer emission in fluorene homopolymers is not suppressed by the spiro-functionalization. Alternate copolymers of 9,9-dihexylfluorene and substituted phenylenes may emit efficient blue ligh both in solution and in film. The optical propertiesare dependent on the substituion on the phenylene ring. The alkoxy-substituted polymers displayed efficient PL and EL andgood thermal spectral stability. The HOMO and LUMO energy levels of the polymers based on the backbone structure couldbe tuned in a wide range by attaching different functional groups on the phenylene ring. By attaching europium(III) complexat the ends of the side chains in the alternate copolymers, we have demonstrated a new approach to achieving red emissionwith a very narrow spectrum. The copolymers of 9,9-dihexylfluorene and thiophene and bithiophene with differentsubstitutions were also synthesized to study the effect of substitution and regioregularity on the optical and other physicalproperties of the polymers. 相似文献
Series
of thiophenes containing mesogenic side chains at the 3rd
position are synthesized. The thermal transitions and thermal stability of
the synthesized monomers and polymers are studied. The polarizing microscopic
studies of synthesized monomers showed nematic liquid crystalline phase and
these mesophases further confirmed by differential scanning calorimetric study.
The obtained melting and the isotropic temperatures decrease linearly with
the increase of aliphatic chain length. The transition temperatures determined
from DSC analysis, overlap well with the temperatures obtained from optical
microscopy studies. Thermal stability of the compounds is analysed using thermogravimetric
studies. Thermal stability of monomers and polymers has been determined by
calculating IPDT values. Structural influence on thermal degradation patterns
of monomers and polymers are also discussed. 相似文献
The structural evolution and properties of poly(9,9-dihexylfluorene-alt-2,5-dialkoxybenzene) with different lengths of alkoxy side chains on phenylene have been systematically investigated by means of thermogravimetric analysis (TGA), X-ray diffraction (XRD), differential scanning calorimetry (DSC), polarizing light microscopy (PLM), atomic force microscopy (AFM), and cyclic voltammetry (CV) techniques. The polymer self-organizes into a lamellar structure consisting of both two- and one-layer packing, and the two-layer packing style is the dominant structure. In addition, the two-layer and one-layer packing structures also accompany the presence of planar stacking and/or crystalline and noncrystalline structures, thus maintaining the stability of the packing. PF6OC6 shows three ordered phases (two crystalline phases and one nematic phase) during the heating process. With further increase of the length of alkoxy side chains, only two ordered phases (one crystalline phase and one nematic phase) are observed and the polymers show a melting-recrystallization phenomenon, which is steadily inhibited as the length of the alkoxy side chains increases. The optical and electrochemical properties of the polymers do not exhibit noticeable dependence on the length of the alkoxy side chains. However, the thermal stability, the vibronic structures, and the full width at half-maximum (fwhm) in photoluminescence spectra of the films gradually decrease, and the oxidation onset potentials and the corresponding HOMO energy levels slightly increase with increasing length of alkoxy side chains on phenylene. These results indicate that the length variation of alkoxy side chains does not change the electronic structure of the polymer backbones, but remarkably affects the microphase separation between the flexible side chains and the conjugated backbones. 相似文献
Studies have been made of the secondary relaxation processes in the solid state of a number of polymers containing aromatic groups in the polymer chain. The polymers investigated include one, polystyrene, with the aromatic group in side-chain positions, and six high polymers in which phenylene rings lie in the main backbone chain. In polystyrene, wagging and torsional motions of the side chain phenyl rings give rise to a low-temperature δ-relaxation which is centered at 33°K (1.7 Hz) and which has an activation energy of about 2.3 kcal/mol. Most of the polymers with phenylene rings in the main chain exhibit a low-temperature relaxation in the temperature region from 100°–200°K. This relaxation process is centered at 159°K (0.54 Hz) in poly-p-xylylene, at 162°K (0.67 Hz) in polysulfone, and at 165°K (1.24 Hz) in poly(diancarbonate). In poly(2,6-dimethyl-p-phenylene oxide), two overlapping low-temperature relaxations are found, one in the range 125–140°K and the other near 277°K (ca. 1 Hz). The low-temperature secondary relaxation process in all of these polymers is believed to be associated with local reorientational motion of the phenylene, or substituted phenylene, rings or with combined motion of the phenylene rings and nearby chain units. For these low temperature relaxation processes, the activation energy is about 10 kcal/-mole. The temperature location of the relaxation appears to depend on the specific units to which the phenylene rings are attached and on steric and polar effects caused by substituents on the ring. In the poly-p-xylylenes the relaxation is shifted to much higher temperatures by a single Cl substitution on the ring but remains at essentially the same temperature position when dichlorosubstitution is made. The effects of water on the magnitude and temperature location of the observed low temperature relaxations, as well as the implications of the study for other polymers containing aromatic groups in their backbone chains, are discussed. 相似文献
The stability of fluorene-based compounds and polymers, especially at the bridged C-9 position under photoirradiation and thermal treatment, has claimed wide attention. We report the electronic, vibrational, and MALDI-TOF mass spectral combined studies for the fluorene oligomers with alkyl and aromatic substitutions under UV-light irradiation. The low-energy emission and the formation of ketonic defects after degradation highly depend on the proportion of alkyl substitution. The oligomer with fully aromatic substitution shows good stability, but when the proportion of alkyl substitution increases, their photostability rapidly decreases. The mass spectra show not only the mass of the fluorenone-fluorene trimer but also another new degradation product with a large mass (pristine oligomer plus 14) from alkyl oxidation, which testify to the assistance of alkyl side chain during degradation. We propose that the degradation of fluorene is a radical chain process propagated by alkyl side chains, and then the different stability between alkyl and aromatic substitution can be well explained. 相似文献
A novel class of the liquid crystal polymers with mesogens laterally attached to flexible main chain backbones has been synthesized recently by us. While the flexible backbones tend to take configuration of maximum entropy the mesogenic side groups tend to orientate because of the anisotropie soft dispersion forces. A mean field theory is presented to describe the competition between these two trends which makes it possible for this class of polymers to show anisotropic (liquid crystal) phase within certain temperature range where the polymer main chains and the side chain mesogens will take approximately parallel arrangement, which is different from the normal side chain liquid crystal polymers. The temperature range of the liquid crystal phase, its ordering and phase transition all depend on the flexibility of the backbone, the strengthof the anisotropic forces of the side groups and the hinge elasticity. The results show that the liquid crystalisotropic phase transition is of the first order. The phase diagram, i. e. the dependence of the transition temperature on the structure of the polymers is also given. 相似文献
A number of series of fluorescent and conducting polymers containing alternating 3-functionalized thienylene/ bithienylene and phenylene/ pyridyl/ biphenylene units were synthesized from a number of central symmetric high oligomers and characterized using UV-Vis, photoluminescence, conductivity measurement, thermal analysis, electrochemistry, XRD and XPS. Structural variation of the polymers was realized by both side chain and polymer backbone modifications. Close structure-property correlation of the polymers was observed. This paper mainly reports the results of two families of them, those substituted by alkyl pendant chains and electro-withdrawing and donating groups. 相似文献
Anionic water soluble siloxane polymers have been synthesized and characterized for electrokinetic chromatography. Siloxane polymers are of interest in electrokinetic chromatography because of the wide variety of chemistries that can be developed based on these backbones, including much of the stationary phase chemistry developed in the last 30 years. The siloxanes in this study have a sulfonate functional group. The siloxanes have different length alkyl chains (C8, C12, C18) attached to the backbone in differing densities. The methylene selectivity generally increases with increasing alkyl chain length and with increasing alkyl chain density. The electrophoretic mobility appears to pass through a maximum as more alkyl chain is added to the siloxane backbone. The efficiency also would seem to pass through a maximum as more alkyl chain is added. The chemical selectivities of the siloxane polymers are very different from sodium dodecyl sulfate but are similar to each other. 相似文献
A series of octakis(dimethylsiloxy)octasilsesquioxanes bearing linear and branched alkyl substituents has been prepared in high yield by Pt-catalyzed hydrosilylation of alkenes with octakis(hydrodimethylsiloxy)octasilsesquioxane, chain length varying between C3 and C8 for the straight-chain derivatives and between C5 and C7 for the branched-chain derivatives. On the basis of a WAXS study, we showed that the linear derivatives are amorphous and that the interdigitation of alkyl chains between neighboring POSS molecules increases as the alkyl chain length increases from propyl to octyl. The thermal behavior of these compounds was studied by DSC, polarized optical microscopy and TGA in nitrogen and air atmosphere. The derivatives with shorter n-alkyl chains from C3 to C6 crystallize below 0 °C whereas the derivatives with longer n-alkyl chains (C7 and C8) can be regarded as amorphous glasses with a Tg around –100 °C. The morphology and thermal properties change considerably with branching of the alkyl chain. Melting points above ambient temperature were found for the iso-hexyl and iso-heptyl POSS derivatives whereas the iso-pentyl POSS derivative is liquid at 25 °C. From the values of the heat of fusion as well as entropy of fusion, it was concluded that packing of the side groups in the crystal structure increases as the size of the branched alkyl group increases. TGA evidenced a negative effect of the branching of the alkyl chain on the thermal stability in air. 相似文献
Novel rod like phenylene thiophene based polyhydroxy amphiphiles, derivatives of gallic acid combining three hydrophilic 2,3‐dihydroxypropyloxy groups and one alkyl chain via central aromatic linking units, have been synthesized by using Ni(II), Pd(0) catalyzed coupling reaction as key steps. The mesophase behavior of such compounds was investigated by POM and DSC. Thereby the influence of the position of the alkyl chains on the mesophase behavior was discussed. All such compounds exhibit smectic A phases. As the alkyl chain moving from the terminal position to the lateral position near the central of the rigid core, the stability of the smectic A phase would be decreased. 相似文献