Abstract:A series of hydroxy-functionalized semi-¯exible polyazomethines has been synthesized and characterized to investigate the e ect of the structure of the diamine monomer on the thermal and mesogenic properties. The diamine monomer introduces structural modi® cations such as exibility, lateral substitution, kinks or alteration of chain coaxiality. The mesomorphic phase of the mesogenic polymers was characterized as nematic in nature, but an evolution of the nematic into a smectic mesophase was observed for the po… Show more
“…The mesophase is identified as nematic by its texture observed by polarizing optical microscopy. However, on annealing the sample at the mesophase temperature for several hours, a change can be observed as the nematic mesophase becomes smectic C. This change in mesophase type was confirmed by X-ray diffraction and reported elsewhere …”
Cross-linked polymeric materials have been synthesized
by copper(II) complexation of a
semiflexible main-chain liquid crystalline polyazomethine. The
influence of the copper(II) cross-linking
density on the thermal properties has been studied by DSC. The
relaxation behavior of both the parent
polymer and the complexed polymers has been investigated by dielectric
spectroscopy and dynamic
mechanical measurements. The parent compound exhibits three
relaxations (denoted by α, β, and γ),
together with a conductive process at low frequency. The
relaxations have been associated with the
glass transition (α), rotational motions located in the rigid
mesogenic core (β), and local motions of the
decamethylene flexible spacer (γ). Semiempirical calculations
have been carried out in order to evaluate
the rotational energy barriers which can account for the β process.
The influence of the degree of cross-linking on the activation energies and on the strength and shape
parameters has also been studied in
the copper(II)-complexed polymers.
“…The mesophase is identified as nematic by its texture observed by polarizing optical microscopy. However, on annealing the sample at the mesophase temperature for several hours, a change can be observed as the nematic mesophase becomes smectic C. This change in mesophase type was confirmed by X-ray diffraction and reported elsewhere …”
Cross-linked polymeric materials have been synthesized
by copper(II) complexation of a
semiflexible main-chain liquid crystalline polyazomethine. The
influence of the copper(II) cross-linking
density on the thermal properties has been studied by DSC. The
relaxation behavior of both the parent
polymer and the complexed polymers has been investigated by dielectric
spectroscopy and dynamic
mechanical measurements. The parent compound exhibits three
relaxations (denoted by α, β, and γ),
together with a conductive process at low frequency. The
relaxations have been associated with the
glass transition (α), rotational motions located in the rigid
mesogenic core (β), and local motions of the
decamethylene flexible spacer (γ). Semiempirical calculations
have been carried out in order to evaluate
the rotational energy barriers which can account for the β process.
The influence of the degree of cross-linking on the activation energies and on the strength and shape
parameters has also been studied in
the copper(II)-complexed polymers.
“…In recent papers we have described the synthesis and properties of a series of polyazomethines, derived from 1,10-bis[(4-formyl-3-hydroxyphenyl)oxy]decane, with the general formula shown in Scheme where X = OH. , Different diamines were tested in order to obtain polymers with low transition temperatures and high stabilities. 1 Schematic Representation of the Synthetic Strategy Applied To Obtain Polyazomethines…”
A number of semiflexible liquid-crystalline polyazomethines have been synthesized by
condensation of two dialdehyde monomers (1,10-bis[(4-formyl-3-hydroxyphenyl)oxy]decane or 1,10-bis[(4-formylphenyl)oxy]decane) with two diamines (2-methyl-1,4-phenylenediamine or 3,3‘-dimethoxybenzidine). Polyazomethines having a hydroxyl group at the ortho position of the imine bond have higher
degrees of polymerization and a remarkable tendency to show an increase in their molecular weight
upon postpolymerization thermal treatments. These hydroxy-functionalized polymers have been coordinated with copper(II) ions to give rise to metallomesogenic cross-linked polymers. Fiber spinning of both
organic and copper(II)-complexed polymers has been carried out, and the structure, orientation, and
morphology of the fibers have been studied by X-ray diffraction, electron paramagnetic resonance, and
scanning electron microscopy. The mechanical properties have also been evaluated. Hydroxy functionalization and copper(II) complexation are the key strategies to obtain highly oriented fibers with good
mechanical properties and strong intermolecular cohesive forces. A highly oriented crystalline phase with
improved mechanical properties could be developed by thermal annealing of “as-spun fibers”.
“…Determination of the average molecular weight and weight distribution of the polymer composites by common techniques such as size exclusion chromatography was restricted due to the lack of solubility of the polyazomethines in common solvents. Nevertheless, information about molecular weight for comparative purposes was available from 1 H NMR and inherent viscosity (η inh ) values but it must be noted that in strong protic acid solvents hydrolysis occurred to some extent and the values are certainly underestimated 32, 33. As a result, the degrees of polymerization were estimated from the 1 H NMR spectra by relative integration of the signals at ∼8.80 ppm (CHN groups) and ∼9.50 ppm (terminal CHO groups), and the results are consistent with about 30–50 repeating units.…”
The synthesis and characterization of a series of nematic SWNT-polyazomethine composites are described. The composites were prepared by in situ polymerization in the presence of 1 wt % of chemically modified SWNTs in such a way that they were either dispersed or covalently bonded to the polymeric matrix. The presence of the SWNTs did not alter the thermal behavior of the polymer matrix and, therefore, highly oriented fibers could be melt-extruded from the composites at moderate temperatures, as revealed by structural and morphological studies. Preliminary tests on tensile properties indicate that strength and stiffness were improved when compared with fibers without CNTs, particularly when SWNTs were covalently bonded to the polymeric matrix. V
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