Fibers of a poly(azomethine) having hydroxyl groups within
the mesogenic core have been
melt extruded from the nematic phase. The polymer obtained by
condensation of 1,10-bis[(4-formyl-3-hydroxyphenyl)oxy]decane and 2-methyl-1,4-phenylenediamine
has a T
g of 54 °C and exhibits a
nematic
phase from 178 to 341 °C. Due to an observed increase in the
melt viscosity upon heating above 200 °C,
the processing temperature (190 °C) has been closely controlled above
T
m. Fibers have been subjected
to
thermal annealing at 100 °C, i.e., above T
g
and below T
m, either in a relaxed state or under
an external
force along the longitudinal fiber axis. Fibers have been studied
by simultaneous TG-DTA, DSC, and
X-ray scattering, and the mechanical properties have been measured.
As-spun fibers show good thermal
stability and good orientation along the fiber axis; the values of the
elastic modulus and tensile strength
are 8.9 GPa and 252 MPa, respectively, and the elongation at break is
3.3%. The mechanical properties
improve after annealing in a relaxed state. After 90 min at 100
°C, the values of the elastic modulus and
tensile strength increase to 11 GPa and 283 MPa, respectively, and the
elongation at break is 2.5%.
Longer heat treatments do not seem to significantly affect the
properties; however, a gradual but
remarkable increase in the degree of crystallinity is promoted. A
highly crystalline phase is achieved
after annealing on a stressed state. It consists of a primitive
triclinic lattice where the chains are packed
side-by-side with the alkyl chains in an all-trans
conformation. After 12 h at 100 °C, an increase in
the
molecular weight is determined from the inherent viscosity values, but
relaxation of the molecular
orientation is not observed. All of these effects lead to an
improvement in the tensile properties: the
values of the elastic modulus and tensile strength increase to 18.4 GPa
and 388 MPa, respectively, and
the elongation at break is 2.2%.
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”.
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