Mechanical Properties of Drawn Smectic Mesophases. Poly(tetramethylenoxypropylene p,p‘-bibenzoate)

Abstract

A smectic main chain polymer, poly(tetramethyleneoxypropylene p,p′-bibenzoate), PPO4B, with thermal transitions Tg ) 26 °C and Ti ) 88.5 °C was studied in and after a drawing experiment. Variation of both strain rate and temperature resulted in materials with normal and anomalous orientations of smectic layers. Mechanical properties vary correspondingly. Samples from PPO4B were drawn at different strain rates and temperatures. The stress-strain curves were recorded. The resulting oriented materials were studied by wide-angle X-ray scattering. Normal orientation (i.e., smectic layer perpendicular to draw direction) is established at high strain rate and low temperature. Anomalous orientation is achieved at low strain rate and high temperature. At intermediate values of the processing parameters a bimodal structure of both normal and anomalous orientation is observed. Dynamic mechanical analysis measurements in tensile mode were carried out on strips cut from oriented sheets in three directions, 0°, 45°, and 90°in relation to the draw direction. The value of the storage modulus in the drawing direction is highest in the case of normal orientation (smectic layer perpendicular to the straining direction). The highest value of the storage modulus coincides with the direction perpendicular to most of the smectic layers. Thus, for anomalous orientation the worst mechanical properties are in the fiber direction.

Synthesis and structural studies of poly(tetramethyleneoxypropylene p, p´-bibenzoate)

“…It has been established that the smectic planes can be oriented perpendicular or parallel to the draw direction depending on the rate of deformation and temperature. The mechanical properties of the corresponding drawn polymer have also been reported [27]. This particular behaviour of molecular orientation displayed by PPO4B is observed in Fig.…”

“…Thus, when the macromolecules are transverse to the fiber, this direction presents the best mechanical properties and the fiber direction shows the worst properties [27]. Since the proportion of macromolecules disposed along the stretching direction or in the transverse direction depends on the rate of deformation and temperature, therefore a fiber with similar mechanical properties in both directions could be prepared using the adequate stretching conditions.…”

“…Most of them are concerned with low-ordered mesophases and discuss orientation either by shearing [28][29][30][31][32][33] or by drawing [7,8,26,27,[34][35][36][37]. This interesting phenomenon has been explained [27,35] by assuming that the macromolecules are disposed in domains that can move rather independently, what means that the macromolecular interconnection between domains is scarce. These domains must have one dimension much larger than the other two, being the macromolecules settled transverse to the longer dimension.…”

Several Interesting Fields Exploited through Understanding of Polymeric Effects on Liquid Crystals of Main-Chain Polyesters

“…1,12,18,19,[57][58][59][60] Figure 24b shows X-ray pattern taken for such a fiber of BB-5. The pattern is similar to that (Figure 24a) of the fiber drawn from the isotropic melt, but quite different in the orientation geometry of reflections with respect to the fiber axis.…”

Thermotropic Liquid Crystals of Main‐Chain Polyesters having a Mesogenic 4,4′‐Biphenyldicarboxylate Unit, 14

“…The orientation in fiber B is quite novel, [21][22][23][24][25][26][27] but commonly seen in a series of the smectic BB-n polyesters forming SmA, SmCA, and SmC mesophases. [6,10,[28][29][30] All the WAXD patterns shown here were taken at smectic temperatures. Identical patterns were observed at room temperature, indicating that the SmCA phase is solidified without crystallization.…”