Polymer, Vol.153, 408-421, 2018
Synchrotron scattering and thermo-mechanical properties of high performance thermotropic polymer. A multi-scale analysis and structure-property correlation
A multi-scale analysis, at the mu m -> nm -> angstrom-scale on the influence of thermal treatment on the microstructure of the thermotropic polymer based on 60 mol% (1,4)-hydroxybenzoic acid (B), 5 mol% (2,6)-hydroxynaphthoic acid (N), 17.5 mol% terephthalic acid (T) and 17.5 mol% biphenol (BP) -named COTBP- was carried out. Extruded tapes 30 mu m thick were heat treated at 300 degrees C for up to 300 min. Wide-angle X-ray scattering of asextruded tapes revealed high macromolecular alignment. Small-angle X-ray scattering exhibited diamond-shaped diffuse scattering along the equatorial axis and, strikingly, meridional scattering revealed long-range order of ca. 43.9 nm periodicity. Heat treatment reduced surface roughness, increased the birefringence, and sharpened the meridional and main interchain reflections indicating an increase of crystallinity, molecular register and alignment. On the other hand, SAXS intensity decreased in 2 theta and became azimuthally narrower evidencing lateral compression of scattering features. The width of scattering objects decreased from 8.7 to 6.6 nm, whereas their length increased from 20.9 to 22.8 nm, and the misorientation angle B. decreased from 2.1 degrees to 0.5 degrees. Because heat treatment was carried out without applied tension, the results also revealed a self-reinforcing effect. The structural re-organization correlated with significant increase of thermal properties, i.e. the changes relative to as-extruded tape of degradation and melting temperatures were Delta T-dec similar to 20 K, Delta T(s -> n)75 K, and the change of Young's modulus was Delta E similar to 50 GPa.