The theological and dynamic mechanical properties of a semi-rigid substituted poly(p-phenylene) were investigated. At temperatures below the glass transition temperature of 152 degrees C the amorphous polymer is very stiff compared with flexible chain polymers. Although the material can be processed in the melt, the melt is unusually elastic. Atomic force and transmission electron microscopy revealed a worm-like morphology. Blends with polycarbonate yield transparent materials. Microscopy and X-ray diffraction of these blends indicated that the flexible chain polymer is located in between the worm-like structures of the semi-rigid polymer.