Tractable polysilanes were prepared by the copolymerization of a methyl-n-propylsilylene (MP) unit into poly(dimethylsilylene), which neither dissolves in common solvents nor melts before decomposition. Although poly(dimethylsilylene-co-methyl-n-propylsilylene) has poor solubility in the composition range of the dimethylsilylene (DM) unit to the MP unit (DM/MP = 7/3 similar to 9/1), the copolymers form the columnar mesophase at elevated temperatures. Highly oriented rods were prepared via the extrusion of the copolymers with a circular tube die in a temperature range in which the transition to the columnar mesophase began to occur (70 degrees C when DM/MP = 7/3 and 8/2 and 120 degrees C when DM/MP = 9/1). The extruded rods were characterized in detail by dynamic viscoelasticity and wide-angle X-ray diffraction (WAXD) to clarify the structure-mechanical-property relationship. The orientation functions of the extruded rods were determined by the azimuthal intensity distribution of the WAXD reflection. The orientation function and dynamic storage modulus increased with an increasing extrusion ratio. The dynamic storage modulus at -150 degrees C was 8 similar to 10 GPa at the highest extrusion ratio and correlated well with the crystal orientation function. The dynamic storage modulus at room temperature was lowered by the structural relaxations at -100 similar to +30 degrees C, which corresponded to the molecular motion of the rigid molecular chains of the copolymer and the local molecular motion of the MP unit.