Dynamic mechanical properties of extruded rods of poly(dimethylsilylene-co-methyl-n-propylsilylene)

Tractable polysilanes were prepared by the copolymerization of a methyl-n-p ropylsilylene (MP) unit into poly(dimethylsilylene), which neither dissolve s in common solvents nor melts before decomposition. Although poly(dimethyl silylene-co-methyl-n-propylsilylene) has poor solubility in the composition range of the dimethylsilylene (DM) unit to the MP unit (DM/MP = 7/3 simila r to 9/1), the copolymers form the columnar mesophase at elevated temperatu res. 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 characterize d in detail by dynamic viscoelasticity and wide-angle X-ray diffraction (WA XD) to clarify the structure-mechanical-property relationship. The orientat ion functions of the extruded rods were determined by the azimuthal intensi ty distribution of the WAXD reflection. The orientation function and dynami c 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 e xtrusion ratio and correlated well with the crystal orientation function. T he dynamic storage modulus at room temperature was lowered by the structura l relaxations at -100 similar to +30 degrees C, which corresponded to the m olecular motion of the rigid molecular chains of the copolymer and the loca l molecular motion of the MP unit. (C) 2000 John Wiley & Sons, Inc.