Mechanical properties and phase behaviour of poly(dimethylsilylene-co-methyl-n-propylsilylene)

The mechanical properties and the phase behaviour of poly(dimethylsilylene- co-methyl-n-propylsilylene) (PDM-co-MPS), were investigated by the measurem ents of dynamic viscoelasticity, wide angle X-ray diffraction, thermal anal ysis and UV spectrum. PDM-co-MPS was soluble in common organic solvents if the ratio of dimethylsilylene (DM) unit to methyl-n-propylsilylene (MP) uni t, DM/MP, was lower than 70/30. The crystal phase was transformed into the columnar mesophase above 80-90 degrees C, and the disordering of conformati on and the orientation relaxation proceeded with further rise in temperatur e in the range of 80-130 degrees C. The PDM-co-MPS films were extensible on ly in the narrow temperature range, in which the crystal to mesophase trans ition started to occur, because the structural relaxation in the columnar m esophase reduced the extensibility of the PDM-co-MPS films. The oriented fi lms of PDM-co-MPS were prepared by stretching the solution-cast films at 70 -80 degrees C to a draw ratio of 7-8. The elastic modulus was much improved in the hot drawn film relative to that of the isotropic films, and the inc rease of modulus was related to the high degree of orientation in the cryst al phase. A large loss tan delta was observed at -20 to -10 degrees C, and the dynamic storage modulus markedly decreased with the rise in temperature in the range of this transition. As the low temperature transition was not detected in the DSC and spectroscopic measurements, it would be assigned t o the local molecular motion of the n-propyl side group and/or to the glass transition. (C) 2000 Elsevier Science Ltd. All rights reserved.