Solid state properties of poly(spiro[2,4]hepta-4,6-diene)

Poly(spiro[2,4]hepta-4,6-diene) (PSHD) is considered to behave like a rigid rod on the basis of the unusually large index (α=1.7) in the viscosity-molecular weight relationship. Thus, some solid state properties were investigated with PSHD samples which contained different ratios of the 1,2- and 1,4-addition units. The thermo-mechanical curve of solvent-cast films showed that there were two tanδ peaks below 300°C. The β peak was located at about 130°C (110 Hz), and affected little by the polymer composition. On the other hand, the position of the α peak shifted linearly from 200°C to 300°C with increasing fraction of the 1,4-unit, and the peak height decreased simultaneously. A loss peak associated with thermal decomposition and/or crosslinking was found at temperatures above 300°C. The TGA curve revealed that the thermal decomposition of PSHD takes place at about 300°C in air and at about 400°C under nitrogen. An exothermic peak was found in the same temperature range in the DSC curve. The crosslinked specimen showed no loss peak in dynamic measurements, which reflected immobilization of the molecule by crosslinks. The PSHD film did not show any indication of crystallinity.