放射線重合ポリエチレンの比表面積

抄録

Fine powdery polyethylene with extremely high specific surface area can be produced by polymerization of ethylene induced by radiation at a lower temperatures than the melting point of the polymer in bulk or in the presence of aqueous tert-butanol.
The specific surface area of the polymer is mainly determined by the polymerization temperature. The polymerization temperature of 30°C, the specific surface area exceeds 100m²/g, while at 90°C the specific surface area is decreases down to 20m²/g.
When the polyethylene slurry is obtained by the polymerization in the presence of tert-butanol, and is dried up as it is, the polymer has small surface area. When the drying is carried out after substitution of butanol for water, the surface area of the polymer increases to the above described values.
In connection with these facts, highly defective nature of fine structure of the polymer has been reported based on X-ray diffraction and NMR measurement. The fine structure must be closely connected with the large specific surface area.
The measurement of pore distribution of the polymer by isothermal capillary condensation of liquid nitrogen has indicated the presence of pores at having a peak radius of less than 100Å. The pore easily disappeared by annealing at a moderate temperature. The presence of hexane vapor remarkably accelerates the annealing.
The specific surface area measured by nitrogen adsorption by the use of BET equation coincides well with the value calculated from the pore volume distribution by assuming that the pore is cylindrical capillary.
These kinds of polymer are easily tend to be deformed by external stress, and they are useful materials for cold forging.