High pressure and high temperature reactions in the organic solid state : polymerization of nitriles

Abstract

Under the extreme conditions at high pressures up to 50 kbar and high temperatures up to about 300℃, dinitriles, such as malononitrile and succinonitrile, are polymerized to give long chain C, N conjugated polymers with the backbone structure : (-C__1=N-)_n. It is shown that high pressure is necessary in conjunction with high temperature to achieve the polymerization. The minimum pressure and temperature to cause the reaction for malononitrile and succinonitrile are 20 kbar, 160℃ and 25 kbar, 200℃, respectively. The product polymers are beat-resistant and soluble only in dimethylformamide and exhibit semiconducting properties. The mechanism of the reaction can be considered in comparison with the thermal reactions of polyacrylonitrile. The reaction rates were measured. On the other hand, aromatic dinitriles, such as isophthalonitrile and terephthalonitrile, are polymerized only in the presence of HPO_3 as catalyst at 40 kbar and 450℃. The thermal reactions of polyacrylonitrile and polymethacrylonitrile, accompanying the polymerization of cyanide groups, were carried out under such extreme conditions. The naphthyridine type product obtained from polyacrylonitrile under high pressure has higher density, which is ascribable to the formation of a crosslinking network structure. The reaction mechanisms of the lower temperature reaction and the higher temperature reaction of polyacrylonitrile under high pressure were studied. In the case of polymethacrylonitrile, the analogous reaction proceeds only slightly even at 300℃ under 30 kbar. By investigating the effect of water on these reations it was found that the polymerization of dinitriles is accelerated and that polyacrylonitrile and polymethacrylonitrile are easily hydrolyzed to give corresponding polyamides.