Growth of Condensed Aromatic Nuclei in Some Condensed Polynuclear Aromatic (COPNA) Resins by Heating

Abstract

Size-increase of polynuclear aromatic nuclei in heated COPNA resins, due to ring closure between aromatic rings, was studied by following up the change of UV spectra and the results were discussed in relation to the composition of resins and to the properties of carbons derived from them.
The resins were prepared by heating a mixture of an aromatic raw material, 1, 4- benzenedomethanol (PXG) as the cross-linking agent, and a catalyst. As raw materials, naphthalene, pyrene, and phenanthrene were used. Tetrahydrofuran solutions of the resins were thinly spread out on quartz plates followed by curing at 120°C. The resulting film specimens on quartz were heated successively at temperatures of 200, 300, 400, 430, and 500°C each for 1 hour in nitrogen. After each 1-hour-heating the specimens were subjected to UV analysis. The results were as follows:
(1) Generally the ring closure starts at ca. 300°C and becomes markedly above 400°C.
(2) The larger the PXG content is, the more the ring closure occurs finally after 500°C heating;
(3) The size of condensed aromatic nuclei in the resins after heating to 500°C increases with the decreasing ratio of PXG/Aro when the same raw material is used, and with the increasing molecular size of the raw material when the ratio of PXG/Aro is kept constant.
(4) The graphitizability of carbons derived from heated resins is enhanced with the increasing size of aromatic nuclei in the resins.