AbstractIn examining the degree of cure of the novolac—hexamine system, higher‐boiling polar solvents such as methylcellosolve and cyclohexanone were found to have better extraction power than that of acetone, even for resins with a relatively high degree of cure. Making use of the difference in their extraction power, the cured resins could be fractionated into four portions, i.e., acetone soluble, acetone insoluble but methylcellosolve soluble, methylcellosolve insoluble but cyclohexanone soluble, and cyclohexanone insoluble. The formation and subsequent diminution of the soluble intermediates and the increase of insoluble crosslinked resins in the curing process were shown clearly by plotting the amount of each fraction against curing time at various temperatures. Further, the same extraction procedure was applied to the resins cured under reduced pressure. The curing reaction was markedly delayed in the latter case. Based on the remarkable difference in the curing behavior under pressure, a curing mechanism has been proposed in which the moisture contained may acelerate the decomposition of hexamine, thus enhancing the reactivity of the resin sys
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