Curing behaviors of two kinds of resols prepared by the reaction of phenol (1 mol), formaldehyde (1.2 mol), and either sodium hydroxide (0.02 mol) or barium hydroxide (0.01 mol), were examined at 120°C by means of Curelastometer, IR spectroscopy, THE extraction, and GPC. Gelling and curing speeds of the resol prepared with barium hydroxide as catalyst (BR) were faster than with sodium hydroxide (NR). The amount of hydroxymethyl groups in BR also decreased more rapidly with an increase in the cure time than that in NR by IR spectrometry. Similar results were confirmed by THF extraction and GPC. It is recognized in the curing of both resols that relatively higher molecular weight compounds gel rapidly and that, after major components in the resol have changed to gel, low molecular weight compounds still remain in the resol as sol state. It is inferred from GPC that NR differs from BR in the molecular weight of the compounds which exist prior to gel formation, namely, the molecular weight of the compounds in BR is smaller than that in NR.
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