GB615488A - Improvements in or relating to the preparation of novolak resins - Google Patents

Abstract

To prepare a phenol-formaldehyde novolak resin, one mol. of a phenol is reacted with not more than 0.9 mol. of formaldehyde in presence of an alkaline catalyst until substantially all the formaldehyde has combined, the reaction mixture is acidified with sufficient acid to prevent formation of a rubbery resin upon subsequent dehydration and the mixture is then dehydrated. Any phenol having at least two free reaction positions may be employed. The proportion of pehnol employed in the initial alkaline reaction may be greater than that specified in which case extra phenol is added to adjust the balance either before or during the acidification. The initial reaction may be at room or elevated temperature. It should be terminated when all the formaldehyde has combined. Condensation may be continued after acidification, particularly if the amount of acid added does not greatly exceed the necessary minimum. Suitable alkaline catalysts are alkaline hydroxides or carbonates or organic bases, e.g. dimethylamine or piperidine. The products may be rinsed with hexamethylenetetramine and fillers to form moulding powders. In the examples: (1) phenol and formaldehyde are condensed in the presence of sodium hydroxide and hydrochloric acid added; (2) cresol-formaldehyde condensate catalysed with caustic soda and then hydrochloric acid; (3) p - tert. - amyl - phenolformaldehyde condensate formed in the presence of caustic soda and sulphuric acid; (4) phenol and formaldehyde condensed with caustic soda, phenol added, followed by hydrochloric acid and the whole condensed further; (5) phenol and formaldehyde are condensed in presence of ammonia, and the mixture acidified with hydrochloric acid before dehydration; (6) magnesium oxide is used as the alkali and hydrochloric as the acid. Specification 159,461, [Class 2 (iii)], is referred to.