GB949635A - Manufacture of condensation polymers - Google Patents

Abstract

Compositions of resins derived from formaldehyde and at least one compound capable of reacting therewith to form a resin, are made by (1) preparing separately two oil-in-water emulsions of a water-immiscible organic liquid, at least one of which contains a catalyst and one of which contains formaldehyde with or without a formaldehyde-reactive compound, (free or as a liquid pre-condensate with formaldehyde), and the other contains a formaldehyde-reactive compound with or without a proportion of formaldehyde (free or as a liquid pre-condensate with the said compound), the total proportions of reactants in each emulsion separately being such that they are stable in the presence of any of the catalyst contained therein but that they form a solid resin when the emulsions are brought together, and (2) mixing the two emulsions to form a solid resin containing the liquid dispersed therein. Preferably one of the emulsions is made with an excess of formaldehyde and a deficiency of the other reactant in the form of a liquid pre-condensate, the other emulsion consisting essentially of the other reactant and a little pre-condensate. The pre-condensate can be made, e.g. by heating urea and paraformaldehyde at 100 DEG C. until complete homogenisation occurs. Other reactants mentioned are melamine, phenol, resorcinol and xylenol. An acid catalyst may be added, and casein may be added to one or both of the emulsions to strengthen the final polymer. The immiscible liquid may be a liquid fuel, e.g. kerosene, or a low-boiling (i.e. 10 DEG to 60 DEG C.) liquid, e.g. pentane or a fluorinated aliphatic hydrocarbon, and when a polymer containing such a low-boiling liquid is heated dielectrically or by hot water or steam, the liquid volatilises to form an expanded polymer. In the example, a mixture of a urea-formaldehyde pre-condensate (mol. ratio 1:4), water, H2SO4 and an emulsifying agent was mixed with kerosene with rapid stirring to form an emulsion; a neutral emulsion was then made by mixing urea, water, an emulsifying agent, casein, a little of the precondensate and kerosene; the two emulsions were then rapidly mixed together and the mixture extruded into a mould, allowed to set and, after removal from the mould, allowed to harden in air. The resulting composition, in the form of a cast block, was suitable for use as a domestic firelighter (see Division C5). Specification 589,594 is referred to.ALSO:In the example, a domestic firelighter in the form of a cast block of a urea-formaldehyde resin containing kerosene dispersed therein (see Division C3), is made by (1) forming an emulsion of a urea-formaldehyde pre-condensate (mol. ratio 1 : 4), water, sulphuric acid, an emulsifying agent and kerosene; (2) forming a neutral emulsion of urea, water, an emulsifying agent, kerosene, a little of the precondensate and casein; (3) repidly mixing the two emulsions together; and (4) extruding the mixture into a mould and allowing the mixture to set and, after removal from the mould, harden in air. Specification 589,594 is referred to.