B.— CHEMISTRY. 41 



of resins of high dielectric capacity is a matter of national importance, 

 and it was with this objective that an investigation of phenol-formaldehyde 

 resins was begun even before the central laboratory was ready for 

 occupation. 



In May 1925 a chemist was appointed to work at this problem in the 

 University of Birmingham, and attention was directed to formaldehyde 

 ■condensations with homologues of phenol, namely, the cresols and xylenols. 

 Experience soon showed that m-cresol and 1:3: 5-xylenol were especially 

 suitable for such condensations, which in the case of the former phenol were 

 «xtended to a semi-works scale. 



According to the nature of the catalyst employed, phenol-formaldehyde 

 •condensations yield, in general, one or other of two distinct types of resin. 

 Alkaline catalysts lead to the production of resins of ' bakelite ' type, 

 which, although originally soluble and fusible, yet possess the property of 

 moulding under the combined effect of heat and pressure into hard 

 insoluble and infusible products constituting by far the more important 

 group of phenol-formaldehyde resins. 



Acid catalysts favour the production of resins of ' novolak ' type, 

 which, being permanently soluble and fusible, are utilised principally as 

 shellac substitutes in lacquers and varnishes. 



Alkaline Condensations. — After successful small-scale tests, alkaline 

 condensations of formaldehyde were performed on 24 lb. of m-cresol, 

 ■carried out under factory conditions in a plant of semi-works scale com- 

 prising a jacketed reaction vessel, reflux condensers, washing and storage 

 tanks, drying and incorporating vessels and a hydraulic press with heated 

 platens. 



A systematic study of this alkaline condensation revealed the presence 

 of several crystalline intermediates which precede the formation of resin. 

 The latter was employed in the production of moulded articles and of 

 laminated boards for electrical testing. 



Acidic Condensations. — The chemical nature of formaldehyde-phenolic 

 resins is still a matter of speculation, but the appearance of crystalline 

 intermediates in the early stages of acidic condensations is of interest as 

 denoting the course of these reactions. During these researches several 

 crystalline intermediate products were isolated for the first time. 



FORMALDEHYDE-KETONE EeSINS. 



In the foregoing formaldehyde-pheuol condensations, acetone is some- 

 times used as a medium, but since in the presence of alkalis this solvent 

 condenses with formaldehyde to yield resins, the chemistry of the process 

 has been elucidated by a study of the interaction of formaldehyde and the 

 ketones under alkaline conditions. As the homologous series is ascended 

 the formation of resin decreases. Acetone yields mainly resin and 

 small proportions of 7-ketobutanol, CH, • CO • CH., • CH, ■ OH and of the 

 tetrahydropyrone formed by dehydration of the tetrahvdric alcohol 

 HO • CH, ■ CH,, • CO ■ C(CH,, • OH),. Methyl ethyl ketone gives con- 

 siderable proportions of the following mono- and di-hvdric alcohols, 

 CH, • CO • CH(CH, ■ OH) ■ CH, and CH, • CO • C(CH,, • OH).;- CH3 with but 

 little resin. Diethyl ketone furnishes no resin but leads to similar mono-, 

 "di- and tri-hydric alcohols. 



