Formaldehyde → Dihydrobenzoxazine

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To a suitably equipped glass resin reactor equipped with stirrer are charged 100 parts bisphenol A, 70 parts toluene and 81.5 parts of aniline. The slurry is warmed and agitated to form a uniform solution. An inert nitrogen atmosphere is maintained over the reaction mixture. The temperature of the reaction mixture is adjusted to 50° C. and 108 parts of 50% formalin are added slowly, while the temperature is maintained at 50° to 55° C. After formalin addition is complete the batch is refluxed at 65° C. for 1 hour under reduced pressure. The batch is then heated to atmospheric reflux and the reflux condensate is permitted to separate into an aqueous phase and organic phase in an oil/water separator. The organic phase of the condensate is returned to the reactor and the aqueous phase is removed. After about 83 parts of water are removed and the reaction temperature reaches 116° C., the clear product solution is cooled while 21 parts of 2-butoxyethanol are added. The clear pale yellow solution of poly(dihydrobenzoxazine) had the following composition and properties: percent closed dihydrobenzoxazine ring 83%, equiv. wt. 278, solids 71.6%, Brookfield viscosity 305 cps.

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