Preparation of Polyamide-6,6 from Hexamethylenediammonium Adipate AH-Salt by Condensation in the Melt

Preparation of Polyamide-6,6 from Hexamethylenediammonium Adipate (AH Salt) by Condensation in the Melt 

Safety precautions Before this experiment is carried out, Sect. 2.2.5 must be read as well as the material safety data sheets (MSDS) for all chemicals and products used. 

The adipic acid solution is now placed in a 250-ml beaker and the diamine solution added dropwise with stirring over a period of 8 min, during which the solution warms up to 40-45 °C. After stirring for a further 30 min and allowing to cool, the crystallized AH salt is filtered off with suction, washed twice with 95% ethanol and dried in vacuum. Yield 90-95% mp 183 °C (with loss of water) pH value of 9.5% aqueous solution 7.62. Impure AH salt can be recrystallized from ethanol/water mixtures (volume ratio 3 1). 

A 50 ml pear-shaped flask, fitted with distillation head, air condenser, vacuum adapter, and receiver is three-quarters filled with AH salt and the air removed by evacuation and filling with nitrogen. It is then heated under nitrogen for 1 h on a silicone oil bath at 220 °C, and for further 3 h at 260-270 °C. After cooling, the flask is broken carefully with a hammer.The polyamide from adipic acid and hexamethylenediamine melts at 265 °C. It can be spun from the melt into threads which can be cold drawn.The viscosity number is determined in concentrated sulfuric acid or in 2 M KCI in 90% formic acid (see 5ect.2.3.3.3.1). 

As in the preparation of polyesters, also in the preparation of polyamides, the reaction temperature can be considerably reduced by using derivatives of dicarbo-xylic acids instead of the free acids. Especially advantageous in this connection are the dicarboxylic acid chlorides which react with diamines at room temperature by the Schotten-Baumann reaction this polycondensation can be carried out in solution as well as by a special procedure known as interfacial polycondensation (see Examples 4-11 and 4-12). 

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