Nylon 7, a fiber forning polyamide

Eight esters of 7‐aminoheptanoic acid were prepared as monomers for nylon 7 (polyheptanamide). They were made from ε‐caprolactone via the route; 6‐chlorohexanoic acid, alkyl‐6‐chlorohexanoate, alkyl‐6‐cyanohexanoate, alkyl‐7‐aminoheptanoate. The stability of these esters against polymer formation during distillation and at room temperature increased with the number of C atoms in the alcohol. When the esters were heated at 270°C. to form the polyamide, the same trend in stability was observed; the polyamides obtained were of too low molecular weight for melt spinning. Upon heating ethyl‐7‐aminoheptanoate with water (mole ratio 1 to > 3) at 100°C., a mixture of 7‐aminoheptanoic acid with mainly dimeric acid and ester was obtained. This product (“precursor”) was a stable solid at room temperature which could readily be converted at atmospheric pressure within 2 hr. to high molecular weight, spinning grade nylon 7. The melting point, density, moisture regain, and sticking temperature of nylon 7 were compared with those of nylons 6, 8, 9, 10 and 11. Nylon 7 was melt spun into high tenacity yarn and its textile properties were discussed in comparison with those of nylons 6 and 66. The low oligomer content of nylon 7 (1.5%) made extraction of the resin before spinning unnecessary.