Long Chain Polyamides: Influence of Methylene Sequence Length and External Forces on Structural Features

Crystallographic studies on a series of even-even polyamides PA10.n (12, 14, 16, and 18) with variable methylene sequence length (n - 2) are performed. Temperature-dependent X-ray diffraction studies show that a triclinic alpha phase is the preferred polymorph after slow cooling to room temperature like in many other even-even polyamides. For PA10.12 and PA10.14 the pseudo-hexagonal high temperature phase gamma is observed between the Brill transition temperature T-B and melting point T-M. For both higher members a distinct Brill transition is absent below T-M. The influence of temperature on the packing state of the stems during cooling is discussed and compared to related polymers. An analysis of well oriented crystalline states in annealed fibers reveals that the crystalline state achieved under ambient conditions is influenced by external forces due to small energetic differences between different alpha and beta polymorphs. All PA10.n samples show in the fiber-oriented state a prominent beta polymorph which is dominant in PA10.12 and PA10.14 but superimposed with a significant alpha fraction in both higher members. The consequences of changes in the polymorphic state under the influence of external forces for crystalline states achieved under application relevant processing conditions are considered.

Automated summary

Crystallographic studies were conducted on a series of even-even polyamides PA10.n with different methylene sequence lengths (n - 2). The results showed that the preferred polymorph after slow cooling to room temperature was a triclinic alpha phase. The higher temperature phase gamma was observed in PA10.12 and PA10.14 between the Brill transition temperature T-B and melting point T-M, while a distinct Brill transition was absent in the higher members. The influence of temperature on the packing state of the stems during cooling was discussed, and the presence of external forces on the crystalline state achieved under ambient conditions was analyzed.