Different Crystalline Transition Behavior in Polyamides 12 16,lO 16 and 8 16

Crystalline transition behavior of polyamides 12 16, 10 16 and 8 16 was studied systematically by variable-temperature WAXD and real-time FTIR. It is surprising that the crystalline transition behavior of these polyamides is different from one another. Brill transition was observed before melting on heating for nylon 8 16 in both single crystal and melt-crystallized samples. For nylon 12 16, Brill transition of the sedimented crystal mats did not occur below its melting point, while the melt-crystallized sample showed the crystalline transition before melting on heating. Furthermore, the Brill temperature could not be detected in both single crystal and melt-crystallized samples of nylon 10 16. A further investigation on the FTIR spectra of -NH- groups upon heating presented helpful information for understanding the mechanism of the crystalline transition.