Crystalline transition behaviors of nylons 12 20 and 10 20

The crystalline transition behaviors under different crystalline conditions of newly synthesized long alkane nylon 12 20 and nylon 10 20 are studied by wide-angle X-ray diffraction (WAXD) and real time Fourier transform infrared spectroscopy (FT-IR). The results show that their crystalline transition behaviors under WAXD were, to a large extend, related to the condition under which the crystals were prepared. The dilute solution-grown lamellar crystals of nylons 12 20 and 10 20 did not show distinct Brill transition behaviors before melting. Unlike the lamellar crystals of many other even–even nylons which display two crystal signals until melting temperature (TM), they presented a broad amorphous-like signal when the temperature increased to around 10 °C below TM. However, the post-annealing samples of nylons 12 20 and 10 20 displayed Brill transition at 155 and 157 °C, respectively, and the solution casting samples of nylons 12 20 and 10 20 at 110 and 135 °C, respectively. Furthermore, the IR spectra of nylons 12 20 and 10 20 displayed an interesting phenomenon: the intensity of the peak at 942 cm−1 declined on heating and finally disappeared around Brill temperature (TB), instead of TM as is in usual nylons. This suggests that the long alkane segments, introduced by 18-octadecanedicarboxylic acid, may undergo a local melting at TB.