Vibrational spectroscopic study of the thermal transition behavior in polyamide 11

Three different sample preparations of polyamide 11, melt-crystallized, meta-cresol cast and trifluoroacetic acid cast, are examined in terms of variable temperature infrared analysis. Digital subtraction, second derivative spectroscopy, curve resolution and thermal transition behavior are used to distinguish between structural differences in the ordered and disordered regions. It is found that the N–H stretching region of the semicrystalline material containing α or α-like crystal forms displays a resolvable peak due to the amide I overtone in Fermi resonance with the N–H stretching fundamental. The N–H stretching region along with various other regions are used to follow the frequency and integrated area changes with increased temperature. The Brill and glass transitions which are detectable in frequency and area versus temperature plots are used to distinguish between the transition behavior in the crystal and amorphous regions of the three sample preparations. It is found that whereas a melt-crystallized film displays very obvious transition behavior, in the remaining two preparations the transitions are not detectable. The basis for the assignment of the frequency and area versus temperature response to specific transition is discussed.