POTENTIAL OF 2-DIMENSIONAL NEAR-INFRARED CORRELATION SPECTROSCOPY IN STUDIES OF PRE-MELTING BEHAVIOR OF NYLON-12

This review paper discusses the potential of generalized two-dimension al (2D) near-infrared (NIR) correlation spectroscopy in studies of pre -melting behavior and hydrogen bonds of nylon 12. A 2D NIR study on di ssociation and hydrogen bonds of N-methylacetamide (NMA) is also revie wed here as a model compound study of nylon 12. Fourier transform (FT) -NIR spectra in the region of 9000-5000 cm(-1) of nylon 12 were measur ed over a temperature range of 30-150 degrees C where gradual weakenin g of inter- or intramolecular associative interactions and decrease of local order leading to the eventual fusion of nylon 12 crystals are o bserved. The 2D correlation analysis provided the following conclusion s for the pre-melting behavior of nylon 12. (i) There are at least eig ht bands in the 6800-6100 cm(-1) region assignable to free- and hydrog en-bonded NH groups of nylon 12 in various environments. The asynchron ous 2D correlation spectrum in the above region indicates that the ami de groups with free carbonyl oxygen appear first and then the unassoci ated free amide and amide groups with free NH follow as the temperatur e is increased. (ii) The asynchronous spectrum in the 6000-5500 cm(-1) region, where the first overtones of the CH2 stretching modes are exp ected to appear, indicates that substantial amount of disordered or di ssociated components start appearing before the disappearance of more ordered components. It seems that they appear as the pre-melting precu rsors (or even possibly as the indirect cause) to the precipitous decr ease of the ordered components associated with melting of nylon 12 occ urring at a much higher temperature.