Infrared spectroscopic analysis of poly(trimethylene terephthalate)

With factor analysis of IR spectra obtained from undrawn poly(trimethylene terephthalate) (3GT) films annealed under various conditions, pure crystalline and amorphous spectra can be extracted and absorption peaks of each pure spectrum can be characterized. A fraction of crystalline phase in an annealed sample was obtained by curve-fitting the sample spectrum with two pure spectra on the basis of the least-squares method. The fraction of the crystalline phase obtained from this method showed a very good correlation to the crystallinity obtained by density measurement. Polarization characteristics of 3GT absorption peaks were determined from on-line measurement of polarized IR spectra of 3GT film under extension. Intrinsic transition moment angles of asymmetric and symmetric stretching vibrations of CH2, several CH2 rocking bands, and the 1037 cm−1 band were obtained experimentally in conjunction with changes in the dichroic ratio of CO stretching vibration of the 3GT molecular chain as a function of draw ratio. The analysis of changes in the IR spectrum of 3GT under cyclic loading and unloading revealed no crystal–crystal transitions, such as reversible α→β transition of the poly(butylene terephthalate).