Structural Changes in Poly(trimethylene adipate) and Poly(trimethylene succinate) During Melt Crystallization Studied Using In Situ Infrared Spectroscopy

This paper investigates the structural changes occurring in poly(trimethylene adipate) (PTAd) and poly(trimethylene succinate) (PTSu) during melt crystallization using differential scanning calorimetry (DSC) and in situ Fourier transform infrared (FT-IR) spectroscopy. Cooling thermograms revealed that PTAd had a faster crystallization rate than PTSu. Infrared (IR) bands of the two polyesters were assigned by correlating with the IR bands of polymers containing the trimethylene and the diacid segments. The bands at 1478, 1459, 1393, and 1364 cm^-1 in PTAd and 1475, 1459, 1393, and 1361 cm^-1 in PTSu were designated to the CH₂ of the trimethylene segment. Changes in the IR band absorbance intensities of the CH₂ and the C-O-C groups were monitored with time during melt crystallization. Structural changes of the trimethylene and diacid segments of PTAd occurred synchronously, while in PTSu the two segments changed sequentially. Normalized band intensities showed a time lag between the trimethylene and succinic acid segments. The acid segment showed a faster change compared to the trimethylene segment. Fourier transform infrared spectroscopy is shown to be a useful technique to study conformational changes during crystallization in polymers.