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

Abstract

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 in PTAd and 1475, 1459, 1393, and 1361 cm in PTSu were designated to the CH of the trimethylene segment. Changes in the IR band absorbance intensities of the CH 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.

Synthesis, Properties, and Enzymatic Hydrolysis of Poly(lactic acid)-co-Poly(propylene adipate) Block Copolymers Prepared by Reactive Extrusion

“…Its melting point (T m ) was observed at 41 °C, and its T g after quenching was −57 °C. These values are consistent with previous reports [ 33 , 34 , 47 , 51 , 52 , 53 ]. The quenched PPAd also showed cold crystallization at T cc = 6.8 °C and melt crystallization at T c = −10.6 °C.…”

“…PPAd (Figure 4a) was received semicrystalline, as witnessed by its melting during the 1st heating scan. Its melting point (T m ) was observed at 41 • C, and its T g after quenching was −57 • C. These values are consistent with previous reports [33,34,47,[51][52][53]. The quenched PPAd also showed cold crystallization at T cc = 6.8 • C and melt crystallization at T c = −10.6 • C. PPAd exhibited a multiple melting behavior, since a secondary melting peak is recorded in its reheating scans at about 30 • C, right after the end of cold crystallization.…”

“…PLA shows characteristic IR peaks at 3488 cm −1 assigned to O-H bending, at 2994-2944 cm −1 of C-H stretching, at 1747 cm −1 caused by C=O stretching, at 1452 cm −1 of -CH 3 asymmetric bending, at 1182 cm −1 and 1040 cm −1 because of the stretching of the -C-O-C-groups [45]. The IR spectra of amorphous and crystalline PPAd have been analyzed in depth in the past [34], and the spectrum recorded here shows the same peaks. While most peaks overlap with those of PLA, two of them witness the presence of the adipic segment; the CH 2 bending at 1467 cm −1 and the C-O/C-C stretch at 1255 cm −1 .…”

“…Poly(propylene adipate) (PPAd) was first synthesized in 2007 by the group of Bikiaris, and it had elongation at break ~400% and tensile strength ~11.5 MPa, with low glass transition, melting and cold crystallization temperatures (T g = −57 °C, T m = 29 °C, T cc = −8 °C) [ 32 ]. It also crystallizes quite fast due to the large number of methylene groups on its macromolecular chain [ 33 , 34 ].…”

Crystallization behavior in miscible blends of poly(ε‐caprolactone) and poly(hexylene adipate) with similar thermal properties studied by time‐resolved Fourier transform infrared spectroscopy

“…Ten scans were averaged for each spectrum recorded. A high temperature sample holder designed by our group was used to obtain the spectra in the melt state. For isothermal crystallization, the samples on the NaCl windows were cooled from the melt to the preset T c in the high temperature cell.…”