Crystallization process of poly(ɛ-caprolactone)-poly(ethylene oxide)-poly(ɛ-caprolactone) investigated by infrared and two-dimensional infrared correlation spectroscopy

The crystallization of poly(ɛ-caprolactone)-poly(ethylene oxide)-poly(ɛ-caprolactone) (PCL-PEO-PCL) triblock copolymer was studied using FTIR and 2D FTIR spectroscopies. The weight ratio of PCL/PEO in the investigated sample was about 20:1. Although it is such a low amount of PEO that it cannot form any crystals, the PEO block undergoes some structural change in the cooling process. It was established that the PCL constituent crystallized quickly, and then forced the noncrystallizable PEO constituent to form a tighter structure (helical conformation) from the trans zigzag conformation. Besides, through the 2D IR analysis, more exact and detailed assignments of the overlapped CH2 bands have been made - the 1193 cm−1 band is attributed to methylene next to the carbonyl group, whereas the 1162 cm−1 and 1295 cm−1 bands are assigned to other common methylenes.