Thermal analysis FTIR spectroscopy of poly(ε-caprolactone)

• Vibrational spectrum of PCL is complicated by changes on crystallization.
• TA–FTIR spectroscopy enables the absorption bands to be unambiguously assigned.
• Crystallinity can be determined from the ratio of crystalline and amorphous bands.

Vibrational spectra of poly(ε-caprolactone) have been measured as a function of temperature and time to assign the molecular origins of the absorption bands, to distinguish crystalline and amorphous bands and measure fractional crystallinity. While many changes occur within the spectrum on crystallization and melting those which occur to the carbonyl absorption band proved to be the most useful in determining the fractional crystallinity and following the development of crystallinity with time.Two-dimensional IR correlation mapping applied to the carbonyl band clearly showed that the broad band at 1735 cm−1 was due to the stretching of the ester carbonyl group in the amorphous regions which decreased in intensity on isothermal crystallization. At the same time a narrower more intense band developed at 1725 cm−1 attributed to the absorption of the ester carbonyl group in the crystalline regions. Deconvoluting the band into these components enabled the intensities of the two to be determined and the fractional crystallinity measured.

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