The Raman spectra of polycaprolactones have been measured over a temperature range of 20 °C to 160 °C to distinguish ordered chain conformers in the melt state and determine the quantitative crystalline bands. Principal component analysis of the spectra in the melt state allows for separation of conformationally ordered peaks from amorphous disordered ones, whereas analysis of spectra measured during crystal melting identify peaks primarily associated with crystallinity. Component spectra of amorphous chains and crystalline components are generated from linear combinations of the principal components associated with vibrations of the ester and methylene groups. A comparison of the component spectra and density functional theory calculations of the Raman spectra indicate that sharp peaks in the ester stretch, C-C stretch, CH2 twist, and CH2 bend vibrational modes can be attributed to single chain modes, not necessarily the crystalline order. Component spectra in the carbonyl stretch region, sensitive to dipole-dipole interactions, are used to quantify crystallinity over a range of molar masses and during melting.
Pub Type: Journals
Polycaprolactone, Raman spectroscopy