Chain folding in poly(epsilon-caprolactone) studied by small-angle X-ray scattering and Raman spectroscopy. A strategy for blending in the crystalline state

Samples of poly (epsilon-caprolactone), including narrow fractions obtained by preparative gel permeation chromatography (GPC), were characterised by analytical GPC and C-13 NMR spectroscopy. The crystallised samples were inv estigated by small-angle X-ray scattering to obtain lamellar spacings and b y low-frequency Raman spectroscopy to obtain LAM-I frequencies. Together th e two methods gave a reliable estimate of the critical stem length for chai n folding in poly(epsilon-caprolactone) crystallised at room temperature or below, i.e. 15 chain units [CL, OCO(CH2)(5)] equivalent to 105 chain atoms . A necessary requirement for molecular blending of block copolymers of eps ilon-caprolactone and ethylene oxide with crystalline high molar mass poly (epsilon-caprolactone) is cocrystallisation. Hence it was concluded that a safe lower limit for successful blending is a poly(epsilon-caprolactone) bl ock of 20 CL units.