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

Abstract

Samples of poly(ε-caprolactone), including narrow fractions obtained by preparative gel permeation chromatography (GPC), were characterised by analytical GPC and ¹³ C NMR spectroscopy. The crystallised samples were investigated by small-angle X-ray scattering to obtain lamellar spacings and by low-frequency Raman spectroscopy to obtain LAM-1 frequencies. Together the two methods gave a reliable estimate of the critical stem length for chain folding in poly(ε-caprolactone) crystallised at room temperature or below, i.e. 15 chain units [CL, OCO(CH ₂ ) ₅ ] equivalent to 105 chain atoms. A necessary requirement for molecular blending of block copolymers of ε-caprolactone and ethylene oxide with crystalline high molar mass poly(ε-caprolactone) is cocrystallisation. Hence it was concluded that a safe lower limit for successful blending is a poly(ε-caprolactone) block of 20 CL units.