Complexation and eutectic crystallization in poly(2-vinyl pyridine)-block-poly(ε-caprolactone) and pentadecylphenol mixtures

Crystallization behavior via hydrogen bonding interaction in amphiphilic block copolymer/surfactant mixtures consisting of poly(2-vinyl pyridine)-block-poly(ε-caprolactone) (P2VP–PCL) and 3-pentadecylphenol (PDP) were investigated by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The P2VP–PCL/PDP mixtures exhibit eutectic crystallization behavior; the eutectic composition is approximately at 70 wt.% PDP. Scanning probe microscopy (SPM) observation revealed the microphase structure in the P2VP–PCL/PDP mixtures and the unique eutectic morphology at the eutectic composition, which was further confirmed by small angle X-ray scattering (SAXS) results. To our knowledge, this is the first example of eutectic crystallization observed in amphiphilic block copolymer/surfactant systems. The FTIR study proved that there are competitive hydrogen bonding interactions between P2VP block/PDP and PCL block/PDP pairs in the P2VP–PCL/PDP mixtures. On the basis of the SPM results and FTIR study, a model describing the microstructure of the P2VP–PCL/PDP eutectic mixtures is proposed. The amorphous P2VP blocks are expelled from the ordered eutectic lamellae formed by the crystalline PCL blocks and PDP, which deviates remarkably from the existing structural model proposed by other authors for poly(vinyl pyridine)/PDP and poly(styrene-block-4-vinyl pyridine)/PDP mixtures.