Intermolecular hydrogen bonding in developing nanostructured epoxy shape memory thermosets: Effects on morphology, thermo-mechanical properties and surface wetting

Abstract

Epoxy resin was modified by the incorporation of poly (ε-caprolactone)-block-poly (dimethyl siloxane)-block-poly (ε-caprolactone) (PCL–PDMS–PCL) triblock copolymer (TBCP) in the presence of 4,4′-diaminodiphenylmethane (DDM). The role of intermolecular hydrogen bonding interaction in cure behavior, morphology, thermo-mechanical and surface wetting properties of TBCP modified epoxy thermoset was investigated. Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), atomic force microscopy (AFM), scanning electron microscopy (SEM), universal testing machine (UTM), thermogravimetric analysis (TGA) and contact angle measurements were used to characterize the samples. It is observed that PCL blocks of the TBCP were miscible with epoxy phase while the PDMS blocks remain immiscible. The miscibility of TBCP was analyzed and confirmed by FTIR and DSC, however, nanoscale inhomogeneities with ca. 20 nm were observed while examining AFM images. Addition of TBCP decreased the crosslink density between the polymers and therefore reduced the glass transition temperature (Tg), signifying the interpenetration of PCL blocks into the epoxy matrix. All the prepared blends showed shape memory effect. TBCP was very effective in improving the mechanical properties of epoxy matrix. Incorporation of 5 phr of TBCP improved the tensile strength, tensile elongation and tensile toughness by ca 20%, 55% and 90%, respectively. The thermal stability and water contact angle remained unaffected with the addition of TBCP.