Morphological evolution and mechanical properties of an “anchor chain” nanodomain structure of a reactive amphiphilic triblock copolymer in epoxy resin
A novel epoxy-reactive amphiphilic poly(3,4-epoxy cyclohexyl methyl methacrylate)-block-poly(dimethylsiloxane)-block-poly(3,4-epoxy cyclohexylmethyl methacrylate) (PMETHB-b-PDMS-b-PMETHB) triblock polymer was synthesized via atom transfer radical polymerization (ATRP) with a controlled molecular chain length and low dispersion, characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance analysis (NMR), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). It can be found that a nano-microphase structure was obtained by introducing the triblock copolymer to the epoxy matrix following a self-assembly mechanism, and the internal and surface morphology evolution has been evidenced by small-angle X-ray scattering (SAXS), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The morphology of the nano-microphase was interconnected from small-size spherical particles to worm-like structure particles, and transformed into a network structure due to the intermolecular hydrogen-bonding and covalent bond cross-linking ability of the epoxy-reactive PMETHB sub-chain with hardener methyl hexahydrophthalic anhydride (MHHPA). The MHHPA-cured PMETHB sub-chain phase can be deemed as the “anchor chain” structure connecting the two hydroxy ether structural units of the PDMS-rich microphase and matrix, which provided a theoretical basis for the toughening and strengthening rigidity of the thermoset matrix. It has been verified by fracture toughness investigation (KIC) and differential scanning calorimetry (DSC) that the fracture toughness of nanodomain blends was 72.8% higher than that of neat epoxy and Tg increased by 13.5 °C.