ABSTRACT
The chemical modification (namely the epoxidation) of a star shaped block copolymer (BCP) based on polystyrene (PS) and polybutadiene (PB) and its effect on structural and mechanical properties of the polymer were investigated. Epoxidation degrees of 37 mol%, 58 mol%, and 82 mol% were achieved by the reaction of the copolymer with meta-chloroperoxy benzoic acid (m-CPBA) under controlled conditions. The BCP structure was found to change from lamellae-like to mixed-type morphologies for intermediate epoxidation level while leading to quite ordered cylindrical structures for the higher level of chemical modification. As a consequence, the glass transition temperature (Tg) of the soft PB component of the BCP shifted towards significantly higher temperature. A clear increase in tensile modulus and tensile strength with a moderate decrease in elongation at break was observed. The epoxidized BCPs are suitable as reactive templates for the fabrication of nanostructured thermosetting resins.
ABSTRACT
The work aims at establishing the optimum conditions for dual thermal and electron beam curing of thermosetting systems modified by styrene/butadiene (SB)-based triblock copolymers in order to develop transparent and toughened materials. The work also investigates the effects of curing procedures on the ultimate phase morphology and mechanical properties of these thermosetâ»SB copolymer blends. It was found that at least 46 mol% of the epoxidation degree of the SB copolymer was needed to enable the miscibility of the modified block copolymer into the epoxy resin. Hence, an electron beam curing dose of ~50 kGy was needed to ensure the formation of micro- and nanostructured transparent blends. The micro- and nanophase-separated thermosets obtained were analyzed by optical as well as scanning and transmission electron microscopy. The mechanical properties of the blends were enhanced as shown by their impact strengths, indentation, hardness, and fracture toughness analyses, whereby the toughness values were found to mainly depend on the dose. Thus, we have developed a new route for designing dual-cured toughened micro- and nanostructured transparent epoxy thermosets with enhanced fracture toughness.
