Enhancement of the mechanical properties at the macro and nanoscale of thermosetting systems modified with a polystyrene-block-polymethyl methacrylate block copolymer

Abstract

A diglycidyl ether of bisphenol A (DGEBA) epoxy monomer-based thermosetting system modified with a varying content of a polystyrene-block-polymethyl methacrylate (PS-b-PMMA) block copolymer and cured with a 4,4′-methylenebis(3-chloro-2,6-diethylaniline) (MCDEA) curing agent was prepared by two different methods, without and with a solvent for the previous solution of the PS-b-PMMA block copolymer. The influence of the modifier content as well as the preparation method on the final properties of the PS-b-PMMA/(DGEBA-MCDEA) cured systems was investigated. DSC characterization confirmed the miscibility of the block copolymer with the thermoset matrix. Regardless of the preparation method, all analyzed thermosetting systems modified with PS-b-PMMA showed a nanostructured morphology, as confirmed by AFM measurement. The mechanical properties studied by a universal testing machine (MTS) at the macroscale were enhanced by the addition of the PS-b-PMMA block copolymer, especially in terms of the fracture toughness which improved considerably up to 25 wt% PS-b-PMMA content, although also the flexural modulus presented a slight increase with the modification with the PS-b-PMMA block copolymer. The quantitative nanomechanical (QNM) properties were studied at the nanoscale by AFM in PeakForce mode, and showed an improvement of the elastic modulus of the PMMA/(DGEBA-MCDEA) matrix up to 25 wt% PS-b-PMMA content. The QNM results allowed also the detection of a high difference between the elastic modulus values corresponding to the microseparated PS block rich phase and the PMMA/(DGEBA-MCDEA) matrix. A similar tendency was exhibited for both preparation methods, although the thermosetting systems prepared with the solvent reached slightly higher elastic moduli.