Epoxy-based divinyl ester resin/styrene copolymers: Composition dependence of the mechanical and thermal properties

Epoxy-based divinyl ester resins (DVER) were obtained by reacting diglycidyl ether of bisphenol A (DGEBA) with methacrylic acid (MA) and characterized by FTIR and 1H-NMR spectroscopies and gel permeation chromatography (GPC). The densities and viscosities of the DVER in styrene (S) solutions were measured at different temperatures, 25, 40, and 60°C and compositions, 3.4 to 100% by weight of styrene. Dynamic mechanical measurements (DMA) and differential scanning calorimetry (DSC) were used to determine the glass transition temperatures of the homopolymers and the DVER/S copolymers: 20, 40, 60, and 80% by weight of styrene. The values obtained are in the range limited by the homopolymers glass transition, 100°C for polystyrene and 173°C for the cured DVER. The data were well fitted if two contributions to the glass transition are taken into account: the “linear copolymer” contribution (Fox eq.) and the “crosslinking” contribution (Nielsen model). Uniaxial static compression tests were carried out to determine the modulus, yield stress, and ultimate stress in samples with different compositions. All the mentioned properties decrease with an increase in the styrene concentration in the final copolymer. It was found that the volumetric contraction during curing increases with styrene concentration.