The mechanical properties of rubber‐modified vinyl esters

Abstract

Synopsis"Vinyl esters" were prepared by reacting an epoxy resin (DGEBA) with acrylic and methacrylic acids, modified with Hycar VTBN, and cured at 90°C for 4 h with t-butyl perbenzoate. The resultant materials showed a two-phase structure in electron micrographs and dynamic mechanical spectra. The domain of the dispersed phase was estimated to be on the order of 10 nm in size. Infrared spectroscopy indicated extensive copolymerization of the internal double bonds or pendant vinyl groups in VTBN during the cure of the resin. The mechanical properties of the modified materials were measured, and the differences in mechanical behavior between the acrylic and methacrylic vinyl esters were discussed

Radical‐cured block copolymer‐modified thermosets

“…We have reviewed the previous work that focused on toughening stepor chain-growth thermosets using rubber particles. [7][8][9][10][11][12][13][14]32 In most cases, rubber-modified epoxies showed larger improvements in toughness than did the radical-cured systems; in fact, problems with toughening chain-growth thermosets is not new. 73 Several authors cited phase separation as the main issue in the use of rubber particles in radical-cured systems, but the use of the block copolymer should have alleviated this phase separation problem, as we observed dispersed spherical micelles in the case of systems modified with OP52 diblocks.…”

“…Previous work involving the toughening of chain‐growth thermosets primarily has focused on the incorporation of a secondary phase, such as homopolymers,4, 5 nanoparticles,6, 28 dendrimers,29–31 and rubber particles 7–9, 32–35. Some of the most promising materials have been created using rubber modifiers.…”

“…Unfortunately, a high degree of crosslinking also makes these materials brittle and prone to fracture. Therefore, considerable effort has been devoted to toughening thermosets 4–27. Two types of thermoset materials can be classified according to their polymerization mechanism, namely, step‐ (e.g., epoxies) or chain‐growth (e.g., vinyl esters, unsaturated polyesters, and epoxies).…”

“…Previous work involving the toughening of chain-growth thermosets primarily has focused on the incorporation of a secondary phase, such as homopolymers, 4,5 nanoparticles, 6,28 dendrimers, [29][30][31] and rubber particles. [7][8][9][32][33][34][35] Some of the most promising materials have been created using rubber modifiers. However, rubber-modified chain-growth thermosets suffer from a decreased modulus and a reduction in the glass transition temperature, T g , [7][8][9]32 which limits the range of applications.…”

“…[7][8][9][32][33][34][35] Some of the most promising materials have been created using rubber modifiers. However, rubber-modified chain-growth thermosets suffer from a decreased modulus and a reduction in the glass transition temperature, T g , [7][8][9]32 which limits the range of applications. This problem also plagues rubber-toughened epoxies.…”