The underlying mechanisms responsible for the toughening of block copolymer modified thermoset epoxies are not completely understood. A current theory targets cavitation of the rubbery cores in dispersed micelles as the key event that triggers shear yielding, resulting in enhanced toughness. To evaluate this hypothesis, we prepared spherical micelle forming block copolymers with rubbery cores (prone to cavitation) and glassy cores (unable to cavitate). Surprisingly, both systems enhance fracture toughness, although the rubbery core micelles outperform the glassy core counterparts. This finding challenges previous deductions regarding the toughening mechanism. We propose that the mechanical integrity of the region immediately surrounding the micelle core is compromised by the presence of the corona blocks, facilitating local deformation of the matrix. We speculate that the compliant nature of the rubber amplifies this effect.

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The development of chemistry is reported to implement selective dual-wavelength olefin metathesis polymerization for continuous additive manufacturing (AM). A resin formulation based on dicyclopentadiene is produced using a latent olefin metathesis catalyst, various photosensitizers (PSs) and photobase generators (PBGs) to achieve efficient initiation at one wavelength (e.g., blue light) and fast catalyst decomposition and polymerization deactivation at a second (e.g., UV-light). This process enables 2D stereolithographic (SLA) printing, either using photomasks or patterned, collimated light. Importantly, the same process is readily adapted for 3D continuous AM, with printing rates of 36 mm h -1 for patterned light and up to 180 mm h -1 using un-patterned, high intensity light.

This study evaluates the degradation of six different elastomeric polymers used for O-rings: EPDM, FEPM, type I-and II-FKM, FFKM, and FSR, in five different simulated geothermal environments at 300°C: 1) non-aerated steam/cooling cycles, 2) aerated steam/cooling cycles, 3)water-based drilling fluid, 4) CO 2 -rich geo-brine fluid, and, 5) heat-cool water quenching cycles.The factors assessed included the extent of oxidation, changes in thermal behavior, microdefects, permeation of ionic species from the test environments into the O-rings, silicate-related scale-deposition, and changes in the O-rings' inverse tensile compliance.The reliability of the O-ring to maintain its integrity depended on the elastomeric polymer composition and the exposure environment. FSR disintegrated while EPDM was oxidized only to some degree in all the environments, FKM withstood heat-water quenching but underwent chemical degradation, FEPM survived in all the environments with the exception of heat-water quenching where it underwent severe oxidation-induced degradation, and FFKM displayed outstanding compatibility with all the tested environments. The paper discusses the degradation mechanisms of the polymers under the aforementioned conditions.