The Design, Synthesis, and Characterization of Epoxy Vitrimers with Enhanced Glass Transition Temperatures

A series of epoxy vitrimers (EVs) with enhanced glass transition temperatures (Tgs) were synthesized by curing epoxy resin E51 with different ratios of phthalic anhydride and sebacic acid as curing agents, and 1,5,7-triazabicyclic [4.4.0] dece-5-ene as a transesterification catalyst, and their curing dynamics, rheological properties, mechanical properties, and thermal stability were comprehensively investigated. By adjusting the molar ratio of the anhydride to the carboxylic acid in the curing agent, the Tgs of the EVs increased from 79 to 143 °C with the increase in the anhydride content. In particular, the material EV-5.5 with a high usable Tg of 98 °C could undergo stress relaxation through the transesterification reaction when exposed to high temperatures (160 to 200 °C), and the correlation between the relaxation time and temperature follows the Arrhenius equation. Moreover, EV-5.5 exhibited elastomeric behavior, where brittle fractures occurred before yielding, which demonstrated a tensile strength of 52 MPa. EV-5.5 also exhibited good thermal stability with a decomposition temperature (Td5) of 322 °C. This study introduces new possibilities for practical applications of thermoset epoxy resins under special environmental conditions.

Tetrafluorophenylene-Containing Vinylbenzyl Ether-Terminated Oligo(2,6-dimethyl-1,4-phenylene ether) with Better Thermal, Dielectric, and Flame-Retardant Properties for Application in High-Frequency Communication

In an integrated circuit, signal propagation loss is proportional to the frequency, dissipation factor (D _f), and square root of dielectric constant (D _k). The loss becomes obvious as we move to high-frequency communication. Therefore, a polymer having low D _k and D _f is critical for copper-clad laminates at higher frequencies. For this purpose, a 4-vinylbenzyl ether phenoxy-2,3,5,6-tetrafluorophenylene-terminated OPE (VT-OPE) resin was synthesized and its properties were compared with the thermoset of commercial OPE-2St resin. The thermoset of VT-OPE shows a higher T _g (242 vs 229 °C), a relatively high cross-linking density (1.59 vs 1.41 mmole cm^-3), a lower coefficient of thermal expansion (55 vs 76 ppm/°C), better dielectric characteristic at 10 GHz (D _k values of 2.58 vs 2.75, D _f values of 0.005 vs 0.006), lower water absorption (0.135 vs 0.312 wt %), and better flame retardancy (UL-94 VTM-0 vs VTM-1 with dropping seriously) than the thermoset of OPE-2St. To verify the practicability of VT-OPE for copper-clad laminate, a laboratory process was also performed to prepare a copper-clad laminate, which shows a high peeling strength with copper foil (5.5 lb/in), high thermal reliability with a solder dipping test at 288 °C (>600 s), and the time for delamination of the laminate in thermal mechanical analysis (TMA) at 288 °C is over 60 min.

Intermediate accumulation and toxicity reduction during the selective photoelectrochemical process of atrazine in complex water bodies

Selective removal of atrazine (ATZ) in wastewater and clarification of the degradation intermediate-toxicity correlation are of great importance. A newly molecularly imprinted, {001} facets-exposed TiO₂ (MI-TiO_2,001) photoanode with strong catalytic and selective ability was designed. ATZ was selectively removed from pesticide wastewater, reaching 1.9 µg L^-1, approximately 1/10 of the concentration achieved with nonselective treatment. This selective removal originated from the preferential adsorption and enrichment of ATZ onto MI-TiO_2,001. The highly specific recognition relied on the halogen bond and strong hydrogen bond formed between the Cl atom and triazine ring π orbital of ATZ and the surface -OH group of MI-TiO_2,001 as well as the recognition of MI-TiO_2,001 to the shape and size of ATZ. The specific interaction leads to different accumulations of intermediates. The correlation of intermediate and toxicity was also discussed. Aquatic toxicity was rapidly reduced through the direct dealkylation path, and due to the accumulation of highly toxic 2‑hydroxy-4-ethylamino-6-isopropylamino-s-triazine, there will be transient fluctuations via the dechlorination-hydroxylation path first. The final product was identified as nearly nontoxic cyanuric acid, the selective accumulation of which indicated that there was almost 100% removal of aquatic toxicity and cytotoxicity with only 9.8% removal of total organic carbon. This work provides new insight into the correlation of pollutant degradation intermediates and changes in toxicity.

Review of Progress in Shape Memory Epoxies and Their Composites

Shape memory polymer (SMP) is capable of memorizing one or more temporary shapes and recovering successively to the permanent shape upon various external stimuli. Beside of the above mentioned one-way variants, also two-way shape memory polymers (SMPs) and shape memory (SM) systems exist which feature a reversible shape change on the basis of "on-off switching" of the external stimulus. The preparation, properties and modelling of shape memory epoxy resins (SMEP), SMEP foams and composites have been surveyed in this exhaustive review article. The underlying mechanisms and characteristics of SM were introduced. Emphasis was put to show new strategies on how to tailor the network architecture and morphology of EPs to improve their SM performance. To produce SMEPs novel preparation techniques, such as electrospinning, ink printing, solid-state foaming, were tried. The potential of SMEPs and related systems as multifunctional materials has been underlined. Added functionality may include, among others, self-healing, sensing, actuation, porosity control, recycling. Recent developments in the modelling of SMEPs were also highlighted. Based on the recent developments some open topics were deduced which are merit of investigations in future works.