Controlling macroscopic material properties of dynamic covalent polyimines via the electronic effect of dianiline monomers based on the Hammett equation.

Polarity-induced effects in dynamic covalent polyimine CANs were studied, revealing a three-step stress relaxation process.

Covalent adaptable networks (CANs) can replace classical thermosets, as their unique dynamic covalent bonds enable recyclable crosslinked polymers. Their creep susceptibility, however, hampers their application. Herein, an efficient strategy to enhance creep resistance of CANs via metal coordination to dynamic covalent imines is demonstrated. Crucially, the coordination bonds not only form additional crosslinks, but also affect the imine exchange. This dual effect results in enhanced glass transition temperature (Tg), elasticmodulus (G′) and creep resistance. The robustness of metal coordination is demonstrated by varying metal ion, counter anion, and coordinating imine ligand. All variations in metal or anion significantly enhance the material properties. The Tg and G′ of the CANs are correlated to the coordination bond strength, offering a tunable handle by which choice of metal can steer material properties. Additionally, large differences in Tg and G′ are observed for materials with different anions, which are mostly linked to the anion size. This serves as a reminder that for coordination chemistry in the bulk, not only the metal ion is to be considered, but also the accompanying anion. Finally, the reinforcing effect of metal coordination is proved insensitive to the metal–ligand ratio, emphasizing the robustness of the applied method.

The introduction of dynamic covalent bonds into cross-linked polymer networks enables the development of strong and tough materials that can still be recycled or repurposed in a sustainable manner. To achieve the full potential of these covalent adaptable networks (CANs), it is essential to understand�and control�the underlying chemistry and physics of the dynamic covalent bonds that undergo bond exchange reactions in the network. In particular, understanding the structure of the network architecture that is assembled dynamically in a CAN is crucial, as exchange processes within this network will dictate the dynamicmechanical material properties. In this context, the introduction of phase separation in different network hierarchies has been proposed as a useful handle to control or improve the material properties of CANs. Here we report�for the first time�how Raman confocal microscopy can be used to visualize phase separation in iminebased CANs on the scale of several micrometers. Independently, atomic force microscopy (AFM) confirmed the phase-separated domains inside the polymer. Remarkably, the materials were found to undergo phase separation despite being built up from miscible monomers, which arguably should yield homogeneous materials. We found that the phase separation not only affected the appearance of the material but�more notably�also had a noticeable effect on the thermal-mechanical properties of the material: CANs (of equal aliphatic/aromatic monomer composition) that displayed phase separation had both a higher crossover temperature (T cross , where tan(δ) = 1, and where the material transits from a rubbery to a viscous state) and an increased elastic modulus (G′). By modifying the CAN architecture, we were able to either suppress or enhance the phase separation, and we propose that the phase separation is driven by favorable π−π interactions between the aromatic components. Our work further shows the importance of phase separation in CANs, including in networks built from miscible components, and provides a handle to control the dynamic material properties. Moreover, our work underlines the suitability of Raman imaging as a method to visualize phase separation in CANs.

Phase separation phenomena have been studied widely in the field of polymer science, and were recently also reported for dynamic polymer networks (DPNs). The mechanisms of phase separation in dynamic...

Background Reducing the number of animals used in experiments has become a priority for the governments of many countries. For these reductions to occur, animal-free alternatives must be made more available and, crucially, must be embraced by researchers. Methods We conducted an international online survey for academics in the field of animal science ( N = 367) to explore researchers’ attitudes towards the implementation of animal-free innovations. Through this survey, we address three key questions. The first question is whether scientists who use animals in their research consider governmental goals for animal-free innovations achievable and whether they would support such goals. Secondly, responders were asked to rank the importance of ten roadblocks that could hamper the implementation of animal-free innovations. Finally, responders were asked whether they would migrate (either themselves or their research) if increased animal research regulations in their country of residence restricted their research. Results While nearly half (40%) of the responders support governmental goals, the majority (71%) of researchers did not consider such goals achievable in their field within the near future. In terms of roadblocks for implementation of animal-free methods, ~ 80% of the responders considered ‘reliability’ as important, making it the most highly ranked roadblock. However, all other roadblocks were reported by most responders as somewhat important, suggesting that they must also be considered when addressing animal-free innovations. Importantly, a majority reported that they would consider migration to another country in response to a restrictive animal research policy. Thus, governments must consider the risk of researchers migrating to other institutes, states or countries, leading to a ‘brain-drain’ if policies are too strict or suitable animal-free alternatives are not available. Conclusion Our findings suggest that development and implementation of animal-free innovations are hampered by multiple factors. We outline three pillars concerning education, governmental influence and data sharing, the implementation of which may help to overcome these roadblocks to animal-free innovations. Electronic supplementary material The online version of this article (10.1186/s41073-019-0067-5) contains supplementary material, which is available to authorized users.

17 Reducing the number of animals used in experiments has become a priority for the 18 governments of many countries. For these reductions to occur, animal-free alternatives must 19 be made more available and, crucially, must be embraced by researchers. We conducted an 20 international online survey for academics in the field of animal science (N=367) to explore 21 researchers' attitudes towards the implementation of animal-free innovations. 22 Through this survey we address three key questions. The first question is whether scientists 23 who use animals in their research consider governmental goals for animal-free innovations 24 achievable and whether they would support such goals. Secondly, responders were asked to 25 rank the importance of ten roadblocks that could hamper the implementation of animal-free 26 innovations. Finally, responders were asked whether they would migrate (either themselves 27 or their research) if increased animal research regulations in their country of residence 28 restricted their research. While nearly half (40%) of the responders support governmental 29 goals, the majority (71%) of researchers did not consider such goals achievable in their field 30 within the near future. In terms of roadblocks for implementation of animal-free methods, 31~80% of the responders considered 'reliability' as important, making it the most highly ranked 32 roadblock. However, all other roadblocks were reported by the majority of responders as 33 somewhat important, suggesting that they must also be considered when addressing animal-34 free innovations. Importantly, a majority reported that they would consider migration to 35 another country in response to restrictive animal research policy. Thus, governments must 36 consider the risk of researchers migrating to other institutes, states or countries, leading to a 37 'brain-drain' if policies are too strict or suitable animal-free alternatives are not available. Our 38 findings suggest that development and implementation of animal-free innovations are 39 hampered by multiple factors. We outline three pillars concerning education, governmental 40 influence and data sharing, the implementation of which may help to overcome these 41 roadblocks to animal-free innovations. 42 Introduction 43 Animal research has played a critical role in many scientific and medical achievements of the 44 past century. Animal models are used across many fields, including fundamental, biomedical, 45 behavioural, military and agricultural research [1]. Around the world, quality of life has been 46 greatly improved by the research, medicines, treatments and safer environments that have 47 been developed as a consequence of animal-based research in these fields. However, the 48 ethical issues associated with using animals and increased concern regarding animal 49 wellbeing [2], together with concerns regarding the translatability of animal models [3] and 50 practical difficulties of using animals [4], are gaining importance. In line with this, the 51 principles of 3R (Replacement...

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