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Photoinduced electron/energy transfer (PET)-reversible addition–fragmentation chain transfer polymerization (RAFT) and conventional photoinitiated RAFT were used to synthesize polymer networks. In this study, two different metal catalysts, namely, tris[2-phenylpyridinato-C2,N]iridium(III) (Ir(ppy)3) and zinc tetraphenylporphyrin (ZnTPP), were selected to generate two different catalytic pathways, one with Ir(ppy)3 proceeding through an energy-transfer pathway and one with ZnTPP proceeding through an electron-transfer pathway. These PET-RAFT systems were contrasted against a conventional photoinitated RAFT process. Mechanically robust materials were generated. Using bulk swelling ratios and degradable cross-linkers, the homogeneity of the networks was evaluated. Especially at high primary chain length and cross-link density, the PET-RAFT systems generated more uniform networks than those made by conventional RAFT, with the electron transfer-based ZnTPP giving superior results to those of Ir(ppy)3. The ability to deactivate radicals either by RAFT exchange or reversible coupling in PET RAFT was proposed as the mechanism that gave better control in PET-RAFT systems. 

An ongoing challenge in soft materials is to develop networks with high mechanical robustness while showing complete self-healing and stress relaxation. In this study we develop triple network (TN) materials with three different polymers with distinct dynamic linkers (Diels–Alder, boronic acid-ester and hydrogen bonding). TN materials exhibit significant improvement of strength, stability and excellent self-healing properties simultaneously compared to their analogous double networks (DNs). All the TNs (TN-FMA 5%, 7% and 9%) show higher tensile strength over all DNs. In addition, TN-FMA (9%) demonstrates an excellent fracture energy over 20 000 J m −2 , 750% elongation and fast stress relaxation. This highlights how dynamic bonding multiplicity and network structure can play a major role in improving the quality of dynamic materials. 

Dynamic bonds introduce unique properties such as self‐healing, recyclability, shape memory, and malleability to polymers. Significant efforts have been made to synthesize a variety of dynamic linkers, creating a diverse library of materials. In addition to the development of new dynamic chemistries, fine‐tuning of dynamic bonds has emerged as a technique to modulate dynamic properties. This Review highlights approaches for controlling the timescales of dynamic bonds in polymers. Particularly, eight dynamic bonds are considered, including urea/urethanes, boronic esters, Thiol–Michael exchange, Diels–Alder adducts, transesterification, imine bonds, coordination bonds, and hydrogen bonding. This Review emphasizes how structural modifications and external factors have been used as tools to tune the dynamic character of materials. Finally, this Review proposes strategies for tailoring the timescales of dynamic bonds in polymer materials through both kinetic effects and modulating bond thermodynamics.

 

Dynamic bonds introduce unique properties such as self‐healing, recyclability, shape memory, and malleability to polymers. Significant efforts have been made to synthesize a variety of dynamic linkers, creating a diverse library of materials. In addition to the development of new dynamic chemistries, fine‐tuning of dynamic bonds has emerged as a technique to modulate dynamic properties. This Review highlights approaches for controlling the timescales of dynamic bonds in polymers. Particularly, eight dynamic bonds are considered, including urea/urethanes, boronic esters, Thiol–Michael exchange, Diels–Alder adducts, transesterification, imine bonds, coordination bonds, and hydrogen bonding. This Review emphasizes how structural modifications and external factors have been used as tools to tune the dynamic character of materials. Finally, this Review proposes strategies for tailoring the timescales of dynamic bonds in polymer materials through both kinetic effects and modulating bond thermodynamics.

 

Interpenetrating networks (IPN) comprise two or more networks which are woven but not covalently bonded to each other. This is in contrast to simple, or single Networks (SN), which contain only one network that is covalently crosslinked. This study develops SNs and IPNs using 2-hydroxyethyl acrylate as the monomer and (2-((1-(2-(acryloyloxy)ethyl)-2,5-dioxopyrrolidin-3-yl) thio)ethyl acrylate) (TMMDA) as a thermoresponsive dynamic thiol-Michael crosslinker. In the case of the IPN and SN materials the TMMDA is used as a thermoresponsive linker in each network, since TMMDA undergoes dynamic covalent exchange above 90 °C. In this way the SN and IPNs are kinetically trapped in their as synthesized structures until exposed to thermal stimulus. The focus of this study is to investigate how dynamic bond exchange can modulate material properties, after the material has been synthesized using the SN and IPN materials as model systems. The dynamic nature of the thiol-Michael crosslinker allows the transition of IPNs into SN like structures above 90 °C resulting in similar polymer architecture in both SN and IPN. Surprisingly, upon heating the SN materials also changed their mechanical properties, upon activation of the dynamic thiol-Michael bonds. This enhancement is proposed to occur by thermally activating the thiol-Michael bonds and reducing the number of floppy loops at higher temperature. 

Dynamic materials (DMs) or dynamers have potential applications across a broad range of material science challenges. These applications include sustainable materials as a part of the circular plastics economy, advanced materials with tailored high stress properties and biomedical agents. DMs are comprised of polymers that crosslinked through reversible covalent and noncovalent linking groups. This group provides reversible bonds, which impart properties such as (re)healing, adaptability, toughness into a material. The nature of the linker dictates the dynamer's stability and dynamic properties, although for many applications one linker alone cannot give materials with complex multiresponsive functions. The combination of multiple dynamic linkers can introduce complementary functionalities into a single material. This combination of linkers enhances the collective material properties by matching their strengths and offsetting the weaknesses, or by selecting linkers for specific functions, such as one linker for rapid exchange and the other to respond to external stimuli. This contribution highlights the possibilities and unique features of materials containing multiple dynamic linkers, reviewing both fundamental discoveries of materials possessing multiple dynamic bonds and applications facilitated by the presence of multiple linking group chemistry.

 

Covalent adaptable networks (CANs) based on the thiol–Michael (TM) linkages can be thermal and pH responsive. Here, a new vinyl‐sulfone‐based thiol–Michael crosslinker is synthesized and incorporated into acrylate‐based CANs to achieve stable materials with dynamic properties. Because of the reversible TM linkages, excellent temperature‐responsive re‐healing and malleability properties are achieved. In addition, for the first time, a photoresponsive coumarin moiety is incorporated with TM‐based CANs to introduce light‐mediated reconfigureability and postpolymerization crosslinking. Overall, these materials can be on demand dynamic in response to heat and light but can retain mechanical stability at ambient condition.