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  1. Integration of multiple types of dynamic linkages into one polymer network is challenging and not well understood especially in the design and fabrication of dynamic polymer nanocomposites (DPNs). In this contribution, we present facile methods for synthesizing flexible, healable, conductive, and recyclable thermoresponsive DPNs using three dynamic chemistries playing distinct roles. Dynamic hydrogen bonds account for material flexibility and recycling character. Thiol-Michael exchange accounts for thermoresponsive properties. Diels–Alder reaction leads to covalent bonding between polymer matrix and nanocomposite. Overall, the presence of multiple types of orthogonal dynamic bonds provided a solution to the trade-off between enhanced mechanical performance and material elongation in DPNs. Efficient reinforcement was achieved using <1 wt % multiwalled carbon nanotubes as nanocomposite. Resulting DPNs showed excellent healability with over 3 MPa increase in stress compared to unreinforced materials. Due to multiple responsive dynamic linkages, >90% stress–relaxation was observed with self-healing achieved within 1 h of healing time. Increased mechanical strength, electrical conductivity, and reprocessability were achieved all while maintaining material flexibility and extensibility, hence highlighting the strong promise of these DPNs in the rapidly growing fields of flexible compliant electrodes and strain sensors.
    Free, publicly-accessible full text available September 9, 2023
  2. 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.
    Free, publicly-accessible full text available September 7, 2023
  3. Designing a surface that can disinfect itself can reduce labor-intensive cleanings and harmful waste, and mitigate spread of surface borne diseases. Additionally, since COVID-19 is an airborne pathogen, surface modification of masks and filters could assist with infection control. Styrene-maleic acid (SMA) copolymers and their derivatives were shown to have lipid-bilayer disrupting properties, making them candidates as anti-viral materials. A series of network polymers with styrene-maleic acid-based polymers and control over polymer chain-length and composition were synthesized. All the polymers formed mechanically robust structures, with tunable Young's moduli on the order of MPa, and tunable swelling capability in water. The SMA-based bulk materials, containing a zwitterionic polar unit, showed excellent lipid disrupting properties, being up to 2 times more efficient than a 10% Triton solution. The highest performance was observed for materials with lower crosslink densities or shorter chain-lengths, with lipid disruption capability correlating with swelling ratio. Additionally, the material can capture the spike protein of SARS-CoV-2, with up to 90% efficiency. Both the lipid disrupting and spike protein capture ability could be repeated for multiple cycles. Finally, the materials are shown to modify various porous and non-porous substrates including surgical and KN95 masks. Functional network modified masks had upmore »to 6 times higher bilayer disruption ability than the unmodified masks without inhibiting airflow.« less
    Free, publicly-accessible full text available August 9, 2023
  4. 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.
    Free, publicly-accessible full text available June 21, 2023
  5. Polymer networks crosslinked with spring-like ortho -phenylene ( o P) foldamers were developed. NMR analysis indicated the o P crosslinkers were well-folded. Polymer networks with o P-based crosslinkers showed enhanced energy dissipation and elasticity compared to divinylbenzene crosslinked networks. The energy dissipation was attributed to the strain-induced reversible unfolding of the o P units. Energy dissipation increased with the number of helical turns in the foldamer.
    Free, publicly-accessible full text available May 5, 2023
  6. Polymer molecular weight, or chain length distributions, are a core characteristic of a polymer system, with the distribution being intimately tied to the properties and performance of the polymer material. A model is developed for the ideal distribution of polymers made using reversible activation/deactivation of chain ends, with monomer added to the active form of the chain end. The ideal distribution focuses on living chains, with the system having minimal impact from irreversible termination or transfer. This model was applied to ATRP, RAFT, and cationic polymerizations, and was also used to describe complex systems such as blended polymers and block copolymers. The model can easily and accurately be fitted to molecular weight distributions, giving information on the ratio of propagation to deactivation, as well as the mean number of times a chain is activated/deactivated under the polymerization conditions. The mean number of activation cycles per chain is otherwise difficult to assess from conversion data or molecular weight distributions. Since this model can be applied to wide range of polymerizations, giving useful information on the underlying polymerization process, it can be used to give fundamental insights into macromolecular synthesis and reaction outcomes.
    Free, publicly-accessible full text available February 15, 2023