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Carbodiimides and pyridines form reversible adducts that slowly deliver carbodiimide "fuels" to out-of-equilibrium reaction networks, slowing activation kinetics and elongating transient state lifetimes. More-nucleophilic pyridines give more adduct under typical conditions. This approach can be used to extend the lifetimes of transient polymer hydrogels.

Although dispersity has been demonstrated to be instrumental in determining many polymer properties, current synthetic strategies predominantly focus on tailoring the dispersity of linear polymers. In contrast, controlling the primary chain dispersity in network polymers is much more challenging, in part due to the complex nature of the reactions, which has limited the exploration of properties and applications. Here, a one-step method to prepare networks with precisely tuned primary chain dispersity is presented. By using an acid-switchable chain transfer agent and a degradable crosslinker in PET-RAFT polymerization, the in situ crosslinking of the propagating polymer chains was achieved in a quantitative manner. The incorporation of a degradable crosslinker, not only enables the accurate quantification of the various primary chain dispersities, post-synthesis, but also allows the investigation and comparison of their respective degradation profiles. Notably, the highest dispersity networks resulted in a 40% increase in degradation time when compared to their lower dispersity analogues, demonstrating that primary chain dispersity has a substantial impact on the network degradation rate. Our experimental findings were further supported by simulations, which emphasized the importance of higher molecular weight polymer chains, found within the high dispersity materials, in extending the lifetime of the network. This methodology presents a new and promising avenue to precisely tune primary chain dispersity within networks and demonstrates that polymer dispersity is an important parameter to consider when designing degradable materials., Competing Interests: The authors declare no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

Repairable adhesive elastomers are emerging materials employed in compelling applications such as soft robotics, biosensing, tissue regeneration, and wearable electronics. Facilitating adhesion requires strong interactions, while self-healing requires bond dynamicity. This contrast in desired bond characteristics presents a challenge in the design of healable adhesive elastomers. Furthermore, 3D printability of this novel class of materials has received limited attention, restricting the potential design space of as-built geometries. Here, we report a series of 3D-printable elastomeric materials with self-healing ability and adhesive properties. Repairability is obtained using Thiol-Michael dynamic crosslinkers incorporated into the polymer backbone, while adhesion is facilitated with acrylate monomers. Elastomeric materials with excellent elongation up to 2000%, self-healing stress recovery >95%, and strong adhesion with metallic and polymeric surfaces are demonstrated. Complex functional structures are successfully 3D printed using a commercial digital light processing (DLP) printer. Shape-selective lifting of low surface energy poly(tetrafluoroethylene) objects is achieved using soft robotic actuators with interchangeable 3D-printed adhesive end effectors, wherein tailored contour matching leads to increased adhesion and successful lifting capacity. The demonstrated utility of these adhesive elastomers provides unique capabilities to easily program soft robot functionality.

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.

Rational design of protein-polymer bioconjugates is hindered by limited experimental data and mechanistic understanding on interactions between the two. In this communication, nuclear magnetic resonance (NMR) paramagnetic relaxation enhancement (PRE) reports on distances between paramagnetic spin labels and NMR active nuclei, informing on the conformation of conjugated polymers. 1 H/ 15 N-heteronuclear single quantum coherence (HSQC) NMR spectra were collected for ubiquitin (Ub) modified with block copolymers incorporating spin labels at different positions along their backbone. The resultant PRE data show that the conjugated polymers have conformations biased towards the nonpolar β-sheet face of Ub, rather than behaving as if in solution. The bioconjugates are stabilized against denaturation by guanidine-hydrochloride, as measured by circular dichroism (CD), and this stabilization is attributed to the interaction between the protein and conjugated polymer., (This journal is © The Royal Society of Chemistry 2020.)

Transiently crosslinked dynamic polymer networks are developed, using carbodiimide hydration to link carboxylic acids as anhydrides. From aqueous polymer solutions, non-equilibrium hydrogels are transiently formed, which dissolve upon anhydride hydrolysis. The materials can be refueled using a subsequent injection of carbodiimide. The gels exhibit higher storage moduli compared to transient supramolecular gels as a result of their covalent crosslinks.

For more than 40 years, protein-polymer conjugates have been widely used for many applications, industrially and biomedically. These bioconjugates have been shown to modulate the activity and stability of various proteins while introducing reusability and new activities that can be used for drug delivery, improve pharmacokinetic ability, and stimuli-responsiveness. Techniques such as RDRP, ROMP and "click" have routinely been utilized for development of well-defined bioconjugate and polymeric materials. Synthesis of bioconjugate materials often take advantage of natural amino acids present within protein and peptide structures for a host of coupling chemistries. Polymer modification may elicit increased or decreased activity, activity retention under harsh conditions, prolonged activity in vivo and in vitro , and introduce stimuli responsiveness. Bioconjugation has resulted to modulated thermal stability, chemical stability, storage stability, half-life and reusability. In this review we aim to provide a brief state of the field, highlight a wide range of behaviors caused by polymer conjugation, and provide areas of future work., Competing Interests: Conflicts of interest Richard C. Page has recently served as an expert in a case associated with Granulocyte colony-stimulating factor.

The kinetics and mechanism of the thermally activated dynamic covalent exchange of thiol-Michael adducts is investigated. A model system of thiol-Michael adducts between thiophenol and phenylvinylketone derivatives and adducts between 2-mercaptoethanol phenylvinylketone derivatives in N,N-dimethylformamide (DMF) at elevated temperatures is used to probe the underlying exchange mechanism. The kinetic data show negligible free Michael acceptor, which is consistent with the highly efficient thiol-Michael reaction being a "click"-like reaction that significantly favors the adduct form. At elevated temperatures of 90 °C in DMF the thiol-Michael adducts reach equilibrium after 24 h, although equilibration did not occur within 24 h at 60 °C or 75 °C, and negligible exchange occurs under ambient conditions. A kinetic model was developed to describe the dynamic covalent exchange and equilibration. The experimental and simulation kinetic data of dynamic covalent exchange are consistent with the thiol-Michael adducts undergoing a retro-Michael reaction, followed by subsequent addition of a free thiol to the liberated Michael acceptor. Kinetic analysis is consistent with the fragmentation, or retro-Michael reaction, being the rate-determining step in the dynamic covalent exchange. This suggests that the key step in dynamic covalent exchange is not enhanced by addition of free thiol or free Michael acceptor, since the addition reaction is much faster than the retro-Michael reaction. This fundamental study will guide the design of organic compounds, materials, and bioconjugates that utilize the thermally activated dynamic covalent thiol-Michael linkages.

Hydrophilic polymers were attached to lysozyme by a combination of grafting-to and grafting-from approaches using RAFT polymerization. A hydrophilic oligomer was synthesized, and attached to the protein. The protein-oligomer hybrid contained the RAFT end group, enabling chain extension in solution. Lysozyme maintained activity throughout this process.

Alternating-block hyperbranched polymers were synthesized using the highly versatile thiol-yne reaction. Dimethyl acrylamide-styrene and tert-butyl acrylate-styrene polymers were prepared, with subsequent hydrolysis of the tert-butyl ester to acrylic acid. The dimethyl acrylamide-styrene hyperbranched polymers self-assembled into large aggregates, as did the acrylic acid-styrene system at low pH. However, high pH triggers the formation of very well defined small particles in the latter system.