Poly(β-hydroxyl amine)s: Valuable Building Blocks for Supramolecular Elastomers with Tunable Mechanical Performance and Superior Healing Capacity

Supramolecular elastomers integrated with high mechanical toughness and excellent self-healing ability offer attractive applications in various fields such as biomedical materials and wearable electronics. However, the multistep preparation process for creating functional polymer precursors and the expensive stock materials required are two factors that limit the widespread use of supramolecular elastomers. Herein, for the first time, poly(β-hydroxyl amine)s generated by amine-epoxy polymerization were used in the development of supramolecular polymer materials. Based on the novel silicon-containing poly(β-hydroxyl amine)s synthesized by the polymerization between 1,3-bis(3-glycidyloxypropyl)tetramethyldisiloxane and 3-amino-1,2-propanediol, dually cross-linked supramolecular elastomers with both hydrogen bonding and metal coordination were achieved, displaying adjustable mechanical properties with the tensile strength varying from 0.70 MPa to 2.52 MPa, respectively. Thanks to the dynamic nature of the supramolecular interactions, these elastomers exhibited favorable hot-pressing reprocessability and excellent self-healing performance, with the healing efficiency reaching up to 98% at 60 °C for 48 h. Potential applications for photoluminescent materials and flexible electronic devices were demonstrated. We believe that its simplicity of synthesis, adjustable mechanical properties, and robust self-healing capacities bode well for future applications of this new supramolecular elastomer.

Thermoresponsive Poly(ß-hydroxyl amine)s: Synthesis of a New Stimuli Responsive Amphiphilic Homopolymer Family through Amine-Epoxy 'Click' Polymerization

A new synthesis of amphiphilic homopolymers is described. In this synthesis, commercially available and inexpensive primary amines and di-epoxide molecules are utilized as AA- and BB-types of monomers in an amine-epoxy ‘click’ polymerization process. This process can be carried out in water and at room temperature. It does not require a catalyst or inert conditions and forms no byproducts. Therefore, the polymer synthesis can be carried out in open-air and bench-top conditions and a post-synthesis purification step is not required. The modularity of the synthesis, on the other hand, allows for facile structural modulation and tuning of the thermally triggered aggregation process in the temperature range of 7 to 91 °C. Finally, the underlying principles can be translated from linear architectures to polymer networks (hydrogels).

A Modular and Practical Synthesis of Zwitterionic Hydrogels through Sequential Amine-Epoxy "Click" Chemistry and N-Alkylation Reaction

In this work, the amine-epoxy "click" reaction is shown to be a valuable general tool in the synthesis of reactive hydrogels. The practicality of this reaction arises due to its catalyst-free nature, its operation in water, and commercial availability of a large variety of amine and epoxide molecules that can serve as hydrophilic network precursors. Therefore, hydrogels can be prepared in a modular fashion through a simple mixing of the precursors in water and used as produced (without requiring any post-synthesis purification step). The gelation behavior and final hydrogel properties depend upon the molecular weight of the precursors and can be changed as per the requirement. A post-synthesis modification through alkylation at the nitrogen atom of the newly formed β-hydroxyl amine linkages allows for functionalizing the hydrogels. For example, ring-opening reaction of cyclic sulfonic ester gives rise to surfaces with a zwitterionic character. Finally, the established gelation chemistry can be combined with soft lithography techniques such as micromolding in capillaries (MIMIC) to obtain hydrogel microstructures.

A catalyst-free, temperature controlled gelation system for in-mold fabrication of microgels

Anisometric microgels are prepared via thermal crosslinking using an in-mold polymerization technique. Star-shaped poly(ethylene oxide-stat-propylene oxide) polymers, end-modified with amine and epoxy groups, form hydrogels, of which the mechanical properties and gelation rate can be adjusted by the temperature, duration of heating, and polymer concentration. Depending on the microgel stiffness, the rod-shaped microgels self-assemble into ordered or disordered structures.