Supramolecular and dynamic covalent polymers

When polymer chemists discuss supramolecular or dynamic covalent polymers the conversation invariably turns to the fascinating applications of the resulting materials. Supramolecular and dynamic covalent polymers have been used as key materials for applications ranging from the delivery of therapeutics by stimuli-triggered release, to sensors for multi analyte detection, and materials that have the ability to self-heal cracks and defects (just in this issue!). The performance of these polymers is driven by the unique combination of polymer properties and non-covalent molecular interactions, which has led to an explosion in the number of original research manuscripts and review articles over the past two decades focusing on supramolecular polymers or macromolecules containing dynamic covalent bonds. The publication of a themed issue dedicated to this topic is therefore both timely and relevant.

It is easy to deduce what first attracts researchers to this area: the blend of a high degree of control over polymer properties with the diversity of non-covalent chemistry. This combination, coupled with synthetic polymer chemistry, makes it possible to construct responsive macromolecular assemblies with controlled architecture and size containing almost any functional group. For example, this issue contains reports of star polymers prepared through supramolecular interactions, the preparation of stimuli-responsive micellar assemblies and formation of single chain nanoparticles, the synthesis of surface-confined polymers, and the creation of polypseudorotaxanes. In fact, it is tempting to say that we are limited more by our imagination than the synthetic strategies available to us, making research in this area incredibly stimulating and exciting.

Several types of non-covalent interactions are commonly employed, including hydrogen bonding, Coulombic interactions, π–π interactions, metal–ligand interactions, and dynamic covalent bonding (for example boronic esters). Of these, hydrogen bonding, the most popular non-covalent interaction, contains the largest diversity, being either “tailor-made” by synthetic chemists or derived from nature. The quadruple hydrogen bonding ureidopyrimidinone group and the Hamilton wedge are examples of “tailor-made” groups, while the thymine–adenine and thymine–diamidopyridine pairs are examples of recognition pairs taken from or inspired by nature. All of these different interactions have been explored in work contained within this issue, and several papers reference seminal reviews for further reading.

Supramolecular and dynamic covalent polymers can be categorized into broad areas. They include random-coil polymers, or copolymers prepared through conventional methods (whether radical, ionic, ring opening, etc.) that are modified with groups enabling non-covalent chemistry. In this issue, Stuparu, Kahn and Hawker (DOI: 10.1039/c2py20368e) review the phase separation of supramolecular and dynamic covalent block copolymers, with an eye to how the morphologies of these systems can lead to new properties and material performance. When recognition units in the side-chains of a polymer are functionalized in a non-covalent or dynamic covalent fashion, unique side-chain functionalized materials are obtained. This issue describes some of the exciting trends in this area, ranging from the use of such a strategy to fabricate tunable bottle brush polymers, to assembling quantum dots through hydrogen bonding. Another subsection of supramolecular polymer science encompasses molecules, oligomers, or telechelic polymers that are designed to directly assemble through non-covalent interactions into polymer chains or block copolymers. Rowan's group (DOI: 10.1039/c2py20307c) provides an example of this category, where defined oligomers are prepared using a combination of control over stoichiometry and redox conditions. It is important to remember that these categories or subsections in supramolecular polymer chemistry are rather arbitrary, and often work from a particular research group or contained within a manuscript will encompass elements from some (or all) of these areas.

The manuscripts within this themed issue of Polymer Chemistry represent some of the cutting edge research in the field of supramolecular and dynamic covalent polymers, ranging from understanding fundamental molecular properties to the creation of new materials for diverse applications. We have been honored to serve as guest editors, and hope this collection of articles will be both educational and stimulating for newcomers and expert researchers in this area.

Neil Ayres
Marcus Weck

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