Precision Macromolecular Chemistry

Abstract

The readers of Macromolecular Rapid Communications will probably be surprised by the title of this special issue. Indeed, Precision Macromolecular Chemistry does not correspond yet to a known sub-discipline in the field of polymer science. However, the adjective “precision” has been frequently used in recent years to describe certain aspects of polymer synthesis.1-5 In fact, it implicitly underlines a certain degree of accuracy in synthesizing macromolecules. Indeed, “precision” evokes immediately the skills of a traditional watchmaker. Thus, this term has been associated to certain aspects of polymer synthesis, which are generally difficult to control without accurate and adequate chemical tools. For instance, crucial macromolecular parameters such as polydispersity, tacticity, monomer sequences, and folding are still not fully mastered in current polymer science. Yet, very interesting approaches for controlling these molecular features have been reported during the past few years. These emerging trends are describe under the label Precision Macromolecular Chemistry in this special issue. In fact, the research topics presented herein differ in some ways from mainstream polymer science. During the past twenty years, polymer chemists developed unprecedented ways to control the architecture of synthetic polymers. Since the introduction of controlled radical polymerization techniques, such as atom transfer radical polymerization or reversible addition-fragmentation chain-transfer polymerization, and afterward of “click” ligation tools, such as copper-catalyzed azide-alkyne cycloadditions or thiol-ene chemistry, the possibilities of macromolecular engineering have exploded.5-7 For instance, macromolecular architectures such as block copolymers, graft copolymers, star polymers, or macrocycles can nowadays be routinely synthesized. In addition, new types of architectures such as miktoarm stars or macromolecular bottle brushes emerged during the past decades. However, it seems that most of these architectural possibilities have now been explored, and progress is therefore slowly reaching a creativity plateau in synthetic polymer chemistry. Hence, in terms of fundamental research, the new challenges for polymer chemists in the 21st century are probably elsewhere. Actually, most of the authors of this special issue share one belief, which is that the control over the primary structure (i.e., tacticity, monomer sequences) and secondary structure (i.e., macromolecular folding) in synthetic macromolecules could be considered a new avenue for polymer design. Indeed, it is known from nature that these molecular parameters allow the design of microscopic or macroscopic materials with unrivaled properties. For instance, protein-based biomaterials are still in many ways superior to most synthetic polymer materials. Their mechanical properties are often highly purpose adapted (e.g., muscle tissues, spider silk). Their biocatalytic properties (e.g., enzymes) are by far more specific and efficient than man-made organocatalysts. Their transport properties (e.g., globular proteins) cannot be matched by any synthetic colloids. This list could be continued over several pages. Therefore, it seems highly important to import the controlled molecular features of biopolymers in the world of synthetic polymers. Yet, this exciting scientific adventure is only starting. For instance, in terms of controlled primary structures, we are still miles away from the perfection of nature.8 Similar remark applies, although to a lower extent, to the field of macromolecular foldamers (i.e., polymers with controlled secondary and tertiary structures). In this context, we display in the present issue of Macromolecular Rapid Communications a collection of carefully selected papers, which represent the avant-garde in the field of Precision Macromolecular Chemistry. In particular, this special issue contains various contributions from Asia, Europe, and North America and is organized around four main topics: i) the synthesis of monodisperse macromolecules;9 ii) the control over polymer tacticity;10, 11 iii) the synthesis of sequenced-defined or sequence-controlled polymers;12-17 and iv) the design and utilization of functions of those precision polymers.18-23 All these aspects are indeed still very fundamental. It will certainly take several years of prospective research until some of these new polymers will lead to industrially applicable materials. Nevertheless, the trends highlighted in this special issue constitute undoubtedly the core of a new discipline in the field of polymer science.