Polymers are ubiquitous in our daily lives. They have revolutionized almost every aspect of modern life, from low cost materials with short lifetimes such as packaging or other single-use products, to those with longer lifetimes such as clothing or construction, through to higher value materials that are components in high value products such as plastic electronics or healthcare applications. As may be expected from the age of petroleum, a majority of polymers that are commonly used are derived from petrochemical resources. Inevitably, with the high current focus on sustainable sourcing of polymers and the need for reducing plastic waste that enters and persists in the environment, when polymers enter the public consciousness, discussions quickly turn to the consideration of their negative points over the many positives in a blessing-and-curse style of argument.

While the benefits of polymers are clearly understood, the major points of criticism focus on the environmental impact of the polymers, from their end-of-life treatments that include limited recycling, burning to produce CO₂ and other harmful greenhouse gasses, disposal in landfill or worse, littering our environment. Furthermore, the leaching of potentially harmful polymer additives such as plasticisers, residual monomers or catalysts all have potentially negative effects on the environment and ultimately people.

The environmental issues, as well as concerns over the depletion of fossil fuel resources from which many polymers are made, have led to a significant and growing interest in ‘green’ chemistries. This is a broadly defined topic that, with relation to polymer science, is dedicated to increasing the sustainability of polymer synthesis and the connected process technologies, with a strong focus on improving the sustainability of all aspects of plastics technology from removal of harmful solvents to using more sustainably sourced precursors to alleviate environmental concerns, health hazards and resource efficiency. As one of the guiding principles of green chemistry, the application of catalysis is a critical piece of the puzzle. Of all the tools in the chemists’ arsenal, catalysis is probably the one able to contribute the most to these goals. In polymer synthesis, catalysis plays an essential role in increasing the rate of reactions and reducing side reactions that occur to improve selectivity thus leading to more predictable outcomes and less waste. Given the excellent performance and vast array of opportunities that metallo-organic chemistry offers through the almost infinite ligand/metal combinations, it is not surprising that transition metals and organometallic catalysts have dominated the field of polymerisation catalysis. However, in part due to concerns over the availability of some widely used metals such as zinc or silver, which risk complete disappearance in the next 100 years, or ruthenium, lithium or copper, which will be seriously threatened in the future if their consumption continues to increase, the use of organic compounds to catalyse polymerisation reactions is gaining increasing interest. In the past two decades, the remarkable ability of small organic molecules to mediate a variety of polymerisation processes has brought about the rapid evolution of metal-free, organocatalytic polymerisation techniques.

While the interest in organic catalysis had been growing for mediating an array of organic transformations, its initial translation into the world of polymer synthesis was in the ring-opening transesterification polymerisation of lactide in order to produce ‘soft-etch’ polymers for potential microelectronics applications that were readily degradable in mild acidic etching conditions and would not leave any metal residues. While the potential for leaving no metals in the polymer was also quickly recognised in the biomedical field where metal-based impurities can be prohibitively expensive to remove, organocatalysed polymerisation has now progressed far beyond the fact of merely being ‘metal-free’, presenting ways to lower toxic byproducts in polymers and to address resource efficiency concerns associated with metals. Inspired by nature with the use of enzymes to catalyse biochemical reactions, metal-free polymerisations offer unique polymerisation pathways, access to various macromolecular architectures and novel selectivities, quite often in combination with excellent control over important polymer parameters such as molecular weights, polydispersity, end groups and copolymer constitution. Indeed, the field has progressed to the point that organic catalysts now provide many potential advantages to their metallo-organic counterparts that mean that in many cases they are now preferred (at least in the academic world) for polymerisation. Many organocatalytic species are inexpensive, commercially available molecules that either can be used as received or can be made and purified through a limited number of steps. Indeed, a wide range of the most commonly used species, although not all, are stable to both water and oxygen, which beyond providing an advantage in handling also results in longer shelf lives without the need for storage in inert atmospheres. While some applications may still require removal of air/moisture (i.e. ring-opening transesterification polymerisation), this is a process that is only undertaken to ensure high end group fidelity and a good match of molecular parameters to those predicted/desired rather than any need for the organic catalyst to work. Many of the most commonly used organic catalysts are also stable to a large array of reaction conditions, solvents, and monomers, making them highly versatile. Finally, the acidic, basic or ionic nature of a majority of the materials enables their ready removal from polymer mixtures by low cost methodologies such as washing or trapping in resin beads.

The field of organic catalysis for ring opening polymerisation has grown significantly in the past 15 years to the point that the advantages of the approaches are being recognised and organocatalytic approaches are being sought in preference to metal-based catalysts. A much broader range of monomers can now be polymerised, being extended far beyond its original scope to include not only lactones and carbonates, but also epoxides, anhydrides, siloxanes, lactams, acrylic monomers and many others. Alongside the development of innovative catalyst families that are able to be highly selective towards one functionality over another, the field is blossoming. While there are some reviews and viewpoints in the journal literature, the many facets of organopolymerisation and an ever increasing number of publications has raised the demand for a comprehensive review, especially since no comparable collection of information is currently available. As such, the presented edited book on Organic Catalysis for Polymerisation is the first of its kind on this research topic. Eminent experts in their respective fields have taken a detailed look at all relevant aspects of metal-free polymerisation approaches. The close interconnections between catalyst development and the investigation of novel polymers and materials are mirrored in the organization of the chapters, where two different viewpoints are taken. The first part of the book presents the fundamental, metal-free catalyst polymerisation principles (nucleophilic, acid- and base-catalysed as well as dual or supramolecular catalysis, Chapters 1–4). Here all relevant types of organocatalysts are detailed, with an emphasis on polymerisation mechanisms and on elucidating the impact of structural changes in the catalyst on the resulting polymers. Together, this delivers an informative profile on the evolution of the field and describes how the different catalyst families are able to polymerise the various monomer classes, highlighting the crucial differences between them to present clearly the opportunities that remain in those areas. In the second part of the book, the focus is turned onto the different classes of monomer, detailing the existing metal-free polymerisation strategies for a given class of compounds (lactones, lactides, carbonates, epoxides, other cyclic and acrylic monomers, Chapters 5–11) to provide a one-stop guide to select the most appropriate catalyst for any given process, as well as inspiration for where the future challenges lie. These chapters will not only provide a comprehensive overview for the polymerisation of conventional monomers such as lactide, epoxides or trimethylene carbonate but also summarize the most relevant results about the use of organocatalysis for the ring opening polymerisation of aziridines or phosphester monomers amongst many others. Taken together, this will facilitate access to this research field both for readers interested in catalyst design and development as well as those focusing on the best methodologies to synthesise a specific type of polymer using organocatalytic routes. Finally, the focus is shifted to the more nascent, yet highly important areas of organocatalysed step-growth reactions and metal-free controlled radical polymerisation (Chapters 12–13). In this third part, the potential of organocatalysis for step-growth polymerisation reaction and the preparation of industrially relevant polymers such as polyurethanes and in the emerging area of organocatalysed controlled polymerisation for the preparation of well-defined specific polymer structures are described. Subsequently, Chapter 14 is focussed on the emerging subject of organocatalysis in polymer recycling/depolymerisation. No doubt this area will grow significantly in importance over the coming years and, given the environmental credentials of organocatalysis, it could play an important role to facilitate the implementation of inexpensive and sustainable chemical recycling processes. Finally, an outlook (Chapter 15) provides a commentary of the most important developments in organic catalysis for polymerisation to date and summarises some of the major challenges that face the field in the coming decade.

We like to conclude with the grateful acknowledgement of all contributors, who with their expertise and diligence were crucial to the success of this project and wish that readers may find Organic Catalysis for Polymerisation an informative and thought-provoking inspiration.

Stefan Naumann, Haritz Sardon and Andrew P. Dove