**About the Editors**

**Sławomir Rubinsztajn** graduated from the Faculty of Chemistry at the Technical University of Łod´ z in 1979. In the same year, he began working in the group of Prof. Julian Chojnowski at ´ the Centre for Molecular and Macromolecular Research at the Polish Academy of Sciences (CMMS PAS) in Łod´ z. He received his Ph.D. in Chemistry in 1986 for his work on the mechanism of the ´ polycondensation of siloxane oligomers. From 1988–1992 he worked as a postdoctoral researcher in the group of Prof. Martel Zeldin at Indiana University–Purdue University in Indianapolis. In 1992, he started work at General Electric's Central Research Centre in Niskayuna, NY. In 1998, he was promoted to the principal chemist's position at GE Silicones. Dr. Rubinsztajn received the title of Dr. hab. in 2013 from the CMMS PAS for novel works in the field of polysiloxane chemistry. Dr. Rubinsztajn retired from GE Company in 2016. In the same year, he began work in CMMS PAS, where he directs a research team working in silicon chemistry. Dr. Rubinsztajn has co-authored 62 US patents and 63 publications.

**Marek Cypryk** was born in Łod´ z, Poland. He received his MSc degree in 1974 in Polymer ´ Chemistry from the Technical University in Łod´ z and PhD in 1982 from the Centre of Molecular and ´ Macromolecular Studies of Polish Academy of Sciences under the supervision of Professor Julian Chojnowski. He worked as a postdoctoral fellow at the Carnegie-Mellon University in Pittsburgh, PA, from 1990–1991 in the group of Professor Krzysztof Matyjaszewski. In 2002, he completed his DSc (habilitation) in Polymer Chemistry on the mechanisms of polymerization reactions in organosiloxane chemistry. He is currently a full professor and a head of the Research Group for Computer Modeling in the CMMS PAS. His main research interests are organosilicon polymer chemistry, reactions mechanisms in heterorganic chemistry, computational chemistry, and molecular modeling. He is an author or co-author of over 100 original papers and reviews.

**Wlodzimierz Stanczyk** is a leader of the Inorganic–Organic Composites Research Group at the Centre of Molecular and Macromolecular Studies of the Polish Academy of Sciences in Łod´ z.´ He obtained his MSc Eng., PhD, and DSc from the Chemistry Department of the Łod´ z University ´ of Technology. He spent over two years working with Prof. Colin Eaborn at the School of Molecular Sciences of the University of Sussex. He has published over 100 papers on various aspects of organosilicon polymers and organometallic reaction mechanisms, liquid crystal polymers, and nanoconjugates. His current interests focus on silsesquioxanes as drug nanocarriers.

#### **Preface to "Various Aspects of Silicon Polymer Chemistry: A Themed Issue in Honor of Professor Julian Chojnowski on the Occasion of His 85th Birthday"**

This special edition is dedicated to Professor Julian Chojnowski on the occasion of his 85th birthday for his outstanding achievements in the field of organosilicon chemistry.

Professor Chojnowski was born on 17th of June, 1935, in Warsaw, Poland. He obtained his MSc degree in chemistry from Technical University of Łod´ z in 1957. He moved to the newly created ´ Centre of Molecular and Macromolecular Studies of Polish Academy of Sciences in 1972, where he became the head of the Laboratory of Hetero-organic Polymers. In 1983, he obtained the academic title of Professor of Chemistry. He retired in 2005 but, to date, he continues research at the Centre of Molecular and Macromolecular Studies as a professor emeritus. Professor Chojnowski is the promoter of 15 doctoral dissertations. He published about 180 original papers, 16 review papers and chapters in books, as well as several Polish and US patents. He was also a co-editor of two books. In 2005, Professor Chojnowski was awarded with the Jan Zawidzki medal by the Polish Chemical Society for outstanding achievements in the field of physical chemistry. He serves as a member of the Advisory Board of The Journal of Inorganic and Organometallic Polymers and Materials, Silicon (Springer), and Main Group Chemistry.

Professor Chojnowski is an outstanding chemist who has significantly contributed to the development of many fields of organosilicon chemistry and organosilicon polymers chemistry. His fundamental research in the field of kinetic and thermodynamic aspects of polymerization processes and the substitution at silicon atom has led to understanding of the mechanisms of ring-opening polymerization reactions of cyclic siloxanes, as well as the discovery of the importance of inter- and intramolecular catalysis in siloxane polymerization and polycondensation processes. His expertise in the field of siloxane polymer chemistry has resulted in cooperation with the leading silicone materials manufacturers such as Dow Corning and General Electric Company. His collaboration with GE resulted in the discovery of several new reactions of hydride-functional silanes and siloxanes involving activation of Si-H bond by electron-deficient boranes. Recently, he extended his research interest into silicon-based materials. He developed the synthesis of a new class of polymers, poly(oxymultisilylene)s, and new processes leading to the synthesis of highly cross-linked polyorganosiloxane beads, which can be subsequently converted into ceramic materials.

This special edition of Molecules contains one review and eleven original articles written by prominent experts on various aspects of silicon polymer chemistry which reflect the tireless passion of Professor Chojnowski to the development of organosilicon chemistry.

#### **Sławomir Rubinsztajn, Marek Cypryk, Wlodzimierz Stanczyk** *Editors*

*Review*

#### **Applications of Hybrid Polymers Generated from Living Anionic Ring Opening Polymerization**

**Jonathan Goff \*, Santy Sulaiman and Barry Arkles**

> Gelest Inc., 11 Steel Road East, Morrisville, PA 19067, USA; ssulaiman@gelest.com (S.S.); executiveoffice@gelest.com (B.A.) **\***

 Correspondence: jgoff@gelest.com

**Abstract:** Increasingly precise control of polymer architectures generated by "Living" Anionic Ring-Opening Polymerization (Living AROP) is leading to a broad range of commercial advanced material applications, particularly in the area of siloxane macromers. While academic reports on such materials remain sparse, a significant portion of the global population interacts with them on a daily basis—in applications including medical devices, microelectronics, food packaging, synthetic leather, release coatings, and pigment dispersions. The primary driver of this increased utilization of siloxane macromers is their ability to incorporate the properties of silicones into organic structures in a balanced manner. Compared to organic polymers, the differentiating properties of silicones— low *Tg*, hydrophobicity, low surface energy, and high free molal space—logically lend themselves to applications in which low modulus, release, permeability to oxygen and moisture, and tactile interaction are desired. However, their mechanical, structural and processing properties have until recently precluded practical applications. This review presents applications of "Living" AROP derived polymers from the perspective of historical technology development. Applications in which products are produced on a commercial scale—defined as not only offered for sale, but sold on a recurrent basis—are emphasized. Hybrid polymers with intriguing nanoscale morphology and potential applications in photoresist, microcontact printing, biomimetic soft materials, and liquid crystals are also discussed. Previously unreported work by the authors is provided in the context of this review.

**Keywords:** hybrid polymers; ring-opening polymerization; contact lenses; breathable films; membranes; high elongation elastomers; biomimetic polymers; photoresists
