Controlled/Living Radical Polymerization: Progress in ATRP In Controlled/Living Radical Polymerization: Progress in ATRP; Matyjaszewski, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 2009. In Controlled/Living Radical Polymerization: Progress in ATRP; Matyjaszewski, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 2009. ACS SYMPOSIUM SERIES 1023 Controlled/Living Radical Polymerization: Progress in ATRP Krzysztof Matyjaszewski, Editor Carnegie Mellon University Sponsored by the ACS Division of Polymer Chemistry, Inc. ACS Petroleum Research Foundation Arkena, Bayer, Boston Scientific, Ciba, CIP, Dionex, DSM, Elsevier, Evonik, General Electric, JSR, Lion, Mitsui Chemicals, National Starch, PPG and Sumitomo American Chemical Society, Washington DC In Controlled/Living Radical Polymerization: Progress in ATRP; Matyjaszewski, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 2009. Library of Congress Cataloging-in-Publication Data Controlled/living radical polymerization : progress in ATRP / Krzysztof Matyjaszewski, editor. p. cm. -- (ACS symposium series; 1023) Includes bibliographical references and index. ISBN 978-0-8412-6995-8 (alk. paper) 1. Polymerization--Congresses. 2. Free radical reactions--Congresses. I. Matyjaszewski, K. (Krzysztof) QD281.P6C6555 2009 547'.28--dc22 2009020531 The paper used in this publication meets the minimum requirements of American National Standard for Information Sciences—Permanence of Paper for Printed Library Materials, ANSI Z39.48n1984. Copyright © 2009 American Chemical Society Distributed by Oxford University Press All Rights Reserved. Reprographic copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Act is allowed for internal use only, provided that a per-chapter fee of $40.25 plus $0.75 per page is paid to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. 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PRINTED IN THE UNITED STATES OF AMERICA In Controlled/Living Radical Polymerization: Progress in ATRP; Matyjaszewski, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 2009. Foreword The ACS Symposium Series was first published in 1974 to provide a mechanism for publishing symposia quickly in book form. The purpose of the series is to publish timely, comprehensive books developed from the ACS sponsored symposia based on current scientific research. Occasionally, books are developed from symposia sponsored by other organizations when the topic is of keen interest to the chemistry audience. Before agreeing to publish a book, the proposed table of contents is reviewed for appropriate and comprehensive coverage and for interest to the audience. Some papers may be excluded to better focus the book; others may be added to provide comprehensiveness. When appropriate, overview or introductory chapters are added. Drafts of chapters are peer-reviewed prior to final acceptance or rejection, and manuscripts are prepared in camera-ready format. As a rule, only original research papers and original review papers are included in the volumes. Verbatim reproductions of previous published papers are not accepted. ACS Books Department In Controlled/Living Radical Polymerization: Progress in ATRP; Matyjaszewski, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 2009. Preface This book and an accompanying volume are addressed to chemists who are interested in radical processes and especially in controlled/living radical polymerization. They summarize the most recent accomplishments in the field. The two volumes comprise the topical reviews and specialists' contributions presented at the American Chemical Society Symposium entitled Controlled/Living Radical Polymerization that was held in Philadelphia, Pennsylvania, August 17-21, 2008. The Philadelphia Meeting was a sequel to the previous ACS Symposia held in San Francisco, California, in 1997, in New Orleans, Louisiana, in 1999, in Boston, Massachusetts, in 2002 and in Washington, DC, in 2005. They were summarized in the ACS Symposium Series Volume 685, Controlled Radical Polymerization, Volume 768, Controlled/Living Radical Polymerization: Progress in ATRP, NMP and RAFT, Volume 854 Advances in Controlled/Living Radical Polymerization and Volume 944, Controlled/Living Radical Polymerization: From Synthesis to Materials. The Philadelphia Meeting was very successful with 90 lectures and 123 posters presented. This illustrates a continuous growth in comparison with the San Francisco Meeting (32 lectures and 35 posters), the New Orleans (50 lectures and 50 posters), the Boston Meeting (80 lectures and 79 posters) and with the Washington Meeting (77 lectures and 119 posters). The fifty chapters submitted for publication in the ACS Symposium series could not fit into one volume and therefore we decided to split them into two volumes. In order to balance the size of each volume we did not divide the chapters into volumes related to mechanisms and materials but rather to those related to atom transfer radical polymerization (ATRP) and to other controlled/living radical polymerization methods: reversible-addition fragmentation transfer (RAFT) and other degenerative transfer techniques, as well as stable free radical polymerizations (SFRP) including nitroxide mediated polymerization (NMP) and organometallic mediated radical polymerization (OMRP). The first chapter in this volume provides an overview of the current status of controlled/living radical polymerization (CRP) systems. The following three chapters discuss important issues relevant to all radical polymerization methods. The mechanistic and kinetic topics of ATRP are xi In Controlled/Living Radical Polymerization: Progress in ATRP; Matyjaszewski, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 2009. covered in eight chapters. The macromolecular architecture, various hybrids and bio-related polymers prepared by ATRP are discussed in the next six chapters, Characterization and materials aspects of ATRP polymers are covered in six chapters, whereas the last four chapters discuss industrial applications of ATRP. The next volume contains 10 chapters on mechanisms and kinetics of RAFT, other degenerative transfer processes, NMP and OMRP. They are followed by six chapters devoted to molecular architecture accessible by these techniques. Various materials aspects of the resulting polymers are covered in six chapters. The last two chapters present commercial application of polymers prepared by NMP and RAFT (or MADIX). Fifty chapters published in two volumes show that CRP has made a significant progress within the last decade. New systems have been discovered; substantial progress has been achieved in understanding the mechanism and kinetics of reactions involved in all CRP systems. Significant progress has been made towards a comprehensive relationship between molecular structure and macroscopic properties. Some commercial applications of CRP were announced at the Philadelphia Meeting and it is anticipated that many new products will be soon on the market. The financial support for the symposium from the following organizations is acknowledged: ACS Division of Polymer Chemistry, Inc., ACS Petroleum Research Foundation, Arkema, Bayer, Boston Scientific, Ciba, CIP, Dionex, DSM, Elsevier, Evonik, General Electric, JSR, Lion, Mitsui Chemicals, National Starch, PPG and Sumitomo. The excellent editorial assistance from Joyce Von Vreckin is gratefully acknowledged. Krzysztof Matyjaszewski Department of Chemistry Carnegie Mellon University 4400 Fifth Avenue Pittsburgh, PA 15213 In Controlled/Living Radical Polymeriza xtioini: Progress in ATRP; Matyjaszewski, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 2009. Chapter 1 Controlled Radical Polymerization: State of the Art in 2008 Krzysztof Matyjaszewski Center for Macromolecular Engineering, Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USA State of the art of Controlled Radical Polymerization (CRP) is presented. Stable free radical polymerization, atom transfer radical polymerization, and degenerate transfer processes, including reversible addition fragmentation transfer are discussed as the most successful CRP techniques. They provide access to new materials from many commercially available monomers under undemanding conditions. Better understanding of the structure-reactivity relationship for the various CRPs and a deeper insight into the mechanistic features can expand range of polymerizable monomers and polymer architectures. Development of a precise relationship between macromolecular structure, processing and final properties of materials will help to find new applications and accelerate commercialization of CRP products. Controlled/living radical polymerization (CRP) is among the most rapidly 1-3 developing areas of chemistry and polymer science. The research on CRP encompasses very fundamental mechanistic studies, synthetic polymer chemistry, many detailed physical chemistry studies to evaluate properties of prepared materials and also search for new applications to commercialize CRP products. During the last fifteen years an explosive increase has been observed in the number of publications on CRP, including a dramatic increase in the number of 4-7 patent applications and several symposia devoted partially, or entirely, to CRP. Figure 1 illustrates results of a recent SciFinder Scholar search using the following terms: controlled radical polymn or living radical polymn © 2009 American Chemical Society 3 In Controlled/Living Radical Polymerization: Progress in ATRP; Matyjaszewski, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 2009. 4 7000 SUM CRP SUM ATRP 6000 SUM SFRP SUM DT 5000 4000 3000 2000 1000 0 Year Figure 1. Results of SciFinder Search on various CRP systems as of November 15, 2008. Detail explanation of terms is provided in the text. (“CRP&LRP” in Figure 1), ATRP or atom transfer (radical) polymn (“ATRP only”, this search does not include terms such as metal mediated or metal catalyzed (living) radical polymerization), NMP or SFRP or nitroxide mediated polymn or stable free polymn (“SFRP&NMP”) and RAFT or reversible addition transfer or degenerative transfer or catalytic chain transfer (“RAFT&DT&CT”). The latter two terms were refined with a term radical polymn since they coincide with other common chemical names such as N- methylpyrrolidone or raft-associated proteins. In summary, since 1995 over 12,000 papers have been published on various CRP systems and more than half of that on ATRP. During the last four years, about 3 papers per day are published daily on ATRP. There is also another trend which can be deduced from Figure 1. Progressively more papers are published on specific techniques of CRP rather than referring to a generic CRP or LRP terms. All CRP methods rely on a dynamic equilibration between tiny amounts of propagating radicals and various types of dormant species. The essence of the process is a rapid reversible deactivation of growing radicals. Radicals always terminate and therefore CRP is never “living” in the pure sense of the living polymerization definition. Indeed, IUPAC recommends to avoid using term “living” for the radical polymerization and suggests to use the term “controlled reversible deactivation radical polymerization”. At the same rate of polymerization (whether it is a conventional process or CRP), the same radical concentration is present and essentially the same number In Controlled/Living Radical Polymerization: Progress in ATRP; Matyjaszewski, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 2009. Cumulative Number of Publications 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 5 (concentration) of chains terminate. However, in the conventional process, all -3 chains are terminated (e.g., 10 M), whereas in CRP, as a result of the large total -1 concentration of chains (e.g., 10 M of dormant and active/terminated), the -3 fraction of terminated chains (10 M) is much smaller (typically between 1 and 10%). The remaining chains are in the dormant state, capable of reactivation, functionalization, chain extension to form block copolymers, etc. Since the proportion of terminated chains in the final product is small, they often do not affect the physical properties of the targeted materials. Perhaps the most important difference between conventional and CRP processes is the approach to the steady state. In a conventional radical polymerization, steady state is achieved by balancing rate of initiation and termination. In order to prepare polymers with high molecular weights (Mn ~100,000, i.e. with DP~1000), propagation rate must be 1000 times higher than termination rate. Consequently initiation must be also 1000 times slower than propagation. This prevents synthesis of well defined polymers. In order to prepare polymers with controlled molecular weights (DPn=Δ[M]/[I]0) and narrow molecular weight distribution, the rate of initiation should be comparable to propagation. In systems controlled by the persistent radical effect, such as ATRP and SFRP, steady state is achieved by balancing rates of activation and deactivation rather than initiation and termination. For the first time in radical polymerization, this allows decoupling the rates of initiation and termination. Termination must still be thousands times slower than propagation, but initiation can now be as fast as propagation. The key to attaining control in CRP is the reversible deactivation of radicals (or intermittent activation of dormant species). Their interconversion should be fast, to provide a similar probability of growth for all chains and, consequently, form polymers with narrow molecular weight distribution. Fine tuning of the exchange rate offers a possibility to design molecular weight distribution and also influence polymer properties. Such polymers will preserve chain end functionalities, will be capable of cross-propagation and block copolymer formation. On the other hand, due to continuously occurring termination, polymers may loose functionality and still keep low polydispersity (especially if termination occurs at high conversion by disproportionation). Thus, a correlation between polydispersity and functionality in CRP is relatively weak. Figure 2 shows three approaches to the intermittent activation required for CRP. SFRP and ATRP employ the persistent radical effect. SFRP (exemplified by nitroxide mediated polymerization, NMP, or organometallic radical polymerization, OMRP) relies on spontaneous homolytic cleavage of covalent species. Deactivators are typically paramagnetic species but compounds with even number of electrons could be also used (e.g. thioketone mediated polymerization, TKMP). The homolytic cleavage can be catalyzed as in ATRP. Both these processes rely on persistent radical effect (PRE). The alternative approach utilizes a degenerative transfer (DT) mechanism with alkyl iodides, dithioesters/xanthates (reversible addition fragmentation transfer, RAFT or MADIX) or organometallic species as transfer agents. DT systems do not obey PRE kinetics but follow a conventional radical polymerization with a steady state established by balancing initiation and termination rates rather than activiation/deactivation. In Controlled/Living Radical Polymerization: Progress in ATRP; Matyjaszewski, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 2009.