Scott G. Gaynor

Bio: Scott G. Gaynor is an academic researcher from Carnegie Mellon University. The author has contributed to research in topics: Radical polymerization & Living free-radical polymerization. The author has an hindex of 41, co-authored 71 publications receiving 7932 citations. Previous affiliations of Scott G. Gaynor include University of North Carolina at Chapel Hill & Dow Chemical Company.

The Synthesis of Densely Grafted Copolymers by Atom Transfer Radical Polymerization

Abstract: Recent progress in the field of densely grafted, or “brush” (co)polymers has prompted a need to develop efficient methods to synthesize a wider variety of materials with the same basic architectural design. These brushlike macromolecules have been prepared previously using the macromonomer method.1-6 Macromonomers, usually prepared by anionic polymerization, were homopolymerized using conventional radical methods to maximize the number of branches possible from a linear backbone based on vinyl monomers. Upon fractionation of these materials using size exclusion chromatography, samples of narrow polydispersities were obtained which could then be cast on surfaces to form highly ordered thin films. To avoid the rigorous methods necessary for ionic polymerizations and sample fractionation, and to extend the variety of compositional content of these types of materials, atom transfer radical polymerization (ATRP) has been used to prepare similar macromolecular architectures. The approach described here involves grafting from a macroinitiator and can offer greater versatility in terms of both the length and the composition of the backbone and/or the side chains than previous methods which employed the synthesis of high molecular weight macromonomers and their subsequent polymerization by uncontrolled radical techniques; to obtain welldefined polymeric brushes required their fractionation, generally by SEC. To our knowledge, there are no known examples of using a macroinitaitor with a grafting site at each repeat unit to make well-defined polymeric brushes. Combinations of nitroxide-mediated, conventional free radical polymerization and ATRP to prepare graft copolymers from macroinitiators have been used previously.7,8 ATRP has also been combined with conventional radical polymerization to prepare amphiphilic graft copolymers9 and thermoplastic elastomers,10 as well. In each of these cases, however, the materials are loosely grafted, having been prepared from a macroinitiator which is a copolymer containing both initiation/ branch sites and spacing repeat units. Controlled radical polymerization and ATRP in particular afford access to materials of controlled molecular weight, predicted by the ratio of consumed monomer to initiation sites.11,12 This method also yields polymer segments of narrow molecular weight distributions13 in addition to being applicable to a host of vinyl monomers such as styrene, (meth)acrylates, acrylonitrile, etc.14 Thus, there are many possibilities which make its application to the area of brush (co)polymers appealing. Included here are preliminary synthetic data and AFM images which show that it is possible to prepare densely grafted copolymers using ATRP. Two approaches were used to prepare the macroinitiators, Scheme 1. The first involved conventional free radical homopolymerization of 2-(2-bromopropionyloxy)ethyl acrylate (BPEA)15 using AIBN in the presence of carbon tetrabromide to attenuate the molecular weight (Mn ) 27 300, Mw/Mn ) 2.3). By use of AIBN as an intiator to prepare the ATRP macroinitiator, a polymer with a broad molecular weight distribution was obtained. Such a macroinitiator would consequently result in the formation of brush polymers with broad molecular weight distributions, no matter how well controlled the polymerization of the side chains. Thus, the preparation of a well-defined macroinitiator was undertaken. In the second approach, trimethylsilylprotected 2-hydroxyethyl methacrylate (HEMA-TMS)16 was polymerized via ATRP and subsequently esterified with 2-bromoisobutyryl bromide (BriBuBr) in the presence of a catalytic amount of tetrabutylammonium fluoride (TBAF) to yield a different macroinitiator, poly(2-(2-bromoisobutyryloxy)ethyl methacrylate) (pBIEM)16 with controlled molecular weight and low polydispersity (Mn ) 55 500, Mw/Mn ) 1.3), Table 1. It should be noted that the macroinitiator prepared using ATRP was composed of a stiffer methacrylate structure and with a 2-bromoisobutyryl initiation site while the free radically prepared pBPEA contained an acrylate backbone and 2-bromopropionyl initiation sites. However, both types of initiating species have been shown to initiate styrene polymerization well.14 Both polymers were then used as macroinitiators for ATRP of styrene (S) and butyl acrylate (BA). Side chains with a degree of polymerization of about 40 from a macroinitiator of pBIEM with a Mn of approximately 50 000 (which contained about 200 initiation sites per Scheme 1 9413 Macromolecules 1998, 31, 9413-9415

Synthesis of branched and hyperbranched polystyrenes

Abstract: The formation of hyperbranched polymers by a one-pot, atom transfer radical polymerization is described using p-(chloromethyl)styrene (CMS) in the presence of Cu(I) and 2,2'-bipyridyl. The synthesis of branched polystyrene by copolymerization of CMS with styrene is also discussed

Improved processes based on atom (or group) transfer radical polymerization and novel (co)polymers having useful structures and properties

Abstract: Improved processes for atom (or group) transfer radical polymerization (ATRP) and novel polymers have been developed and are described. In certain embodiments, novel copolymers comprising a least one polymeric branch or polymeric block with a predominantly alternating monomer sequence are described. Novel copolymers comprising a least one polymeric branch or polymeric block with a gradient monomer structure are described. Additionally, novel copolymers comprising a least one polymeric branch or polymeric block with a predominantly periodic monomer sequence are also described. Novel copolymers having a water soluble backbone and at least two hydrophobic polymeric branches grafted to the water soluble backbone are also described.

Optimization of atom transfer radical polymerization using Cu(I)/ tris(2-(dimethylamino)ethyl)amine as a catalyst

Abstract: The optimization of the synthesis of homopolymers from n-butyl acrylate (BA), styrene (Sty), and methyl methacrylate (MMA), using copper-based atom transfer radical polymerization (ATRP) with tris(2-dimethylaminoethyl)amine (Me6-TREN) as a ligand is reported. Catalyst concentration (copper bromide complexed with 1 equiv of Me6-TREN) as low as 1% relative to initiator (50 ppm in the reaction mixture) was sufficient to successfully prepare well-defined poly(n-butyl acrylate) in bulk. With 50% catalyst to initiator, styrene was polymerized in bulk. The deactivator species had poor solubility in nonpolar solvents. Finally, the polymerization of methyl methacrylate with CuBr/Me6-TREN required the use of a high concentration of catalyst and the addition of Cu(II)Cl2 at the beginning of the reaction; the resulting polymers were of higher molecular weight than predicted by theory and had relatively broad molecular weight distributions.

Preparation of novel homo- and copolymers using atom transfer radical polymerization

Abstract: The present invention is directed to a process of atom (or group) transfer radical polymerization for the synthesis of novel homopolymer or a block or graft copolymer, optionally containing at least one polar group, with well defined molecular architecture and narrow polydispersity index, in the presence of an initiating system comprising (i) an initiator having a radically transferrable atom or group, (ii) a transition metal compound, and (iii) a ligand; the present invention is also directed to the synthesis of a macromolecule having at least two halogen groups which can be used as a macroinitiator component (i) to subsequently form a block or graft copolymer by an atom or group transfer radical polymerization process; the present invention is also directed to a process of atom or group transfer radical polymerization for the synthesis of a branched or hyperbranched polymer; in addition, the present invention is directed to a process of atom or group transfer radical polymerization for the synthesis of a macroinitiator which can subsequently be used to produce a block or graft copolymer.

Living free-radical polymerization by reversible addition - Fragmentation chain transfer: The RAFT process

Abstract: mechanism involves Reversible Addition-Fragmentation chain Transfer, and we have designated the process the RAFT polymerization. What distinguishes RAFT polymerization from all other methods of controlled/living free-radical polymerization is that it can be used with a wide range of monomers and reaction conditions and in each case it provides controlled molecular weight polymers with very narrow polydispersities (usually <1.2; sometimes <1.1). Living polymerization processes offer many benefits. These include the ability to control molecular weight and polydispersity and to prepare block copolymers and other polymers of complex architecturesmaterials which are not readily synthesized using other methodologies. Therefore, one can understand the current drive to develop a truly effective process which would combine the virtues of living polymerization with versatility and convenience of free-radical polymerization.2-4 However, existing processes described under the banner “living free-radical polymerization” suffer from a number of disadvantages. In particular, they may be applicable to only a limited range of monomers, require reagents that are expensive or difficult to remove, require special polymerization conditions (e.g. high reaction temperatures), and/or show sensitivity to acid or protic monomers. These factors have provided the impetus to search for new and better methods. There are three principal mechanisms that have been put forward to achieve living free-radical polymerization.2,5 The first is polymerization with reversible termination by coupling. Currently, the best example in this class is alkoxyamine-initiated or nitroxidemediated polymerization as first described by Rizzardo et al.6,7 and recently exploited by a number of groups in syntheses of narrow polydispersity polystyrene and related materials.4,8 The second mechanism is radical polymerization with reversible termination by ligand transfer to a metal complex (usually abbreviated as ATRP).9,10 This method has been successfully applied to the polymerization of various acrylic and styrenic monomers. The third mechanism for achieving living character is free-radical polymerization with reversible chain transfer (also termed degenerative chain transfer2). A simplified mechanism for this process is shown in