Roshan T. A. Mayadunne
Bio: Roshan T. A. Mayadunne is an academic researcher from Commonwealth Scientific and Industrial Research Organisation. The author has contributed to research in topics: Radical polymerization & Chain transfer. The author has an hindex of 25, co-authored 40 publications receiving 9065 citations. Previous affiliations of Roshan T. A. Mayadunne include DuPont & Monash University, Clayton campus.
TL;DR: The authors proposed a reversible additive-fragmentation chain transfer (RAFT) method for living free-radical polymerization, which 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.
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
TL;DR: In this article, free radical polymerization with reversible addition-fragmentation chain transfer (RAFT polymerization) is discussed with a view to answering the following questions: (a) How living is RAFT polymerization? (b) What controls the activity of thiocarbonylthio compounds in RAFT polymers, and (c) How do rates of polymerization differ from those of conventional radical polymerisation? (d) Can RAFT agents be used in emulsion polymerization; and (e) Retardation, observed when high concentra-
Abstract: Free radical polymerization with reversible addition-fragmentation chain transfer (RAFT polymerization) is discussed with a view to answering the following questions: (a) How living is RAFT polymerization? (b) What controls the activity of thiocarbonylthio compounds in RAFT polymeriza- tion? (c) How do rates of polymerization differ from those of conventional radical polymerization? (d) Can RAFT agents be used in emulsion polymerization? Retardation, observed when high concentra- tions of certain RAFT agents are used and in the early stages of emulsion polymerization, and how to overcome it by appropriate choice of reaction conditions, are considered in detail. Examples of the use of thiocarbonylthio RAFT agents in emulsion and miniemulsion polymerization are provided. # 2000 Society of Chemical Industry
TL;DR: In this paper, two series of chain transfer agents (SC(Z)S−CH2Ph and SC(ZS−C(Me)2CN) were used for styrene polymerization.
Abstract: Free-radical polymerization in the presence of suitable addition−fragmentation chain transfer agents [SC(Z)S−R] (RAFT agents) possess the characteristics of a living polymerization (i.e., polymer products can be reactivated for chain extension and/or block synthesis, molecular weights are predetermined by RAFT agent concentration and conversion, narrow polydispersities are possible). Styrene polymerizations (110 °C, thermal initiation) were performed for two series of RAFT agents [SC(Z)S−CH2Ph and SC(Z)S−C(Me)2CN]. The chain transfer coefficients decrease in the series where Z is Ph > SCH2Ph ∼ SMe ∼ Me ∼ N-pyrrolo ≫ OC6F5 > N-lactam > OC6H5 > O(alkyl) ≫ N(alkyl)2 (only the first five in this series provide narrow polydispersity polystyrene ( trithiocarbonates ∼ dithioalkanoates > dithiocarbonates (xanthates) > dithiocarbamates. However, electron-withdrawing substituents on Z can enhance the...
TL;DR: In this article, the nonbonded electron pair of the nitrogen included as part of an aromatic system was used as an additive component for living radical polymerization with reversible addition−fragmentation chain transfer.
Abstract: Living radical polymerization with reversible addition−fragmentation chain transfer (RAFT polymerization) can be achieved with the use of dithiocarbamate derivatives that have the nonbonded electron pair of the nitrogen included as part of an aromatic system. These compounds have been shown to be highly effective in RAFT polymerization of styrene and (meth)acrylate esters to produce polymers of predetermined molecular weight and narrow polydispersity (usually <1.2). By contrast, simple N,N-dialkyl dithiocarbamates (those compounds previously described as “photoiniferters”) are ineffective as RAFT agents. The reasons for the different behavior are discussed.
TL;DR: In this article, a novel synthesis of functional dithioesters, dithiocarbamates, xanthates and trithiocalarbonates is described, which is compatible with a wide range of functionalities (e.g. carboxy, hydroxy and nitrile).
TL;DR: This review summarizes the main advances published over the last 15 years, outlining the synthesis, biodegradability and biomedical applications ofBiodegradable synthetic and natural polymers.
TL;DR: In this article, a review of recent mechanistic developments in the field of controlled/living radical polymerization (CRP) is presented, with particular emphasis on structure-reactivity correlations and "rules" for catalyst selection in ATRP, for chain transfer agent selection in reversible addition-fragmentation chain transfer (RAFT) polymerization, and for the selection of an appropriate mediating agent in stable free radical polymerisation (SFRP), including organic and transition metal persistent radicals.
TL;DR: In this article, a review summarizes progress in nanocellulose preparation with a particular focus on microfibrillated cellulose and also discusses recent developments in bio-nanocomposite fabrication based on nanocells.
Abstract: Due to their abundance, high strength and stiffness, low weight and biodegradability, nano-scale cellulose fiber materials (e.g., microfibrillated cellulose and bacterial cellulose) serve as promising candidates for bio-nanocomposite production. Such new high-value materials are the subject of continuing research and are commercially interesting in terms of new products from the pulp and paper industry and the agricultural sector. Cellulose nanofibers can be extracted from various plant sources and, although the mechanical separation of plant fibers into smaller elementary constituents has typically required high energy input, chemical and/or enzymatic fiber pre-treatments have been developed to overcome this problem. A challenge associated with using nanocellulose in composites is the lack of compatibility with hydrophobic polymers and various chemical modification methods have been explored in order to address this hurdle. This review summarizes progress in nanocellulose preparation with a particular focus on microfibrillated cellulose and also discusses recent developments in bio-nanocomposite fabrication based on nanocellulose.