Publications, controlled radical

Figure 1 Publication rate of journal papers on radical polymerization and on living, controlled, or mediated radical polymerization for the period 1975-2008 based on SciFinder search (as of March 2010). It does not distinguish forms of controlled radical polymerization. It includes most papers on ATRP, RAFT, and NMP and would also include conventional, non-RDRP, controlled radical polymerizations. It would not include papers, which do not mention the terms living , controlled , or mediated .

Due to the advancements in polymer synthesis there are a number of controlled polymerization techniques available today and, therefore, the number of publications on tailor-made block copolymers has increased especially during the last decade. Besides the living anionic and, to a less extent, also cationic polymerizations various techniques of controlled radical polymerization have become popular. Also some works have been carried out establishing control in polycondensation and even coordination polymerization. Some of the different techniques have been also combined in block copolymer synthesis. Thus an increasing number of monomers have become accessible for the synthesis of tailor-made block copolymers of various chain architectures. 

Figure 1.1 Publication rate of journal papers on radical polymerization and on living, controlled or mediated radical polymerization for period 1975-2002 based on SeiFinder search (as of Mar 2005).

In a recent publication, Schafer and coworkers point out the utility of the electrode as a reagent which is effective in promoting bond formation between functional groups of the same reactivity or polarity [1]. They accurately note that reduction at a cathode, or oxidation at an anode, renders electron-poor sites rich, and electron-rich sites poor. For example, reduction of an a, -un-saturated ketone leads to a radical anion where the )g-carbon possesses nucleophilic rather than electrophilic character. Similarly, oxidation of an enol ether affords a radical cation wherein the jS-carbon displays electrophilic, rather than its usual nucleophilic behavior [2]. This reactivity-profile reversal clearly provides many opportunities for the formation of new bonds between sites formally possessing the same polarity, provided only one of the two groups is reduced or oxidized. Electrochemistry provides an ideal solution to the issue of selectivity, given that a controlled potential reduction or oxidation is readily achieved using an inexpensive potentiostat. 

Identification of free radicals. The existence of free radicals in carbon has been shown by electron spin resonance (e.s.r.) techniques by a large number of scientists, notably by Bennett, Ingram, and Tapley (95), Etienne and Uebersfeld (96a), Uebersfeld etal. (966),andMrozowski and Andrew (97). It is not possible to summarize here all publications dealing with e.s.r. measurements on carbon. Attempts at chemical identification by combination with free radicals were made. The reaction with benzidine blue was used by Garten and Sutherland (98). The reagent is obtained by controlled oxidation of benzidine. It is very unstable, however, and other methods proved to be better suited. 

Leismann et al.[182] have recognized this problem in their publication of 1984, in which they describe a thorough and detailed investigation of the kinetics of formation and deactivation of exciplexes of. S) benzene or toluene and 1,3-diox-ole, 2,2-dimethyl-l,3-dioxole, and 2,2,4-trimethyl-l,3-dioxole. The evolution in time of monomer and exciplex fluorescence after excitation using a nanosecond flash lamp was analyzed, and again it was concluded that the formation of exciplexes is diffusion controlled their decay proceeds mainly (>90%) via radiationless routes. The polar solvent acetonitrile enhances radiationless deactivation, possibly by promoting radical ion formation. Because decay of benzene fluorescence is essentially monoexponential, dissociation of the exciplex into Si benzene and dioxole is negligible. 

In this publication the author describes the phenomenon that most times the thermodynamically less stable product (see 29) of the two possible rings (e.g. 5-exo and 6-endo) is formed. Today looking at the 5-exo cyclization it is known that, although the generated primary radical is less stable than a secondary one, stereoelectronic effects favor reaction to the kinetically controlled product. According to MO-calculations, for a successful cyclization, an angle of 70° of the incoming radical to the plane of the alkene-/alkyne-bond is necessary.11... 

Mrs Besant s conversion attracted enormous publicity. She was by far H.P.B. s most spectacular recruit, the more so since for many years she had been publicly associated with Charles Bradlaugh s National Secular Society, which preached agnosticism and birth control. It must be emphasized that Mrs Besant was a very public figure. Burrows was hardly known outside radical circles. 

Fig-3. The number of literature publications per year though August/2001 in the general field of controlled/ living radical polymerization (CRP) and those related to specifically to CRP copolymers... 

Some of the more recent publications about trace elements, trace minerals, or ultratrace elements or minerals, also described as micronutrients, include Micronutrients in Health and Disease Prevention, edited by Adrianne Bendich and C.E. Butterworth Trace Elements in Nutrition of Children, edited by Ranjit Kumar Chandra and Trace Elements, Micronutrients and Free Radicals, edited by Ivor E. Dreosti. The latter reference raises the important question of the undesirable health effects of the chemical agents called free radicals, and their control or eradication by such vitamins as E, C, and beta-carotene. There is a history of the health effects of trace elements going back to Henry A. Schroeder, who in the early 1970s wrote Trace Elements and Man Some Positive and Negative Aspects and also The Poisons Around Us Toxic Metals in Food, Air, and Water. Even further back there was Karl... 

In a recent publication Okamura et ah (12) describe similar results in a different system. It is believed that the unusual rate increase observed in these various systems which are chemically so different is caused by the physical state of the reaction medium at temperatures a few degrees above Tg. The high viscosity of this gel-like medium presumably favors chain propagation in its competition with termination. This effect, which is kinetically similar to the "gel-effect in free radical polymerizations, can only arise if the termination step (charge recombination) becomes diffusion controlled. The latter process would arise if both ionic species involved in the reaction were of macromolecular size. This is undoubtedly true for the growing chain, but the mobility of the counter ion should only be significantly reduced in such a medium if it is of a polymolecular structure, involving perhaps a voluminous solvation cluster. 

The contribution of the transition state position is usually not discussed as a main factor in controlling the stereochemistry of a radical reaction. However, its importance was recently raised in several publications. Moreover, the reactivity-selectivity principle proposed by Giese to rationalize the influence of the radical trap on the stereochemical outcome of 2-substituted cyclopentyl radicals [39] could also be considered as an influence of the transition state position (Scheme 15) in early transition states (reactive olefins such as fumarodinitrile) the reagent is far away from the radical center and the face discrimination is low. With less reactive olefins such as styrene, a later transition state is occurring and the product stability starts to influence the stereoehemical outcome. Therefore, the most stable trans di-substituted cyclopentanes are produced with a higher degree of stereocontrol. 

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 pol5mierizations (SFRP) including nitroxide mediated polymerization (NMP) and organometallic mediated radical polymerization (OMRP). 

During the last fifteen years an explosive increase has been observed in the number of publications on CRP, including a dramatic increase in the nrrmber of patent applications and several symposia devoted partially, or entirely, to CRP." " Figure 1 illustrates resrrlts of a recent SciFinder Scholar search using the following terms controlled radicalpolymn or living radical polymn... 

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