Cyclic controlled radical polymerization

Aliphatic disulfides are not thought to be effective as initiators in this context. However, Endo et a . K have described the use of the cyclic 1,2-disulfides 11 and 12 as initiators in a controlled radical polymerization. Polymerization of S at 120 °C gave a linear increase in molecular weight with conversion and the PS formed was used as a macroinitiator to form PS-6/oet-PMMA. The precise mechanism of the process has not been elucidated. 

Fig. 4 Reaction scheme for synthesizing cyclic polystyrene using controlled radical polymerization...

Benedicte Lepoittevin has been an Assistant Professor in Pol)nner Chemistry at the University of Paris-sud (France) since 2002. Prior to this she spent one year at the University of Bordeaux as postdoctoral fellow where she studied the synthesis of star and dendritic polymers using atom transfer radical polynierization. In 2000 she defended a Ph.D thesis at the University of Paris VI on the synthesis cyclic polymers by controlled radical and anionic polymerizations under the supervision of Prof. Patrick Hemery. Her scientific interests include PET surface modification, controlled radical polymerization and polymer synthesis using carbohydrates and essential oils derivatives in order to obtain polymer materials with antibacterial properties. 

Copper-mediated controlled radical polymerization, which is known as atom transfer radical polymerization (ATRP), is also a useful tool to control ROP of several cyclic monomers. The copper-mediated ROP of 2-methylene-4-phenyl-... 

Another current trend in controlled radical ROP is the utilization of reversible addition-fragmentation chain transfer (RAFT), which has been widely exploited as a powerful tool to control radical polymerizations of various vinyl monomers. The radical ROPs of 5,6-benzo-2-methylene-l,3-dioxepane, a seven-membered cyclic ketene acetal, and those of 9,10-dihydroanthracene derivatives bearing exo-methylene and cyclopropane moieties have been reported. 

Ionic ring-opening polymerizations of cyclic ether, acetal, ester and siloxane monomers give polymers with controlled molecular weights and well-defined terminal structure that are thus suitable for the synthesis of block copolymers when coupled with controlled radical polymerizations. 

Extending controlled radical polymerization methods to the block copolymerization of cyclic vinyl ethers using commercially available monomers is of... 

Other catalytic reactions involving a transition-metal allenylidene complex, as catalyst precursor or intermediate, include (1) the dehydrogenative dimerization of tributyltin hydride [116], (2) the controlled atom-transfer radical polymerization of vinyl monomers [144], (3) the selective transetherification of linear and cyclic vinyl ethers under non acidic conditions [353], (4) the cycloisomerization of (V2V-dia-llyltosylamide into 3-methyl-4-methylene-(V-tosylpyrrolidine [354, 355], and (5) the reduction of protons from HBF4 into dihydrogen [238]. 

Yuan, J.Y. and Pan, C.Y. (2001) The effects of monomer structure of cyclic ketene acetals on the behavior of controlled radical ring-opening polymerization. Chiru J. Polym. Sci.,... 

More recently, the CRP method has been improved signi cantly with the discovery of very ef cient acyclic nitroxides such as the stable acyclic phosphonylated nitroxide radical SGI (Fig. 11.15), which can control the polymerization of much broader range of monomers than cyclic nitroxides like TEMPO. The radical SGI has a larger equilibrium constant than most other nitroxides, including TEMPO, and is therefore suitable for polymerization temperatures as low as 90°C (SGI K = 1.9x10" mol dm at 125°C TEMPO K = 2.1x10"" moldm- at 125°C). 

As a unique method of controlled/living radical polymerization, ATRP has had a tremendous impact on the synthesis of macromolecules with well-defined compositions, architectures, and functionalities, including star- and comb-like polymers as well as branched, hyperbranched, dendritic, network, cyclic type structures and so forth. 

The synthesis of a siloxane-styrene copolymer by ring-opening polymerization of a cyclic siloxane in the presence of a styrene radical that is generated by nitroxide and bromine was recently reported. With the advancement of controlled free-radical polymerization (CFRP), block copolymers of varying architecture can be prepared. Pollack et al." have synthesized a styrene-siloxane diblock copolymer (Scheme 5) using the hydrolyzed (R=OH) form 9 of Hawkers initiator 8 which was bthiated... 

In spite of the spectacular progress in the last few decades, mostly related to the discovery of the living polymerizations of vinyl and cyclic monomers (including ring-opening metathesis) and then controlled radical and cationic polymerizations of vinyl monomers, the precision of the PCR is not yet achieved in other fields. 

A drastic change of nitroxide stmcture was witnessed with the use of the commercially available DBNO (27). In particular, Moad and Rizzardo showed that the dissociation rate constant of a DBNO-based alkoxyamine was higher than any similar alkoxyamines based on cyclic nitroxides bearing tetra-methyl alkyl groups on the vicinity of the aminoxyl function. The first experimental studies were performed by the group of Catala where it was shown that the polymerization of styrene and substituted styrene monomers could be carried out at 90 ° C with all the criteria of control/livingness. However, the polymerization rate was independent of the alkoxyamine concentration and remained governed by the production of thermal radicals in the medium. The tert-butyl-tert-amyl nitroxide 28 was tested by Moad et to control the polymerization of MMA and appeared to be inefficient. 

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