Radical cations ring opening

Cyclopropane Fragmentations. Cyciopropanes themselves can also be cleaved. A variety of tri- and tetra-substituted rings lead to radical cations in the presence of irradiated acceptors like chloranil (119,120). With the bicyclic radical cation 11, radical cationic ring opening is followed by dehydrogenation to generate oxidized product, eq. 42 (120) ... 

Becer CR, Paulus RM, Hoppener S et al. (2008) Synthesis of poly(2-ethyl-2-oxazoline)-h-poly(styrene) copolymers via a dual initiator route combining cationic ring opening polymerization and atom transfer radical polymerization. Macromolecules 41 5210-5215... 

Poly(s-caprolactone) Poly(e-caprolactone) is a semicrystalline polymer synthesized by anionic, cationic, free-radical, or ring-opening polymerization [94]. It is available in a range of molecular weights and degrades by bulk hydrolysis autocatalyzed by the carboxylic acid end groups. The presence of enzymes such as protease, amylase, and pancreatic lipase accelerates polymer degradation [95], The various methods of preparation of poly(e-caprolactone) nanoparticles include emulsion polymerization, interfacial deposition, emulsion-solvent evaporation, desolvation, and dialysis. These methods and various applications are extensively reviewed [94],... 

Nevertheless, polymerizations other than the anionic ones have also been carried out using enolates as ligands of transition metal cations. Metal acetalyacetonates are indeed organometallic compounds that directly contributed to the control of radical polymerization, ring-opening polymerization and coordination polymerization of specific monomers, as discussed hereafter. 

Transformation of cationic ring-opening polymerization of THF into the copper-catalyzed radical polymerizations of styrene, acrylates, and methacrylates leads to various block copolymers (B-82 to B-88).387,388 Diblock (B-82 to B-84) and ABC-type triblock (B-85) copolymers were prepared via the... 

B-90 and B-91, respectively.390 Another route coupled with cationic ring-opening polymerizations is accomplished for polymer B-92 with the use of a hydroxyl-functionalized initiator with a C—Br terminal, where the OH group initiates the cationic polymerizations of 1,3-dioxepane in the presence of triflic acid.329 Polyethylene oxide)-based block copolymers B-93 are obtained by living anionic polymerization of ethylene oxide and the subsequent transformation of the hydroxyl terminal into a reactive C—Br terminal with 2-bromopropionyl bromide, followed by the copper-catalyzed radical polymerization of styrene.391... 

The oxidation of cyclopropyl trimethylsilyl ethers by copper(II) tetrafluoroborate probably proceeds via cation radicals which ring open and, in suitably substituted examples, cyclize. The main cyclopentyl ketone products were formed as mixtures of stereoisomers and were accompanied by many side products. ... 

However, in contrast to the free-radical process, ring opening in the cationic intermediate will proceed mainly by the disrotatory type [39]. This should lead (Scheme 9b) to the predominant formation of the mesodiad at the chain end. 

In free radical copolymerization interconversion of the growing species proceeds exclusively by crosspropagation. In cationic ring-opening polymerization interconversion of the growing species may occur by two routes i.e., the incoming monomer may attack either the endo- or the exocyclic carbon atom ... 

A major difference between cationic and free radical curing is the degree of shrinkage caused by the polymerization. Cationic ring-opening polymerization... 

Conventional free radical, cationic ControlledA.iving radical and ring opening polymerization and cationic polymetizatlon... 

Figure 1. Polymerization of a methacrylate-substituted spiro orthoester (1) by free radical addition to the methacrylate group followed by cationic ring opening.

Yoshida and Sugita [72, 73] have described the synthesis of polytetrahydrofuran (PTH F) possessing a nitroxy radical by terminating the Hving cationic ring-opening polymerization (CROP) of THF with sodium 4-oxy TEMPO. The polymer obtained in this way acted as a counter-radical in the polymerization of styrene, in the presence of a free radical initiator, to yield PSt-f)-PTHF (Scheme 11.16). 

Figure 27.3 Representative crosslinkers used for star polymer synthesis by the nodulus approach. The letters refer to the polymerization method used A, anionic C, cationic R, radical ROMP, ring-opening metathesis polymerization.

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