Substituents living polymerization

Various block copolymers have been synthesized by cationic living polymerization [Kennedy and Ivan, 1992 Kennedy, 1999 Kennedy and Marechal, 1982 Puskas et al., 2001 Sawamoto, 1991, 1996]. AB and ABA block copolymers, where A and B are different vinyl ethers, have been synthesized using HI with either I2 or Znl2. Sequencing is not a problem unless one of the vinyl ethers has a substituent that makes its reactivity quite different. Styrene-methyl vinyl ether block copolymer synthesis requires a specific sequencing and manipulation of the reaction conditions because styrene is less reactive than methyl vinyl ether (MVE) [Ohmura et al., 1994]. Both monomers are polymerized by HCl/SnCLj in the presence of (n-CrikjtiNCI in methylene chloride, but different temperatures are needed. The... 

We possess more information on systems containing polar monomers. Organolithium and organomagnesium compounds initiate the polymerization of a number of monomers with an electron-withdrawing substituent. These polymerizations are rarely of the living type. The initiator usually reacts not only with the double bond of the monomer, but also with the polar substituent (both on the monomer and the polymer) yielding inactive products. 

In contrast to p-alkylstyrenes, this chloro derivative has reduced reactivity due to the electron-withdrawing p-substituent. Despite this, the initiating systems effective for styrene and p-methylstyrene can also be used for the controlled/living polymerization of p-chlorostyrene, such as TMP-CI/TiCU (with added DMA) [168-170] and PhEtCI/SnCL (with added hBu4NCI) [225]. Interestingly, the latter system permits the controlled/ living process to proceed at room temperature. 

CpTiCl2X (X = NMe2, OEt) have been found to initiate the living polymerization of carbodiimides with reduced activity. The reactivity is largely determined by the steric demands of the monomer. Larger substituents inhibit or prevent the polymerization reaction. The mechanism for this polymerization has been shown to involve initiation by insertion of the monomer into the Ti-X bond to form an intermediate amidinate complex (Scheme 197).497... 

In the present communication some new results in the study of these highly living polymerizations are reported In the first part, the Influence of the presence of carbon-substituents on the "reactivity" of the azlridine monomers will be discussed In the second part, the possibility of sequential polymerization to form block copolymers is described Finally some preliminary results on the copolymerization of these azlrldines with other heterocyclic monomers will be presented ... 

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