Living polymerizations styrene

According to the second method of carbonate block copolymer synthesis, sequential monomer polymerization is proceeded with transformation of the active center. The block copolymers are prepared in three steps. First, the polymerization of one monomer is carried out. After complete conversion of the first monomer the transformation of active centers is performed, and the initiation of the polymerization of the second monomer is proceeded. For example, this approach was applied for obtaining poly(styrene-l7-neopentyl carbonate).After completion of the styrene living polymerization, carbanionic centers were transformed into alkoxide ones via reaction with EO and then the ROP of neopentyl carbonate polymerization was performed. In the case of block copolymers of methyl methacrylate with neopentyl carbonate living PMMA, prepared according to GTP, was used as a macroinitiator for DTC polymerization. A silyl keteneacetal active center was transformed to an alkoxide one. Depending on the functionality of the macroinitiator (A) used for cyclic carbonate polymerization, two types of block copolymers can be obtained A-B or B-A-B. 

Anionic polymerization, if carried out properly, can be truly a living polymerization (160). Addition of a second monomer to polystyryl anion results in the formation of a block polymer with no detectable free PS. This technique is of considerable importance in the commercial preparation of styrene—butadiene block copolymers, which are used either alone or blended with PS as thermoplastics. 

Indeed, cumyl carbocations are known to be effective initiators of IB polymerization, while the p-substituted benzyl cation is expected to react effectively with IB (p-methylstyrene and IB form a nearly ideal copolymerization system ). Severe disparity between the reactivities of the vinyl and cumyl ether groups of the inimer would result in either linear polymers or branched polymers with much lower MW than predicted for an in/mcr-mediated living polymerization. Styrene was subsequently blocked from the tert-chloride chain ends of high-MW DIB, activated by excess TiCU (Scheme 7.2). 

The initiation of the cyclic siloxane monomers with a living polymeric lithium species such as polystyryl lithium leads to block copolymers, as outlined in Scheme 2, were also of interest. These styrenic-siloxane block copolymers were prepared with siloxane contents from 10 to 50 weight percent. 

Block copolymers comprised of PS and polymethacrylate blocks with aliphatic stearyl or decyl side groups were prepared by the sequential addition of monomers, as shown in Scheme 1. Styrene was polymerized in THF at - 78 °C using s-BuLi as the initiator [11,12]. The nucleophilicity of the living polystyryllithium was reduced by reaction with DPE (in order to avoid reactions with the carbonyl groups), followed by the polymerization of the methacrylate monomer. Stearyl methacrylate, SMA is associated with... 

Reaction of the bis-chelate complex 149 and various bis(arylalkyl)barium complexes generates heteroleptic barium complexes with one chelate and one reactive arylalkyl ligand 164. The homoleptic and heteroleptic barium complexes both induce living polymerization of styrene to atactic polystyrene in cyclohexane solution. The fact that no stereocontrol is observed during polymerization despite the presence of the chiral carbanionic ligands is... 

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... 

Well developed is the anionic polymerization for the preparation of olefin/di-olefin - block copolymers using the techniques of living polymerization (see Sect. 3.2.1.2). One route makes use of the different reactivities of the two monomers in anionic polymerization with butyllithium as initiator. Thus, when butyl-lithium is added to a mixture of butadiene and styrene, the butadiene is first polymerized almost completely. After its consumption stryrene adds on to the living chain ends, which can be recognized by a color change from almost colorless to yellow to brown (depending on the initiator concentration). Thus, after the styrene has been used up and the chains are finally terminated, one obtains a two-block copolymer of butadiene and styrene ... 

The homopolymerization of MMA with the soluble catalyst was found to exhibit the characteristic of living polymerization at the initial stage of polymerization ( 5 h) giving poly(MMA) with a narrow molecular weight distribution (Mw/IVln = 1.2, Mn = 2400), at 25 °C. To elucidate the mechanism of the MMA polymerization, the copolymerization of MMA with styrene was carried out. The observed reactivity ratios (rs = 0.5, rMMA = 0.4) indicated that the living polymerization of MMA occurred via a radical intermediate. 

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