Halides initiators

In a series of seven recent publications, these Italian authors21-27 reported isobutylene homo- and copolymerizations using alkylaluminum coinitiators in the presence of halogen, interhalogen compounds and alkyl halide initiators. The following conclusions21 are reported in the first paper. 

In previous papers1,2 we described reactivity studies of cationic isobutylene polymerization using r-butyl halide initiators, alkylaluminum coinitiators and methyl halide solvents. The effects of these reagents as well as temperature on the overall rate of polymerization and polyisobutylene (PIB) yield were studied and reactivity orders were established. These results were explained by a modified initiation mechanism based on an earlier model proposed by Kennedy and co-workers3,4. This paper concerns the effects of f-butyl halide, alkylaluminums and methyl halide, as well as temperature and isobutylene concentration on PIB molecular weights. 

Indoles, pyrroles, and carbazoles themselves are suitable substrates for palladium-catalyzed coupling with aryl halides. Initially, these reactions occurred readily with electron-poor aryl halides in the presence of palladium and DPPF, but reactions of unactivated aryl bromides were long, even at 120 °C. Complexes of sterically hindered alkylmonophosphines have been shown to be more active catalysts (Equation (25)). 8 102 103 In the presence of these more active catalysts, reactions of electron-poor or electron-rich aryl bromides and electron-poor or electron-neutral aryl chlorides occurred at 60-120 °C. Reactions catalyzed by complexes of most of the /-butylphosphines generated a mixture of 1- and 3-substituted indoles. In addition, 2- and 7-substituted indoles reacted with unhindered aryl halides at both the N1 and C3 positions. The 2-naphthyl di-t-butylphosphinobenzene ligand in Equation (25), however, generated a catalyst that formed predominantly the product from A-arylation in these cases. 

Scheme 5 Examples of vinyl monomers (a) and alkyl halide initiators (b) that are used in copper-mediated ATRP...

ATRP, other factors, such as solvent and temperature, must also be taken into consideration. Typical monomers and alkyl halide initiators that are used in ATRP are shown in Scheme 5 [47], The copper complex is perhaps the most important component of this catalytic system because it regulates the dynamic equilibrium between dormant and active species. In this article, structural and mechanistic aspects of copper-catalyzed ATRP are discussed. 

For the simplest case when the initial concentration of the activator [Cu X/L]0 =C0 is equal to the initial concentration of the alkyl halide initiator [RX]0 =/0, the functionF(CunX/L) can be calculated as ... 

ARGET ATRP has been successfully applied for polymerization of methyl methacrylate, ft-butyl acrylate and styrene in the presence of Sn(EH)2 (10 mol% vs. alkyl halide initiator or 0.07 mol% vs. monomer) [164,165]. For all monomers, polymerizations were well controlled using between 10 and 50 ppm of copper complexes with highly active TPMA and Me6TREN ligands. ARGET ATRP has also been utilized in the synthesis of block copolymers (poly(n-butyl acrylate)— -polystyrene and polystyrene-Z -poly(n-butyl acrylate) [164,165] and grafting... 

Alkyl halide initiating system, 14 266 Alkyl halides, 10 485, 530 amination, 2 547... 

This well-known kinetic expression for a drained equilibrium implies that at high values of m the reaction is of zero order, at low values of first order, with respect to m. Few other examples of this type have been reported. However, orders of reaction less than unity with respect to m may also be due to the sequestration of a metal halide initiator by complexation with the monomer [4], Which, if any, of these two causes is responsible in any particular case for a low or varying kinetic order with respect to m may be determined by suitable experiments, and there seems no reason why both may not occur in the same system. 

The BIE, are of course equally relevant to those systems in which a metal halide initiates by a cation which is formed in a self-ionisation BIE reaction, e.g., A1C13 (Grattan and Plesch, 1980) ... 

Of course, even for the cyclic formals there are still unresolved problems, especially the mechanism by which metal halides initiate their polymerisation [16]. Once again it has become evident that attention to impurity effects and side-reactions is of paramount importance if the conclusions from chemical studies of catalytic reactions are to be valid. 

Paulus RM, Becer CR, Hoogenboom R et al. (2008) Acetyl halide initiator screening for the cationic ring opening polymerization of 2-ethyl-2-oxazoline. Macromol Chem Phys 209 794-800... 

Combination with counterion is also important when aluminum alkyl-alkyl halide-initiating systems are used [DiMaina et al., 1977 Kennedy, 1976 Reibel et al., 1979]. 

As already mentioned, once the reaction was initiated by mechanical activation, it continued without additional activation. This phenomenon suggests that the reaction is au-tocatalytic. As known, activators such as iodine and alkylaluminum halide initiate the conventional thermal reaction of aluminum with alkyl halides. In the case discussed, the reaction was initiated by mechanical working without any activator. 

Controlled free-radical polymerization methods, like atom-transfer radical polymerization (ATRP), can yield polymer chains that have a very narrow molecular-weight distribution and allow the synthesis of block copolymers. In a collaboration between Matyjaszewski and DeSimone (Xia et al., 1999), ATRP was performed in C02 for the first time. PFOMA-/)-PMMA, PFOMA-fr-PDMAEMA [DMAEMA = 2-(dimethylamino)ethyl methacrylate], and PMMA-/)-PFOA-/)-PM M A copolymers were synthesized in C02 using Cu(0), CuCl, a functionalized bipyridine ligand, and an alkyl halide initiator. The ATRP method was also conducted as a dispersion polymerization of MMA in C02 with PFOA as the stabilizer, generating a kine-... 

The products from ATRP will most likely contain metallic and halide impurities. The sulfonyl halide initiators for ATRP have considerable advantages over alkyl halides in cost and in operating with any monomer capable of undergoing ATRP. 

Polymerization was carried out in benzene in the presence of bis-(7r-allylnickel halides). The latter were prepared from nickel carbonyl and allyl halide (allyl bromide, crotyl chloride, bromide, or iodide etc.). The results of the polymerization runs are reported in Table I. The data indicate that all of the bis(7r-allylnickel halides) initiate by themselves the stereospecific butadiene polymerization yielding a polymer with 97-98% 1,4-units. The cis-l,4/trans-l,4 ratio depends on the halide in the dimeric r-allylnickel halide but not on the nature of allylic ligand. The case of bis(7r-crotylnickel halides) shows the effect of halide on microstructure, for whereas (C4H7NiCl)2 initiates cis- 1,4-polybutadiene formation, trans-1,4 polymers are produced by (C4H7NiI)2. The reactivity increase in the series Cl < Br < I. 

Other Lewis Acids. Several relatively weak Lewis acids such as zinc halides and mercury halides initiate polymerization of the most reactive monomers such as N-vinyl carbazole, vinyl ethers, and alkoxysty-renes. Many of these acids have poor solubility in hydrocarbons and halo-genated hydrocarbons and are therefore used as acetone or ether solutions. However, such solvents act as nucleophiles, and therefore decrease the acids Lewis acidity. 

Kennedy and collaborators have studied the polymerisation of olefinic monomers induced by catalytic combinations consistir of mixtures of organic chlorides and aluminium alkyls. Although the authors claimed that these mixtures gave rise to carbenium salts capable of initiating viiq l polymermtion, we believe that the process leading to active species does not necessarily imply the formation of transient carbenium ions derived from the catalyst pair. For this reason, these systems are not discussed in this section but rather in Chapter IV together with other aluminium halide initiated polymerisations. 

The purpose of this study was to investigate the mechanism of cationic olefin polymerizations by model experiments using alkyl-aluminum/alkyl halide initiator systems and to correlate the results of model experiments with corresponding polymerization reactions. 

The first part of this paper is a critical review of model studies in cationic polymerization. In the second part we describe and discuss our investigations exploring the effect of a variety of alkylaluminum/alkyl halide initiating systems under a variety of conditions on the competitive reactions of the Keimedy-Gillham scheme (9). This scheme represents a comprehensive set of model reactions developed for the study of competitive reactions in cationic olefin polymerizatioa It involves the cationation of a nonpolymerizable (steric-hindrance) olefin under simulated polymerization conditions and the complete analysis of reaction products which in turn reflect initiation, propagation, termination and transfer. 

Isobutylene polymerizations were carried out by charging isobutylene, methyl chloride, and the alkylaluminum compound in methyl chloride solution and adding the t-butyl halide initiator in methyl chloride rapidly. Polymerizations ensued immediately and were over in 5-10 min. The reactions were terminated after 15 min by the addition of prechilled methanol. The polymers were dried in vacuum at 40° to constant weight and were characterized by number average and viscosity average molecular weights. All reactions were carried out in duplicate. 

B6. ComparistHi of Alkylaluminiim-AIkyl Halide Initiator Systems in Mefliyl Halide Solvents... 

The nature of the counter anion is determined by the alkylalumi-num coinitiator and by the halogen in the t-butyl halide initiator. 

The Me2AICl/t-BuX system consistently produces highest molecular weight polyisobutylenes. Indeed, in the range from — 50° to — 70° this system produces the highest molecular we t polyisobutylenes among alkylaluminum-alkyl halide initiator system investigated to date. 

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