Catalyst, anionic, 17

Cyclic aryl ether ketones have been prepared from l,2-bis(4- uoroben2oyl)ben2ene and bisphenols under pseudo high dilution conditions. These materials undergo ring-opening polymeri2ation in the presence of an anionic catalyst (87). 

Butadiene copolymers are mainly prepared to yield mbbers (see Styrene-butadiene rubber). Many commercially significant latex paints are based on styrene—butadiene copolymers (see Coatings Paint). In latex paint the weight ratio S B is usually 60 40 with high conversion. Most of the block copolymers prepared by anionic catalysts, eg, butyUithium, are also elastomers. However, some of these block copolymers are thermoplastic mbbers, which behave like cross-linked mbbers at room temperature but show regular thermoplastic flow at elevated temperatures (45,46). Diblock (styrene—butadiene (SB)) and triblock (styrene—butadiene—styrene (SBS)) copolymers are commercially available. Typically, they are blended with PS to achieve a desirable property, eg, improved clarity/flexibiHty (see Polymerblends) (46). These block copolymers represent a class of new and interesting polymeric materials (47,48). Of particular interest are their morphologies (49—52), solution properties (53,54), and mechanical behavior (55,56). 

Chromium is conventionally deposited from chromic acid solutions containing at least one anionic catalyst, which is usually the sulfate ion. The weight ratio of chromic acid to catalyst is important and, for sulfate-cataly2ed solutions, is maintained about 100 1. Formulations and conditions for operating hard chromium plating solutions are shown in Table 5. 

Today the term anionic polymerisation is used to embrace a variety of mechanisms initiated by anionic catalysts and it is now common to use it for all polymerisations initiated by organometallic compounds (other than those that also involve transition metal compounds). Anionic polymerisation does not necessarily imply the presence of a free anion on the growing polymer chain. 

Currently, more SBR is produced by copolymerizing the two monomers with anionic or coordination catalysts. The formed copolymer has better mechanical properties and a narrower molecular weight distribution. A random copolymer with ordered sequence can also be made in solution using butyllithium, provided that the two monomers are charged slowly. Block copolymers of butadiene and styrene may be produced in solution using coordination or anionic catalysts. Butadiene polymerizes first until it is consumed, then styrene starts to polymerize. SBR produced by coordinaton catalysts has better tensile strength than that produced by free radical initiators. 

Vinyl monomers with electron-withdrawing substituents (EWG) can be polymerized by basic (anionic) catalysts. The chain-carrying step is conjugate nucleophilic addition of an anion to the unsaturated monomer (Section 19.13). 

Epoxidation systems based on molybdenum and tungsten catalysts have been extensively studied for more than 40 years. The typical catalysts - MoVI-oxo or WVI-oxo species - do, however, behave rather differently, depending on whether anionic or neutral complexes are employed. Whereas the anionic catalysts, especially the use of tungstates under phase-transfer conditions, are able to activate aqueous hydrogen peroxide efficiently for the formation of epoxides, neutral molybdenum or tungsten complexes do react with hydrogen peroxide, but better selectivities are often achieved with organic hydroperoxides (e.g., TBHP) as terminal oxidants [44, 45],... 

Some of the results of bulk polymerization of 61 by using different anionic catalysts are summarized in Table 858 It was easily polymerized in the presence of alkali metal compounds above 60 °C. The polymerization at 150 °C was too fast to be controlled. The yield and the viscosity number, i gp/c, of the resulting polyamide increased with the reaction time. The initial rate of the polymerization became higher with the size of the countercation, in analogy to the case of anionic polymerization of e-caprolactam59. The rate increased also with raising temperature as shown in Fig. 658. ... 

Polymerization of triphenylmethyl methacrylate in the presence of a chiral anion catalyst results in a polymer with a helical structure that can be coated onto macroporous silica [742,804). Enantioselectivity in this case results from insertion and fitting of the analyte into the helical cavity. Aromatic compounds and molecules with a rigid nonplanar structure are often well resolved on this phase. The triphenylmethyl methacrylate polymers are normally used with eluents containing methanol or mixtures of hexane and 2-propanol. The polymers are soluble in aromatic hydrocarbons, chlorinated hydrocarbons and tetrahydrofuran which, therefore, are not suitable eluents. 

Caprolactam can also be prepared by bulk polymerisation process using anionic catalysts like strong bases and metal hybrides. 

The next study of wood modification was that reported by Baird (1969), who performed vapour-phase reactions of spruce with ethyl, n-butyl, /-butyl, allyl and phenyl isocyanate (PhNCO). Unfortunately, DMF was used as a catalyst for the reactions, which resulted in polymerization of PhNCO in the cell wall of the wood, leading to unpredictable results. No evidence was presented in support of the contention that polymerization had occurred, and since this requires an anionic catalyst initiator, this is considered unlikely. However, the presence of side reactions when DMF is used in conjunction with isocyanates has already been mentioned. Greater success was reported when butyl isocyanate was reacted with wood (presumably a consequence of the lower reactivity of this isocyanate... 

Carbonvlation of Benzyl Halides. Several organometallic reactions involving anionic species in an aqueous-organic two-phase reaction system have been effectively promoted by phase transfer catalysts(34). These include reactions of cobalt and iron complexes. A favorite model reaction is the carbonylation of benzyl halides using the cobalt tetracarbonyl anion catalyst. Numerous examples have appeared in the literature(35) on the preparation of phenylacetic acid using aqueous sodium hydroxide as the base and trialkylammonium salts (Equation 1). These reactions occur at low pressures of carbon monoxide and mild reaction temperatures. Early work on the carbonylation of alkyl halides required the use of sodium amalgam to generate the cobalt tetracarbonyl anion from the cobalt dimer(36). 

In the course of an extensive study of the mode of action of anionic catalysts, A. G. Evans used exclusively h.v.t. His investigation of the electron-transfer reactions involving 1,1,3,3-tetraphenylbutene-l, tetraphenylethylene and sodium naphthalide is of particular interest here because all the reaction mixtures were prepared by h.v.t. and both UV and ESR spectra were measured (J. E. Bennett et al, 1963). The paper contains full experimental details. 

A large cationic radius generally increases the nucleophilic reactivity of the anion in an ion pair. A small cationic radius results in stronger electrostatic attraction and lesser reactivity of the anion. Catalysts with the active site separated from the polymer backbone by an aliphatic chain have higher activity than those prepared by quatemi-zation of a chloromethylpolystyrene with a tertiary amine or tertiary phosphine, leaving only one carbon atom between the active site and the aromatic ring. 

This attribute is justified by the fact that the growth of the macromolecules does not show any termination it stops when the monomer is removed, but is resumed immediately at the same rate when the monomer concentration is restored to its initial value. In some cases (e.g., the case of living polymers of Szwarc, obtained with anionic catalysts), it is exactly the same macromolecule which continues to grow, yielding polymers whose molecular weight increases with the polymerization time. 

The anionic catalysts listed earlier react with lactam monomer to first form the salt, which in turn will dissociate to the active species, namely, the lactam anion. A strongly dissociating catalyst in low concentrations, therefore, is always preferable to weakly dissociating catalysts in higher concentrations. The catalytic activity of the various alkali metal and quaternary salts of a lactam generally follows the extent of their ionic dissociation that is controlled by the cation. Activity of a salt decreases with increasing size of the cation due to restricted mobility and decreased ionization potential. 

Recently, we found that the polymerization of TrMA with chiral anionic catalysts gave an optically active polymer the chirality of which is caused by helicity (12). This is the first example of optically active vinyl polymer the activity of which arises only from the helicity. This article describes the detailed results of the polymerization of TrMA by chiral anionic catalysts in addition to a brief review on our earlier studies described above. 

Isocyanates can be polymerized in the presence of anionic catalysts to form 1-nylons ... 

The use of more anionic catalysts gave the highly anionic system which produced syndiotactic structures. The ionic requirements of this balance depend on the electron attracting effect of the carbonyl substituent at the propagating end of the double bond. These results are summarized in Fig. 4. 

Fig. 5. Anionic catalysts and their effectiveness lor steric control in the polymerization of styrene...

Styrene and alphamethylstyrene have been polymerized with a number of different catalyts. Phillips, Hanlon and Tobolsky (38) found that low-styrene content copolymers are obtained with cationic Friedel-Crafts type catalysts while high styrene containing copolymers are obtained with anionic catalysts. Aluminum bromide or BFS etherate... 

The effects of even more highly anionic catalysts have been shown (Table 6) by Rembaum, Ells, Morrow and Tobolsky (50). 

The strongly anionic alkali metal naphthalene compounds produced very large amounts of 1.2 (or 3.4) structure. The remainder of the polymer was 1.4-trans. No 1.4-cis polymer was produced. Increasing anionic catalysts such as rubidium and cesium produce even larger amounts of 1.4-trans-polybutadiene. 

Studies of the copolymerization of butadiene, isoprene and styrene with anionic catalysts allow interpretation of the relative anionicity required for polymerizing these monomers. 

These results show that the 1,2-polymerization of butadiene requires a less anionic catalyst than the anionic polymerization of styrene. Tobolsky and Rogers (58) studied the same effects of catalyst anionicity on the copolymerization of styrene and isoprene. They found that the increased anionic character of the lithium-THF combination relative to butyllithium catalysts increased the styrene content of the polymer as well as decreased the 1.4-structure of the polyisoprene. 

Studies of the reactions of propylene and alpha-olefins show that the Ziegler-Natta isotactic polymerizations are between the highly cationic and mildly anionic catalysts. 

Syndiotactic polypropylene has been made by Zambelli, Natta and Pasquon (75). The anionic catalysts made from dialkylaluminum chloride, vanadium acetylacetonate and anisole reverse the addition to the propylene molecule so that control by an ultimate asymmetric carbon is no longer possible. The formation of syndiotactic polypropylene is shown in Fig. 8 close to the region of inverted reaction of the propylene molecule. 

This asymmetric end has the alkoxy group of alkyl vinylethers by cationic polymerization, phenyl group of styrene when either anionically or cationicaiiy polymerized, the vinyl group of butadiene under anionic catalysts to poly-1,2-butadiene, the ester and methyl of methylmethacrylate under anionic catalysis and the methyl of propylene by cationic catalysis. 

Unfortunately, no polymerization of such type has been carried out up to now the only case of this type described in literature is the polymerization of an optically active ester of sorbic acid carried out in the presence of anionic catalysts, which however did not give unequivocal experimental evidence of the above theoretical possibility. 

The hydride, with the base and CO, reforms the carbonyl anion catalyst ... 

Cundall, R. B. Sodiomalonic ester as an anionic catalyst. Proc. Chem. Soc. 1958, 170-171. 

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