Anionic polymerization complex bases

Cyanoacrylate adhesives cure by anionic polymerization. This reaction is catalyzed by weak bases (such as water), so the adhesives are generally stabilized by the inclusion of a weak acid in the formulation. While adhesion of cyanoacrylates to bare metals and many polymers is excellent, bonding to polyolefins requires a surface modifying primer. Solutions of chlorinated polyolefin oligomers, fran-sition metal complexes, and organic bases such as tertiary amines can greatly enhance cyanoacrylate adhesion to these surfaces [72]. The solvent is a critical component of these primers, as solvent swelling of the surface facilitates inter-... 

In an attempt to combine the syndioselectivity of half-sandwich titanium catalysts with the living characteristics of anionic polymerization initiators, the use of half-sandwich calcium-based catalysts has been described.363 364 In neat styrene complex (152) affords 76% rr triad PS. However, polydispersities are still quite high (Mw/Mn > 2.2)... 

An alternative strategy for catalyst immobilisation uses ion-pair interactions between ionic catalyst complexes and polymeric ion exchange resins. Since all the rhodium complexes in the catalytic methanol carbonylation cycle are anionic, this is an attractive candidate for ionic attachment. In 1981, Drago et al. described the effective immobilisation of the rhodium catalyst on polymeric supports based on methylated polyvinylpyridines [48]. The activity was reported to be equal to the homogeneous system at 120 °C with minimal leaching of the supported catalyst. The ionically bound complex [Rh(CO)2l2] was identified by infrared spectroscopic analysis of the impregnated resin. 

Traditionally, potentiometric sensors are distinguished by the membrane material. Glass electrodes are very well established especially in the detection of H+. However, fine-tuning of the potentiometric response of this type of membrane is chemically difficult. Solid-state membranes such as silver halides or metal sulphides are also well established for a number of cations and anions [25,26]. Their LOD is ideally a direct function of the solubility product of the materials [27], but it is often limited by dissolution of impurities [28-30]. Polymeric membrane-based ISEs are a group of the most versatile and widespread potentiometric sensors. Their versatility is based on the possibility of chemical tuning because the selectivity is based on the extraction of an ion into a polymer and its complexation with a receptor that can be chemically designed. Most research has been done on polymer-based ISEs and the remainder of this work will focus on this sensor type. 

Like other, 8-dicarbonyl compounds, the substituted keto amides (X)—(XV) are very reactive and represent the key intermediates in a complex set of side reactions [95]. A considerable amount of research has been devoted to the elucidation of the reactions of these compounds under polymerization conditions [118—120,124,125,127,128, 130,131, 134—143]. With respect to the high reactivity of carbonyl groups and the adjacent —CH2— or i CH- groups, the structures like (X)—(XV) are unstable at elevated temperatures and even less stable in the presence of a strong base. Bukac and Sebenda [137] showed that keto amides with one hydrogen atom at the nitrogen decompose very easily in the presence of base into isocyanate which takes part in many subsequent reactions, scheme (45). The most important consequence of side reactions is the fact that water is present even if the anionic polymerization is started under... 

There are various procedures for the preparation of polyethers. These procedures typically start with oxirane or oxirane derivatives (e.g. propylene oxide, etc.). Base catalyzed anionic polymerization, acid initiation, or complex coordination catalysis can be used for the reaction [1-3], Not only oxiranes can generate polyethers. Diols also can be used for polyether synthesis. Other source compounds include tetrahydrofuran, which can be polymerized to a polyether using fluorosulfonic acid (HSO3F) as a catalyst, oxetane (trimethylene oxide) or oxetane derivatives, which can be polymerized to generate polyethers with practical applications such as poly[bis(chloromethyl)oxetane], etc. 

Of course, if the only polymerizations performable were those of styrene, complex bases would be of little interest in the anionic polymerization field. 

These examples are representative of only a small part of all our experiments. However we have shown that Complex Bases are also very interesting cheap reagents in the initiation of the very important anionic polymerization reactions. 

Effect of Tertiary Amines.—Though the influence of ethereal solvents and additives in anionic polymerizations has been widely investigated, it is only relatively recently that attention has been focussed on the effect of tertiary amines. The complex between Bu"Li and tetramethylethylene diamine (TMEDA) is known to be a powerful base readily capable, for example, of abstracting a proton from aromatic hydrocarbons and generating lithiated derivatives. Not surprisingly, therefore, tertiary amines do indeed have significant effects in carboanionic propagations. 

This method for the preparation of poly(styrene-fc-tBuA) is based upon the procedure described by Jerome et al. Teyssie and co-workers demonstrated that the addition of LiCl can be effective in the living anionic polymerization of the acrylic monomers, because a p,-type complex" is formed between LiCl and the growing site. This complex prevents the occurrence of side-reactions at the propagating site, thus markedly narrowing the molecular weight distribution. 

Also, addition of small quantities of Lewis bases such as amines to alkyllithium reagents in hydrocarbons markedly affects reactivity, especially in connection with various anionic polymerization reactions. Findings such as these prompted a number of research groups in the early 1950 s to study in detail the role of Lewis bases in the structures of organolithium compounds (4, 5). In each case it was concluded that coordination complexes form when amines are added to organolithium reagents in hydrocarbons. 

Most of the early mechanistic investigations of anionic polymerization were concerned with reactions taking place in liquid ammonia. The system liquid ammonia-alkali metals will be dicussed first, followed by a review of heterogeneous reactions taking place on alkali or alkali-earth surfaces. Thereafter homogeneous electron-transfer processes and the addition of negative ions to monomer will be discussed. Finally some esoteric reactions, such as initiation by Lewis bases, charge-transfer complex initiation, etc. will be briefly reviewed. 

The anionic polymerization of cyclosiloxanes is a complex process. For the alkali metal silanolate catalysts the weight of experimental evidence supports a mechanism based on growth from the metal silanolate ion pair. The ion pair is in dynamic equilibrium with ion-pair dimers which, for the smaller alkali metal ions like lithium and sodium, are themselves in dynamic equilibrium with ion-pair dimer aggregates. The fractional order in catalyst which is observed is a direct result of the equilibria between ion pairs, ion-pair dimers and ion-pair dimer aggregates. Polar solvents break down the aggregates and increase the concentration of ion-pair dimers and hence the concentration of ion pairs. Species like crown ethers and the [2.1.1] cryptate which form strong complexes with the metal cation increase the dissociation of ion-pair dimers into ion pairs. In the case of the lithium [2.1.1] cryptate dissociation into ion pairs is complete and the order in catalyst is unity. 

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