Anionic polymerization oligomers

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-... 

Ito, K., and Yamashita, Y., Propagation and depropagation rates in the anionic polymerization of e-caprolactone cyclic oligomers, Macromolecules. Ij., 68-72, 1978. 

An interesting procedure has been proposed for the synthesis of amylose-b-PS block copolymers through the combination of anionic and enzymatic polymerization [131]. PS end-functionalized with primary amine or dimethylsilyl, -SiMe2H groups were prepared by anionic polymerization techniques, as shown in Scheme 56. The PS chains represented by the curved lines in Scheme 56 were further functionalized with maltoheptaose oligomer either through reductive amination (Scheme 57) or hydrosilyla-tion reactions (Scheme 58). In the first case sodium cyanoborohydride was used to couple the saccharide moiety with the PS primary amine group. 

Pille et al. used living PBS chains to initiate the anionic polymerization of EGDM and 1,4-butanediol dimethacrylate. They obtained highly crosslinked microgels together with slightly branched oligomers of PBS of a low molar mass [260]. 

Siloxane containing block or segmented copolymers can be synthesized either by living anionic polymerization of the cyclic organosiloxane trimers with appropriate vinyl monomer(, 4 ) or by step-growth or condensation copolymerization of preformed a,w-difunctional siloxane oligomers with conventional difunctional... 

The anionic polymerization of 2-furyl oxirane 4a (17) proceeds smoothly and can be made to yield oligomers bearing a hydroxyl group at each end ... 

Anionic polymerization of -caprolactone has been studied in several laboratories and it was found that considerable amounts of oligomers were found as by-products.— — We have studied the formation of oligomers in the anionic polymerization of 6-capro-lactone by gpc technique.A In view of the very facile intra- and intermolecular transesterification reactions in this system- -, the product distribution seems very interesting to check the validity of the thermodynamic equilibrium. 

In the anionic polymerization of 6-caprolactone in THF with potassium tert-butoxide, monomer consumption is very fast and monomer could not be detected in any appreciable amount in the equilibrated mixture obtained after several minutes from the initiation. Upon terminating the reaction at 6 seconds after the introduction of the initiator solution, 6% monomer remained unreacted accompanied with polymers (68%) and oligomers (26%). 

The anionic polymerization of D4, in toluene, at room temperature, with Li+ + [211] as counterion appears to follow a different course than in the case of D3. The rate of polymerization is much lower and cyclic oligomers formation is more important as can be seen from the results shown in figure 6 for [C] 2.76 10" mole.l". ... 

The first results of anionic polymerization (the polymerization of 1,3-butadiene and isoprene induced by sodium and potassium) appeared in the literature in the early twentieth century.168,169 It was not until the pioneering work of Ziegler170 and Szwarc,171 however, that the real nature of the reaction was understood. Styrene derivatives and conjugated dienes are the most suitable unsaturated hydrocarbons for anionic polymerization. They are sufficiently electrophilic toward carbanionic centers and able to form stable carbanions on initiation. Simple alkenes (ethylene, propylene) do not undergo anionic polymerization and form only oligomers. Initiation is achieved by nucleophilic addition of organometallic compounds or via electron transfer reactions. Hydrocarbons (cylohexane, benzene) and ethers (diethyl ether, THF) are usually applied as the solvent in anionic polymerizations. 

Anionic ring-opening polymerization of l,2,3,4-tetramethyl-l,2,3,4-tetraphenylcyclo-tetrasilane is quite effectively initiated by butyllithium or silyl potassium initiators. The process resembles the anionic polymerization of other monomers where solvent effects play an important role. In THF, the reaction takes place very rapidly but mainly cyclic live- and six-membered oligomers are formed. Polymerization is very slow in nonpolar media (toluene, benzene) however, reactions are accelerated by the addition of small amounts of THF or crown ethers. The stereochemical control leading to the formation of syndiotactic, heterotactic or isotactic polymers is poor in all cases. In order to improve the stereoselectivity of the polymerization reaction, more sluggish initiators like silyl cuprates are very effective. A possible reaction mechanism is discussed elsewhere49,52. 

Some cyclic oligomers were formed as by-products in the polymerization of e-caprolactone. Yamashita et al. [136] reported that the anionic polymerization of e-caprolactone with f-BuOK in THF results in a living ring-chain... 

The anionic polymerization of DXO using f-BuLi or CH3Li in THF or toluene solution was unsuccessful and only oligomers could be obtained [88]. 

Anionic polymerization of a sodium salt (61) of a bromosubstituted bicyclic lactam (60) is very unusual. It proceeds in dimethylformamide at 0 and 25 °C with elimination of sodium bromide and gives oligomers 62 having a bicyclic oxalactam ring in each repeating unit. [70]... 

Almost all compounds polymerizing by the radical mechanism belong to the classical monomers with a double or triple bond. Radicals of relatively low reactivity formed from the initiators do not usually attack the bonds of electron-rich atoms (with an excess of electrons). They react readily with electron-deficient atoms. Thus the anionically polymerizing monomers usually also polymerize by a radical mechanism. Typical cationic monomers do not undergo radical polymerization. The quite neutral ethylene forms a transition between the two groups. It polymerizes reluctantly by the radical and ionic mechanisms cationically it only yields oligomers. 

Monomer reactivity is a broad concept, and it can not always be limited only to reactions of the double or triple bonds of a vinyl or acetylene group. Weakly polar monomers, such as styrene or butadiene, react almost exclusively by their double bonds. The anionic polymerization of polar monomers, such as a, /S-unsaturated esters and nitriles, is accompanied by many side reactions. A fairly large amount of oligomers and side products are formed, and these may affect the active centres, thus indirectly modifying propagation. 

Anionic polymerization of ethylene has been used to prepare terminally functionalized ethylene oligomers. The reaction proceeds as shown in equation (12). Phosphite as well as phosphine-hmctionalized ethylene oligomers have been prepared. Nickel(O) phosphine complexes can be bound to such a functionalized oligomer. The bound complexes have similar activity as their homogeneous counterparts for the cyclooligomerization of butadiene. 

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