Monomers anionically polymerizable

Another important consequence of the limitations concerning cross-addition is that anionic polymerization is not suited for the synthesis of random copolymers. If a mixture of two anionically polymerizable monomers is reacted with an initiator, the most electrophilic monomer will polymerize while the other is left almost untouched 30). In other words, a general feature of anionic binary copolymerization is that one of the reactivity ratios is extremely high while the other is close to zero. 

In the case of the anionic polymerizability it is possible to find limits of the quantum chemical parameters which separate those monomers capable of polymerization from those not (see Table 9). 

The polydispersity of polymers prepared in this way is usually very low for example, a value MJM of 1.05 was found for a sample of poly(a-methylsty-rene). Living polymers can also be used for the preparation of block copolymers after the consumption of the first monomer, a second anionically polymerizable monomer is added which then grows onto both ends of the initially formed block. By termination of the living polymer with electrophilic compounds the polymer chains can be provided with specific end groups for example, living polystyrene reacts with carbon dioxide to give polystyrene with carboxylic end groups. 

Some anionically polymerizable monomers are listed below, roughly in the order of increasing electroaffinity, i.e. in the order of increasing tendency to polymerize anionically. 

Anionically Polymerizable Monomers Listed in the Order of Increasing Electroaffinity... 

The metallocene catalyst with cationic nature and spatially opened active site provides favorable condition for the incorporation of p-alkylstyrene (p-ms) to polyolefins. The p-ms groups can be easily metallated to produce "stable" polymeric anions for graft-from polymerization. With the coexist of anion-polymerizable monomers, we have prepared many graft copolymers, such as PE-g-PS, PE-g-PMMA, PE-g-PAN, PP-g-PS, PP-g-PB, PP-g-PI and PP-g-PMMA. 

The lithiated polyethylene copolymer was then suspended in hexane or THF solvent. The graft-from reactions were carried out in slurry solution by reacting the lithiated polyethylene copolymer with anionic polymerizable monomers, such as styrene and p-methylstyrene. After certain reaction time, 10 ml of isopropanol was added to terminate the graft-from reaction. The precipitated polymer was filtered and then subjected to fractionation. Good solvents for backbone and side chain polymers were used during the fractionization, using a Soxhlet apparatus under N2 for 24 hours. The soluble fractions were isolated by vacuum-removal of solvent. Usually, the total soluble fractions were less than 5 % of the product. The major insoluble fraction was PE graft copolymer, which was completely soluble in xylene or trichlorobenzene at elevated temperatures. 

The lack of anionic polymerizability of 69 can be ascribed to the instability of 71 due to a stereoelectronic effect. [9] One of the lone pair orbitals on the nitrogen atom of 71 is perfectly antiperiplanar to the C(l) —0(2) bond, which causes this bond to cleave fadly. Thus, as soon as 71 is formed, it is transformed to 72, so that anionic polymerization by the activated monomer mechanism does not take place. 

Not all monomers are anionically polymerizable. Nevertheless, one can take advantage of the activity of the living ends to introduce reactive end groups at the extremity of homopolymers and then use such end groups to initiate the polymerization of anionically non polymerizable monomers. This method has been applied to the synthesis of copolymers with polyvinyl and polylactone blocks19 and of copolymers with polyvinyl and polypeptide blocks20-2S). One can at last use both anionic and cationic polymerization to prepare block copolymers of tetrahydrofuran with styrene or methylstyrene2. ... 

A list of some anionically polymerizable unsaturated monomers is given in Table 5. They can be listed in four classes styrenic monomers, hydrocarbons monomers, halogenated monomers, and polar monomers. As a general principle, a good match between the nucleophilicity of the initiator and the electron affinity of the double bond is essential to obtain good initiation efficiency without side reactions. 

Woods, J.G. Rooney, J.M. Imaging Method for Vapor Deposited Photoresists of Anionically Polymerizable Monomer U.S. Patent 4,675,270, June 23, 1987. 

J.4.2.3 Heterocyclic Monomers A variety of heterocyclic monomers can be polymerized by anionic ring-opening polymerizations. The types of anionically polymerizable heterocyclic monomers include oxiranes (epoxides), thiacyclopropanes, thiacyclobutanes, lactones, lactides, lactams, anhydrides, carbonates, and silicones... 

Figure 5.1 Cyclic monomers capable of anionic polymerization. Table 5.1 Anionic polymerizability of vinyl monomers.

Both, 2- and 4-vinylpyridines show a higher anionic polymerizability than those of styrene and 1,3-diene monomers, because the electron-deficient pyridine ring... 

Various substituted styrenes also anionically polymerize readily. These include methyl, methoxy, dimethylamino, t- butyl and other groups which are electron donating to the benzene ring and do not themselves react with carbanion centers. Substituents such as chloro or nitro can be anionically polymerized only at imder very carefolly controlled conditions. 2,3, or 4 vinylpyridine can also be anionically polymerized. Any aromatic or condensed aromatic compounds with a vinyl substituent is potentially anionically polymerizable, or co polymerizable with any other anionically polymerizable monomer. 

Reaction 17 shows that carboxylate containing polymers have been used to initiate graft polymerizations of anionically polymerizable monomers such as lactones (54). 

Although, there are many more cationicaUy polymerizable monomers than anionically polymerizable ones, relatively few cationic polymerizations (e.g., isobutene polymerization to produce polyisobutene and butyl rubber - copolymer of isobutene with small fractions of isoprene [18]) are performed industrially because macrocations are highly reactive and prone to suffer termination and chain transfer reactions. 

One of the limitations of anionic polymerization is the types of monomers which can be polymerized without termination and chain transfer. The most well-behaved systems are the vinyl monomers based on styrene and butadiene which are available primarily from petroleum feedstocks. Several years ago we began a search for anionically polymerizable monomers which would be available from renewable natural resources. One of the monomers uncovered (rediscovered) in this search was myrcene (4) 7-methyl-3-methylene-1,6-octadiene,... 

The anionic polymerizability of vinyl monomers cannot be deduced from the thermodynamics of polymerization since almost all vinyl monomers exhibit negative free energies of polymerization that is, if a suitable pathway exists, the polymerization will proceed spontaneously to form the polymer from the monomer. This is exemplified by the fart that cyclopropane does not undergo anionic polymerization in spite of its high ring strain and exothermic energy of polymerization (AG = -22.1 kcalmol" ). The proviso that there exists a suitable pathway provides the major limitation on the... 

Scheme 1 Anionically polymerizable styrene monomers with protecting...

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