Anionic cyclic monomers

Anionic copolymerization of cyclic monomers occurs only between similar monomer pairs. Random copolymers are not formed between vinyl monomers and epoxides or lactones198 because the propagating species are very different. Thus, the success of the copolymerization of cyclic disulfide and nitropropylene was an exceptional case... 

Cyclosilazanes are found to be reluctant to polymerize by the ring-opening process, probably for thermodynamic reasons. On the other hand, six- and eight-membered silazoxane rings are able to undergo anionic polymerization under similar conditions to those which have been widely used for cyclosiloxane polymerization provided there is no more than two silazane units in the cyclic monomer. They can also copolymerize with cyclosiloxanes however, the chain length of the linear polymer formed is substantially decreased with increasing proportion of silazane units. 

Ring-opening polymerization of cyclic monomers, usually by anionic or cationic catalysts, is another route to elastomers. These include the polymerization of octamethylcyclotetrasiloxane... 

The ionic chain polymerization of unsaturated linkages is considered in this chapter, primarily the polymerization of the carbon-carbon double bond by cationic and anionic initiators (Secs. 5-2 and 5-3). The last part of the chapter considers the polymerization of other unsaturated linkages. Polymerizations initiated by coordination and metal oxide initiators are usually also ionic in nature. These are called coordination polymerizations and are considered separately in Chap. 8. Ionic polymerizations of cyclic monomers is discussed in Chap. 7. The polymerization of conjugated dienes is considered in Chap. 8. Cyclopolymerization of nonconjugated dienes is discussed in Chap. 6. 

The range of monomers that can be incorporated into block copolymers by the living anionic route includes not only the carbon-carbon double-bond monomers susceptible to anionic polymerization but also certain cyclic monomers, such as ethylene oxide, propylene sulfide, lactams, lactones, and cyclic siloxanes (Chap. 7). Thus one can synthesize block copolymers involving each of the two types of monomers. Some of these combinations require an appropriate adjustment of the propagating center prior to the addition of the cyclic monomer. For example, carbanions from monomers such as styrene or methyl methacrylate are not sufficiently nucleophilic to polymerize lactones. The block copolymer with a lactone can be synthesized if one adds a small amount of ethylene oxide to the living polystyryl system to convert propagating centers to alkoxide ions prior to adding the lactone monomer. 

In Eq. 7-5a Z represents a functional group, such as O, NH, Si—O, CO—O, and CO—NH in ethers, amines, siloxanes, esters, and amides, respectively. In Eq. 7-6 Z represents an anionic propagating center, such as alkoxide or carboxylate, derived from the cyclic monomer. 

Lactones (cyclic esters) undergo anionic and cationic polymerization to form polyesters (Eq. 7-75) [Duda and Penczek, 2001 Johns et al., 1984 Kubisa, 1996 Lundberg and Cox, 1969 Young et al., 1977]. The reactivity of different lactones generally follows the pattern for other cyclic monomers, except that the 5-membered lactone (y-butyrolactone) does... 

Polycarbonates, both aliphatic and aromatic, have been prepared by the ring opening polymerization of cyclic monomers or oligomers [22], Cyclic monomeric precursors are more common in aliphatic polycarbonates, but because of steric reasons aromatic polycarbonates can only be prepared from cyclic oligomers. Both cationic and anionic initiators have been examined and anionic initiators appear to be more efficient. 

The ring-opening polymerization of cyclic monomers can be performed by ionic chain polymerization, as is the case of epoxy monomers. Anionic polymerization of ethylene oxide propylene oxide, and caprolactone can be initiated by alkoxides ... 

In addition to the thermodynamic feasibility of a polymerization, there must also be a kinetic pathway for the polymerization to occur. A heteroatom in a cyclic monomer provides a site for coordination with an anionic, cationic, or coordination type of initiator [Eq. (33)]... 

Detailed analysis of the kinetics of polymerization of cyclic monomers has only relatively recently reached the sophistication of analogous vinyl systems. Despite this an ever increasing volume of relevant data is emerging, and, indeed many reactions are proving to be more amenable to investigation in an absolute manner, than the more extensively studied vinyl polymerizations. This situation has arisen partly as a result of the inherent lower reactivity of these monomers, and also from the fact that, in general, the polymerizations are less susceptible to impurities and side reactions. Even monomer transfer is absent in most of these systems, and a situation approaching that found in anionic vinyl polymerization prevails. 

The similarity in the reactivities of free ions and corresponding ion pairs derived from the same cyclic monomer is more intriguing. Whereas ion pair reactivities are about 10 times smaller than corresponding free ion values in the anionic polymerization of vinyl monomers [39], and probably of the same relative proportions in cationic systems, the difference in cationic ring opening polymerizations is considerably less. For polymerization of THF in methylene chloride the factor is only 7, and for polymerization of 3,3-dimethylthietan, 40 in methylene chloride and 1 in nitrobenzene. Because the overall reactivity in cyclic monomer reactions is lower than for olefinic polymerizations, it might be expected that difference between free ion and ion pair reactivities, within one system, would also be less. However, this does not seem to be the whole answer. Plesch [44] has pointed out that in the polymerization of cyclic ethers and thietans (and presumably, therefore, other cyclic monomers)... 

The present volume is particularly concerned with the use of the different modes of controlled radical polymerisation for the preparation of copolymers such as random copolymers, linear block copolymers, as well as graft copolymers and star-shaped copolymers. It also presents the combination of controlled radical polymerisation with non-controlled radical copolymerisation, cationic and anionic polymerisation,both of vinyl monomers and cyclic monomers, and ringopening metathesis polymerisation. 

The size of substituents may also influence the polymerizability of cyclic monomers. This was shown for the cationic (and anionic) polymerization of cyclic esters of phosphoric acid 11... 

Coordination-insertion, anionic, cationic, and nucleophilic polymerization are the most frequently reported controlled ring-opening polymerization (ROP) of cyclic monomers in the literature [37, 38]. The coordination-insertion and nucleophilic polymerization are undoubtedly the most efficient and general methods reported so far for the ROP of lactones, with cationic and anionic polymerization being much less investigated. While coordination-insertion polymerization uses metal-alkoxides and related complexes as catalysts, the organocatalytic nucleophilic polymerization is a metal-free approach to ROP. 

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