Cationic polymerization of monomers

Crivello, J. V. Malik, R. Synthesis and Photoinitiated Cationic Polymerization of Monomers Containing the Silsesquioxane Core. In Silicones and Silicone-Modified Materials-, Glarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Eds. AGS Symposium Series 729 American Chemical Society Washington, DC, 2000 pp 284-295. 

The cationic polymerization of monomer 25 occurs via the initial coordination the electrophilic initiator, PF5, at the indicated ring oxygen atom to produce the oxonium ion 26. The latter is attacked by another molecule of 25 at its electrophilic site, C-1, to form a new oxonium ion 27. Repetition of this process leads to the consecutive formation of a set of glycosidic bonds in a stereospecific fashion as defined by inversion of configuration in every single attack at C-1. It is clear that the nature of the reaction and the structure of the monomer ensures both the desired stereo- and regiospecificity. Debenzylation of the final polymer 28 readily affords the target product 23. 

Crivello, J.V. Malik, R. Synthesis and photoini-tiated cationic polymerization of monomers with the silsesquioxane core. J. Polym. Sci. Polym. Chem. 1997, 35, 407. 

A dloxacarbenlum Ion mechanism for blcycllc orthoesters. The equilibrium between carbenlum Ions and oxonlum Ions In the cationic polymerization of monomers containing heteroatoms has been discussed In the literature, specifically In the case of cyclic ethers and acetals (27-29). In analogy, the growing center In the polymerization of blcycllc orthoesters can be either a blcycllc oxonlum Ion or a dloxacarbenlum Ion. In this reaction sequence either step can be... 

Various initiators can be used to bring about cationic polymerization of monomers which have electron-releasing substituents. Initiation is brought about by addition of an electrophile to a monomer molecule [cf. Eq. (8.2)]. Compounds used more commonly are the various protonic and Lewis acids. 

Problem 8.19 Arrange the following initiators and coinitiators in the general order of activity for initiating cationic polymerization of monomers ... 

Problem 8.20 Give plausible explanation for the following facts. Primary and secondary alkyl halides are generally ineffective as initiators of cationic polymerization of monomers such as isobutene and styrene, but t-butyl and cumyl chlorides are effective. On the other hand, triphenylmethyl chloride and cyclo-heptatrienyl (tropylium) chloride are not very efBcient in polymerizing isobutylene and styrene but produces rapid polymerization of p-methoxystyrene, vinyl ethers and N-vinylcarbazole. 

FeCl3 is an efficient Lewis acid initiator for the cationic polymerization of monomers like NVC [60]. It is also an efficient dopant for PNVC enhancing its bulk conductivity [61]. Accordingly, in the study of the NVC-MMT polymeriza-tion/nanocomposite formation system, the addition of FeCl3 was considered to be interesting. Results of a recent study [33] (Table 2) indicated that in NVC-... 

Polymerizations. A variety of polymerization conditions were examined for both the monovinyl and divinyl compounds. It was hoped that cationic polymerization of monomer 3 would give a vinyl polymer possessing tetraethylene glycol pendant groups. 

Over the years, a number of compounds have been identified to photoinitiate cationic polymerization of monomers designed for radiation curing applications generally, and negative-resist applications specifically. The most prominent of these initiators are onium salts. 

Scheme 10.13 Possible initiation routes in the cationic polymerization of monomer M. Initiating system onium salt/sensitizer.

Some radical sources will, in the presence of oxidizing agents, or light or heat energy, initiate cationic polymerizations of monomers, like n-butyl vinyl ether. Those that are most readily oxidized are carbon atom centered radicals that have substituents like benzyl, allyl, alkoxy, or structures with nitrogen or sulfur. Also, radicals that are formed by addition of other radicals to alkyl vinyl ethers are particularly reactive. 

Synthesis and Photoinitiated Cationic Polymerization of Monomers Containing the Silsesquioxane Core... 

Table I. Conditions and Results of Cationic Polymerization of Monomers Bearing NBD Moieties ...

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