Vinyl monomers initiated polymerization

Although diarylazo compounds are stable toward light, alkylazo compounds readily dissociate upon irradiation to give free radicals. The use of a per-fluoro derivative of azomethane, namely hexafluoro azomethane, as a photoinitiator of vinyl polymerization is well known [98-100]. This compound can be photolyzed to give F3C radicals that do, in the presence of the excess vinyl monomer, initiate polymerizations. 

Kinetics and mechanism of polymerization of vinyl monomers initiated by ylides. 

In the presence of radical initiators such as benzoyl peroxide (BPO), azobisisobutyronitrile (AIBN), persulfates (S208 ), etc., grafting of vinyl monomers onto polymeric backbones involves generation of free radical sites by hydrogen abstraction and chain transfer processes as described below ... 

If a vinyl monomer is polymerized in the presence of cellulose by a free radical process, a hydrogen atom may be abstracted from the cellulose by a growing chain radical (chain transfer) or by a radical formed by the polymerization catalyst (initiator). This leaves an unshared electron on the cellulose chain that is capable of initiating grafting. As cellulose is a very poor transfer agent [10], very little copolymer results from the abstraction of hydrogen atoms by a growing chain radical. The... 

Polymerization of some vinyl monomers initiated by those colored aromatic complexes was described by Scott38 over twenty years ago, and recently the mechanism of this reaction has been elucidated in our laboratory43 where we demonstrated that polymerization initiation is due to an electron transfer to monomer, namely A - -M A-f-M . This system is useful, therefore, in... 

The polymer formation in the radical polymerization of vinyl monomers initiated by a usual initiator R-R is expressed by Eqs. (4) and (5) if termination proceeds via combination and disproportionation and no chain transfer reaction occurs. 

Initially, there was a problem casting lenses from CR-39 because there is typically shrinkage, with the polymer denser than the liquid monomer, when vinyl monomers are polymerized. In this case there was 14% shrinkage. This was not a problem when casting flat lenses since... 

In summary, some of the important factors in polymerization reactions of vinyl monomers initiated by macrocellulosic radicals are, as follows (1) the lifetimes of the macrocellulosic radicals (2) the accessibility of the radicals to the monomers ... 

In contrast to the above situations, parylene polymer deposition has very poor adhesion to a smooth surface substrate but can penetrate deep into small cavities. para-Xylylene prefers to react with another para-xylylene or its derivatives. Although it has the feature of difunctional free radical, it is rather stable and does not initiate polymerization of other monomers for conventional free radical polymerization. In spite of numerous attempts, the polymerization of various vinyl monomers initiated by para-xylylene or copolymerization of vinyl monomers with /7ura-xylylene has been elusive. 

Generalized methods of initiating the polymerization of these monomers have recently been reviewed in detail [9], and were also mentioned briefly earlier in this Chapter. As with vinyl monomers initiation can be efficient and rapid, with the production of a fixed number of active centres. Propagation appears to be much slower, however, and rates of polymerization are comparable to those in free radical addition polymerizations. Techniques such as dilatometry, spectrophotometry etc. are therefore convenient for kinetic investigation of this type of cationic reaction. 

On the other hand, the stabilization of monomers for storage in the factory or during road, rail or sea transportation, is a great problem in terms of monomer quality, and especially in terms of safety. Indeed, for all vinyl monomers, the polymerization reaction is exothermic and autocatalytic once initiated. It is therefore very difficult to have storage equipment that can withstand such pressures (ref. 23). The main selection criteria for such package-inhibitors are their effectiveness at ambient temperature, their colourlessness and their ability to be removed before polymerization or to be overcome by the use of moderate amounts of initiator under the customer s polymerization conditions. 

Impregnation and polymerization of vinyl monomers in polymeric films. Vinyl monomers swell some kinds of polymer films styrene and divinylbenzenes swell poly(vinyl chloride) films substantially. After a polymer film such as poly(vinyl chloride) or polyethylene has been swollen in a vinyl monomer mixture containing a radical initiator, the film is covered with another film that does not swell with the vinyl monomers, e.g. cellulose film, poly(vinyl alcohol) film, and heated to polymerize the monomers in the film. Ion exchange groups are introduced into the resulting precursor membrane, for example by sulfonation, chloromethylation... 

It is possible to prepare block copolymers by free-radical initiation, as R. B. Seymour, G. A. Stahl, D. R. Owent, and H. Wood discuss in their chapter. Methyl methacrylate macroradicals were made with peroxide and azo initiators in diluents, and different vinyl monomers were polymerized onto them. Block copolymers of two ethylene imines, one having a long (lauroyl) side chain and one with a short (propionyl) side chain were synthesized by M. H. Litt and T. Matsuda in a two-step cationic polymerization process. Block and random copolymers of episulfides were prepared by E. Cernia, A. Roggero, A. Mazzei, and M. Bruzzone using anionic catalysts of metalated sulfoxides and sulfones. 

K. Fujiki, M. Sakamoto, A. Yoshida, and H. Maruyama. Radical grafting from glass fiber surface Graft polymerization of vinyl monomers initiated by azo groups introduced onto the surface. J. Polym. ScL, Part A Polym. Chem., 37(13) 2121-2128, July 1999. 

The most common monomers in carhocationic polymerization are alkenes, often termed vinyl monomers. Carbocationic polymerization of vinyl monomers proceeds by the electrophilic attack of the initiating and/or propagating carbenium ion on the double bond of the monomer. In order to sustain the chain reaction of propagation in competition with termination or transfer reactions, the carbenium ion has to be sufficiently stable and the monomer has to be sufficiently nucleophilic to ensure long enough lifetime of the active center to propagate. 

Figure 4e represents interfacial poljmierization processes in which a solution of water-immiscible vinyl monomer(s), vinyl monomer initiator, and core material is dispersed in an aqueous phase that contains a dispersing agent. Polymerization is then initiated, eg, by heating. The polymer produced within the droplets of the core material is designed to precipitate or deposit at the core material-aqueous... 

Polymerization kinetics. Radical polymerization of vinyl monomers initiated by the diphenylphosphinoyl radical has been investigated by time-resolved CW and FT EPR. The diphenylphosphinoyl radicals (DPO) were generated by photo-cleavage of 2,4,6-trimethylbenzoyldiphenylphosphine (TMDPO) by laser pulses of 335 nm and 10 mJ in benzene solutions. The reaction scheme of the initiation and the first polymerization step are shown in Figure 13. Well-resolved hyperfine structures of the starting radicals (first addition step) were observed for vinyl acetate, ethyl vinyl ether, styrene, methyl methacrylate and... 

Protonation of vinyl monomers initiates their cationic polymerization. Hopefully, the presence of the resulting carbonium ions might be observed spectrophotometrically and then their concentration in the polymerizing system could be determined. In cooperation with Prof. David Pepper, who stayed with us for 6 months, we investigated by stop-flow technique polymerization of styrene initiated by perchloric acid. The formation of the -CH2 CH(Ph) was indeed observed and the propagation constant calculated. This study is continued by Pepper and the detailed features of the reaction require further clarification. 

For example, the polymerization of vinyl monomers initiated by benzoyl peroxide (BPO) and 2,2 -azobisisobutyronitrile (AIBN) in ionic liquids has been reported. It is interesting to note that the rate of the radical polymerization and molecular weight of resulting polymer in ionic liquids were much larger than those in a conventional organic solvent. 

Radical graft polymerization of vinyl monomers initiated by azo groups introduced onto silica nanoparticle and carbon black surface in ionic liquid... 

---