Divinyl compounds, monomers

Nonlinear addition polymers are readily obtained by copolymerizing a divinyl compound (e.g., divinylbenzene) with the vinyl monomer (e.g., styrene), as already mentioned. Products so obtained exhibit the insolubility and other characteristics of space-network structures and are entirely analogous structurally to the space-network polymers produced by the condensation of polyfunctional compounds. Owing to... 

The polymerization mixture for the preparation of rigid, macroporous monolithic materials in an unstirred mold generally contains a monovinyl compound (monomer), a divinyl compound (crosslinker), an inert diluent (porogen), as well as an initiator. The mechanism of pore formation of such a mixture has been postulated by Seidl et al. [101], Guyot and Bartholin [102], and Kun and Kunin [103] and can be summarized as in the following text. 

Increasing the amount of cross-linking agent (divinyl compound) at expense of monomer causes a decrease in pore size, which is accompanied by a distinct increase in surface area [101-104]. Even if this has been observed for macroporous beads prepared by suspension polymerization, the results can directly be transferred to the fabrication of rigid monolithic materials in an unstirred mold by thermally [105,106] as well as photochemically [107] initiated free radical copolymerization. 

The recent development of living cationic polymerization systems has opened the way to the preparation of rather well defined star homopolymers and miktoarm star polymers [19 and see the chapter in this volume]. Divinyl ether compounds were used as linking agents in a manner similar to the DVB method for anionic polymerization. Typically the method involves the reaction of living polymer chains with a small amount of the divinyl compound. A star polymer is formed carrying at the core active sites capable of initiating the polymerization of a new monomer. Consequently a miktoarm star copolymer of the type AnBn is produced. 

If one of the monomers in a copolymerization is a divinyl compound or any other entity with a functionality greater than 2, a branched polymer can be formed and... 

Cross-linking occurs early or late in the copolymerization depending on the relative reactivities of the two double bonds of the divinyl compound or diene. By the proper choice of a monomer with two double bonds it is possible to reduce the reactivity of one double bond just enough so that it will not enter polymerization under the same conditions as the other, but can be made to react under more drastic conditions. This leads to postpolymerization cross-linking reactions of which vulcanization reactions are an example. 

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. 

Recent advances in living cationic polymerization have led to the preparation of miktoarm stars. The method involves the generation of living polymers and their reaction with a small amount of an appropriate divinyl compound leading to the formation of a star polymer with a central core, formed by polymerization of the divinyl compound, carrying active sites. These sites can be used for the polymerization of another monomer, thus producing miktoarm stars of the AnBn type, as follows (Scheme 91). 

We have considered so far only copolymerization of bifunctional vinyl monomers. However, if any of the monomers in the copolymerization is a divinyl compound... 

We have considered so far only copolymerization of bifimctional vinyl monomers. However, if any of the monomers in the copolymerization is a divinyl compound or any other ole rue monomer with functionabty greater than 2, a branched polymer can result and, furthermore, the growing branches can intercormect to form an in nite crosslinked network known as gel . It is useful to be able to predict the conditions imder which such gel formation will occur. 

Fig. 23. The fraction of fully reacted monomer units in the polymer (C) as a function of monomer conversion P. Experimental points on continuous curve are for HDDA Dashed-dotted line results from mean-field assumption (equal reactivity of pendent and free double bonds, cf Ref. Dotted line results from the percolation model for the polymerization of a pure divinyl compound in three dimensions...

M TS 00 iS V oo 3 Crosslinking during polymerization Free radical polymerization Theimal polymerization Photopolymerization Radiation polymerization Plasma polymerization Copolymerization between various divinyl monomers and divinyl compounds... 

If we express a vinyl monomer as M and a divinyl compound as B-B, the basic reaction of the crosslink formation process follows the free radical copolymerization theory [3, 8] ... 

In the method to crosslink simultaneously with polymerization, the majority of combinations are between a vinyl monomer and a divinyl compound. Heat, catalyst, light, radiation, plasma, and electric fields merely act as initiators for initiation reactions of free radical polymerization. However, these external energies interact uniquely with monomers and solvents. As a result, the state of crosslinking and properties of gels strongly reflect this fact. Table 1 summarizes the gel preparation methods that use free radical polymerization. 

One method of achieving a polymerised polymer-network is by the use of two distinct types of compounds, a monomer and a crosslinker. A simple example of this combination is styrene as a monomer and divinyl... 

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