Cross-linker, divinyl monomers with

Atom transfer radical polymerization (ATRP) was selected as an exemplary CRP technique to systematically study the kinetics and gelation behavior during the concurrent copolymerization of monovinyl monomers and divinyl cross-linkers (Scheme 2). The effect of different parameters on the experimental gelation was studied, including the initial molar ratio of cross-linker to initiator, the concentrations of reagents, the reactivity of vinyl groups present in the cross-linker, the efficiency of initiation, and the polydispersity of primary chains. Experimental gel points based on the conversions of monomer and/or cross-linker at the moment of gelation, were determined and compared with each other in order to understand the influence of each parameter on the experimental gel points. 

Another method involves the use of a multifunctional monomer in the simultaneous polymerization and cross-hnking of polymers. Taking poly(ethyl acrylate) as an example, with divinyl benzene as cross-linker,... 

Kitagawa and coworkers have recently described an interesting but different host-guest-polymerization concept to synthesize cross-linked polymers such as polystyrene, methylmethacrylate, and vinylacetate with pseudo-crystallinity in non-photochemical route [57]. In order to achieve this, they have first incorporated the cross-linker 2,5-divinyl-benzene-1,4-dicarboxylate (DVTP) into the porous CP [Cu(DVTP)(triethylenediamine)o.5] (51). The host framework containing porous channels with dangling vinyl groups provides a suitable environment for radical polymerization of these monomers as shown in Fig. 31. This is obviously different from photopolymerization by [2+2] cycloaddition reaction. 

Scheme 29 Illustration of chain growth and gelation process by copolymerization of monomer (M) and divinyl cross-linker (X) using ATRP with fast initiation. Reprinted from Li, W. Gao, H. Matyjaszewski, K. Macromolecules2099, 42.927-932, " with permission from the ACS.

For network polymer formation a small amount of an appropriate divinyl monomer can be included in the monomer feed as a cross-linking agent. By analogy with copolymerization, as long as the monomer and cross-linker are of similar reactivity then the degree of cross-linking will be statistical and can be controlled by the molar proportion of monomer to cross-linker. An example of the preparation of acrylic network LCPs is shown in Fig. 

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