Cross-linker, divinyl

For example, polymerizing inorganic nanoparticles with cross-linker divinyl-benzene yields composite polymer-inorganic latex particles functionalized with vinyl groups. In the process of composite miniemulsion polymerization, vinyl groups were easily introduced to the particle surface by using cross-linker divinylbenzene, thiol-terminated polymers can be further clicked on the particle surface via a thiol-ene approach catalyzed by V-50 as a free-radical source (Figure 8.27) [48]. 

Fig. 1.7 Synthesis of branched vinyl polymer using a divinyl comonomer and balancing level of thiol-free radical transfer agent - the Cross-linker/ Transfer Method (CTM).

Free radical copolymerization of a monovinyl compound and a divinyl cross-linker is by far the most commonly employed mode of polymerization for the preparation of organic monoliths. 

As common examples of monomers used for the production of resins, methacrylate and styrene can be mentioned, where the cross-linkers are ethylene dimethacrylate (EDMA) or divinyl benzene (DVB), respectively [205], The most important resins of this type are the poly(styrene-divinyl benzene) type or Amberlite resins, as well as the Wofatit and Lewatit [192] types. These materials have been widely applied as adsorbents [191,192,207] and as ion exchangers [193,194,208],... 

Application As is well-known in the industry, any microporous material which is formed through a nonequilibrium process is subject to variability and nonuniformity, and thus limitations such as block thickness, for example, due to the fact that thermodynamics is working to push the system toward equilibrium. In the present material, the microstructure is determined at thermodynamic equilibrium, thus allowing uniformly microporous materials without size or shape limitations to be produced. As an example, the cubic phase consisting of 44.9 wt% DDAB, 47.6% water, 7.0% styrene, 0.4% divinyl benzene (as cross-linker), and 0.1% AIBN as initiator has been partially polymerized in the authors laboratory by themal initiation the equilibrated phase was raised to 8S°C, and within 90 minutes partial polymerization resulted S AXS proved that the cubic structure was retained (the cubic phase, without initiator, is stable at 65°C). When complete polymerization by thermal initiation is accomplished, then such a process could produce uniform microporous materials of arbitrary size and shape. 

Gelation in Atom Transfer Radieal Copolymerization with a Divinyl Cross-linker... 

ATRP was applied to the copolymerization of a monovinyl monomer and a divinyl cross-linker to study the experimental gelation behavior. The fundamental features of ATRP, including fast initiation and reversible deactivation reactions, resulted in a retarded gelation and the formation of a more homogeneous network in the ATRP process compared to gel formation in a conventional radical polymerization. The experimental gel point based on the monomer conversion in the ATRP reaction occurred later than the calculated value based on Flory-Stockmayer s mean-field theory, which was mainly ascribed to intramolecular cyclization reactions. The dependence of the experimental gel points on several parameters was systematically studied, including the ratio of cross-linker to initiator, the concentration of reagents, reactivity of vinyl groups, initiation efficiency of initiators, and polydispersity of primaiy chains. 

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. 

Scheme 2. Structures of monomers and divinyl cross-linkers used during the...

Polymerization Processes. A variety of processes are used commercially to homopolymerize and copolymerize acrylic acid and methacrylic acid. On the basis of economics and environmental considerations, water is generally the preferred industrial solvent or polymerization medium. However, the choice of process is usually dictated by the requirements of the polymer to be produced. As already indicated, pH influences the rate of polymerization. Comonomers and molecular weight of the polymer to be produced also have a profound effect on the tsqje of polymerization process that can be used and on the type of product obtained. The contents of Table 2 indicate the change from water-soluble to alkab-soluble emulsions and ultimately emulsion polsrmers is dependent on the comonomers in copolymers of acryUc and methacryUc acids. This transition from water-soluble polymer to emulsion polymer as the acidic monomer is decreased depends on the hydrophobicity of the comonomer. Introduction of divinyl monomers causes transition to gel materials in all compositions. The gels may vary from highly swollen to tightly bound copolymers, depending on the cross-linker level. 

Phase Continuity in Sequentiai iPNs. The question has been repeatedly raised Do IPN morphologies really exhibit dual phase continuity Evidence for dual phase continuity in sequential IPNs was examined by Widmaier and Sperling (40,41). A series of sequential IPNs were prepared from poly(ra-butyl acrylate) and polystyrene. Two cross-linkers were used, divinyl benzene (DVB), which forms ordinary covalent cross-links, and aciyUc anhydride (AA), which forms labile crosslinks. The AA cross-links were cut by soaking the samples in a 10% aqueous ammonium hydroxide solution for about 12 hours. 

Data from manufacturers. PS = polystyrene. DVB = divinyl benzene cross-linker. The XAD series is from Rohm and Haas under the generic name of Amberlite, and the XE series is from the same company under the name of Ambersorb. The XUS series is from Dow under the generic name of Dowex. 

Divinyl benzene, with two vinyl groups, is a common cross-linker for chain polymerizations,... 

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,... 

In order to form a network, at least some of the mers need to have a functionality greater than 2 that is, more than two chain portions must emanate from those mers. In the structure depicted in Figure 9.3, the functionality of each cross-link is 4. When divinyl benzene or sulfur is used as a cross-linker, the functionality will indeed be 4. 

A 75/25 polybutadiene/polystyrene sequential IPN has 1% cross-linking in the polybutadiene and 1.5% cross-linking in the polystyrene, using divinyl benzene as the cross-linker. What is the diameter of the polystyrene domains at 25°C ... 

Star microgels have also been produced using a living linear polymer as the arms of the microgel structure, which were prepared first. The living polymer was then reacted with a divinyl cross-linker to form a star microgel consisting of a central core and surrounded by linear polymeric arms. Experimental details are reported elsewhere [8]. 

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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