Cross-linking with divinyl monomers

Vinyl polymers cross-linked with divinyl monomers, for example, polystyrene polymerized in the presence of divinyl benzene. 

Hydroxyl containing polymers may be cross-linked with diisocyanates. Fordyce and Ferry cross-linked styrene-maleic anhydride copolymers through the action of glycols. The copolymerization of divinyl with vinyl monomers may be looked upon as a method of cross-linking chain polymers. The cross-linkages are introduced simultaneously with the growth of the linear polymer chains, rather than afterwards, but this difference is secondary. 

The cross-linking of unsaturated polymer chains by polymerization with divinyl monomers can be considered to occur in three... 

Porapak is a polymer of ethylvinyl benzene cross-linked with various amounts of divinyl benzene to produce polymers of various porosities. The eight basic types are listed in order of increasing polarity P, P-S, Q, Q-S, R, S, N, and T. These materials do not require a liquid phase, because the organic polymer apparently acts like a liquid phase. Porapak P and Q are the same, except that P has a larger pore size. The other Porapaks are modified by adding specific monomers. 

Disulfide Formation in Polystyrene Networks. Polymer-bound thiols were prepared by copolymerizations of bis -vinylbenzyl)disulfide with other divinyl monomers followed by diborane reduction (Scheme 5) (fiS). The initially formed thiols were juxtaposed for reoxidation to disulfides. Polymer-bound thiols were prepared also by copolymerization of p-vinylbentyl thiolacetate with divinyl monomers followed by hydrolysis (Scheme 6). llie latter thiols were distributed randomly throughout the polymer network. The copolymer reactivity ratios for p-vinylbenzyl thiolacetate and styrene are unknown, but should be similar to those of styrene (Mi) and p-vinyl-bentyl chloride (M2) ri = 0.6, r2 = 1.1 (fifi). Copolymeiizations with equal volumes of monomers and 1/1 acetonitrile/toluene product macroporous 40-48% DVB-cross-linked networks (651. 

A munber of other synthetic polymer networks have been developed and commercialised for liquid chromatography including polyvinylacetate cross-linked with butanediol divinyl ether, Merkogel GPC packings (Merck), polyvinylalcohol, Frac-togel and Toyopearl (Toyo Soda), a hydroxylated acrylic monomer cross-linked with a bifunctional agent, Trisacryl (Sepracor) and a hydrophilic vinyl polymer, TSKgel PW (Toyo Soda). 

In earlier work preformed polymer was cross-linked, e.g. by ionizing radiation (39, 103, 104) with suitable assumptions as to randomness of the reaction, the molecular statistics of product can be calculated as a function of the degree of cross-linking. An alternative method is to co-polymerize with small amounts of tetra-functional monomer, e.g. divinyl benzene (36, 105, 107). Both these methods produce highly poly-disperse products, having tetra-functional branch-points. 

Cross-linking Effect on Polymerization. The general cross-linking reaction that occurs during polymerization and involves components with a functionality greater than one (two or more double bonds, divinyl monomer) has been studied extensively. The statistical analysis of molecular distributions in such reactions is due to Flory (36). 

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. 

Polymerization of divinyl benzene in DODAB vesicles also resulted in phase separation where broccoH parachutes were observed [15]. The latex beads in these cases appear as clusters of fuzzy latex particles. Phase separation appears to be sHghtly suppressed by the cross-linking, but the incompatibiUty of the aromatic monomer with the surfactant bilayer apparently dominates the final morphology as phase separation is obvious. Interestingly, when the alkyl chain surfactant is replaced with an aromatic polymerizable one, phase separation is completely suppressed [16]. With the A1 and A2 surfactants illustrated in Fig. 4, German et al. were able to successfully copolymerize styrene and divinyl benzene. The authors concluded that using a polymerizable amphiphile is a prereq-... 

Difunctional monomers such as DVB or divinyl ether have been found to be efficient in the synthesis of star (co)polymers having a cross-linked core from which homopolymer or block copolymer arms radiate outwards. However, so far only core last method has been reported in cationic polymerization. This method is particularly suited to prepare stars with many arms. The average number of arms per molecule is a function of several experimental and structural parameters. 

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