Anionically Polymerized IPNs

Nearly all of the materials described in this monograph were prepared by some combination of free-radical and/or condensation reactions. Most recently, however, Lipatova et obtained grafted sequential IPNs on the basis of matrices from living network polymers, using anionic polymerizations for both networks I and II. 

Monomers a,(y-dimethacrylbis (triethylene glycol) phthalate (MGP) or trioxyethylene a,o -dimethacrylate (TMA) were polymerized with Na-naphthalene. Styrene and divinyl benzene were swollen in, and the reaction continued. Network I is densely crosslinked under these conditions. 

This synthesis, undertaken by Klempner, Frisch, and Frisch makes use of two noninteracting types of latexes. These are synthesized separately as linear polymers, mixed together, along with crosslinkers and catalysts, and co-coagulated. The material is then subjected to a simultaneous crosslinking step via heating. Table 5.4 delineates materials employed in the synthesis. One latex usually was a polyurethane. 

The materials are designated as lENs because both latexes are normally elastomeric and to help distinguish them from other types of IPNs. 

Poly(urethane-urea) U-1033 50% water emulsions of Wyandotte Chemicals 

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Free-radical chemistry is the most widely used but not the only one. Frontal curing of epoxy resins has been studied (14-18). Begishev et al. studied anionic polymerization of e-caprolactam (19). Frontal Ring-Opening Metathesis Polymerization (FROMP) has been successfully achieved with dicyclopentadiene (20) and applied to making IPNs (21). Mariani et al. have achieved FP with urethane chemistry (22). 

T. E. Lipatova, V. V. Shilov, N. P. Bazilevskaya, and Yu. S. Lipatov, The Formation of Interpenetrating Polymeric Networks on the Basis of Oligoester Acrylate, Styrene, and Divinylbenzene by an Anionic Mechanisms, Br. Polym. J. 9(2), 159 (1977). Oligoester acrylate/PS anionically prepared IPNs. 

V. V. Shilov and T. E. Lipatov, Structure of the Interpenetrating Networks Obtained by Anionic Polymerization, Vysokomol. Soedin. Ser. A. 20(1), 62 (1978). Anionic IPNs based on PS and oligoester acrylates. 

G. S. Solt, Improvements Relating to the Production of Ion-Exchange Resins, Br. Pat. 728,508 (1955). Anionic/cationic IPNs. Ion-exchange resins. Suspension polymerization. 

Special Considerations in IPN and SIN Synthesis. Most of the IPNs and SINs made to date rely on chain and/or step pol)mierization, although other methods, such as anionic polymerization, have been occasionally employed. Of course, appropriate cross-finkers, initiators, and so forth must be added. 

Sequential IPNs Obtained Using Anionic Polymerization. 80... 

IPNs based on oligoester acrylates synthesized using anionic polymerization [135]. 

Pre-crosslinked Latex Blends. In these materials the individual latexes are crosslinked during synthesis, then blended, and a film is formed. Because of limited deformation and/or interdiffusion capabilities, such films tend to be weak, and only used for special purposes [Zosel and Lay, 1993 Lesko and Sperry, 1997], However, light crosslinking, as occurs in SBR latexes, may be tolerated. Pre-crosslinked latex blends materials are actually not IPNs, because the definition requires that at least one of the polymers be polymerized and/or crosslinked in the immediate presence of the other. An application of pre-crosslinked suspension-polymerized blends, in anionic and cationic form, is as ion-exchange resins. In suspensions, the particles are larger, usually of the order of 10-200 pm. 

J. M. Widmaier, Anionic Crosslinking of Polystyrene in the Presence of Free Polymeric Chains, Makromol. Chem. 179 (7), 1743 (1978). PS-based semi-IPNs. 

In recent years, there has been a significant increase in the number of IPN products (see Table 4). These materials range from false teeth to ion exchange resins. The latter depend on putting anionic and cationic networks on the same suspension polymerized particles, in juxtaposition, but not molecularly dissolved. 

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