Monomers elastomers swollen with

The polymers used to produce blends may be thermoplasts, thermosets, or elastomers. A monophase system is often sought in blends of two elastomers after vulcanization, both components form a single-phase network. In the ideal case of an interpenetrating network (IPN), a network of one component is first formed. This network is then swollen with the monomer of the second component. After cross-linking polymerization of the second component, two mutually interpenetrating but still mutually independent networks are produced. 

It has been shown by Angier and Watson [A8, W2] that if an elastomer is swollen with a vinyl monomer (styrene, chlorostyrene, acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, vinyl pyridine, methyl vinyl ketone, etc.), mastication in the absence of oxygen can lead to the formation of block copolymers. This would seem to occur through the mechanism... 

Another procedure for synthesis of polsrmer blends is by formation of interpenetrating polymer networks. A network of one polymer is swollen with the other monomer or prepol5mier after that, the monomer or prepolymer is crosslinked (63). In contrast to the preceding methods used for thermoplastics and uncrosslinked elastomers, blends of reactoplastics are prepared by this method. Phase Structure Development in Molten State. 

Stirring (300 rpm) was started, and the mass was heated and kept at the desired temperature for 2 hours. During this preliminary treatment, the elastomer was swollen and partially dissolved by the monomer. Finally, the remaining water containing the initiator in suspension was introduced, and the reaction was allowed to proceed until the monomer conversion reached the desired value. The polymer, in the form of pearls, was separated from the suspending liquid by centrifugation, washed thoroughly with water, and dried in an oven at reduced pressure. 

Sequential IPNs are started with one polymer that is already cross-linked. It is swollen, and a monomer along with an initiator and a cross-linking agent are added and polymerized in place. A typical example (37) is an elastomer such as butadiene or ethyl acrylate cross-linked with divinylbenzene as the first polymer. The monomer that is polymerized in the swollen polymer is styrene or methyl methacrylate cross-linked with divinylbenzene or tetraethylene glycol dimethacrylate. The initiator is potassium for butadiene, and benzoin for the other monomers. 

Crosslinking can be used to overcome the aforementioned obstacles, as in the case of the calamitic networks in which the orientation and polarity are preserved. First experiments were performed by swelling a calamitic LCE with a low-molar-mass BCLC [182, 183]. Up to 35 mol% of this material could be incorporated into the network. The resulting gel had a flexoelectric cmistant e-i of 20 nC/m. This is one-third of the value of the low-molar-mass BCLC, which corresponds to the volume fraction of the BCLC. Only recently has a pure bent-core elastomer (BCFLCE) been made [139, 169]. Following the synthetic route of Finkelmann, an oriented, transparent nematic elastomer sample could be obtained. As a polysiloxane backbone was used, the Tg was close to room temperature. The flexoelectric constant of 40 nC/m is somewhat smaller than for the pure bend-core monomer, but larger than the value obtained for the swollen elastomer. 

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