Other Interpenetrating Networks

An interpenetrating network of PEDOT and poly(ethylene oxide) formed a material capable of a reversible angular deflection owing to the built-in gradients of polymer and conductivities [158]. A further network of PEDOT and polybutadiene/poly(ethylene 

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Interpenetrating networks of DMPPO and polymers such as polystyrene, polybutadiene, poly(urethane acrylate), and poly(methyl methacrylate) have been prepared by cross-linking solutions of DMPPO containing bromomethyl groups with ethylenediamine in the presence of the other polymer (68). 

Coagents ate often used with peroxides to increase the state of cure. Some coagents, such as polybutadiene or multifimctional methacrylates, are used at high levels to form polymer grafts or interpenetrating networks. Other coagents such as triaHyl cyanurate, triaHyl trimelHtate, and y /i -phenjiene bismaleimide are used at low levels to reduce the tendency of the polymer to degrade by chain scission. 

Other methods of blending include (1) fine powder mixing, and (2) monomer as a solvent for other components of the blend, followed by polymerization for making an interpenetrating network (IPN) [15]. 

An interpenetrating polymer network (IPN) is defined as a material comprising two or more networks which are at least partly interlaced on a molecular scale, hut not covalently bonded to each other. These networks caimot he separated unless chemical bonds are broken. Two possible methods exist for preparing them, as follows ... 

While copolymerization/cross-linking of reactive monomers and cross-linking of linear polymers are the main methods for producing hydrogels, there are other techniques which also deserve mention, particularly chemical conversion and the formation of interpenetrating networks. 

The first type, termed sequential IPN s, involves the preparation of a crosslinked polymer I, a subsequent swelling of monomer II components and polymerization of the monomer II in situ. The second type of synthesis yields materials known as simultaneous interpenetrating networks (SIN s), involves the mixing of all components in an early stage, followed by the formation of both networks via independent reactions proceeding in the same container (10,11). One network can be formed by a chain growth mechanism and the other by a step growth mechanism. 

Simultaneous Interpenetrating Networks. An interpenetrating polymer network, IPN, can be defined as a combination of two polymers in network form, at least one of which was polymerized or synthesized in the presence of the other (23). These networks are synthesized sequentially in time. A simultaneous interpenetrating network, SIN, is an IPN in which both networks are synthesized simultaneously in time, or both monomers or prepolymers mixed prior to gelation. The two polymerizations are independent and non-interfering in an SIN, so that grafting or internetwork crosslinking is minimized (23-26). 

In the simultaneous interpenetrating networks (SIN), the two reactions are run simultaneously. This reaction will be emphasized in the present paper. One reaction, for example, can be a polyesterification or a polyurethane stepwise reaction, while the other is an addition reaction using styrene to make polystyrene via free radical chemistry. 

Interpenetrating network (IPN) A combination of two polymers into a stable interpenetrating network. In a true IPN each polymer is cross-linked to itself, but not to the other, and the two polymers interpenetrate each other. In a semi-lPN, only one of the polymers is cross-linked the other is linear and by itself would be a thermoplastic. The purpose of producing IPN is to improve strength, stiffness, and chemical resistance of certain polymeric systems. 

One of the principal features of the compounds discussed above is their ability to be transformed into final products and/or articles from mixtures of almost any composition, even those whose components have little compatibility. The use of oligomers and monomers of various chemical structures expands the assortment of materials and articles that can be produced by combining different components. The interest in so-called hybrid binders, interpenetrating networks, polymer-oligomer systems, and other possible reactive components has increased during recent years. 

In discussing the formation of interpenetrating networks, we may reasonably assume as a first approximation that the synthesis of each component occurs irrespective of the others, and that the kinetics of the process is determined by the concentration of one or another component. However, this is a rather rough approximation, which is more or less valid at low concentrations of the polyurethane component. As was shown before,51 when the content of polyurethane exceeds 50%, its network begins to work as a cage, preventing polyester formation because the primary polyurethane network hampers diffusion of the ester. This means that in such systems, mutual interference of the components occurs even in the absence of chemical interactions between them. 

These reactions can also be used to form networks that interpenetrate,18,237,261-267 as illustrated in Figure 4.10.237 For example, one network could be formed by a condensation end-linking of hydroxyl-terminated short chains and the other by a simultaneous but independent addition end-linking of vinyl-terminated long chains. Interpenetrating networks are of interest because they can be unusually tough, and could have unusual dynamic mechanical properties. 

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