Mixed interpenetrating polymer network

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). 

Polymer blends and interpenetrating polymer networks (IPNs) are different from copolymers but like copolymers are used to bring together the properties of different polymers [Paul et al., 1988]. The total of all polymer blends (produced by both step and chain reactions) is estimated at about 3% of the total polymer production—about 3 billion pounds per year in the United States. There is considerable activity in this area since new products can be obtained and markets expanded by the physical mixing together of existing products. No new polymer need be synthesized. 

Simultaneous Mixing or Reacting. One of the advantages of the proposed nomenclature is the preservation of the time sequence of polymer reactions. Examples include grafting reactions and interpenetrating polymer networks. In some cases, like the blends or random copolymerization, the time sequence has no meaning. 

These IPNs, prepared by the mixing of two components, were essentially simultaneous interpenetrating polymer networks (SIN). 

Interpenetrating polymer networks are defined eis a combination of two polymers, each in network form. From a practical point of view, an IPN is comprised of two polymers which cannot be separated chemically, do not dissolve or fiow, and are not bonded together. Like most other multicomponent polymer materials, IPN s usually phase separate due to their very small entropy of mixing. However, the presence of the crosslinks tends to reduce the resulting domain size, hence yielding a unique method of controlling the final morphology. 

There are two general methods of synthesizing IPN s, see Figure 1. For sequential IPN s, polymer network I is synthesized, and monomer II plus crosslinker and activator is swelled in and polymerized. For simultaneous interpenetrating polymer networks, SIN s, both monomers and their respective crosslinkers and activators are mixed together and polymerized, usually by separate and non-interfering kinetic methods such as stepwise and chain polymerizations. Of course, there are many... 

An interpenetrating polymer network (IPN) is an intimate assembly of two polymers in network form, one of which is usually either prepared or crosslinked in the presence of the other. Typically, the initial polymer network is. swollen in the presence of the second monomer together with a crosslinking agent, and the second monomer allowed to polymerise and crosslink. Alternatively, simultaneous. synthesis is possible in which the monomeric components of both networks are first mixed and then allowed to polymerise. 

Fig. 11. Automotive finishes such as that on the Honda Civic have depth, luster and environmental resistance that is the result of a complex mixture of hybrid organic-inorganic materials cured into mixed graft interpenetrating polymer network systems.

An interpenetrating polymer network (IPN) is defined as a combination of two crosslinked polymers, at least one of which has been synthesised [98] and/or crosslinked in the immediate presence of the other. From the topological point of view, IPNs are closely related to pol)nner blends and to block, graft and crosslinked copolymers. From the synthesis point of view, IPNs can be classified, broadly, into two general types (a) sequential IPNs where a polymer network is formed which is then swollen by the monomer, plus a crosslinking agent and an activator, which is then polymerised in situ to form the second network and (b) simultaneous IPNs (SIPN) where the components necessary to form both networks are mixed and polymerised, at the same time, by non-competing mechanisms. If one of the two polymers is linear (uncrosslinked), a semi-IPN results. A homo-IPN results if both the network polymers are identical in chemical composition [98]. 

Yu. S. Lipatov, L. M. Sergeeva, L. V. Karabanova, A. E. Nesterov, and T. D. Ignatova, Thermodynamic and Sorption Properties of Interpenetrating Polymer Networks Based on Polyurethane and a Styrene-Divinylbenzene Copolymer, Vysokomol. Soedin. Ser. A. 18(5), 1025 (1976). Transition layer studies of PU/PS IPNs. IPN heat of mixing. 

Methods of Blend Preparation. Most polymer pairs are immiscible, and therefore, their blends are not formed spontaneously. Moreover, the phase structure of polymer blends is not equilibrium and depends on the process of their preparation. Five different methods are used for the preparation of polymer blends (60,61) melt mixing, solution blending, latex mixing, partial block or graft copolymerization, and preparation of interpenetrating polymer networks. It should be mentioned that due to high viscosity of polymer melts, one of these methods is required for size reduction of the components (to the order of /ttm), even for miscible blends. 

Many poly(methyl methacrylate)-based denture teeth are based on a specialized interpenetrating polymer network technology (90,91). First, densely cross-linked suspension-polymerized particles are prepared. These are then placed in a similar monomer mix (with appropriate inorganic materials, etc.), and the mix re-polymerized. Because they are highly cross-linked, they are more abrasion resistant, as described above, ffowever, they swell less in the presence of triglycerides such as butter, salad oU, fats, and similar materials which swell and damage uncross-linked poly(methyl methacrylate)-based teeth. 

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