Simultaneous IPN

Simultaneous IPN. According to the statistical theory of rubber elasticity, the elasticity modulus (Eg), a measure of the material rigidity, is proportional to the concentration of elastically active segments (Vg) in the network [3,4]. For negligible perturbation of the strand length at rest due to crosslinking (a reasonable assumption for the case of a simultaneous IPN), the modulus is given by ... 

Because v, is a fractional quantity. Equation 18 always predicts modulus values larger than the corresponding expression for a simultaneous IPN(Equation 13). For the special case of a network with no defects or trapped entanglements (i)) 1, "), an earlier... 

Note 2 An IPN may be further described by the process by which it is synthesized. When an IPN is prepared by a process in which the second component network is formed following the completion of formation of the first component network, the IPN may be referred to as a sequential IPN. When an IPN is prepared by a process in which both component networks are formed concurrently, the IPN may be referred to as a simultaneous IPN. 

Simultaneous IPN was obtained by dissolving BPA/DC in an unsaturated polyester resin (UPR) and crosslinking at elevated temperature using benzoyl peroxide and a zinc compound as cyclotrimerization catalyst. Prolonged post-curing at 180 °C was needed to reach elevated Tg values [132, 133],... 

A more selective approach consists in trying to influence the kinetics of formation of at least one network in this case, the two networks are formed more or less simultaneously, and the resulting morphology and properties can be expected to vary to some extent without changing the overall composition. The same system as previously studied, PUR/PAc, has been utilized in order to prepare a series of in situ simultaneous IPNs (SIM IPNs), by acting essentially on two synthesis parameters the temperature of the reaction medium and the amount of the polyurethane catalyst. Note that the term simultaneous refers to the onset of the reactions and not necessarily to the process. The kinetics of the two reactions are followed by Fourier transform infra-red (FTIR) spectroscopy as described earlier (7,8). In this contribution, the dynamic mechanical properties, especially the loss tangent behavior, have been examined with the aim to correlate the preceding synthesis parameters to the shape and temperature of the transitions of the IPNs. 

Xie et al. (92, 93) synthesized simultaneous IPN from castor oil polyurethane and copolymers of vinyl monomers, including styrene, methyl methacrylate, and acrylonitrile, without cross-linker using a redox initiator at room temperature and both the formation kinetics of cross-linking and grafting on phase separation were examined. It was demonstrated that the resulting materials were mainly grafted IPN... 

A number of variations of the above-mentioned full IPNs have also been stated in the literature. One of them involves having either Polymer I or II as linear (not crosslinked) polymer, in which case it is called semi-IPN. The other variation involves the formation of Polymer I and II simultaneously through two noninterfering polymerization processes (such as stepwise and chain polymerizations) in which case it is called simultaneous IPN (SIN). If a linear polymer is formed simultaneously with a crosslinked polymer, then we have a semisimultaneous IPN (semi-SINS). Still another type is taking a mixture of two linear polymers, and crosslinking both components simultaneously, in which case it is called interpenetrating elastomeric network (lEN). The common feature of... 

There are at least four general types of combinations of crosslinked (x) and linear (1) polymers in a two-component system both components crosslinked (xx), one or the other component crosslinked (lx or xl), and both components linear (11). Where at least one of the components has been polymerized in the presence of the other, the xx forms have often been called interpenetrating polymer networks (IPN), the lx and the xl forms termed "semi-IPNs", and the last, linear or in situ blends. There are also a number of ways in which the components can be formed and assembled into a multicomponent system. Sequential IPNs are prepared by swelling one network polymer with the precursors of the second and polymerizing. Simultaneous IPNs are formed from a mixture of the precursors of both components polymerization to form each component by independent reactions is carried out in the presence of the other precursors or products. Usually, the simultaneous IPNs that have been reported are extremes in the component formation sequence the first component is formed before the second polymerization is begun. Sequential IPNs and simultaneous IPNs of the same composition do not necessarily have the same morphology and properties. 

A simultaneous IPN of epoxy with unsaturated polyester, cross-linked using microwave radiation, has been reported (1). The radiation was intended to yield a more isotropic structure because of uniform heating also, it could reduce grafting reactions between the two networks and produce a more classical IPN structure. Unfortunately, the mechanical properties and morphology of the network were not reported. 

Simultaneous IPNs are formed by homogeneously mixing together monomers, prepolymers, linear polymers, initiators, and crosslinkers, The monomers and prepolymers are simultaneously polymerized by independent reactions that differ enough to avoid interfering with each other. For example, a polyure-thane/polymethacrylate and a polyurethane/polystyrene were made in a process in which both monomers were prepolymerized, dissolved together, and reacted to form an IPN. Another urethane system was made from castor oil reacted with toluene diisocyanate and sebacic acid polyesters. The resultant urethane prepolymer was then mixed with polystyrene to form an IPN. 

Polymer comprising two or more polymer networks which are at least partially interlaced on a molecular scale (Figure 1.16) but not covalently bonded to each other and cannot be separated rmless chemical bonds are broken [206,411]. A mixture of two or more preformed polymer networks is not an IPN. An IPN may be further described by the process by which it is synthesized e. g. when an IPN is prepared by a process in which the second component network is polymerized following the completion of polymerization of the first component network, the IPN may be referred to as a sequential IPN. In contrast, a process in which both component networks are polymerized concurrently, the IPN may be referred to as a simultaneous IPN. An IPN is distinguished from other multipolymer combinations, such as polymer blends, blocks, and grafts, in two ways (1) an IPN swells, but does not dissolve in solvents and (2) creep and flow are suppressed. 

IPNs are formed sequentially by more than one IPN in a process, whereas simultaneous IPNs are formed simultaneously. However, semi-IPNs are formed by the polymerisation of a monomer in the presence of a polymer. All the types of IPN listed earlier are found in vegetable oil-based polymers. These IPNs have some advantages over polymer blends or cross-linked polymers. 

A series of castor oil polyurethane/poly(methyl methacrylate) interpenetrating polymer networks (IPNs) and gradient IPNs, cured at room temperature, were prepared by a simultaneous IPN method, and nanocomposites with BaTiOs superfine fibre were reported for the systems. A dose-dependent improvement in thermoelectric and mechanical properties was observed in the nanocomposites compared to the pristine 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]. 

These samples, simultaneous PU/PS IPNs, were synthesised by a one-short route. The IPN topology appears to restrict phase separation, which results in materials with broad transition regions. By variation of the crosslink level in either or both polymer networks, the controlled introduction of internetwork grafting or the incorporation of compatibilisers into the PS network, the compatibility of the two polymer networks can be increased. For simultaneous IPNs, it has been found [129] that the network which is first formed... 

A simplified mold construction often made from a light metal casting alloy or from an epoxy resin to obtain information for the final mold and/or part design. Simultaneous IPN in which mie polymer is in network form and the other linear. 

Besides sequential and simultaneous IPN synthetic methods, there are several other methods of preparation ... 

It may well be that the temperature of formation of the first network is also of much importance, the normal IPN s showed considerably higher T(tan values than the inverse and simultaneous IPN s. There was also some indication for inhomogeneity of the normal IPN s, not for the other systans. 

Hydrogel beads composed of calcium alginate and crosslinked polyisopropylacrylamide were prepared based on a simultaneous IPN process. The themially reversible formation of the core-shell structure in the hydrogel was applied to temperature modulated drug release using indomethacin. 12 refs. 

According to the mode of synthesis, IPNs are distinguished into five different types (i) sequential IPNs, (ii) simultaneous IPNs, (iii) interpenetrating elastomeric networks, (iv) thermoplastic IPNs and (v) gradient IPNs ... 

Some properties of IPNs are simple averages of the properties of the eom-ponent polymers. Sometimes the values are higher than expeeted. Density measurements on PU/PS simultaneous IPNs showed a density higher than expected. This was due to the partial interpenetration of chains of the rubbery and glassy polymer components." ... 

The kinetic conditions of the IPNs formation are different from conditions for individual networks,and therefore transferring data on the kinetics of the the individual networks to the kinetics of IPNs is difficult for the following reasons. In the case of simultaneous or successive IPNs, the reaction proceeds almost from the very beginning in the matrix of one of the networks, since even for simultaneous IPNs, the kinetics of the constituent network formation is different, and so a certain network is formed earlier and serves as a matrix for the formation of the other. 

Simultaneously IPN Simultaneously IPN system is formed by the simultaneous polymerization of both components of polymer [69]. 

Simultaneous IPNs involve monomers or reactive oligomers and crosslinkers of two or more reactive systems. These systems are generally chosen such that the reaction of one component does not interfere with or is involved with the reactions of the second component. Otherwise, grafting reaction would compete with interlocking ring formation as the method of compatibilization. An example of a simultaneous IPN is the reaction of free radical polymers (such as polyacrylates) in the presence of condensation polymers such as polyurethanes, as has been the subject of many investigations [171-174]. A PU/PMMA simultaneous IPN exhibited transparency and showed only limited phase separation below 30% PMMA [171]. This IPN... 

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