Components, IPN

Three-component IPNs prepared from polyurethane, epoxy, and unsaturated polyester resin resulted in even broader tan 5 values when compared to two component (PU/E) IPN elastomers. Furthermore, the tan S values for the three component IPN systems were still high after the transitions were apparently complete, which is of enormous significance in sound energy absorption applications. IPN foams prepared by using PU/E (two-component) showed excellent energy absorbing abilities. This was reflected in rebound, hysteresis, and sound absorption studies. 

Thus, this research focused on the synthesis of IPNs which have a high and broad tan S. Two-component IPN systems that proved the most promising were used as the foundation for foams. Three-component IPN foams have yet to be prepared. 

The IPN elastomers were synthesized by the mixing of two components. In the case of two-component PU/E IPN elastomers, one component contained Nlax 31-28, Isonol-100, T-12 and epoxy catalyst (BFs-etherate, Eastman Chemical). The other component contained epoxy resin (DER-330, Dow Chemical) and Isonate-143L. Whereas In the case of three-component IPN elastomers composed of PU/E/UPE, polyester resin catalyst (TBPB) and unsaturated polyester resin were Incorporated, respectively. In the former and latter components. 

Table VII. Formulations of Polyurethane/Epoxy/Unsaturated Polyester Three-Component IPN Elastomers...

Two-component IPN foams consisting of polyurethane and epoxy were prepared by the one-shot, free-rise method. The effects of PU/E ratio on the sound absorption and mechanical energy attenuation characteristics were determined with varying levels of different fillers and plasticizers. The formulations (Table IX) were based on the best elastomer results. An average of over 90X absorption was obtained at high frequencies by the Impedance tube method. However, this average drops dramatically at low frequencies. This reduction may be seen in Figs. 3 and 4 for 90/10 and 70/30 IPN foams vlth 20X... 

Foams made from the two-component IPNs showed a significant Increase in energy absorbing ability as compared to the 100% polyurethane foams. This is indicated by increased sound absorption. Increased hysteresis, and decreased rebound. 

Two- and Three-Component IPN Elastomers with Enhanced Sound... 

Fig. 8.1. According to eq. (8.1) a spinorbital is a mixture of a and orbital components ipn(r) and respectively. Figure shows two sections of such a spinorbital (x denotes the Cartesian axis perpendicular to the plane of the pagej section 2 = 0, o- = 4 (solid isolines) and section z = 0, cr = —1 (dashed isolines). In practical applications most often a restricted form of spinorbitals is used either ipn = 0 or

IPNs can be considered as a new class of polymer composite materials made of two different components. IPNs may also serve as hybrid binders for traditional composite materials. As distinct from traditional binders, hybrid binders [49] are the systems where segregation of microvolumes of constituent components has occurred due to incomplete microphase separation. The hybrid binders can be considered as self-reinforced (filled) or disperse-... 

Interpenetrating Polymer Network (IPN) A subclass of PBs reserved for the mixture of two polymers where both components form a continuous phase and at least one is synthesized or crosslinked in the presence of the other [8]. 

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]. 

The term IPN was first used in 1960 to describe the apparently homogeneous product obtained from styrene crosslinked with divinylbenzene. IPNs were prepared from this system by taking a crosslinked poly(styrene) network and allowing it to absorb a controlled amount of styrene and a 50% divinylbenzene-toluene solution containing initiator. Polymerisation of this latter component led to the formation of an IPN, the density of which was... 

Typically IPNs exhibit some degree of phase separation in their structure depending on how miscible the component polymers are. However, because the networks are interconnected such phase separation can occur only to a limited extent, particularly by comparison with conventional polymer blends. Polymer blends necessarily have to be prepared from thermoplastics IPNs may include thermosets in their formulation. 

Silicone co-polymer networks and IPNs have recently been reviewed.321 The development of IPNs is briefly described, and the definitions of the main (non-exclusive) classes of the IPNs are cited. Examples of latex IPNs, simultaneous and sequential IPNs, semi-IPNs, and thermoplastic IPNs are provided. The use of silicone-silicone IPNs in studies of model silicone networks is also illustrated. Networks in which siloxane and non-siloxane components are connected via chemical bonds are considered co-polymer networks, although some other names have been applied to such networks. Today, some of the examples in this category should, perhaps, be discussed as organic-inorganic hybrids, or nanocomposites. Silicone IPNs are discussed in almost all of the major references dealing with IPNs.322-324 Silicone IPNs are also briefly discussed in some other, previously cited, reviews.291,306... 

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. 

The temperature-sensitive poly(A-isopropyl acrylamide) and pH-sensitive poly(methacrylic acid) were used as the two component networks in the IPN system. Since both A-isopropyl acrylamide (NIPAAm) (Fisher Scientific, Pittsburgh, PA) and methacrylic acid (MAA) (Aldrich, Milwaukee, Wl) react by the same polymerization mechanism, a sequential method was used to avoid the formation of a PNIPAAm/PMAA copolymer. A UV-initiated solution-polymerization technique offered a quick and convenient way to achieve the interpenetration of the networks. Polymer network I was prepared and purified before polymer network II was synthesized in the presence of network I. Figure I shows the typical IPN structure. 

This is a theoretical study on the entanglement architecture and mechanical properties of an ideal two-component interpenetrating polymer network (IPN) composed of flexible chains (Fig. la). In this system molecular interaction between different polymer species is accomplished by the simultaneous or sequential polymerization of the polymeric precursors [1 ]. Chains which are thermodynamically incompatible are permanently interlocked in a composite network due to the presence of chemical crosslinks. The network structure is thus reinforced by chain entanglements trapped between permanent junctions [2,3]. It is evident that, entanglements between identical chains lie further apart in an IPN than in a one-component network (Fig. lb) and entanglements associating heterogeneous polymers are formed in between homopolymer junctions. In the present study the density of the various interchain associations in the composite network is evaluated as a function of the properties of the pure network components. This information is used to estimate the equilibrium rubber elasticity modulus of the IPN. 

Comparisons of the theory with experiment can not be presently made due to the lack of data on well characterized molecular IPN. Indications about its validity can, however, be deduced by examining its consistency at extreme cases of material behavior. The agreement at the one-component limit, for example, provided that the rubber is not very weak (iji not very small), has been successfully demonstrated by Ferry and coworkers [ ]. A useful result is obtained at the version of the theory applicable to the fluid state (i.e., at the limit of zero crosslinking). From the last two terms of Equation 13, the following relationship can be derived for the plateau [ ] and time dependent relaxation modulus of miscible polymer blends ... 

Interpenetrating polymer networks are defined in their broadest sense as an intimate mixture of two or more pol)Mners in network form [1,2]. Ideally, they can be synthesized by either swelling the first crosslinked polymer with the second monomer and crosslinker, followed by in-situ polymerization of the second component (sequential IPN s) or by reacting a pair of monomers and crosslinkers at the same time through different, non-interfering reaction mechanisms, simultaneous interpenetrating networks, SIN s. In fact, many variations of these ideas exist in both the scientific and the patent literature. In any case, at least one of the two components must have a network structure, as an IPN prerequisite. ... 

In a system of significant interest to the present works, Graillard, et al. [62] studied the ternary phase diagrams of the systems polybutadiene-styrene-polystyrene and polybutadiene-block-polystrene-styrene-polystyrene. They showed that the presence of block copolymer increased the miscibility of the two poljrmers, as the styrene component polymerized. Similar effects are probable in the IPN s, as compared with the corresponding blends. 

Figure 18 illustrates a model of the three component phase diagram of an IPN, where poljrmer I, poljrmer II, and monomer II are chosen for generality in expressing sequential IPN formation. On poljrmerizatlon of monomer II, first phase separation is initiated, probably by nucleation and growth. However, shortly a modified spinodal decomposition mechanism sets in as the overall composition is driven deeper into the phase separation region. 

Polyurethane-acrylic coatings with interpenetrating polymer networks (IPNs) were synthesized from a two-component polyurethane (PU) and an unsaturated urethane-modified acrylic copolymer. The two-component PU was prepared from hydroxyethylacrylate-butylmethacrylate copolymer with or without reacting with c-caprolactonc and cured with an aliphatic polyisocyanate. The unsaturated acrylic copolymer was made from the same hydroxy-functional acrylic copolymer modified with isocyanatoethyl methacrylate. IPNs were prepared simultaneously from the two-polymer systems at various ratios. The IPNs were characterized by their mechanical properties and glass transition temperatures. 

IPNs can be prepared by either the "sequential" or the "simultaneous" technique. IPNs synthesized to date exhibit varying degrees of phase separation depending primarily on the compatibility of the component polymers (4-7). 

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. 

Thermosets are generally used in advanced composites due to their excellent thermal and dimensional stability, high modulus, and good mechanical properties. Because thermoset resins are inherently brittle, however, some applications require improved fracture resistance. Toughening of thermosets has been achieved through various methods, such as incorporation of reactive liquid rubber [1-9], elastomer [10], or rigid thermoplastics [11-25], and IPN formation with ductile component [26]. 

Continuity can also be reached by polymerizing one of the components within the other. In such a case the blend is called an IPN, an interpenetrating network it is, in most cases formed by a thermoset in a thermoplastic polymer. An example is a compound built-up from 50% of a thermoplast (polycarbonate or polysulphone), and 50% of a cross-linked polymer on the basis of dicyanate bisphenol-A. The skeleton... 

---