Interpenetrating polymer network types

Materials known as interpenetrating polymer networks, IPN s, contain two or more polymers, each in network form (6 9), A practical restriction requires that at least one of the polymer networks has been formed (i.e. polymerized or crosslinked) in the immediate presence of the other. Two major types of synthesis have been explored, both yielding distinguishable materials with different morphologies and physical properties. 

Urethane-Based IPN Foams. Interpenetrating polymer networks (IPNs) are types of polymer alloys composed of the entanglement of at least two cross-linked components (112). An ideal IPN has essentially no covalent bonds between the polymers. The resulting morphology shows... 

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. 

Interpenetrating polymer networks (IPNs) are relatively novel types of polymer alloys consisting of two or more crosslinked polymers held together by permanent entanglements with only accidental covalent bonds between the polymers, i.e. they are polymeric catenanes (1-6). 

Although interpenetrating polymer networks (IPNs) are now beginning to be commercially exploited, little is known about many types of engineering behavior, such as fatigue. In this paper, energyabsorbing simultaneous interpenetrating networks (SINs) based on polyether-type polyurethanes (PU) and poly(methyl methacrylate)... 

The structures listed in Table 1.6 are divided into three categories Short sequences, Long sequences, and Networks. Within the first category a sequence of placement of individual CRU is considered, within the second the placement of long sequences of CRU defines the copolymer type, while to the third belong crosslinked networks, crosslinked polymers, and chemical-type interpenetrating polymer networks. The network is a crosslinked system in which macromolecules of polymer A are crosslinked by macromolecules of polymer B [Sperling, 1992]. The composition can be expressed as, e.g., Woc -co-poly(butadiene/styrene) (75 25 wt%), or gra/i-co-poly[isoprene/ (isoprene acrylonitrile)] (85 15 mole %). 

Interpenetrating polymer networks (IPN s) have been studied since the 1960 s although specific blends exhibiting those features were prepared long before. Barrett and Sperling [1993] recendy reviewed the types of IPN s available along with present and potential applications. Specific applications presently utilized include biomedical,... 

A similar study has been performed on EPI blends in which the vinyl ether was replaced by an acrylate monomer (HDDA) to produce, by different mechanisms, two interpenetrating polymer networks. With the onium salt as sole photoinitiator, the cationic polymerization of the EPI epoxy groups occurred as fast in the formulation containing 20% of HDDA by weight as in the EPI/DVE-3 blend, to reach nearly 100% conversion within 0.6 s (Fig. 11). The polymerization quantum yield was found to be similar to that measured in the EPI/vinyl ether blend Op 650 mol E. By contrast, the acrylate double bonds were found to polymerize at a much slower pace, most probably because of the low reactivity of the free radicals generated by the cationic-type photoinitiator. 

I. J. Constable, G.J. Crawford, Interpenetrating polymer network (IPN) as a permanent joint between the elements of a new type of artificial cornea, J. Biomed. Mater. Res. 28 (1994) 745-753. 

Figure 1 An illustration of three main types of hydrogels. Homopolymers (left) are composed of a single polymer type multipolymers (middle) are composed of two or more polymers cross-linked together (or arranged on individual chains) and interpenetrating polymer networks (IPNs) (right) comprise two different polymers that are separately cross-linked.

This is not the case of real-time infrared (RTIR) spectroscopy, " a technique that permits one to look at the chemical processes by monitoring in situ the disappearance of the monomer reactive group upon UV exposure. By this technique conversion versus time curves have been directly recorded for polymerizations occurring within a fraction of a second. RTIR spectroscopy proved also well suited to study the photopolymerization of monomer mixtures, which leads to the formation of copolymers or interpenetrating polymer networks, as it allows the disappearance of each type of monomer to be accurately followed in the course of the reaction. The performance of the three analytical techniques most commonly used to follow in real time high-speed photopolymerizations are summarized in Table 1. 

Interpenetrating polymer networks (IPN s) are a novel type of polyblend composed of crossllnked polymers. They are more or less intimate mixtures of two or more distinct crosslinked polymers with no covalent bonds between the polymers. True IPN s may be described as combinations of chemically dissimilar polymers in which the chains of one polymer are completely entangled with those of the other, i.e., a homogeneous morphology results. 

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