Semi-IPNs

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... 

Extensive research has been conducted and reviewed on interpenetrating polymer networks during the past decade (31-33). IPNs can be categorized into Semi-l-IPN and Semi-2-IPN. Semi-2-IPNs are those in which crosslinkable oligomers or materials are polymerized into the linear matrix. Semi-interpenetrating networks could have combined polymers that have same or different repeating units. 

An increase in heat deflection temperature of some thermoplastic polymers can be achieved by the addition of polyfunctional aromatic cyanates (BPA/DC in particular) and trimerization catalysts. A rigid network is formed as a resul t of the cyanate trimerization. The polymer material consists of a linear polymer and a crosslinked network and belongs to the class of semi-IPNs (semi-interpenetrating Polymer Networks) the corresponding classification is given in [34-37]. 

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... 

To prepare an interpenetrating polymer network (IPN) structure, PU networks having ACPA units were immersed with MMA and polymerized. PU-PMMA semi-lPN thus formed was given improved interfacial strength between PU and PMMA phases and showed flexibility with enforced tear strength [65,66]. 

Semi-gloss alkyd paint formulation, 18 6 It Semi-interpenetrating network (IPN) approaches, 10 436 Semi-IPN (interpenetrating polymer network) hydrogels, 13 733 Semikilled steels, 23 291 Semimoist pet foods, 10 849 Semipermanent cells, 14 228 Semiphorone, 14 583 Semiportable mri system, 23 860-861 Semiregenerative reforming operations, 25 166... 

Full-IPNs have higher compressional strength (2929 g load for 50 % compression) than the corresponding semi-IPNs (1883 g load for 50 % compression) [42],... 

Figure 3. High magnification electron micrograph of a semi-I IPN shown in Figure 2, revealing the fine structure detail. (Reproduced with permission from Ref. 17 Copyright 197 Plenum Press.)...

Figure 5. Modulus-composition curves for crass-polybutadiene-inier-cross-polystyrene semi-I and full IPNs (16). (a) Kerner equation (upper bound) (b) Budiansky model (c) Davies equation and (d) Kerner equation (lower bound). (Reproduced from ref. 23. Copyright 1981 American Chemical Society.)...

Figure 6. Modulus-composition behavior of cross-poly(n-butyl acrylate)-/ iter-cross-polystyrene IPNs and semi-I IPNs at 25 C. (Reproduced with permission from ref. 23. Copyright 1981 Polymer Engineering and Science.)...

Table III shows the result of SANS analysis on fully polymerized PB/PS IPN s, seml-IPN s, and chemical blends by Fernandez et al. [ n.] The specific interfacial surface area was shown to increase with Increasing crosslink density, S decreasing in the order full-IPN s, semi-I IPN s, seml-II IPN s afid chemical blends, as expected from many earlier studies. Its value ranges from 20 to 200 m /gm, in the range of true colloids. This result is particularly important because interfacial surface area is closely related to toughness and impact strength.

Figure 17. Logarithmic dependence of the scattered light intensity, I, on time, t, for polystyrene-inter-cross-poly(butyl methacrylate) Semi-II IPN s. Registration anglel 8F) 10 ...

Pseudo or semi-IPNs are combinations of linear with crosslinked polymers resulting in various degrees of interpenetration. (28-34)... 

Figure 1. Effect of different compositions of PU/VMGC on the tensile strength of semi-IPN coatings with or without opposite charge groups.

Figure Micrographs of semi-IPN with and without opposite charge groups by scanning electron microscopy (SEM),...

Figure 3.17 Tg behavior of semi-IPNs cured at 210°C Tgs of (O) BPACY-rich phase, (O) PEI-rich phase and (O) homogeneous state...

There are several interesting applications reported in the literature, such as insulated wire and cable, UV cross-linking of drawn fibers, and tapes from ultra-high-molecular-weight polyethylene. Semi-interpenetrating networks (IPNs) from acrylates and polyurethanes are suitable as UV curable adhesives with high elasticity, good impact resistance, and excellent adhesion to a variety of substrates. ... 

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. 

St. Clair [36] synthesized and evaluated the properties of a semi-2-IPN comprising Thermid 600 (an acetylene terminated imide oligomer from National Starch and Chemical Company) and LaRC-TPI (a thermoplastic polyimide with a Tg of 257 °C). The composition having the ratio of 65 35 of thermosetting Thermid 600 to LaRC-TPI showed the best flexural strength at ambient temperature [36]. 

Pater also prepared a semi-2-IPN, LaRC-RP41, from a mixture having the ratio of 80 20 of thermosetting PMR-15 to LaRC-TPI polyamic acid(44). LaRC-RP41 exhibited significantly improved toughness and micro-cracking resistance, but showed somewhat poorer mechanical properties at 316 °C, compared to those of PMR 15 near resin (see Fig. 13). 

Pascal et al. [49-50] studied semi-2-IPN derived from linear thermoplastic polyimides and thermosetting bismaleimides from the same type of starting... 

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