Full IPN

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

The search for theoretical relations concerning domain size and shape is ongoing, and several efforts to derive a theoretical formulation have been made. The first attempt was by Donatelll et al, in 1977 [29], who derived an equation especially for seml-IPN s of the first kind (polymer I crosslinked, polymer II linear) and extended to full IPN s by assuming that the molecular weight of polymer II is infinite. Later, this equation was simplified for... 

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.)...

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.

Fig. 5 Schematic illustrations of different IPN architectures attainable for CELL/P(VP-co-GMA) composites, a Semi-IPN b Full-IPN c Joined-IPN...

Exclusively mechanically interlocked linear polymer blends, typically, are not thermodynamically phase stable. Given sufficient thermal energy (Tuse>Tg), molecular motion will cause disentanglement of the chains and demixing to occur. To avoid phase separation, crosslinking of one or both components results in the formation of a semi-IPN or full-IPN, respectively. Crosslinking effectively slows or stops polymer molecular diffusion and halts the phase decomposition process. 

The advantage of the swelling method is that it is not limited by the crosslinking reactions of each phase so any interference from these will be limited. A good representative example is the synthesis developed by Hamurcu and Baysal [75]. They synthesized a bimodal PDMS (15 000 gmoD1)/ PDMS (75 000 g mol ) IPN with the same condensation curing system. First, the 75 000 g mol 1 PDMS network was formed from the corresponding a, tw-dihydroxypolydimethylsiloxane and tetraethylorthosilicate catalyzed by stannous 2-ethylhexanoate. It was then swollen in a 15 000 g mol 1 a,a>-dihydroxy-poly(dimethylsiloxane) monomer. The second monomer was then crosslinked via the same condensation cure. The sequential full IPN structure... 

If both 1 and 2 form networks, an IPN, designated as a full IPN, arises (26) as shown in Figure 6. This structure also has an inverse— that is, if 2 is synthesized first and then monomer 1 is swollen in and polymerized. A material may be considered an IPN rather than just a... 

Figure 6. A schematic of a full-IPN (polymer 1 and polymer 2 are crosslinked). No graft sites are included.

Figure 6. Differential scanning calorimetry of a PVME/PS physical blend and full-IPN. 50 wt % PS in each sample. Heating rate 10 C/min.

Figure 7. Linear loss modulus versus temperature curves for PVME/PS full-IPN s and homopolymer networks. Frequency llOHz.

Figure 8. Linear loss modulus curves for two 50/50 PVME/PS chemical blends, and for a 50/50 full-IPN. Baseline corrections are also shown.

These compounds have the structure of an interpenetrating polymer network (IPN) of phenolic resin with materials having elastomeric properties. (3-8) Except for early work by Aylsworth in 1914, there has been no work on full IPN phenolic materials. 

This paper describes the preparation and testing of full IPN phenolic systems with vinyl compounds. 

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... 

Since this paper will be restricted to sequential IPN s based on cross-poly butadiene-inter-cross-polystyrene. PB/PS, it is valuable to examine the range of possible compositions, see Figure 2 ( ). The PB/PS IPN polymer pair models high-impact polystyrene, and in fact, many of the combinations made are actually more impact resistant than the commercial materials. In general, with the addition of crosslinks, especially in network I, the phase domains become smaller. The impact resistance of high-impact polystyrene, upper left, is about 80 J/ra. In the same experiment, the semi-I IPN, middle left is about 160 J/m, and the full IPN, lower left, is about 265 J/m (g). Since the commercial material had perhaps dozens of man-years of development, and the IPN composition was made simply for doctoral research with substantially no optimization, it was obvious that these materials warranted further study. 

Figure 2. Transmission electron micrographs of six polybutadiene/polystyrene sequential IPN s and related materials, the polybutadiene portion stained with osmium tetroxide. Upper left high-impact polystyrene, commerciaL Upper right a similar composition made quiescently. Middle left semi-I IPN, PB (only) crosslinked. Middle right semi-II IPN, PS (only) crosslinked. Lower left full IPN, both polymers crosslinked. Lower right full IPN, PB with higher crosslink level. (Reproduce from ref. 5. Copyright 1976 American Chemical Society.)...

Figure 6.2. Selected morphologies of IPNs based on SBR and polystyrene, SBR stained with osmium tetroxide. Upper left Commercial high-impact polystyrene. Upper right, Ostromislensky s material, with no phase inversion middle left, semi-IPN, SBR crosslinked middle right, semi-11 IPN, PS crosslinked lower left, full IPN lower right, full IPN, higher crosslinking in the SBR.

The full IPNs shown here (as in numerous other cases) have dual phase continuity. The domains, as cut in thin section for transmission electron microscopy, appear to be ellipsoidal. Actually, they are more probably thin sections of cylinders, cut at various angles. Other studies show that both phases may be continuous. Spinodal decomposition kinetics, thought to apply in many such cases, results in interconnected cylinders [Utracki, 1994]. 

FIGURE 10.8 Illustration of formation and structure of semi- and full IPN. 

FIGU RE 10.9 Schematic structures for preparing semi- and full-IPN hydrogels with alginate and PNIPAAm. 

A schematic representation of an ideal IPN (full IPN) in which hoth the polymers are cross-linked is shown in Figure 4.45a. If one of the two polymers is in network form (cross-linked) and the other a linear polymer, i.e., not cross-Knked, the product is called a setni-IPN (Figure 4.45h). 

This full IPN combines the network of an NLO active epoxy-based polymer and the network of an NLO active phenoxy-silicon polymer. l The epoxy-based NLO network is prepared from the epoxy prepolymer (BPAZO) based on the diglycidyl ether of bisphenol A and 4-(4 -nitrophenylazo)aniline functionalized with crosslinkable acryloyl groups. The second NLO network of a phenoxy-silicon polymer is based on an alkoxysilane dye (ASD) of (3-glycidoxypropyl)trimethoxysilane and 4(4 -nitrophenylazo)aniline, and the multifunctional phenoxyl molecule 1,1,1- tris(4-hydroxyphenyl)ethane (THPE).22 Figure 4 shows the chemical structures of BPAZO, ASD, and THPE. Each network can be formed... 

Full IPN membrane of PVA and copolymer of acrylic acid and acrylamide. PVA cross-linked with glutaraldehyde, copolymer with MBA... 

Semi and full IPNs have also been prepared by the in situ polymerization of styrene in chemically cross-linked SBR and SBS (17-20). Using the method of Plati and Williams (21) Gc values of up to 10 kJm and breaking strains exceeding 50% can be obtained particularly when highly cross-linked SBS is used as polymer I. The addition of divinyl benzene crosslinker to the styrene causes an enhancement in stiffness, transparency and solvent resistance, with significant retention of toughness and ductility. 

Figure 1. a,b Quenched uncross-linked Solprene 416 (Bar = 100 nm), low and high magnification (Bar = 50 nm) c cross-linked, annealed Solprene 416 (Bar = 50 nm) d full IPN based on lightly cross-linked 416 (Bar = 50 nm)... 

Sample Codes A = low cross-linked 1205 Semi IPN. B = low cross-linked 1205 Full IPN C = high cross-linked 1205 Full IPN. 

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