Interpenetrating network theory

Several analytical techniques have been used to characterize the polymer/ silane coupling agent interphase. Culler et aL [2] used Fourier transform infrared (FT-IR) spectroscopy to characterize the chemical reactions at the matrix/silane interphase of composite materials. They correlated the extent of reaction of the resin with the coupling agent (as determined by FT-IR) with the extent of interpenetration. Culler et al. [2] have also used observations of improved resistance of the interphase region to solvent attack as indirect evidence to support the interpenetrating network theory. 

Historically, many reinforcement theories have been proposed. Those include the chemical bonding theory (28), restrained layer theory (29), deformable layer theory (30), and coefficient friction theory (31). However, only the chemical bonding theory could sufficiently explain the observed results. However, the chemical bonding theory alone is not adequate to explain the necessity of more than a monomolecular equivalent of silane for optimum composite strength. Thus, this concept is coupled with interpenetrating network theory (31,32). These theories have been developed primarily for thermosetting resin composites. Thermoplastic-matrix composites rely on different mechanisms. 

Figure 25.3 Interpenetrating network theory bonding to polymers.

Figure 15.3 Interpenetrating network theory—bonding to polymers.

The information available on aqueous polymer blends is qualitative in nature because of the lack of a suitable theory to interpret the experimental observations. Mixed gels can be comprised of an interpenetrating network, a coupled network (as discussed above), or a phase-separated network [2]. The latter is the most common as the blends have a tendency to form two phases during gelation. In such cases the miscibility and thermodynamic stability have to be empirically investigated and proper conditions for miscible blends identified. This involves a phase diagram study as is described in [3]. 

Ideally, a simultaneous interpenetrating network should have extensive mixing at the molecular level, even to the extent of forming one uniform phase. As with other polymer blends, blocks, and grafts, SIN s exhibit phase separation attributed to the low entropy of mixing of two polymers which limits interpenetration in the real case. Thus there is an apparent discrepancy between theory and practice however, the pursuit of the ideal has led to a new understanding of the ways that super-molecular structure can be controlled, and new understanding of the relationship between polymer structure and properties. 

The chapters in this volume represent the current trends in the fields of polymer blends and ionomers, including materials development, characterization, theory, and processing. They are grouped into six sections the first three are concerned with polymer blends and interpenetrating networks and the latter three with ionomers. 

Many theories have been proposed to account for the profound effect minute proportions of silane coupling agents at the dispersed particle interface have on the performance of composites.These include chanical bonding theory acid—base interactions formation of interpenetrating networks wetting and surface energy effects polymer morphology modification deformable layer theories restrained layer theory. 

Entanglements between chains also serve as a type of crosslink. In a linear or branched polymer, entanglements can slip or move, and so are very impermanent. However, chemical (or physical) crosslinking limits their motion, and increases their effect on bulk properties. At this time, the phantom network theory is calling into question the reality of entanglements. While a monograph such as this cannot of itself resolve the controversy, some of the properties of interpenetrating polymer networks described in later chapters bear on the problem. 

B. N. Kolarz, Interpenetrating Polymer Networks Part II. Poly(methacrylic acid co-divinyl benzene)-Poly(styrene-co-divinylbenzene), Report No. 8, Instytut Technologii Organicznej I Tworzyw Sztucznych (1979). IPNs of Polystyrene/Poly(methacrylic acid). Electron microscopy showing inhomogeneities within each network and between networks. Theory of interpenetration vs. void filling. Ion exchange properties. 

L. H. Sperling, K. B. Ferguson, J. A. Manson, E. M. Corwin, and D. L. Siegfried, Isomeric Graft Copolymers and Interpenetrating Polymer Networks. Theory and Experiment, Macromolecules 9(5), 743 (1970). Application of ring theory concepts to IPN nomenclature. Decrosslinking of PS as example. 

Simha [53] made the first attempts to model the transition from a dilute to a concentrated solution. He assumed that in the range from lscaling laws a theory has been developed which allows for the prediction of the influence of Mw c and the solvent power on the screening length [54,55]. This theory is founded on the presumption that above a critical concentration, c, the coils overlap and interpenetrate. Furthermore it is assumed that in a thermody-... 

The diffusion theory states that interpenetration and entanglement of polymer chains are additionally responsible for bioadhesion. The intimate contact of the two substrates is essential for diffusion to occur, that is, the driving force for the interdiffusion is the concentration gradient across the interface. The penetration of polymer chains into the mucus network, and vice versa, is dependent on concentration gradients and diffusion coefficients. It is believed that for an effective adhesion bond the interpenetration of the polymer chain should be in the range of 0.2-0.5 pm. It is possible to estimate the penetration depth (/) by Eq. (5),... 

The examples summarized above are but indicative of the increasing body of evidence in support of the chemical bonding theory, and of the role of the silane organofunctional group in the formation of covalent bonds at the coupling agent/ matrix interphase by reaction or by co-polymerization with the formation of an interpenetrating polymer network. 

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