Basic Physical Properties of Networks

Time and energy can be saved if one recognizes that there is only one qualitative difference between a linear and a tridimensional polymer the existence in the former and the absence in the latter of a liquid state (at a macroscopic scale). For the rest, both families display the same type of boundaries in a time temperature map (Fig. 10.1). Three domains are characterized by (I) a glassy/brittle behavior (I), (II), a glassy/ductile behavior, and (III) a rubbery behavior. The properties in domain I are practically 

Structural scale Typical size Typical entities 

Macro- Rubber molecular elasticity, science solvent swelling 

Materials Microscopies, science scattering methods, thermal analysis 

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The effect (or lack of effect) of crosslinks on basic physical properties of thermosetting polymers is discussed in Chapter 10, while the effect on elastic and viscoelastic properties is analyzed in Chapter 11. Yielding and fracture of neat and modified thermosetting polymers are discussed in Chapters 12 and 13. Finally, the very important problem of the durability of polymer networks is presented in Chapter 14. 

It is possible to calculate a number of different kinds of "effective" crosslink densities. Bauer et al have used a quantity they termed the "elastically effective crosslink density " (Cel) correlate cure with solvent resistance and other physical properties of coatings (7-10). The correlation was basically empirical. Formally, the is a calculation of the number of functional groups attached to the infinite network for which there are at least two other paths out to the network on the given polymer or crosslinker. Thus, chains with only one or two paths to the infinite network are excluded. The following expression can be written for... 

The chemical bonding and the possible existence of non-nuclear maxima (NNM) in the EDDs of simple metals has recently been much debated [13,27-31]. The question of NNM in simple metals is a diverse topic, and the research on the topic has basically addressed three issues. First, what are the topological features of simple metals This question is interesting from a purely mathematical point of view because the number and types of critical points in the EDD have to satisfy the constraints of the crystal symmetry [32], In the case of the hexagonal-close-packed (hep) structure, a critical point network has not yet been theoretically established [28]. The second topic of interest is that if NNM exist in metals what do they mean, and are they important for the physical properties of the material The third and most heavily debated issue is about numerical methods used in the experimental determination of EDDs from Bragg X-ray diffraction data. It is in this respect that the presence of NNM in metals has been intimately tied to the reliability of MEM densities. 

Although development of a formulation for a specific product and process requires a great deal of knowledge and experience, there are some basic rules typical of FKM compounding. The levels of acid acceptor (MgO) and activator (Ca(OII)2) in the bisphenol cure system strongly affect not only the cross-linked network as reflected by the physical properties of the material, but also the behavior of the compound during vulcanization. Therefore, the curing system must be optimized to achieve the best balance of properties. 

We reported the incorporation of (lJ ,2J )-diaminocyclohexane in hydrophobic and hydrophilic nanopores by the co-condensation of N-[(triethoxysilyl)propyl]-(-)-(ll ,2R)-diaminocyclohexane, respectively, with (MeO)3SiCH2CH2Si(OMe)3, (BTME) and TEOS in basic media [120]. After complexing with [Rh(cod)Cl]2, the chiral catalyst in the hydrophobic nanopore affords 96% conversion with 23% ee in the ATH of acetophenone using i-PrOH as the hydrogen source, while the chiral catalyst in hydrophilic nanopore only shows 48% conversion with 14% ee under identical conditions. This is probably due to the specific adsorption and physical properties of the mesoporous network bridged with ethane groups, particularly the hydrophobic properties. 

The tetrahedral network can be considered the idealized stmcture of vitreous siUca. Disorder is present but the basic bonding scheme is still intact. An additional level of disorder occurs because the atomic arrangement can deviate from the hiUy bonded, stoichiometric form through the introduction of intrinsic (stmctural) defects and impurities. These perturbations in the stmcture have significant effects on many of the physical properties. A key concern is whether any of these defects breaks the Si—O bonds that hold the tetrahedral network together. Fracturing these links produces a less viscous stmcture which can respond more readily to thermal and mechanical changes. 

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