Rigid-rod networks

Carfagna C, Amendola E, Giamberini M (1994c) Rigid-rod networks—liquid-crystalline epoxyresins. Compos Stmct 27 37 3... 

Zhou, W., Islam, M.F., Wang, H., Ho, D.L., Yodh, A.G., Winey, K.I., and Fischer, J.E. (2004) Small angle neutron scattering from single-wall carbon nanotube suspensions Evidence for isolated rigid rods and rod networks. Chem. Phys. Lett. 384, 185-189. 

More recently Morse produced a complete microscopic tube theory for stiff polymers that successfully interpolates between the rigid-rod and flexible chain limits. This theory explains many features of semiflexible polymer rheology, including the two mechanisms for plateau moduli described above (which depend on a comparison of timescales), with the tube diameter being the sole fitting parameter as in the Doi-Edwards theory. More recently, Morse successfully computed a tube diameter from two different approaches (self-consistent binary collision and continuum effective medium) that give similar results, e.g. modulus G p and respectively). An elastic network approximation... 

PBZT and PBO are ordered polymers which form long rigid-rod molecules which give rise to a microfibrillar network structure in biaxially oriented films (Figure 1). Such biaxial films have been used in combination with low dielectric constant resins, such as cyanate ester resins, to make circuit substrates for use in MLBs... 

Polymers are normally classified into four main architectural types linear (which includes rigid rod, flexible coil, cyclic, and polyrotaxane structures) branched (including random, regular comb-like, and star shaped) cross-linked (which includes the interpenetrating networks (IPNs)) and fairly recently the dendritic or hyperbranched polymers. I shall cover in some detail the first three types, but as we went to press very little DM work has been performed yet on the hyperbranched ones, which show some interesting properties. (Compared to linear polymers, solutions show a much lower viscosity and appear to be Newtonian rather than shear thinning [134].) Johansson [135] compares DM properties of some hyperbranched acrylates, alkyds. and unsaturated polyesters and notes that the properties of his cured resins so far are rather similar to conventional polyester systems. 

Figure 4.9 X-ray structure of [Ag(dmb)2]TCNQ - 1.5TCNQ° - The parallel Ag(dmb)j polymer chains are seen along their z-axis where the Ag zig-zag are clearly seen. The TCNQ ") bi-dimen-sional network lies between the polymer rigid rods. The box indicate the unit cells...

Rigid-rod epoxy thermosets have been investigated more extensively than other rigid-rod thermosets, with more than 20 papers and patents published to date. Epoxy LC networks were first claimed in a Japanese patent issued in 1984 [12]. Following that, Bayer AG and the Dow Chemical Company were issued a number of patents on thermosets based on glycidyl end-capped mesogenic structures. Recently, these materials were initially developed and intensely studied commercially for structure materials with improved performance [13-16],... 

RIGID AND SEMIRIGID-ROD NETWORKS BASED ON HYBRID ORGANIC-INORGANIC DESIGNS... 

For flexible polymers, i.e. those that are able to undergo internal rotation about their backbones, the following classification can be made according to various constraints that we can place on the solidification process (Figure 1.9). There are two other classes of polymer worthy of mention these are rigid rod like molecules where the shape of the polymer has a major effect on its ability to pack, and crosslinked polymers. In the latter system, the morphology of the polymers will be influenced by the size of the chain elements that exist between the network crosslinks. In a polymer system such as a silicone rubber, the... 

Because the OLK model assumes a completely random array of straight rigid rods, an analysis based on this model gives no estimation of PSD. Instead, the SE curve is interpreted as an intrinsic result of wall effect of the network to the solutes, and gives the information on the width and density of the rods constituting the network. The partition coefficient is defined in this case as the ratio of permeable volume for a solute to total gel volume including that of solid material and is given by the formula ... 

Liquid crystalline thermosets (LCT) with a rigid rod-like mesogenic group capped firom both ends by reactive fimctional groups can be used as matrices for production of advanced composites, coatings or adhesives (1, 2). hi this case ordering of the chains of the final network polymer is the only way to improve its physical and mechanical properties. 

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