Amorphous structural skeleton

The presence in these copolymers of hetero-substituted monomeric units randomly dispersed along the phosphazene skeleton brings about the extreme difficulty of the polymeric chains to be packed in regular structures. They lose, therefore, the original stereo-regularity of the parent phosphazene homopolymers (microcrystalline materials), and show only amorphous structures, with sharp decrease in the values of the Tg (collapsed up to about -90 °C) and with the onset of remarkable elastomeric properties [399,409,457]. 

An effective way to obtain amorphous polyethers is by grafting low molecular weight PEO to the polymer skeleton and form comb- or star-like structures. Since ionic conduction is closely related to the movement of chain segments, it can be expected that a polymer with an amorphous structure together with low Tg will meet the need for fast ionic conduction at room temperature. There are two common ways to synthesize comb polyethers [1] ... 

Micaceol (12) was isolated as a light yellow amorphous solid. Its UV spectram showed maximum absorption at 246 mu indicahng the presence of a conjugated n system. The IR spectmm exhibited intense absorption bands at 3,425 (OH) and 1,601 (C = C) cm". The Chemical Ionization Mass Spectrum (CI-MS) of 12 showed molecular ion peak at m/z 399 [M-H]+. The HREIMS of this compound showed molecular ion peak at m/z 398.2392, which provided the molecular formula (calcd = 398.2360) and indicated the presence of six degrees of unsatura-hon in 12. These six double bond equivalents were accounted for by the steroidal skeletons with two double bonds incorporated in its structure. 

Poly (acetylenes) [16], There are several catalysts available for polymerization of substituted acetylenes. Whereas Ziegler-Natta catalysts are quite effective for polymerization of acetylene itself and simple alkylacetylenes, they are not active towards other substituted acetylenes, e.g. phenylacetylenes. Olefin-metathesis catalysts (Masuda, 1985 Masuda and Higashimura, 1984, 1986) and Rh(i) catalysts (Furlani et al., 1986 Tabata, 1987) are often employed. In our experience, however, many persistent radicals and typical nitrogen-containing functional groups serve as good poisons for these catalysts. Therefore, radical centres have to be introduced after construction of the polymer skeletons. Fortunately, the polymers obtained with these catalysts are often soluble in one or other organic solvent. For example, methyl p-ethynylbenzoate can be polymerized to a brick-coloured amorph- See the Appendix on p. 245 of suffixes to structural formula numbers. 

Organisms use three conceptually different strategies to build their skeletal parts. The easiest approach to the filling of a given shape with solid material applies when there is no internal order or structure, that is, when the material is amorphous. A beautiful example is found within the Euplectella species of marine sponge, which comprises at least seven hierarchical levels within its silica skeleton, the lowest level consisting of silica nanoparticles.1 A second approach involves building skeletal materials... 

The hydrated amorphous mineral silica (opal) is widely used by many plants and animals for structural purposes. Most skeletons are formed by unicellular organisms (diatoms Figure 2(a), radiolarians Figure 2(b)), but silica is also present within multicellular organisms (sponge spicules, plant... 

Opal is related to the very common Si02 mineral species, quartz. Oceans are at present undersaturated with respect to opal (Broecker, 1971) possibly because of the biological formation of animals with silicified skeletons such as the diatoms. These delicate structured creatures, which proliferate in the upper photic zone, dissolve at depth. Therefore, only robust siliceous skeletons such as sponge spicules are retained in sediments that accumulate in deep waters, although some diatoms survive on the continental shelf under zones with high productivity. The initial deposition of the amorphous hydrated silica, opal, converts first to opal-CT and eventually to crystalline quartz (Kastner, 1981). 

Ooh = 1) is obtained after preliminary treatment of the samples in vacuo at 180-200 °C, when for each Si atom there is approximately one OH group. The average value of the silanol number for such a state, aon = 4.6 OH groups per square nanometer, is a physicochemical constant (it is independent of the type of the amorphous silica used, the method of preparing it, and the structural characteristics, that is, the specific surface area, the type of pores, the distribution of the pores according to their diameter, the packing density of the particles, and the skeleton structure of Si02). 

Lignins. Lignins are amorphous, cross-linked phenolic polymers that occur uniquely in vascular plants and comprise 20-30% of most wood. Lignins isolated from wood are polydisperse, with molecular weights in the range of thousands to hundreds of thousands (4). Lignins are produced almost exclusively from three cinnamyl alcohols, whose structures are shown in Chart I. These structural units have propylphenyl carbon skeletons and differ... 

Deuterium-exchange measurements have shown that various types of amorphous dispersed silica contain not only surface hydroxyl groups but also structurally bound water inside the silica skeleton and fine ultramicropores. According to infrared spectral measurements [53], such bound water consists of silanol groups inside the silica sample (the adsorption band of stretching vibrations is about 3650 cm ). The distribution of OH groups between the surface and the bulk of the sample depends on a number of factors, but mainly on the method of preparation of the silica sample and its subsequent treatment. 

Inverse opal structures have been classified into three structures, the so-called residual volume structure , shell structure and skeleton structure . The residual volume structure is a perfect inverse opal structure, which can be produced if the whole space among the opal spheres is completely filled by the product materials. If the space is incompletely filled, the surface of the sphere template is covered by the product materials, and a shell structure is generated. Most amorphous compounds tend to form a shell structure. On the other hand, crystalline compounds tend to form a skeleton structure. 

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