Construction of polymerization

As discussed in detail in Section 2.4, the pronounced tendency of tellurium to participate in both hypervalent bonding and secondary 5p2 —> 5a interactions can lead to the construction of polymeric telluride networks. 

The study of thermotropic, as well as of lyotropic LC polymers is directly linked to a series of practical tasks, regarding the construction of polymeric materials with set properties. For instance, making use of anisotropy of the LC state in processing (particularly in moulding) of polymeric materials discloses impressive prospects for the production of so called high modulus fibers and films 18 25). 

Repetitive Diels-Alder reactions utilizing bis-ort/io-quinodimethane units have been employed[14bl for the construction of polymeric and oligomeric [60]-fullerenes with molecular weights up to 80,000 amu. The potential of using this method for dendrimer construction was suggested. 

With a few exceptions, polymerizations are strongly exothermic (see Chap. 5, Sect. 1.1). Therefore removal of the heat of polymerization is the main problem affecting the construction of polymerization reactors and the technology of the process. The kinetics of the process also determines the technology, with the stringent requirement of the purity of medium. In chemistry perhaps only the preparation of semiconductors poses higher requirements on the purity of raw materials and on the prevention of contamination than... 

Like all soccer balls made since the 1980s, the official ball for the 2006 World Cup was constructed of polymeric materials. Four layers of polyurethane, with a total thickness of 1.1 mm, make up the outer covering. Polyurethanes are normally prepared from a diol and a diisocyanate, such as toluene diisocyanate. 

By adsorbing the perylene derivative tetraazaperopy-rene (TAPP) on Cu(lll) and annealing at 150°C, a Cu-coordinated porous network develops. Annealing at even higher temperatures (250 °C) results in the formation of ID chains—most probably with the Cu substrate acting as a catalyst—which consist of covalently coupled TAPP monomers (Figure 10). The reaction is supposed to proceed via a carbene intermediate. The first example shows that a reaction, which is well known from solution chemistry, can be adopted for the construction of polymeric struc-tnres on surfaces. In contrast, the second example demonstrates that on-surface reactions can allow for the formation of polymers which cannot be obtained via solution-based chemistry at all. 

Another interesting example of Ag(I)-backbone organometallic polymers are those based on diallylmelamine and poly-carboxylates. Silver-vinyl bonding represents a versatile synthon for the construction of polymeric metallosupramolecular architectures. The particular structural motifs result from the introduction of different auxiliary polycarboxylates into the silver/diallylmelamine system and the diverse coordination modes and conformations of diallylmelamine (Fig. 29.3) [108]. Remarkably, apparent silver-vinyl interactions with a ri mode were commonly observed in the solid-state structures of these complexes (Ag-C = 2.311(4)-2.467(5)A). In addition, they display solid-state photoluminescence and moderate thermal stabilities at room temperature. 

Bifunctional reagents have been considered for the construction of polymeric structures. The reaction of a,(o-bis(tetrazol-5-yl)perfluoroalkane 75 with (o-cyanoperfluoroanhydrides 79 (at 150 °C) produces bis-oxadiazoles 80 from which further functionalization may be added on the two terminal nitriles (Scheme 23) [42,43]. 

Scheme 23 Bifunctional reagents in the construction of polymeric structures...

Tezuka, Y. and Fujiyama, K. (2005) Construction of polymeric (5-graph A doubly fused tricyclic topology. Journal of the American Chemical Society, 127,6266-6270. 

The orthogonal coupling strategy can be applied to the synthesis of other polymeric compounds. Several approaches have been reported for construction of polymeric and dendritic structures on the basis of the orthogonal coupling strategy [29] (Figure 10). 

The LbL assembly has not yet found industrial application in spite of its versatility. The main reason for this is the time-consuming multistep assembly procedure, which often is additionally complicated with particle agglomeration. As noted elsewhere, deposition of a film consisting of dozens of layers takes more than 10 h using a robotic dipping apparatus [57]. Nonetheless, recently the use of spray-assisted LbL assembly, both for planar films as well as for the construction of polymeric particles, has emerged as a possible strategy to reduce the deposition times per layer from tens of minutes to a few seconds [57]. 

More recently, with the advent of host-guest chemistry, the chemistry of molecular recognition, and supramolecular science, polymeric inclusion compounds have attracted attention not only for their unique structures, but also for the construction of polymeric assembly materials and more complex systems with unique properties and functions [3]. 

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