Multi-chain step methods

This idea was realized impressively in 1991 with the first synthesis of a soluble, conjugated ladder polymer of the PPP-type [41]. This PPP ladder polymer, LPPP 26, was prepared according to a so-called classical route, in which an open-chain, single-stranded precursor polymer was closed to give a double-stranded ladder polymer. The synthetic potential of the so-called classical multi-step sequence has been in doubt for a long time in the 1980s synchronous routes were strongly favoured as preparative method for ladder polymers. 

Cause-effect-relations of these dynamics in the value chain may still be obvious, when operating a simple value chain comprising few products, locations and production steps. Considering the global multi-stage, multilocation value chain network, price changes in raw materials cannot directly be related to intermediate or even sales products and their prices. This problem requires specific planning models and methods. 

Catalytic aldol reactions are among the most useful synthetic methods for highly stereo-controlled asymmetric synthesis. In this account we discuss the recent development of a novel synthetic technique which uses tandem enzyme catalysis for the bi-directional chain elongation of simple dialdehydes and related multi-step procedures. The scope and the limitations of multiple one-pot enzymatic C-C bond formations is evaluated for the synthesis of unique and structurally complex carbohydrate-related compounds that may be regarded as metabolically stable mimetics of oligosaccharides and that are thus of interest because of their potential bioactivity. 

Side chain liquid crystalline and nonlinear optical polymers (e.g. 37 and 38), which are conventionally produced by multi-step processes, are also available very easily via active ester synthesis. A unique feature of the active ester method for this purpose is that a single activated polymer intermediate can be used for the synthesis of any number of macromolecular structures, all by a simple single-step reaction pathway. Synthesis of such polymers by copolymerization of the... 

To learn about the real effects of antioxidants, it is therefore important to obtain specific chemical information about which products of lipid oxidation are inhibited. Several specific assays are needed to elucidate how lipid oxidation products act in the complex multi-step mechanism of lipid oxidative deterioration of foods. The results of several complementary methods are required to determine lipid oxidation products formed at different stages of the free radical chain. Since antioxidants show different activities toward hydroperoxide formation and decomposition, it is important that more than one method be used to monitor Upid oxidation. 

Both processes may be carried out in one or two reaction steps, the so-called one-shot process and prepolymer method , respectively (Vermette et al., 2001). In two-step synthesis (Fig. 6.3), an isocyanate end-capped prepolymer is first synthesised through the reaction between a polyol and a diisocyanate then, adding a chain extender that reacts with the residual isocyanate functionality, the chain is extended producing a multi-block copolymer (Lamba et al., 1998 Vermette et al., 2001 ... 

The incorporation of carbohydrates into non-polysaccharide structures is an important strategy to attain i) highly functional polymers U) specific biological functions, and Hi) complex systems that act as smart materials. Polyesters with carbohydrate or polyol repeat units in the chain can be produced by chemical methods. However, elalH)rate protection-deprotection steps are needed to avoid crosslinking between polyol units. Multi-step routes to non-crosslinked polyol polyesters limit the potential of their practical use. 

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