Polymer analogous conversion step

The difficulties of the second, stepwise, synthesis of ladder polymers involve, in particular, the final step, namely the polymer-analogous formation of the double-stranded structure. Here, an optimal design of the open-chain precursor polymer is mandatory to arrive at a quantitative conversion with hi chemo-and regioselectivity in order to minimize structural defects. These problems have raised serious doubts in the literature [3] about the feasibility of this concept. 

The introduction of mono-, di-, and oligosaccharide units on dendritic surfaces is usually carried out as the final synthetic step in monodendron and dendrimer synthesis. For this purpose, well-known polymer analogous/ organic conversion steps are used amidation, esterification, reductive amina-tion, nucleophilic substitution, addition/elimination, thiol-ene reaction, 1,3-dipolar cycloaddition, and others (Fig. 5.22). 

The cationic polymerization of tetrahydrofuran is used commercially to produce a,CD-dihydroxypoly(tetramethylene oxide) (PTMO glycol). Although this polymer is not used by itself as an elastomer, it is used as one of the elastomeric block components for preparation of segmented thermoplastic polyurethane [133] and thermoplastic polyester [134] elastomers. The cationic polymerization of tetrahydrofuran (THF) is a living polymerization under proper experimental conditions [135-139], i.e., it does not exhibit any termination step, very much like the analogous anionic polymerizations which are discussed in Section VIII. However, these polymerizations are complicated by the fact that the ceiling temperature, where the free energy of polymerization is equal to zero, is estimated to be approximately 83 2°C in bulk monomer solution [140] therefore, the polymerization is reversible and incomplete conversion is often observed, especially in the presence of added solvent. For... 

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