Phosphor oligomers, synthesis

The Fischer indole synthesis itself is catalysed in this case by polyphosphoric acid (PPA), a sticky gum based on phosphoric acid (H3PO4) but dehydrated so that it contains some oligomers. It is often used as a catalyst in organic reactions and residues are easily removed in water. 

The phosphite method is effective for the synthesis of DNA oligomers, because the preparation requires no protection of the phosphoric acid moieties. ... 

Early studies on isobutene oligomerization have revealed that this olefin dimerizes selectively to give a mixture of 77 and 18 (Eq. (17)) in the presence of an 0x0 acid such as sulfuric and phosphoric acids. However, selective synthesis of isobutene oligomers higher than the trimer has not been possible to date. A detailed... 

The most widely studied example is the SCCG of poly(4-oxybenoate), FOB, also called poly(4-hydroxybenzoic acid).PHB. Since the abbreviation PHB is also used for poly(/ -hydroxybutyric acid), this abbreviation is avoided in this text. Early attempts to polymerize 4-hydroxybenzoic acid, 4-HBA are discussed in Chap. 2. In the twentieth century several derivatives of 4-HBA were successfully used as monomers (see Formula 13.4), but polymerization of 4-HBA itself was also conducted in solution by means of dehydration agents, such as trifluoroacetic acid [60], thionyl chloride [61], poly(ethyl phosphate) plus imidazole [62], and various other phosphorous reagents [63]. However, these polycondensations were typically conducted at temperatures <150 °C and yielded oligomers. More than 90 % of all publications dealing with synthesis and characterization of POB are based on polycondensations of 4-acetoxybenzoic acid, 4-ABA, at temperatures around or above 300 °C. A first attempt to polymerize 4-ABA in bulk at temperatures up to 300 °C was published in 1959 [64]. The resulting polyester was described as intractable and thermally unstable above 350 °C. 

---