4- Hydroxybenzoic acid 3-Hydroxybutyrate

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. 

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