Polyester secondary structures

Helicopters are being designed using glass fiber-TS polyester primary and secondary structures, including rotor blades. 

In the cutin structure, a polyester intramolecular structure exists where cross-linking is mainly influenced by the availability of secondary hydroxyl groups. Thus cutins which contain large amounts of epoxy, 0X0 and cy-hydroxy monomers must be predominantly linear (Table 2.7) (Deas and Holloway, 1977). Esterification appears to occur chiefly through... 

There are no current structural data of polyester synthases. The secondary structure content was inferred by predictions implementing the multiple alignments of synthases. The use of JPred indicated that polyester synthases are mostly composed of variable loops (49.7%) and a-helical (39.9%) secondary structures, whereas only 10.4% were proposed as P-sheet secondary structures [38]. However, circular dichroism spectroscopy suggested that the class II synthase from P. aeruginosa is comprised of the secondary structures 10% a-helix, 50% P-sheet, and 40% random coil [39]. 

Flame retarded polyesters cured, as prepregs, at 135 - 163 C for vacuum-bag or low pressure press cure. Suitable for laminate or sandwich panel construction in aircraft and other secondary structural applications requiring good mechanical performance, low flammability and excellent electrical properties. 

The superior characteristics of polyester polyol based polyurethanes are explained by a better crystalline structure [1, 7] in the urethane segment, compared to the majority of poly ether polyols which are amorphous [except polytetrahydrofuran (PTHF)], due to the superior secondary forces between the polyester chains [8] and also due to a superior thermal and fire resistance, compared to polyether polyol based polyurethanes. Polyester-based polyurethanes (flexible foams, coatings), have a superior solvent resistance compared to the polyether-based polyurethanes [8]. 

The positive ion FAB mass spectra of these polyesters are very similar, since these polymers differ only in the isomeric structure of the dihydroxybenzene unit present in their repeating unit. Figure 7.9 shows the FAB-mass spectrum of Polyester II, which indicates, essenhally, a series of intense peaks at m/z 241, 481, 721, 961, 1201, 1441, 1681, and 1921, corresponding to protonated molecular ions of cyclic oligomers (from monomer up to octamer). The other two mass series, which appear with low intensity at m/z 371 + n240 and 389 + n240, are due to secondary ion fragmentation phenomena. ... 

Kim, Y. L. and Hercides, D. M., Structural characterization of polyesters by transesterification and time-of-flight secondary ion mass spectrometry, Macro-rrwlecules, 27, 7855,1994. 

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