Add time:09/02/2019         Source:sciencedirect.com

N,O-Bistrimethylsilyl-4-aminobenzoic acid was selectively acylated at the amino group with 4-acetoxy-3-methoxybenzoyl chloride. The resulting dimer with silylated carboxyl group was polycondensed in situ at 300 or 350°C using Marlotherm-S as an inert reaction medium. In an alternative approach the silylester group of the dimer was hydrolysed and the resulting N-(4′-acetoxy-3-methoxybenzoyl)-4-aminobenzoic acid was polycondensed at 300 or 350°C. Furthermore, copolyesters rich in vanillic acid units were prepared by co-condensations with 4-acetoxy-3-methoxybenzoic acid or its trimethylsilylester. Elemental analyses and 1H nuclear magnetic resonance spectra indicate that the vanillic acid units partially decompose at 350°C, whereas at 300°C the composition of the copolyesters agrees well with the feed ratio. Infra-red spectra support this conclusion. Wide-angle X-ray diffraction powder patterns indicate that the crystallinity increases with higher molar fractions of vanillic acid. The 1:1 copolymers are nearly amorphous. The copoly(ester—amide)s obtained from the monomers with free carboxyl groups form globular aggregates regardless of composition. In contrast, the silylated monomers yield columnar particles with lengths of 10–15 μm and aspect ratios ⩾ 10 for copoly(ester—imide)s with a 6:4 and 5:5 composition. Transmission electron microscopy revealed ordered structures in these columnar particles, but the ‘crystal growth’ cannot yet be interpreted.

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