UV-Curable Polyester Oligomers Containing Triptycene Segments

Abstract

A series of UV-curable polyesters containing triptycene segments were synthesized via the melt polycondensation of 1,4-cyclohexanedicarboxylic acid, triptycene-1,4-hydroquinone-bis(2-hydroxyethyl) ether, and various comonomer diols including 1,6-hexanediol, neopentyl glycol, and 1,4-cyclohexanedimethanol. The polyesters were characterized by ¹H nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, gel-permeation chromatography, and differential scanning calorimetry. Thin films were prepared by solvent casting and were cured via exposure to UV-light at elevated temperature. The crosslinked films were subsequently analyzed by differential scanning calorimetry, dynamic mechanical analysis, Soxhlet extractions, and tensile tests. Most of the samples that contained a high concentration of the triptycene monomer resulted in brittle materials with relatively high moduli and tensile strengths, but poor extensibilities. However, the 1,6-hexanediol/1,4-cyclohexanedicarboxylic acid polyester with 30 mol% of triptycene-1,4-hydroquinone-bis(2-hydroxyethyl) ether exhibited a T _g above room temperature, a relatively high modulus (~1.1 GPa) and tensile strength (~25 MPa), and ductility (144% elongation-at-break). These unique properties were attributed to the triptycene monomer, which is capable of threading polymer chains through its V-shaped cavities to reinforce the polymer network. When these polyesters were formulated into UV-curable coatings, the coatings displayed excellent impact resistance and substrate adhesion.