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 1 H 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.