Diyne polycyclotrimerizations initiated by transition-metal catalysts afforded hyperbranched polyphenylenes, which exhibited low viscosity, outstanding thermal stability, and small optical dispersion. Under optimized reaction conditions, polycyclotrimerizations of 1,8-nonadiyne (1) and 1,9-decadiyne (2) catalyzed by TaCl5-Ph4Sn produced hyperbranched poly(1,2,4-benzenetriyl-1,5-pentanediyl) (3) and poly(1,2,4-benzenetriyl-1,6-hexanediyl) (4),1-5 respectively, in high yields (up to 93%). The polymers were completely soluble and film-forming, and possessed high molecular weights (Mw up to ∼1.4 × 106) but low intrinsic viscosities ([η] down to 0.13 dL/g). Their structures and properties were analyzed and evaluated by IR, UV, NMR, SEC, TGA, DSC, spectrofluorometry, light scattering, and spectroellipsometry. The structural characterizations confirmed the expected hyperbranched molecular architectures of 3 and 4 (comprising of 1,2,4-benzene rings and αω-alkyl spacers) and revealed the regioselective feature of the diyne polycyclotrimerizations. Polymers 3 and 4 underwent glass transitions at 43 and 23°C, respectively, and lost almost no weights when heated to ∼500°C. Polymer 3 emitted UV light upon excitation, whereas 4 was practically nonluminescent. The thin films of 3 were highly transparent (>99.5% transmittance) and displayed an optical dispersion as low as 0.009 in the visible spectral region, much superior to those of the commercially important "organic glasses" such as poly(methyl methacrylate) and polycarbonates.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry