The helical chirality and self-assembling structures of an unnatural polymer, poly(p-ethynylbenzoyl-l-valine) (1), are readily manipulated by a simple environmental perturbation of pH change. The amino acid appendages of l-valine create an asymmetric force field, inducing the polyacetylene backbones to helically rotate, and form intra- and interchain hydrogen bonds, stabilizing the screw-sense conformation of the polymer chains. The polymer exhibits a large Cotton effect in methanol, which decreases with an increase in pH upon addition of KOH into the polymer solution. The change in the chain helicity is reversible:  the unfolded polymer chains refold back to their original helical conformations when the solutions are neutralized. Natural evaporation of the methanol solutions of 1 on mica gives long, bundled nanofibers of macromolecular assemblies; in contrast, evaporation of the methanol/KOH solutions yields short, unraveled nanofibers with sizes of roughly single macromolecular chains. The ionization of the carboxy groups of the valine moieties by KOH breaks the hydrogen bonds, and the entropy-driven randomization leads to the observed chain helicity attenuation. The electrical repulsion between the polyelectrolyte chains carrying the negatively charged carboxylate ions disassembles the macromolecular association, resulting in the formation of the nanofibers of single chain dimension.

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 TaCl 5-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 × 10 6 ) 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 R,ω-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 (g99.5% 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.