Synthesis of polyarylacetylenes by gamma-ray-induced polymerization of terminal alkynes. Nanostructures of ortho-substituted derivatives

Terminal aryl alkynes RC6H4CCH with substituents of different electronic properties and ring position (R= H, 4- CF3, 4-OMe, 2-CF3, 2-OMe, 2-Me) were exposed to c-radiation (50-400 kGy) in organic solvents (hexane, 1,4-dioxane, ethylacetate, methanol, tetrahydrofuran), at room temperature. The effects arising from substituent, solvent, dilution, and radiation dose allowed to define the conditions suitable for polymerization, which was favored in methanol at increasing dilution of the alkyne. Ortho-substitution represented the key structural element in the substrate, and the derived polyarylacetylenes were characterized in detail, including gel permeation chromatography, thermal analysis, infrared, NMR, UV-vis, fluorescence, and scanning electron microscope spectroscopy. The results are consistent with the formation of irregular polymers mainly composed of trans-transoid chains. Controlled aggregation of the polymers by means of an osmosis-based procedure in solvent/non-solvent mixtures allowed the formation of nanostructured materials, in particular of hollow nanospheres from THF/water. The methodology sets the basis for the development of gamma-rays-induced polymerization of alkynes, in a transition metal catalyst-free environment.