High-pressure polymerization of phenylacetylene and of the benzene and acetylene moieties

The reactivity induced in acetylene, benzene and phenylacetylene crystals by the application of high external pressure is discussed. Acetylene, the simplest model system involving the CdropC triple bond, reacts above 3.0 GPa in the orthorhombic crystal phase. The molecular arrangement in this phase determines the final conformation of the recovered polymer. The role of laser irradiation in branching the polyenic chains, through the dissociation of the double bonds, is revealed. Benzene, the model aromatic molecule, starts to react in the solid state above 23 GPa. A progressive distortion of the rings is observed on increasing pressure up to 50 GPa but the transformation becomes complete, close to ambient pressure, only during the decompression run. An amorphous hydrogenated carbon compound (a-C : H) is formed in this reaction. Laser irradiation with suitable wavelengths reduces the reaction pressure threshold revealing the role of the S, excited state in driving the high-pressure reaction. Finally, phenylacetylene was taken into account since it is the simplest molecule involving both the triple bond and the aromatic ring and its reactivity could be possibly interpreted according to the previous model systems. Phenylacetylene starts to react in the solid state above 8 GPa. The reaction mainly involves the triple bond of the ethynyl fragment forming polyphenylacetylenic chains. On the basis of the infrared spectra a possible polymer structure is proposed. Copyright (C) 2003 John Wiley Sons, Ltd.