Carbon nanotubes (CNTs) are formed in bulk compositions from thermal decomposition of metal-containing organometallic compounds in the presence of a multi(ethynyl)aromatic compound. Our unique method involves a precursor composition that melts and is soluble in common solvents ensuring processability into shaped components. The method permits the large-scale production of CNTs in a solid, film, fiber, or powdered form. Heat treatment of various precursor compositions, formulated from the organometallic compound and an excess amount of a multi(ethynyl)aromatic compound to temperatures up to 1400oC, results in the decomposition of the organometallic compound and the formation of metal nanoparticles in the polymeric-to-carbon nanoparticle-to-carbon nanotube compositions. The growth of the CNTs proceeds in the solid phase during the carbonization process. In the synthesis, only a minute quantity of metal nanoparticles is required to initiate the formation of CNTs in the developing carbonaceous media. The metal nanoparticles are the key to the formation of the CNTs. X-ray diffraction, Raman spectroscopy, and high resolution scanning electron microscopy (HRSEM) studies show the formation of CNTs in the developing carbon composition above 600oC. The shaped compositions have structural integrity, which enhances their importance for potential nanoelectronic, electrical, magnetic, and structural composite applications.