Dimensionally and thermally stable polymer, containing disordered graphitic structure and adamantane

Abstract

In an attempt to develop a low-k interlayer dielectric, adamantane-diphenyldiethynyl moiety containing oligomer is prepared. Oligomerization of 1,3,5,7-tetra-kis[3/4-ethynylphenyl]adamantane (4) is accomplished by a Glaser-Hay oxidative coupling with 1,3,5-triethynylbenzene and phenylacetylene end-capping agent. The CHCl3 soluble oligomer is then thermally treated by step-curing at 200, 300, 380, and 450°C for 30 min at each temperature under nitrogen flow to render a shiny voidfree black polymer. TGA analysis indicates that the polymer is stable under nitrogen up to 500°C with a marginal decomposition up to 800°C. Solid-state 13C NMR, Raman scattering, and FTIR are used to characterize the structure of the polymer. The polymer consists of amorphous carbon networks with the adamantane moieties and nanosized graphitic regions (clusters), which are generated from the thermal crosslinking of the diphenyldiethynyl units. It shows a remarkably low linear coefficient of thermal expansion (∼25 ppm/°C), presumably due to the presence of the disordered graphitic structure. Its high density (∼1.21 g/cm3), refractive index (∼1.80 at 632 nm), and Young's modulus (∼17.0 GPa) are also consistent with the interpretation. This study reveals important details about the effect of microscopic structure on the macroscopic properties of the highly crosslinked polymer. © 2006 Wiley Periodicals, Inc.