Novel carbosilane containing polymers: Synthesis, characterization and applications

Cyclolinear carbosilane polymers with disilacyclobutane (DSCB) rings in the main chain structure were prepared by means of acyclic diene metathesis (ADMET) polymerization of the corresponding 1,3-dibutenyl-1,3-disilacyclobutanes. The copolymerization of a monomer of this type with a non-cyclic organosilane diene allowed for the incorporation of a varying number of DSCB rings into the polymer backbone. Subsequent hydrogenation of the double bonds with p-toluenesulfonhydrazide resulted in a saturated hydrocarbon structure in the main chain without affecting the DSCB ring. All of the resultant polymers are well-defined materials with a DSCB ring incorporated into the backbone structure, as evidenced by NMR spectroscopy and GPC analyses. The thermal behavior of these polymers was characterized by DSC and TGA. DSC indicated low Tgs and TGA evidenced high thermal stability in an inert atmosphere. In addition, large exothermic peaks were observed in the DSC, which indicated, along with the IR and Solid State 29Si NMR spectra, that crosslinking occurs during heating to ca. 250°C via opening of the imbedded DSCB rings. The dielectric constant of the dense, fully crosslinked polymer is quite low (2.37), which is substantially lower than that of any other known, non-fluorinated, non-porous, dielectric material. The dielectric constant of this material is also lower than the 2.6 effective dielectric constant value that is currently targeted for the next two generations of integrated circuits. Furthermore, we have found that the thermally induced crosslinking of this cyclolinear polycarbosilane is initiated at a considerably lower temperature (ca. 160°C) on a copper metal surface than on a Si or glass surface (ca. 250°C). This allows the selective coating of Cu by this electrically insulating, chemically inert, and thermally stable polymer, which has the potential for use as a dielectric material that will not require the use of a separate barrier layer to prevent Cu diffusion or, if desired, as a separate Cu barrier layer in conjunction with another dielectric material. Poly(methyltolylsilylenemethylene), the carbosilane analog of poly(alpha, p-dimethylstyrene), dimethylstyrene), was prepared by transition-metal catalyzed ring-opening polymerization of the corresponding monomer 1,3-dimethyl-1,3-ditolyl-1,3-disilacyclobutane. Subsequent partial bromination of this polymer provided a useful macroinitiator. Styrene grafting from this macroinitiator was performed by atom transfer radical polymerization (ATRP). Preliminary results showed that the graft copolymers derived from macroinitiator 1 have no microscopic phase separation due to the low molecular weight of the PS grafts; while the graft copolymers derived from macroinitiator 2 can be used to prepare phase separated polymer nanocomposites.