M.Sc Thesis

M.Sc StudentAmir Noa
SubjectOrganosilicon-Polymer Hybrids: Molecular Structure and
Thermal Degradation
DepartmentDepartment of Materials Science and Engineering
Supervisor PROF. Michael Silverstein


Organic-inorganic hybrid systems are candidate low dielectric constant (“low-k”) materials in the upcoming generation of integrated circuits. The demand for a material with a dielectric constant of less than 2 reflects the need to avoid time delays in electronic devices. These hybrid materials are composed of an inorganic Si-O network to which organic groups are attached. The Si-O network provides the necessary thermal and mechanical stability while the organic groups reduce the dielectric constant by reducing the polarity, density, and water adsorption. The dielectric constant of hybrid materials can be reduced further through the introduction of porosity.

The objectives of this research are to synthesize several organosilicon-polymer hybrid materials, to characterize their chemical structure, and to characterize their behavior on exposure to elevated temperatures. The systems studied were: (1) copolymers of polyhedral oligomeric silsesquioxane (POSS) and methyl methacrylate (MMA) synthesized by free radical polymerization in solution; (2) poly(MMA-co-POSS) mixed with poly(methylsilsesquioxane) (MSQ) in solution. The molecular structures were characterized using nuclear magnetic resonance, Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography. The thermal degradation was characterized using thermal analysis (differential scanning calorimetry and thermogravimetric analysis) in combination with FTIR.

The copolymerization of MMA with POSS enhanced the thermal stability of the polymer. The methacrylate groups decompose at elevated temperatures, while the organic groups on the POSS remain thermally stable. The MSQ silanol groups underwent condensation at elevated temperatures, forming an Si-O-Si network and changing the ratio of short (“cage”) Si­O bonds to long (“network”) Si­O bonds. The changes to the Si-O bond structure were minimal in the POSS materials. The amount of POSS in the poly(MMA-co-POSS) mixed with MSQ was relatively small, and, therefore, at elevated temperatures the mixtures were quite similar to neat MSQ.