Iain A. MacKinnon

A higher yielding route for T8 silsesquioxane cages and X-ray crystal structures of some novel spherosilicates

The synthesis of T8 silsesquioxane cages from trialkoxysilanes using tetra n-butylammonium fluoride is described. The yields are in the range 20–95%, which is a great improvement on other literature routes. This methodology enables a wide range of functionalised T8 cages to be prepared. The X-ray crystal structures of three new T8 cages, octacyclopentylsilsesquioxane, octaisobutylsilsesquioxane and octa(4-carboxymethyl-3,3-dimethylbutyl)silsesquioxane are also reported.

Ring-Opening Olefin Metathesis Polymerisation (ROMP) as a Potential Cross-Linking Mechanism for Siloxane Polymers

Reported here are some results of rapid Ring Opening Metathesis Polymerization (ROMP) of norbornene-functional oligomeric siloxanes using a Ru-based catalytic system. The in situ formation of the active metal carbene catalyst by addition of a diazo compound to norbornene-functional siloxane containing the catalytic system, [(p-cymene)RuCl2]2/PCy3 allowed fast but controlled polymerization of the norbornene functionalities. Thus, in a solventless system, polymerization of a norbornene-functional siloxane, e.g., 1,1,1,2,3,3,3-heptamethyl-2-norbornen-5-yltrisiloxane, at 60°C with low catalyst levels (2 to 200 ppm) led to a colourless monolithic gel in less than 30 seconds. Besides being an efficient cross-linking technology, ROMP of suitable precursors may also be a source of novel silicone-organic materials.

Preparation of Microporous ORMOSILs by Thermal Degradation of Organically Modified Siloxane Resin

Silicon containing materials have traditionally been used in microelectronic fabrication. Semi-conductor devices often have one or more arrays of patterned interconnect levels that serve to electrically couple the individual circuit elements forming an integrated circuit. These interconnect levels are typically separated by an insulating or dielectric film. Previously, a silicon oxide film was the most commonly used material for such dielectric films having dielectric constants (k) near 4.0. However, as the feature size is continuously scaling down, the relatively high k of such silicon oxide films became inadequate to provide efficient electrical insulation. As such, there has been an increasing market demand for materials with even lower dielectric constant for Interlayer Dielectric (ILD) applications, yet retaining thermal and mechanical integrity. We wish to report here our investigations on the preparation of ultra-low k ILD materials using a sacrificial approach whereby organic groups are burnt out to generate low k porous ORMOSIL films. We have been able to prepare a variety of organically modified silicone resins leading to highly microporous thin films, exhibiting ultra-low k from 1.80 to 2.87, and good to high modulus, 1.5 to 5.5 GPa. Structure property influences on porosity, dielectric constant and modulus will be discussed.

Polysiloxane-Modified Mesoporous Materials

We report the preparation of polysiloxane-modified mesoporous silica gels derived from the acid catalysed hydrolysis of tetraethoxysilane (TEOS) and oligomeric silanol terminated polydimethylsiloxane (PDMS) in the presence of the non-ionic surfactant, octaethylene glycol monohexadecyl ether. The gels were characterised using thermal gravimetric analysis (TGA), infra-red (IR) spectroscopy, X-ray diffraction (XRD) and 29Si solid state cross-polarisation (CP) magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. TGA and IR spectroscopy showed the loss of surfactant after calcination and a decrease in the Si–OH band at 950 cm−1 indicated further condensation had occurred. This was confirmed by the increase in Q4 at −110 ppm, in 29Si MAS NMR spectroscopy, which also showed that calcination had led to the redistribution of PDMS forming a T species. XRD data showed ordering within the structure, with an initial d-spacing of 45 Å, decreasing to 35 Å after calcination.