Since silicone science is not big in Australia, I thought I’d cover an unusual chemical used in my research; Polyhedral Oligomeric Silsesquioxane (POSS). POSS comes from a class chemicals with the molecular formula RnSinO1.5n (the most common n=8) arranged in a 3D cage structure approximately 1 nm in size (see Figure 1). Each silicon atom in POSS carries an R-group, which can be chosen to be tailored for specific applications. POSS typically comes in a mono-functionalised form (7 inert R-groups with 1 R-group bearing a reactive moiety) or octa-functionalised (all 8 R-groups are the same).
Figure 1 – Schematic diagram of a mono-functionalised (left) and an octa-functionalised (right) POSS. Typical R-groups consist of alkanes (cyclic, branched or linear), phenyl groups or reactive groups, such as amines, thiols, alcohols, epoxides and various others. (X represents reactive groups where R≠X) |
R-groups can be inert functional groups, such as alkanes (methyl, ethyl, isobutyl, iso-octane, cyclo-hexane, etc), phenyl groups, or bear reactive functional groups, such as alcohols, amines, diamines, thiols, halogens, epoxides, alkenes, methacrylates, acrylates, etc. Reactive groups are of particular interest as they can act as the building blocks of nanoscale architectures, by tethering to polymers [1, 2] (typically for the use as nano-fillers to alter thermomechanical properties), or in the case of octa-functionalised POSS, as cross-linkers [3] or be used as a core for dendrimers [2] (see Figure 2). An advantage POSS has over other nanoparticles is that POSS is (usually) completely soluble in the appropriate solvent, and can be easily modified using conventional organic chemistry [4].
Figure 2 – Schematic of the architectures possible when the appropriate POSS molecule is used
A range of these POSS materials are readily available from Hybrid Plastics (some are available through Sigma Aldrich and other chemical suppliers).
For those looking for more information, I’ve supplied articles dealing with synthesis and functionalisation of POSS [4], research into use in polymeric systems [1, 2], for use in dendrimer synthesis [2] and other applications [2].
Posted by Jonathan Sierke, Supervisor: Professor Amanda Ellis
References:
1. Williams, K.G., Gido, S.P., and Coughlin, E.B., Polymers and Copolymers Containing Covalently Bonded Polyhedral Oligomeric Silsesquioxanes Moieties Applications of Polyhedral Oligomeric Silsesquioxanes, C. Hartmann-Thompson, Editor. 2011, Springer Netherlands. p. 167-207.
2. Tanaka, K. and Chujo, Y., Advanced functional materials based on polyhedral oligomeric silsesquioxane (POSS). Journal of Materials Chemistry, 2012. 22(5): p. 1733-1746.
3. Strachota, A., Kroutilová, I., Kovářová, J., and Matějka, L., Epoxy Networks Reinforced with Polyhedral Oligomeric Silsesquioxanes (POSS). Thermomechanical Properties. Macromolecules, 2004. 37(25): p. 9457-9464.
4. Cordes, D.B., Lickiss, P.D., and Rataboul, F., Recent Developments in the Chemistry of Cubic Polyhedral Oligosilsesquioxanes. Chemical Reviews, 2010. 110(4): p. 2081-2173.
“… building blocks of nanoscale architectures …” Following the development of nano technology rather closely in recent years, I have just one concern with particles like that: as with rather inert asbestos and other “mineral dust” are we not creating a potential health threat by releasing these silicon “nodules” into the environment? I would imagine that after they may have there ligands “shown off” in a reaction that they were intended to facilitate, they might then have an afterlife or does their spatial structure readily disintegrate into just silicon eventually?