Polysiloxane nanocomposites

Fig. 13. Overview over some properties to be derived from inorganic-organic hetero polysiloxane nanocomposites and potential applications...

Degradative Thermal Analysis and Dielectric Spectroscopy Studies of Aging in Polysiloxane Nanocomposites... 

Historically, polysiloxane elastomers have been reinforced with micron scale particles such as amorphous inorganic silica to form polysiloxane microcomposites. However, with the continued growth of new fields such as soft nanolithography, flexible polymer electronics and biomedical implant technology, there is an ever increasing demand for polysiloxane materials with better defined, improved and novel physical, chemical and mechanical properties. In line with these trends, researchers have turned towards the development of polysiloxane nanocomposites systems which incorporate a heterogeneous second phase on the nanometer scale. Over the last decade, there has been much interest in polymeric nanocomposite materials and the reader is directed towards the reviews by Alexandre and Dubois (4) or Joshi and Bhupendra (5) on the subject. 

Examples of the synthesis of polysiloxane nanocomposites reported in the literature include Work by Ma et al (6) who modified montmorilIonite with short segments of PDMS and blended this into a polymer melt/solution to yield examples of fully exfoliated or intercalated PDMS/clay nanocomposites. Pan, Mark et al (7) synthesized well defined nano-fillers by reacting groups of four vinyl terminated POSS cages with a central siloxane core. These materials were subsequently chemically bonded into a PDMS network yielding a significant improvement in the mechanical properties of the polymer. 

The aging behavior of conventional filled polysiloxane materials has been relatively well studied. However, there is little currently known about the long term stability and aging behavior of polysiloxane nanocomposites. This is a key issue that must be addressed if polysiloxane nanocomposites are to become part of the next generation of polymeric materials. 

It is reasonable to link the mass loss with the observed changes in thermal stability and dielectric response, indeed some of this material that is evolved from the systems on aging is likely to be water and the reaction residues implicated as pro-degradants. However, the level of material lost the ongoing nature of the process and the clear link once again with a moist air environment points to an explanation other than simple passive loss of volatile residues from the nanocomposites. Cleary, an identification of this volatile material is desirable if the nature of the aging processes occurring within these polysiloxane nanocomposites is to be elucidated. 

Lewidd, J.P., Liggat, (.(., Hayward, D., Pethrick, R.A., and Patel, M. (2009) Degradative thermal analysis and dielectric spectroscopy studies of aging in polysiloxane nanocomposites, in Polymer Degradation and Performance (ed. M. Celina), American Chemical Society, Washington, DC. 

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