**3.3.3 Applications of POSS-modified thermoplastic polymers**

POSS are a class of versatile building blocks used for the preparation of organic-inorganic hybrid polymers with designed properties. The POSS molecules can be modified into monomers, initiators, or chain transfer agents (CTA) for a living polymerization. The POSS molecule was used as monomer to prepare the POSS-containing homopolymers or copolymers (Lichtenhan et al., 1995). In recent years the preparation of the POSS-containing hybrid polymers with the novel architecture has been focused on a living and controlledliving polymerization techniques, e.g. the synthesis of the homopolymers and triblock copolymers from a POSS-based methacrylate monomer using atom transfer radical polymerization (ATRP) was carried out (Pyun et al., 2003). The star-shaped hybrid polymers were prepared via ATRP of methyl methacrylate using the octafunctional POSS molecule as an initiator (Costa et al., 2001).

Reversible addition-fragmentation chain transfer (RAFT) polymerization has a wider selectivity of the monomers containing carboxyl, amino and ionic groups and it can be used under a broad range of experimental conditions including aqueous solutions. The POSScontaining RAFT agent, prepared of minopropylisobuthyl polyhedral oligomeric silsesquioxane was used in the RAFT polymerization of N-isopropylacrylamide (NIPAM) to produce tadpole-shaped organic-inorganic hybrid poly(N-isopropylacrylamide) (PNIPAM). The same POSS-containing RAFT agent was also successively applied in the RAFT polymerization of styrene to produce the organic-inorganic hybrid homopolymers and block copolymers (Zhang et al., 2009).

Recently the living/controlled polymerization technique is combined with "click chemistry" which is based on the copper-catalyzed Huisgen 1,3-dipolar cycloaddition between azides and alkynes. This reaction can be performed under mild conditions and it has a good tolerance of functional groups. Click chemistry has been mostly used to functionalize the end-groups or pendant groups of polymers or to built polymers with well-defined structures. The click reaction occurs between a polymer and small organic molecules or between two different polymer chains. The copper-catalyzed click reaction between alkynefunctional POSS molecules and mono-, di-, and pentafunctional azido-terminal polymers made by ATRP proceeds smoothly to form monochelic (tadpole-shaped), and ditelechelic (dumbbell-shaped) linear hybrid polymers as well as pentatelehcelic, star-shaped hybrids. The inversion of the procedure is also possible, i.e. the reaction of azido-functional POSS molecule was "clicked" to alkyne-terminated polymers (Müller et al., 2010).

It should be noted that most of the POSS molecules are intrinsically hydrophobic, while many commercial monomers are polar. Attachment of the polar group to POSS molecules make these compounds compatible with many polymers. For example oligosilsesquioxanes with poly(ethylene glycol)s, POSS-PEG monomers, because of their hydrophilic chemical structure are soluble in water and readily dispersed in polar monomers. The hydroxyl containing POSS molecules were used as an initiator in the ring-opening polymerization of lactide in the presence of a stannous catalyst.

cross-linked polyethylene. Lu et al. (2005) prepared methacryloxypropyltrimethoxysilane (MAPTMS)-grafted PE (PE-*g*-MAPTMS) by melt grafting reaction, and then blend it with

POSS are a class of versatile building blocks used for the preparation of organic-inorganic hybrid polymers with designed properties. The POSS molecules can be modified into monomers, initiators, or chain transfer agents (CTA) for a living polymerization. The POSS molecule was used as monomer to prepare the POSS-containing homopolymers or copolymers (Lichtenhan et al., 1995). In recent years the preparation of the POSS-containing hybrid polymers with the novel architecture has been focused on a living and controlledliving polymerization techniques, e.g. the synthesis of the homopolymers and triblock copolymers from a POSS-based methacrylate monomer using atom transfer radical polymerization (ATRP) was carried out (Pyun et al., 2003). The star-shaped hybrid polymers were prepared via ATRP of methyl methacrylate using the octafunctional POSS molecule as

Reversible addition-fragmentation chain transfer (RAFT) polymerization has a wider selectivity of the monomers containing carboxyl, amino and ionic groups and it can be used under a broad range of experimental conditions including aqueous solutions. The POSScontaining RAFT agent, prepared of minopropylisobuthyl polyhedral oligomeric silsesquioxane was used in the RAFT polymerization of N-isopropylacrylamide (NIPAM) to produce tadpole-shaped organic-inorganic hybrid poly(N-isopropylacrylamide) (PNIPAM). The same POSS-containing RAFT agent was also successively applied in the RAFT polymerization of styrene to produce the organic-inorganic hybrid homopolymers and block

Recently the living/controlled polymerization technique is combined with "click chemistry" which is based on the copper-catalyzed Huisgen 1,3-dipolar cycloaddition between azides and alkynes. This reaction can be performed under mild conditions and it has a good tolerance of functional groups. Click chemistry has been mostly used to functionalize the end-groups or pendant groups of polymers or to built polymers with well-defined structures. The click reaction occurs between a polymer and small organic molecules or between two different polymer chains. The copper-catalyzed click reaction between alkynefunctional POSS molecules and mono-, di-, and pentafunctional azido-terminal polymers made by ATRP proceeds smoothly to form monochelic (tadpole-shaped), and ditelechelic (dumbbell-shaped) linear hybrid polymers as well as pentatelehcelic, star-shaped hybrids. The inversion of the procedure is also possible, i.e. the reaction of azido-functional POSS

It should be noted that most of the POSS molecules are intrinsically hydrophobic, while many commercial monomers are polar. Attachment of the polar group to POSS molecules make these compounds compatible with many polymers. For example oligosilsesquioxanes with poly(ethylene glycol)s, POSS-PEG monomers, because of their hydrophilic chemical structure are soluble in water and readily dispersed in polar monomers. The hydroxyl containing POSS molecules were used as an initiator in the ring-opening polymerization of

molecule was "clicked" to alkyne-terminated polymers (Müller et al., 2010).

organically modified montmorillonite to make PE-*g*-MAPTMS/MMT nanocomposite.

**3.3.3 Applications of POSS-modified thermoplastic polymers** 

an initiator (Costa et al., 2001).

copolymers (Zhang et al., 2009).

lactide in the presence of a stannous catalyst.

Optical transparent films of a single POSS compound are hardly formed without crosslinking reagents due to their high symmetry and crystallinity. It could be speculated that lower the symmetries of the POSS derivatives decrease their crystallinity and would provide optical transparent film forming properties. Such kinds of materials are regarded as thermoplastic hybrids possessing low-k or refractive index.

Dumbbell-shaped trifluoropropyl substituted POSS derivatives linked by simple aliphatic chains (ethane, propane, hexane) to reduce their symmetries were synthesized. These derivatives formed optical transparent films depending on their aliphatic linkages under the low temperature, which would open the way to apply to coating on various thermally unstable materials (Araki & Naka, 2011).
