**2.5 Polyhedral Silsesquioxanes (POSS)**

158 Thermoplastic Elastomers

The hydrosilylation is the fundamental reaction used for the preparation of the carbofunctional polysiloxanes (Brook, 2000; Marciniec et al., 1992b), and platinum Speier's and Karstedt's catalysts are not enough effective in the case of addition of allylamine to tetramethylcyclotetrasiloxane D4H (DH = MeHSiO), giving low yield and selectivity of products (Wu & Feng, 2001). Instead of a very useful catalyst of this reaction is platinum oxide PtO2, resistant to "poisoning" by amine groups, giving the product with almost 100 % yield and the very good selectivity, determined by a ratio of isomers to 93:7 (Zhou et al., 2004).

A very common method of the preparation of the carbofunctional polysiloxanes are catalytic equilibration reactions of cyclic siloxanes, e.g. octamethylcyclotetrasiloxane (Me2SiO)4 (D4) with carbofunctional disiloxanes, which are carried out in acidic or basic media (Scheme 2)

**H+/OH-**

Scheme 2. The preparation of CFPS by the catalytic equilibration of the carbofunctional

For example, by the equilibration of D4 (D = Me2SiO) with (3-aminopropyl)methyldiethoxysilane and hexamethyldisiloxane Me3SiOSiMe3, polydimethyl-*co*-[(aminopropyl)(methyl)] siloxane oils (containing side aminopropyl groups) were prepared (Yang et al., 2007).

By anionic copolymerization of D4 with (Ph4SiO)4 and (ViMeSiO)4 towards 1,3-bis(3-aminopropyl)tetramethyldisiloxane (as a chain terminating agent) poly(dimethyl-*co*-diphenyl) siloxane containing terminal aminopropyl groups was prepared. This product was utilized for a synthesis of a segmented poly(imide-siloxane) copolymer, and subsequently for the preparation of a hybrid nanocomposite, reinforced with silica (Liaw, 2007a) or titania TiO2

The carbofunctional polysiloxanes, in which alkylfunctional groups are attached to the silicon atoms inside of the polymer chain were also prepared by the catalytic equilibration of cyclotetrasiloxane, containing aminopropyl functional groups (D3DNH2), with decamethyltetrasiloxane MD2M (D = Me2SiO, M = Me3SiO0.5) in the presence of Me4NOSiMe3 (TMAS)

D3DH D3DNH2

**TMAS 3**

Scheme 3. The preparation of CFPS with pendant aminopropyl functional groups.

**[ Pt ]**

**Me3Si-O Si <sup>O</sup>** (**Si <sup>O</sup>**) **SiMe3 Me Me**

> **(CH2)3 NH2**

**Si**

**Me <sup>O</sup> Si**

**Me**

**(CH2)3NH2** 

**O**

**3**

**Me**

**Me <sup>n</sup>**

**RX XR OSi Si**

**Me Me**

( )**4n + 1**

**RX**

**Me Me**

(Yilgor & McGrath, 1988; Harabagiu et al., 1996).

**Me Me**

**Me Me**

(Zhou et al., 2004; Yang et al., 2007), as it is presented on a Scheme 3:

**+ CH2=CH-CH2-NH2**

**n D4 + XR OSi Si**

disiloxanes with D4.

(Liaw, 2007b).

**Si**

**Me <sup>O</sup> Si**

**3**

**D3DNH2**

**Me H O**

**MD2M**

**Me**

Silsesquioxanes (SSO) are important hybrid materials. Silsesquioxane or T unit of general formula RSiO1.5 can exist in several structural types such as random, ladder, cage or semicage structures. SSO with a cage structure is also called polyhedral oligomeric silsesquioxane (POSS). POSS are organic-inorganic molecules, approximately 1-3 nm in size, with a general formula (RSiO1.5)n or Tn, where R is mostly organic group, which can be suitable for polymerization or grafting (Baney et al., 1995). Among various oligosilsesquioxanes, aromatic POSS are the most interesting compounds because of their high temperature stability (> 500 °C for octaphenylsilsesquioxane).

Fig. 2. Chemical structure of T8 (Williams et al., 2011).
