**2.3 Carbofunctional Silanes (CFS)**

Carbofunctional silanes (CFS), which are used for a long time in a processing of plastics may be considered as precursors of carbofunctional polysiloxanes. The carbofunctional silanes are compounds with a general formula XnSi(R'Y)4-n, where: R' – alkylene chain, Y – functional group, e.g. Cl, NH2, NR2, OH, OCOR, NCO, CH2=CH, SH, and X – a functional group sensitive to hydrolysis (Cl, OR, OCOR). Alkylene chain R' is usually built of three methylene groups (Marciniec et al., 1990, 1992a, 1993; Chruściel et al., 2008a).

The carbofunctional silanes are usually prepared in a three step synthesis. In a first step a catalytic hydrosilylation reaction of allyl chloride with hydro(alkyl)chlorosilanes is carried out, in a second step – alcoholysis of addition products, and in a last step – substitution of chlorine atom in (chloropropyl)trialkoxysilane Cl(CH2)3SiMen(OR)3-n by a catalytic nucleophilic substitution - take place (Guliński et al., 2003).

### **2.4 Carbofunctional Polysiloxanes (CFPS)**

156 Thermoplastic Elastomers

In organosilicon chemistry most important are following functional groups: Si-Cl, Si-OR, SiOCOR (R – usually alkyl group), Si-H, and Si-CH=CH2. They are present both in all kinds of organosilicon compounds and polymers and can be grafted on silica, silicates, and some inorganic fillers. Functional organic silanes include first of all: chlorosilanes, alkoxysilanes, and acetoxysilanes (e.g. dimethyldichlorosilane, methyltriethoxysilane, methyltriacetoxysilane, etc.), and different functional and carbofunctional silanes (Brook, 2000, Eaborn, 1960; Kricheldorf, 1996). Moreover very often are used inorganic chlorosilanes: silicon tetrachloride SiCl4, trichlorosilane HSiCl3, and dichlorosilane H2SiCl2, and silicate compounds: esters of silicic acid, and especially tetraethoxysilane Si(OEt)4, tetramethoxysilane Si(OMe)4, and tetracetoxysilane Si(OAc)4. Chlorosilanes are produced on an industrial scale by Rochow-Miller process, and their fast reactions with alcohols (or metal alkoxides) and carboxylic acids

Siloxane oligomers (linear and cyclic) and polysiloxanes (silicones) are mainly prepared by so called a multistep "hydrolytic polycondensation" of chlorosilane monomers of different functionality. This step-growth process consists of elementary hydrolysis and condensation

Linear oligo- and polysiloxanes with diferent functional (,-terminal or pendant) groups and functional cyclosiloxanes find many applications in further syntheses. These functionalities include most often silanol, chlorosilyl, hydrosilyl, vinyl, and allyl groups.

Carbofunctional silanes (CFS), which are used for a long time in a processing of plastics may be considered as precursors of carbofunctional polysiloxanes. The carbofunctional silanes are compounds with a general formula XnSi(R'Y)4-n, where: R' – alkylene chain, Y – functional group, e.g. Cl, NH2, NR2, OH, OCOR, NCO, CH2=CH, SH, and X – a functional group sensitive to hydrolysis (Cl, OR, OCOR). Alkylene chain R' is usually built of three

The carbofunctional silanes are usually prepared in a three step synthesis. In a first step a catalytic hydrosilylation reaction of allyl chloride with hydro(alkyl)chlorosilanes is carried out, in a second step – alcoholysis of addition products, and in a last step – substitution of chlorine atom in (chloropropyl)trialkoxysilane Cl(CH2)3SiMen(OR)3-n by a catalytic nucleo-

methylene groups (Marciniec et al., 1990, 1992a, 1993; Chruściel et al., 2008a).

Si-Cl + H2O → Si-OH + HCl (1)

Si-Cl + HO-Si → Si-O-Si + HCl (2)

Si-OH + HO-Si → Si-O-Si + H2O (3)

**2. Reactive silanes and siloxanes** 

**2.1 Functional groups and reactive silanes in silicon chemistry** 

lead to appropriate alkoxysilanes or acyloxysilanes, respectively.

**2.2 Functional siloxanes and polysiloxanes** 

**2.3 Carbofunctional Silanes (CFS)** 

philic substitution - take place (Guliński et al., 2003).

reactions:

Weak interactions between polysiloxane chains (through van der Waals forces) are responsible for poor mechanical properties of these polymers at room temperature, even in the case of PDMS with a very high molecular weights (Abe & Gunji, 2004). An improvement of mechanical properties of PDMS can be reached by addition of fillers (most often silica is used), by a dense crosslinking in the presence of peroxides, or by synthesis of siloxaneorganic copolymers of different structures (block, segmented, or graft). Since both systems are thermodynamically non-miscible it is impossible to prepare siloxane-organic copolymers from (,-dihydroxy) polydimethylsiloxanes, and it was necessary to use for this purpose ,-dihydro- or ,-divinylpolysiloxanes, but first of all to use the carbofunctional polysiloxanes (CFPS) (Chruściel et al., 2008b).

The general structure of carbofunctional polysiloxanes is presented on Fig. 1.

Fig. 1. The chemical structure of ,-dihydro-, ,-divinyl-, and the carbofunctional polysiloxanes (R = H, CH = CH2, aminoalkyl, hydroxyalkyl, chloroalkyl groups, etc.)

### **2.4.1 Synthesis of CFPS**

Macromolecules of the carbofunctional polydimethylsiloxanes (CFPS) are terminated with different functional alkylene groups. Most often on both ends of CFPS chains exist hydroxypropyl, aminopropyl, glicydoxypropyl, or methacryloxypropyl groups. The carbofunctional polysiloxanes may also be terminated with alkene groups (e.g. allyl groups) or with arylamine end groups: -C6H4NH2 (Kawakami & Abe, 1992). Quite often for synthesis of the carbofunctional polydimethylsiloxanes are used ,-dihydrosiloxanes, which are synthesized in condensation reactions of polysiloxane-,-diols with chloro(hydro) dimethylsilane. The CFPS containing terminal carbinol groups (C-OH) are products of hydrosilylation reaction of different ,-dihydropolysiloxanes with allyl derivatives (Marciniec et al., 1992b), e.g. allyloxytrimethylsilane (Greber & Jäger, 1962), followed by hydrolysis reaction of alkoxysilane end groups (Scheme 1).

Scheme 1. The preparation of ,-di(hydroxypropyl)polydimethylsiloxanes.

Modification of Thermoplastics with Reactive Silanes and Siloxanes 159

By a controlled hydrolytic copolycondensation of (3-aminopropyl)(methyl)diethoxysilane and [(3-aminoethylamino)propyl](methyl)dimethoxysilane - a mixture of linear and cyclosiloxane oligomers containing 3-aminopropyl and [(3-aminoethylamino)propyl substituents was prepared (Kichler et al., 2003). They were applied as new generation polycationic

Carbofunctional PDMS with different photoactive linkages, i.e. benzoin (Yagci et al., 1994), glicydoxyl (Harabagiu et al., 1995), or benzylacryl groups (Iojoiu et al., 2000) were also

The synthetic methods, mentioned in this Chapter, do not cover many other methods of the

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

supports of DNA ("*gene transfer reagents*").

preparation of the carbofunctional polysiloxanes.

stability (> 500 °C for octaphenylsilsesquioxane).

**O**

**Si O Si**

**O O**

**R R**

**Si**

**OSi Si**

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

**O**

**3.1 Applications of carbofunctional silanes** 

**O**

**R**

**R**

**O**

**O**

**Si O Si**

**R R**

**Si O**

**R**

An interest concerning the carbofunctional silanes is still growing and broadens a scale of their numerous applications. A great practical meaning have also carbofunctional polysiloxanes.

The carbofunctional silanes XnSi(R'Y)4-n have found misceleneous practical applications thank to the presence of two kinds of the functional groups X and Y. In practice formation of chemical bonds with an inorganic material is possible, as a result of reactions of functional groups X, which most often are alkoxy groups. On the other hand the functional groups Y enable reactions with organic polymers. Most popular, available on market, are compounds of a structure (RO)3Si(CH2)3Y, in which as alkoxy substituents are present methoxy or

**O**

**3. Technical applications of reactive silanes and siloxanes** 

**R**

**2.5 Polyhedral Silsesquioxanes (POSS)** 

prepared.

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 D4 H (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) (Yilgor & McGrath, 1988; Harabagiu et al., 1996).

Scheme 2. The preparation of CFPS by the catalytic equilibration of the carbofunctional disiloxanes with D4.

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 (Liaw, 2007b).

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

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

By a controlled hydrolytic copolycondensation of (3-aminopropyl)(methyl)diethoxysilane and [(3-aminoethylamino)propyl](methyl)dimethoxysilane - a mixture of linear and cyclosiloxane oligomers containing 3-aminopropyl and [(3-aminoethylamino)propyl substituents was prepared (Kichler et al., 2003). They were applied as new generation polycationic supports of DNA ("*gene transfer reagents*").

Carbofunctional PDMS with different photoactive linkages, i.e. benzoin (Yagci et al., 1994), glicydoxyl (Harabagiu et al., 1995), or benzylacryl groups (Iojoiu et al., 2000) were also prepared.

The synthetic methods, mentioned in this Chapter, do not cover many other methods of the preparation of the carbofunctional polysiloxanes.
