**3.2.2.4 Modification of polycarbonates by CFPS**

Polycarbonates (PCs) belong to an extremely useful class of engineering thermoplastics known for their toughness and optical properties. Most commercialized PCs are based on bisphenol A and these polyesters have the advantageous properties of superior heat resistance, transparency, dimensional stability and self-extinction, exceptional impact resistance and ductility at or below room temperature. Other properties such as the modulus, dielectric strength and tensile strength, are comparable to those of other amorphous thermoplastics. The main limitations of PCs are their poor scratch, ultraviolet (UV), and solvent resistance, and their sharply decreased impact strength at low temperature.

PC/silicone oil blends, based on two kind of silicone oils: PDMS and polydimethyldiphenylsiloxane PDMDPS, have been studied (Kim & Kim, 2008). A transition from brittle to ductile

adhesion. The unique properties of the imide-siloxane copolymeric materials (PSIs) make them

A series of amorphous poly(imide siloxane)s (PIS) with different PDMS contents and segmental lengths were synthesized via condensation reaction by Ku & Lee (2007). A variety of morphologies of PIS films, including unilamellar vesicle, multilamellar vesicle, sea-island and others, were found as the function of the content and the segmental length of PDMS, as well as the coexistence of large-scale phase separations and nano-scale phase separation of

Lu et al. (2006) prepared, using sol-gel method, polyimide/polydiphenylsiloxane (PI/PDPS) composite films with high thermal stability near pure PI. Polysiloxanes well dispersed in polyimide matrix, without macroscopic separation for the composite films was observed with low content of DPS, while large domain of polysiloxane was formed in films with high DPS content. The introduction of DPS into PI improved the elongation at break but the

Aromatic polyimides (PIs) have been of great interest in gas separation membranes because of their gas selectivity and excellent thermal and mechanical properties. Recently, novel triaminebased hyperbranched PIs are applied for high-performance gas-separation materials. Hybridization of PIs with inorganic compounds has been focused also to improve the gas transport properties. Hyperbranched PIs prepared by polycondensation of a triamine 1,3,5 tris-(4-aminophenoxy)benzene and 4,4'-(heksafluoroisopropylidene) diphthalic dianhydryde (6FDA) were modified by sol-gel reaction using tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMS), and 3-aminopropyltrimethoxysilane (Suzuki et al., 2008).

New copolymers, polysiloxane-imides (PSIs), have been prepared from α,ω-(bisaminopropyl)dimethylsiloxane oligomers (ODMS) and aromatic dianhydrides: 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), and 6FDA, (Krea et al., 2004). Membranes of these

Bismaleimide (BMI) has the unique combination of a high service temperature, good toughness and epoxy-like processing. Composites of BMI with surface-modified SiO2 nanoparticles by amino-functionalized silane coupling agent has been studied (Yan et al., 2008). The nanocomposites with surface-modified SiO2 showed better wear resistance and

Polycarbonates (PCs) belong to an extremely useful class of engineering thermoplastics known for their toughness and optical properties. Most commercialized PCs are based on bisphenol A and these polyesters have the advantageous properties of superior heat resistance, transparency, dimensional stability and self-extinction, exceptional impact resistance and ductility at or below room temperature. Other properties such as the modulus, dielectric strength and tensile strength, are comparable to those of other amorphous thermoplastics. The main limitations of PCs are their poor scratch, ultraviolet (UV), and solvent resistance, and

PC/silicone oil blends, based on two kind of silicone oils: PDMS and polydimethyldiphenylsiloxane PDMDPS, have been studied (Kim & Kim, 2008). A transition from brittle to ductile

new PSIs have been used to remove polar organics from water by pervaporation.

lower frictional coefficient than that with unmodified fillers.

their sharply decreased impact strength at low temperature.

**3.2.2.4 Modification of polycarbonates by CFPS** 

especially attractive for applications in microelectronics and as structural adhesives.

composite films still remained with higher modulus and tensile strength.

approximately 20 nm.

failure was observed with increasing PDMDPS content. At temperature of –30 C the impact strength increased from 8 kgfcm/cm to 52 kgfcm/cm for neat PC and PC/PDMDPS blends respectively.

An interesting group of thermoplastic elastomers (TPE), characterized by a great stiffness at low temperature, are block copolymers prepared from polycarbonates (PC) and PDMS (PC/PDMS). Copolymers PC/PDMS are usually prepared in reaction of phosgene with bisphenol A in the presence of PDMS containing terminal bisphenol groups (van Aert et al., 2001). Block PC/PDMS copolymers find applications in a manufacture of membranes, which are used for selective separation of gases (LeGrand, 1972).

Multi-walled carbon nanotubes/polycarbonate nanocomposites (MWNT/PC) have been prepared (Wang et al., 2010). Functionalized MWNTs-COOH with α,ω-3-aminopropyl-PDMS, were used to produce MWNT/PC nanocomposites. The results showed that siloxane–modified carbon nanotubes were dispersed well in the PC matrix, and the tensile strength, flexural strength, flexural modulus, and flame retardancy of MWNT/PC composites were better than these of MWNT-COOH/PC. Siloxane-modified MWNTs can improve the electrical properties of the nanocomposites at low loading in PC.

### **3.2.3 Modification of polyurethanes and polyureas by CFPS**

Thermoplastic polyurethanes (TPUs) are obtained by a polyaddition reaction of diisocyanates to long, hydroxyl-terminated oligomers (polyols) and short diols, which are often named as chain extenders. The polyurethanes are multi-block copolymers consisting of hard segments (HS) and soft segments (SS). The thermodynamic incompatibility between alternating segments usually induces a two-phase structure with soft domains containing mostly the polyol moieties, and hard domains made up of diisocyanate-chain extender sequences. If incompatibility exists between the two block components, a microphase separation will occur and the hard domains will provide a reinforcement to the system. The type of diisocyanate has a marked effect on a strength of a final material. The most often applied isocyanates are: 4,4'-methylenediphenyl diisocyanate (MDI), tolylene diisocyanate (TDI), bis(4-isocyanatocyclohexyl) methane (HMDI), isophorone diisocyanate (IPDI). TPUs are widely used for high-performance applications, as: medical implants (Arkles, 1983), membranes, adhesives and coatings, especially when a high tear and a tensile strength or good wear and abrasion resistance are required. Another special features of TPUs are their low-temperature elasticity, a smoothness for the touch, an electrical insulation and a good chemical resistance.

Over the past three decades, considerable attention has been directed to utilization of the PDMS as a soft segment component in polyurethanes and polyurethaneureas. Polysiloxane SS are introduced by PDMS-diols or hydroxyalkenyl or aminopropyl or ethyl-piperazine terminated PDMS. However, the tensile strength and elongation at break of these materials compared to those based on polyether (PET) or polyester (PES) SS are visibly poorer. Thus, various co-SS components, mainly based on poly(alkenyl oxide) have been utilized. Sheth et al. (2005) selected poly(propylene oxide) (PPO) as a second SS component, because his solubility parameter (23.5 J1/2/cm3/2) is in between that of PDMS (15.6 J1/2/cm3/2) and urea (45.6 J1/2/cm3/2). The inter-segmental mixing between PPO and urea segments could modify the nature of interphase between the soft matrix and the hard urea microdomains.

Modification of Thermoplastics with Reactive Silanes and Siloxanes 173

copolymer PY-PDMS. Classical conductive polymers are insoluble and infusible. A common way to facilitate their processing are syntheses of block or graft copolymers containing conductive segments and conventional segments, increasing solubility of copolymer, e.g. block copolymers of styrene and acetylene, styrene and thiophene, graft copolymers of pyrrole on polystyrene, and on poly(methyl methacrylate). Recently a new multifunctional polysiloxanes, containing mercapto-, thiocarbamide, and (hydroxyalkyl)ether linkages were applied for the modification of silica fillers used for the production of rubber tires (Kalaycioglu et al., 1998). Copolymers with siloxane moieties serve as connectors with organic polymers (compatibilizers). Siloxane segments of the copolymers migrate to the surface, while organic

Composite materials consist of a polymer matrix and various inorganic fillers. They have been widely used in order to improve the mechanical, thermal, barrier, and other properties of the polymer. However it is known that the improvement of one property can result the worsening of another. It is anticipated that such problems can be overcome if the inorganic additive exists in the form of a fine dispersion within the polymer matrix producing a nano-

The carbofunctional silanes are most often applied as so called adhesion promoters, which are also called as "*silane coupling agents*" (Pleuddeman, 1991). The silane adhesion promoters are directly added to polymer compositions (usually in a quantity 0.2–2 % wt. %) or in a form of water and water-alcoholic dispersions. The substituent X (e.g. alkoxy group) may

**OH + RO-Si O-Si + ROH** 

**Si - OR + H2O Si - OH + ROH** 

**P O L Y M E R**

**N-(CH2)3Si-O** filler **OH**

**OH**

Thus alkoxy groups are replaced with silanol groups Si-OH, which are able to form chemical bonds with inorganic materials, e.g. glass, metals or fillers (Scheme 7) (Haas & Wolter, 1999):

**H2O**

Scheme 7. An adhesion model in a system: polymer–silane–filler.

segments act as anchors of siloxane blocks in the polymeric material.

**3.3 Composites and nanocomposites from thermoplastic polymers** 

composite. Silane modified fillers and nanofillers are used for these purposes.

undergo condensation reactions with hydroxyl groups of the filler:

**3.3.1 Modification of fillers properties by CFS** 

or hydrolysis reactions:

 **(CH3O)3Si(CH2)3NH2**

**+ polymer**

**+ filler**

In order to reduce emission of volatile organic compounds, water borne polyurethanes (WPUs) have attracted much attention. However, the WPUs have shortcomings, such as lack of resistance to water, a surface hydrophilicity and the low strength. These disadvantages can be eliminated by using a different mixing composition of soft segments. Chen et al. (2005) prepared the anionic WPUs from hydroxyl-terminated PDMS, poly(tetramethylene oxide) (PTMO) as the soft segments, IPDI as the hard segment, and 2,2-bis(hydroxymethyl) propionic acid (DMPA) as the ionic centre. DMPA was used to form a water-dispersible urethane prepolymer. The tensile strength of WPU-PDMS films decreased with an increasing content of PDMS and a water repellency reached 80 %, which was equal to a capability of the silicone rubber. These waterborne siloxane containing PUs are useful as textile coatings, leather finishing, sealants, plastic coatings, and a glass-fibre sizing.

A POSS-modified ionomeric polyurethane aqueous dispersion have been also reported for their improved reaction to fire and resistance to atomic oxygen as well as to the possibility to build nanostructured surfaces. As with other polymer systems, many of the POSS hybrids do yield elastomeric PU with improvements in physical and thermal properties at relatively low levels of POSS incorporation. The waterborne PU hybrid dispersions were synthesized by incorporating amino- and hydroxyl-terminated POSS macromers into the PU ionomeric backbones, using a homogeneous solution polymerization, followed by a solvent exchange with water (i.e., the "acetone process") (Nanda & Wicks 2006). The absence of crystalline domains evidenced the incorporation of POSS macromer in the PU hard segments.

Various researchers have shown that the gas permeability of PU membranes increases with the decrease of the hard segment content and the increase of the soft segment molecular weight. In addition, a correlation has been established between the gas permeability and the chemical nature of the polyols and chain extenders. Queirez & de Pinho (2005) investigated structural characteristics and gas permeation properties of PDMS-PPO-urethane/urea bisoft segment membranes. The permeability of the membranes to CO2, O2 and N2 increased with the increase of PDMS content. The P(CO2)/P(N2) permeability ratio was higher for the bi-soft segment membranes in comparison with PDMS/PU membranes.

Some properties of PUs (high tear, tensile strength, good wear, abrasion resistance) are strongly jeopardized as soon as the service temperature of the material exceeds 70 to 80C, mostly because of a creep phenomena. Dassin et al. (2002) tried to improve the working temperature of commercial TPU by creating a well-controlled chemical curing. The idea was to have an easily processible material with an improved thermomechanical behaviour. A commercial polyester-type TPU at first was reacted with a diisocyanate to create allophanate branching units, which at second step was grafted with 3-aminopropyltrimethoxysilane. Such materials could be crosslinked by a hydrolytic condensation mechanism, resulting in increased thermomechanical properties.

#### **3.2.4 Modifications of other polymers and polymeric materials by CFPS**

The CFPS were also used for synthesis of conductive siloxane-pyrrole block copolymers. An incorporation of flexible PDMS chains into the rigid polymer chain improves not only mechanical properties, but also solubility in different non-polar solvents. (N-pyrrole) polysiloxane precursor, prepared in reaction of N-glicydylpyrrole with aminopropyl groups of PDMS was copolymerized with pyrrole (PY) by electrochemical methods, giving block

In order to reduce emission of volatile organic compounds, water borne polyurethanes (WPUs) have attracted much attention. However, the WPUs have shortcomings, such as lack of resistance to water, a surface hydrophilicity and the low strength. These disadvantages can be eliminated by using a different mixing composition of soft segments. Chen et al. (2005) prepared the anionic WPUs from hydroxyl-terminated PDMS, poly(tetramethylene oxide) (PTMO) as the soft segments, IPDI as the hard segment, and 2,2-bis(hydroxymethyl) propionic acid (DMPA) as the ionic centre. DMPA was used to form a water-dispersible urethane prepolymer. The tensile strength of WPU-PDMS films decreased with an increasing content of PDMS and a water repellency reached 80 %, which was equal to a capability of the silicone rubber. These waterborne siloxane containing PUs are useful as

textile coatings, leather finishing, sealants, plastic coatings, and a glass-fibre sizing.

domains evidenced the incorporation of POSS macromer in the PU hard segments.

bi-soft segment membranes in comparison with PDMS/PU membranes.

**3.2.4 Modifications of other polymers and polymeric materials by CFPS** 

increased thermomechanical properties.

A POSS-modified ionomeric polyurethane aqueous dispersion have been also reported for their improved reaction to fire and resistance to atomic oxygen as well as to the possibility to build nanostructured surfaces. As with other polymer systems, many of the POSS hybrids do yield elastomeric PU with improvements in physical and thermal properties at relatively low levels of POSS incorporation. The waterborne PU hybrid dispersions were synthesized by incorporating amino- and hydroxyl-terminated POSS macromers into the PU ionomeric backbones, using a homogeneous solution polymerization, followed by a solvent exchange with water (i.e., the "acetone process") (Nanda & Wicks 2006). The absence of crystalline

Various researchers have shown that the gas permeability of PU membranes increases with the decrease of the hard segment content and the increase of the soft segment molecular weight. In addition, a correlation has been established between the gas permeability and the chemical nature of the polyols and chain extenders. Queirez & de Pinho (2005) investigated structural characteristics and gas permeation properties of PDMS-PPO-urethane/urea bisoft segment membranes. The permeability of the membranes to CO2, O2 and N2 increased with the increase of PDMS content. The P(CO2)/P(N2) permeability ratio was higher for the

Some properties of PUs (high tear, tensile strength, good wear, abrasion resistance) are strongly jeopardized as soon as the service temperature of the material exceeds 70 to 80C, mostly because of a creep phenomena. Dassin et al. (2002) tried to improve the working temperature of commercial TPU by creating a well-controlled chemical curing. The idea was to have an easily processible material with an improved thermomechanical behaviour. A commercial polyester-type TPU at first was reacted with a diisocyanate to create allophanate branching units, which at second step was grafted with 3-aminopropyltrimethoxysilane. Such materials could be crosslinked by a hydrolytic condensation mechanism, resulting in

The CFPS were also used for synthesis of conductive siloxane-pyrrole block copolymers. An incorporation of flexible PDMS chains into the rigid polymer chain improves not only mechanical properties, but also solubility in different non-polar solvents. (N-pyrrole) polysiloxane precursor, prepared in reaction of N-glicydylpyrrole with aminopropyl groups of PDMS was copolymerized with pyrrole (PY) by electrochemical methods, giving block copolymer PY-PDMS. Classical conductive polymers are insoluble and infusible. A common way to facilitate their processing are syntheses of block or graft copolymers containing conductive segments and conventional segments, increasing solubility of copolymer, e.g. block copolymers of styrene and acetylene, styrene and thiophene, graft copolymers of pyrrole on polystyrene, and on poly(methyl methacrylate). Recently a new multifunctional polysiloxanes, containing mercapto-, thiocarbamide, and (hydroxyalkyl)ether linkages were applied for the modification of silica fillers used for the production of rubber tires (Kalaycioglu et al., 1998).

Copolymers with siloxane moieties serve as connectors with organic polymers (compatibilizers). Siloxane segments of the copolymers migrate to the surface, while organic segments act as anchors of siloxane blocks in the polymeric material.

#### **3.3 Composites and nanocomposites from thermoplastic polymers**

Composite materials consist of a polymer matrix and various inorganic fillers. They have been widely used in order to improve the mechanical, thermal, barrier, and other properties of the polymer. However it is known that the improvement of one property can result the worsening of another. It is anticipated that such problems can be overcome if the inorganic additive exists in the form of a fine dispersion within the polymer matrix producing a nanocomposite. Silane modified fillers and nanofillers are used for these purposes.

#### **3.3.1 Modification of fillers properties by CFS**

The carbofunctional silanes are most often applied as so called adhesion promoters, which are also called as "*silane coupling agents*" (Pleuddeman, 1991). The silane adhesion promoters are directly added to polymer compositions (usually in a quantity 0.2–2 % wt. %) or in a form of water and water-alcoholic dispersions. The substituent X (e.g. alkoxy group) may undergo condensation reactions with hydroxyl groups of the filler:

or hydrolysis reactions:

**Si - OR + H2O Si - OH + ROH** 

Thus alkoxy groups are replaced with silanol groups Si-OH, which are able to form chemical bonds with inorganic materials, e.g. glass, metals or fillers (Scheme 7) (Haas & Wolter, 1999):

Scheme 7. An adhesion model in a system: polymer–silane–filler.

Modification of Thermoplastics with Reactive Silanes and Siloxanes 175

from" methods. "Grafting to" method involves the reaction of appropriate end-capped functional groups or side pendant groups in the polymers with the particles. This method is simple, but the graft density is fairly low because the diffusion of polymer chains to the surface of the particles is hindered sterically. "Grafting to" method gives relatively low grafting densities. "Grafting from" technique, in which a monomer polymerization is initiated from groups bound to particle surface is expected to lead to higher surface grafting densities, because monomer can more easily diffuse towards the reactive centre. In the "grafting through" method the surface of the particle is modified with a polymerizable group. The graft density may be relatively high as compared with the "grafting to" method, but since the monomer-modified particle is multifunctional cross-linking between polymer

A variety of polymerization techniques, including conventional free radical, cationic, anionic, ring-opening, and controlled radical polymerizations (CRPs) or living radical polymerization (LRP) have been used to graft the polymer onto the particle surfaces. In comparison with the conventional radical polymerization CRPs can control the architecture, molecular weight, and molecular weight distribution, and they are simple on operation procedure and versatile on monomers in comparison with ionic polymerizations. Out of the three most common LPR methods, nitroxide mediated polymerization (NMP), atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, RAFT is arguably the most applicably technique (Chrissopoulou &

Silica is the most applied filler in polymers based acrylate moieties. Polyacrylate-SiO2 particle are usually produced by emulsion or microemulsion polymerization. The investigations on developing emulsifier-free latexes have been made. An emulsifier-free emulsion polymerization and sol-gel process were used for preparation of polyacrylate-silica hybrids in which tetraethoxysilane (TEOS) and poly(vinyl alcohol) (PVAL) were used as a silica

Surfactant-free emulsion polymerization, in which neither surface treatment for nanosilica particles nor additional surfactant or stabilizer is required is one of the methods for preparation of inorganic-organic composites. SiO2-PMMA composite particles were prepared via conventional emulsion polymerization by the aid of acid-base interaction between the silanol groups of unmodified silica surface and amino groups of 4-vinylpyridine. The morphology of the composite particles could be multicore-shell, rapsberrylike or normal core-shell, depending upon the emulsifier content, monomer/silica ratio,

Sol-gel process is often applied to prepare polymer-silica organic-inorganic hybrids, in which a nanometer size silica component is dispersed in a polymer matrix. In polymer-silica hybrids films silica component works as the hard segment in soft polymer matrix. Silane coupling agents are commonly used to achieve miscibility of the polymer and silica. Transparent polyacrylic-silica hybrid thin films were obtained from MMA, trimethylolpropanetrimathacrylate, water based monodispersed colloidal silica and coupling agent: MAPTMS. A mixture of ethylene glycol and ethyl ether was used for preventing the phase

chains may be occur.

Anastasiadis, 2011).

**3.3.2.1 Composites based on polyacrylates** 

precoursor and colloid stabilizer, respectively (Shen et al., 2009).

silica particles size, and monomer feed method (Cheng et al., 2006).

The silanol functional groups Si-OH also undergo homocondensation reactions, with a formation of thermodynamically more stable siloxane systems Si–O–Si. Alternatively, Si-OH groups may react with OH groups of a surface of the filler. This way on the surface of the filler a layer of crosslinked polysiloxane is formed. An universality of an application of the fillers in plastics results from necessity of an improvement of mechanical, thermal, electrical, and magnetic properties of the polymers. The most often used fillers are: silica, calcium carbonate, calcium sulfate (gypsum), barium sulfate, calcium, aluminum (kaolin), and magnesium (talc and sepiolite) silicates, aluminum oxide and hydroxide, metal oxides (e.g. ZnO, MgO, CaO, TiO2, Fe2O3, Pb3O4). An addition of nanofillers of particie size 10–50 nm profitably affects an increase of abrasion resistance of transparent polymer coatings and enables preparation of homogeneous composite of nanoparticles in a polymer matrix. The addition of 20–40 wt. % of the silica and alumina can improve abrasion resistance of material. The non-modified silicon and aluminum oxides have a large number of hydroxyl groups on the surface and thus they are hydrophilic materials. In the presence of non-polar liquids, e.g. acrylates, an aggregation of nanoparticles of these fillers takes place, which causes "thickening" of their mixtures with acrylates. The modification of the fillers surfaces with the carbofunctional silanes substantially improves their dispersibility in organic media. The use of trimethoxysilanes with methacryloxypropyl or vinyl groups for the modification of nanoparticles of SiO2 and Al2O3 allows to prepare transparent abrasion resistant coatings on the surface. Acrylic laquers containing nanoparticles of the fillers are utilized as top, decorative layers of furniture, as decorative layers of aluminum foils and as varnishes for floor and coatings.

Nanosphers of a mesoporous silica, functionalized with (3-aminopropyl)trimethoxysilane and a sol of gold form nanocomposites with a specific surface area around 1000 m2/g (Botella et al., 2007) were prepared. Instead of (trialkoxy)propylsilanes containing different carbofunctional groups: amine, aldehyde, acrylate, isocyanate, thiol, ether, triacetoxydiamine, and trialkoxysilanes containing aldehyde and nitrile groups attached to a longer alkylene "connector" were grafted on the surface of cobalt ferrite CoFe2O4. They were utilized for the preparation of water dispersions of nanoparticles with supermagnetic properties (de Palma et al., 2007).

#### **3.3.2 Applications of silane-modified nano-fillers in thermoplastic composites**

Depending on chemical structure and geometry three classes of nanoparticles were widely investigated:


For good properties of these polymer nanocomposites it is required the homogeneous dispersion of nanoparticles in the polymer matrices. The best way to avoid aggregation is to graft polymer chains onto the particles covalently, forming organic-inorganic hybrid materials. Grafting techniques include the "grafting to", "grafting through", and "grafting

The silanol functional groups Si-OH also undergo homocondensation reactions, with a formation of thermodynamically more stable siloxane systems Si–O–Si. Alternatively, Si-OH groups may react with OH groups of a surface of the filler. This way on the surface of the filler a layer of crosslinked polysiloxane is formed. An universality of an application of the fillers in plastics results from necessity of an improvement of mechanical, thermal, electrical, and magnetic properties of the polymers. The most often used fillers are: silica, calcium carbonate, calcium sulfate (gypsum), barium sulfate, calcium, aluminum (kaolin), and magnesium (talc and sepiolite) silicates, aluminum oxide and hydroxide, metal oxides (e.g. ZnO, MgO, CaO, TiO2, Fe2O3, Pb3O4). An addition of nanofillers of particie size 10–50 nm profitably affects an increase of abrasion resistance of transparent polymer coatings and enables preparation of homogeneous composite of nanoparticles in a polymer matrix. The addition of 20–40 wt. % of the silica and alumina can improve abrasion resistance of material. The non-modified silicon and aluminum oxides have a large number of hydroxyl groups on the surface and thus they are hydrophilic materials. In the presence of non-polar liquids, e.g. acrylates, an aggregation of nanoparticles of these fillers takes place, which causes "thickening" of their mixtures with acrylates. The modification of the fillers surfaces with the carbofunctional silanes substantially improves their dispersibility in organic media. The use of trimethoxysilanes with methacryloxypropyl or vinyl groups for the modification of nanoparticles of SiO2 and Al2O3 allows to prepare transparent abrasion resistant coatings on the surface. Acrylic laquers containing nanoparticles of the fillers are utilized as top, decorative layers of furniture, as

decorative layers of aluminum foils and as varnishes for floor and coatings.

properties (de Palma et al., 2007).

referred to as 0D nanoparticles.

investigated:

Nanosphers of a mesoporous silica, functionalized with (3-aminopropyl)trimethoxysilane and a sol of gold form nanocomposites with a specific surface area around 1000 m2/g (Botella et al., 2007) were prepared. Instead of (trialkoxy)propylsilanes containing different carbofunctional groups: amine, aldehyde, acrylate, isocyanate, thiol, ether, triacetoxydiamine, and trialkoxysilanes containing aldehyde and nitrile groups attached to a longer alkylene "connector" were grafted on the surface of cobalt ferrite CoFe2O4. They were utilized for the preparation of water dispersions of nanoparticles with supermagnetic

**3.3.2 Applications of silane-modified nano-fillers in thermoplastic composites** 

Depending on chemical structure and geometry three classes of nanoparticles were widely


For good properties of these polymer nanocomposites it is required the homogeneous dispersion of nanoparticles in the polymer matrices. The best way to avoid aggregation is to graft polymer chains onto the particles covalently, forming organic-inorganic hybrid materials. Grafting techniques include the "grafting to", "grafting through", and "grafting from" methods. "Grafting to" method involves the reaction of appropriate end-capped functional groups or side pendant groups in the polymers with the particles. This method is simple, but the graft density is fairly low because the diffusion of polymer chains to the surface of the particles is hindered sterically. "Grafting to" method gives relatively low grafting densities. "Grafting from" technique, in which a monomer polymerization is initiated from groups bound to particle surface is expected to lead to higher surface grafting densities, because monomer can more easily diffuse towards the reactive centre. In the "grafting through" method the surface of the particle is modified with a polymerizable group. The graft density may be relatively high as compared with the "grafting to" method, but since the monomer-modified particle is multifunctional cross-linking between polymer chains may be occur.

A variety of polymerization techniques, including conventional free radical, cationic, anionic, ring-opening, and controlled radical polymerizations (CRPs) or living radical polymerization (LRP) have been used to graft the polymer onto the particle surfaces. In comparison with the conventional radical polymerization CRPs can control the architecture, molecular weight, and molecular weight distribution, and they are simple on operation procedure and versatile on monomers in comparison with ionic polymerizations. Out of the three most common LPR methods, nitroxide mediated polymerization (NMP), atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, RAFT is arguably the most applicably technique (Chrissopoulou & Anastasiadis, 2011).

#### **3.3.2.1 Composites based on polyacrylates**

Silica is the most applied filler in polymers based acrylate moieties. Polyacrylate-SiO2 particle are usually produced by emulsion or microemulsion polymerization. The investigations on developing emulsifier-free latexes have been made. An emulsifier-free emulsion polymerization and sol-gel process were used for preparation of polyacrylate-silica hybrids in which tetraethoxysilane (TEOS) and poly(vinyl alcohol) (PVAL) were used as a silica precoursor and colloid stabilizer, respectively (Shen et al., 2009).

Surfactant-free emulsion polymerization, in which neither surface treatment for nanosilica particles nor additional surfactant or stabilizer is required is one of the methods for preparation of inorganic-organic composites. SiO2-PMMA composite particles were prepared via conventional emulsion polymerization by the aid of acid-base interaction between the silanol groups of unmodified silica surface and amino groups of 4-vinylpyridine. The morphology of the composite particles could be multicore-shell, rapsberrylike or normal core-shell, depending upon the emulsifier content, monomer/silica ratio, silica particles size, and monomer feed method (Cheng et al., 2006).

Sol-gel process is often applied to prepare polymer-silica organic-inorganic hybrids, in which a nanometer size silica component is dispersed in a polymer matrix. In polymer-silica hybrids films silica component works as the hard segment in soft polymer matrix. Silane coupling agents are commonly used to achieve miscibility of the polymer and silica. Transparent polyacrylic-silica hybrid thin films were obtained from MMA, trimethylolpropanetrimathacrylate, water based monodispersed colloidal silica and coupling agent: MAPTMS. A mixture of ethylene glycol and ethyl ether was used for preventing the phase

Modification of Thermoplastics with Reactive Silanes and Siloxanes 177

while impact strength was preserved when the silane-treated nanosilica was used (Bailly &

In order to promote dispersion of nano-silica in PP grafted polymerizable foaming agent pvinylphenylsulfonylhydrazide (VPSH) onto nanoparticles was prepared via free-radical polymerization. The grafted VPSH played double role when it was melt mixed with PP. The side sulfonylhydrazide groups were decomposed with volatile gas products, which blowed up the surrounding matrix that pulled apart the agglomerated nanoparticles, while the remaining backbone of the grafted polymer helped to improve the filler-matrix interaction

Aluminium anhydride is an effective flame retardant for thermoplastics for two decades. Surface treatment of mineral fillers can ease their incorporation into thermoplastic melts, such as PP. Whilst most surface modifiers can act as effective dispersant for fillers, only the silane and functionalised polymer based systems can also act as effective coupling agents in thermoplastics based composites. Liauw et al. (1995) compared three surface modifiers including a dicarboxylic acid anhydride (DAA), a silane based system and a maleanised polybutadiene (MPBD) in PP/Al(OH)3 composites. At filler levels below these required for effective flame retardation, the DAA treated filler gave the composite with the best mechanical properties. At higher filler levels, i.e. above 59 % w/w, the composites based on Al(OH)3 coated with the strongly coupling silane afforded the best properties. The latter treatment proved to be most effective when the polymer matrix was an impact modified PP. A special case of nanocomposites is obtained by mixing polymers with layered silicates (nanoclays). The best known of layered silicates is montmorillonite (MMT). Layered silicates composed of sheet-like platelets that are about 1 nm in thickness and 100-1000 nm in width and length, so they possess high aspect ratios and large surface area. The high aspect ratio of the clay platelets permits significant reinforcement at relatively low loadings if the high degree of exfoliation or intercalation is achieved. It is well known that the dispersion of clay tactoids in a polymer matrix can result in the formation of three types of composites: (1) conventional composites that contain clay tactoids dispersed simply as a segregated phase; (2) intercalated polymer-clay nanocomposites, which are formed by the infiltration of one or more molecular layers of polymer into the clay host galleries; (3) exfoliated polymer-clay nanocomposites as characterized by low clay content, a monolithic structure, and a separation between clay layers that depend on the polymer content of the composite. Exfoliation is particularly desirable for improving specific properties that are affected by the degree of

dispersion and the resulting interfacial area between polymer and clay nanolayers.

dispersion of layered structure within the polymer matrix.

The layered silicate particles are usually hydrophilic and their interaction with non-polar polymers are unfavourable. There are two main objectives of surface modification on MMT: (1) to expand the interlayer space, allowing large polymer molecules to enter into the clay galleries, and (2) to improve the miscibility of MMT with the polymer to achieve a good

The maleic-anhydride functionalized polypropylene or polyethylene are the most commonly used to improve the interfacial bonding between the clay and respective polymers. Maleated polyethylene (PEgMA)/aminosilane compatibilizer has been very effective for preparing polyethylene-clay nanocomposites (Sanchez-Valdes et al., 2009). Silane grafting is one of methods to functionalize polyolefins, particularly for the preparation of silane-grafted water-

Kontopoulou, 2009).

(Cai et al., 2006).

separation of the prepared hybrid materials (Yu & Chen, 2003). PMMA-silica composites were synthesized via sol-gel reaction. The base acrylic polymers were prepared by copolymerization of MMA with MPTMS or vinyltrimethoxysilane (VTMS) and obtained copolymers were following condensed with TEOS (Brostow et al., 2008).

Covalent linking of polymer chains onto silica surface can be achieved by grafting methods. PMMA-grafted silica microparticles were synthesized via radical photopolymerization of MMA, initiated from N,N-diethyldithiocarbamate (DEDT) groups previously bound to the silica surface ("grafting from") (Derouet & Thuc, 2008). The same technique of grafting was used for preparation of poly(octadecyl acrylate)(PODA)-grafted silicas (Mallik et al., 2009). They synthesized two kinds of ATRP initiators, immobilized them on silica, and then ATRP was carried out from these initiator-grafted silicas to obtain comb-shaped polymer-grafted silica. Polymers possessing long side groups, i.e. PODA are often termed comb-shape polymers. These PODA-SiO2 composites showed unique separation behaviour with ordered-disordered phase transition of long alkyl chains and high selectivity towards polycyclic aromatic hydrocarbons (PAHs) in the ordered (crystalline) state.

Mesoporous silicas are worthwhile fillers for polymers. The pores can be occupied by polymer chains, especially during melt blending. To realize the polymerization inside the silica pores, the pores should be empty, so the most suitable method is bulk polymerization. Perez et al. (2007) used mesoporous silica, with the interconnected porous structure where the monomer can be trapped, as a reinforcement agent for PMMA. Some polymeric chains grew into the silica and the interaction of polymer with filler was increased.

Silicone nitride (Si3N4) is an important ceramic material used for various applications because of its high strength, high thermal-shock resistance, low coefficient of thermal expansion, and good wear resistance. It has been proved to be an effective filler for the improvement of mechanical properties, and in particular the wear resistance of polymeric materials. To limit the nanoparticles agglomerates and improving their dispersivity in polymer matrix the surface modification of fillers is necessary. A novel macromolecular coupling agent tercopolymer BA-MMA-VTES (useful for surface modification of silicone nitride nanopowder) was synthesized. The macromolecular coupling agent bonded covalently on the surface of nano-sized Si3N4 particles was used for preparing of an organic coating layer (Xia et al., 2008).

#### **3.3.2.2 Composites based on polyolefins**

Isotactic polypropylene PP is a commodity polymer with widespread applications. To improve its ductility and toughness, impact modifiers like various polyolefinic elastomers (POEs) are commonly used. Inorganic fillers such as talc, silica, CaCO3, BaSO4, Mg(OH)2 and Al(OH)3 are used as reinforcing agents in these PP-blends. During the last decade PP-based nanocomposite blends, containing finely dispersed nanofillers, have received great interest. Due to the nonpolar character of the PP, functionalization of the polymer matrix and/or treatment of the nanoparticles are needed to achieve a good dispersion of the rigid nanoparticles and satisfactory mechanical properties. PP was functionalized by peroxideinitiated grafting of vinyltriethoxysilane (VTES), to give a PP-*g*-VTES derivative, which resulted in improved compatibility between the matrix and the filler. The mechanical properties of the composites were greatly enhanced in terms of tensile and flexural strength,

separation of the prepared hybrid materials (Yu & Chen, 2003). PMMA-silica composites were synthesized via sol-gel reaction. The base acrylic polymers were prepared by copolymerization of MMA with MPTMS or vinyltrimethoxysilane (VTMS) and obtained

Covalent linking of polymer chains onto silica surface can be achieved by grafting methods. PMMA-grafted silica microparticles were synthesized via radical photopolymerization of MMA, initiated from N,N-diethyldithiocarbamate (DEDT) groups previously bound to the silica surface ("grafting from") (Derouet & Thuc, 2008). The same technique of grafting was used for preparation of poly(octadecyl acrylate)(PODA)-grafted silicas (Mallik et al., 2009). They synthesized two kinds of ATRP initiators, immobilized them on silica, and then ATRP was carried out from these initiator-grafted silicas to obtain comb-shaped polymer-grafted silica. Polymers possessing long side groups, i.e. PODA are often termed comb-shape polymers. These PODA-SiO2 composites showed unique separation behaviour with ordered-disordered phase transition of long alkyl chains and high selectivity towards

Mesoporous silicas are worthwhile fillers for polymers. The pores can be occupied by polymer chains, especially during melt blending. To realize the polymerization inside the silica pores, the pores should be empty, so the most suitable method is bulk polymerization. Perez et al. (2007) used mesoporous silica, with the interconnected porous structure where the monomer can be trapped, as a reinforcement agent for PMMA. Some polymeric chains

Silicone nitride (Si3N4) is an important ceramic material used for various applications because of its high strength, high thermal-shock resistance, low coefficient of thermal expansion, and good wear resistance. It has been proved to be an effective filler for the improvement of mechanical properties, and in particular the wear resistance of polymeric materials. To limit the nanoparticles agglomerates and improving their dispersivity in polymer matrix the surface modification of fillers is necessary. A novel macromolecular coupling agent tercopolymer BA-MMA-VTES (useful for surface modification of silicone nitride nanopowder) was synthesized. The macromolecular coupling agent bonded covalently on the surface of nano-sized Si3N4 particles was used for preparing of an organic

Isotactic polypropylene PP is a commodity polymer with widespread applications. To improve its ductility and toughness, impact modifiers like various polyolefinic elastomers (POEs) are commonly used. Inorganic fillers such as talc, silica, CaCO3, BaSO4, Mg(OH)2 and Al(OH)3 are used as reinforcing agents in these PP-blends. During the last decade PP-based nanocomposite blends, containing finely dispersed nanofillers, have received great interest. Due to the nonpolar character of the PP, functionalization of the polymer matrix and/or treatment of the nanoparticles are needed to achieve a good dispersion of the rigid nanoparticles and satisfactory mechanical properties. PP was functionalized by peroxideinitiated grafting of vinyltriethoxysilane (VTES), to give a PP-*g*-VTES derivative, which resulted in improved compatibility between the matrix and the filler. The mechanical properties of the composites were greatly enhanced in terms of tensile and flexural strength,

copolymers were following condensed with TEOS (Brostow et al., 2008).

polycyclic aromatic hydrocarbons (PAHs) in the ordered (crystalline) state.

grew into the silica and the interaction of polymer with filler was increased.

coating layer (Xia et al., 2008).

**3.3.2.2 Composites based on polyolefins** 

while impact strength was preserved when the silane-treated nanosilica was used (Bailly & Kontopoulou, 2009).

In order to promote dispersion of nano-silica in PP grafted polymerizable foaming agent pvinylphenylsulfonylhydrazide (VPSH) onto nanoparticles was prepared via free-radical polymerization. The grafted VPSH played double role when it was melt mixed with PP. The side sulfonylhydrazide groups were decomposed with volatile gas products, which blowed up the surrounding matrix that pulled apart the agglomerated nanoparticles, while the remaining backbone of the grafted polymer helped to improve the filler-matrix interaction (Cai et al., 2006).

Aluminium anhydride is an effective flame retardant for thermoplastics for two decades. Surface treatment of mineral fillers can ease their incorporation into thermoplastic melts, such as PP. Whilst most surface modifiers can act as effective dispersant for fillers, only the silane and functionalised polymer based systems can also act as effective coupling agents in thermoplastics based composites. Liauw et al. (1995) compared three surface modifiers including a dicarboxylic acid anhydride (DAA), a silane based system and a maleanised polybutadiene (MPBD) in PP/Al(OH)3 composites. At filler levels below these required for effective flame retardation, the DAA treated filler gave the composite with the best mechanical properties. At higher filler levels, i.e. above 59 % w/w, the composites based on Al(OH)3 coated with the strongly coupling silane afforded the best properties. The latter treatment proved to be most effective when the polymer matrix was an impact modified PP.

A special case of nanocomposites is obtained by mixing polymers with layered silicates (nanoclays). The best known of layered silicates is montmorillonite (MMT). Layered silicates composed of sheet-like platelets that are about 1 nm in thickness and 100-1000 nm in width and length, so they possess high aspect ratios and large surface area. The high aspect ratio of the clay platelets permits significant reinforcement at relatively low loadings if the high degree of exfoliation or intercalation is achieved. It is well known that the dispersion of clay tactoids in a polymer matrix can result in the formation of three types of composites: (1) conventional composites that contain clay tactoids dispersed simply as a segregated phase; (2) intercalated polymer-clay nanocomposites, which are formed by the infiltration of one or more molecular layers of polymer into the clay host galleries; (3) exfoliated polymer-clay nanocomposites as characterized by low clay content, a monolithic structure, and a separation between clay layers that depend on the polymer content of the composite. Exfoliation is particularly desirable for improving specific properties that are affected by the degree of dispersion and the resulting interfacial area between polymer and clay nanolayers.

The layered silicate particles are usually hydrophilic and their interaction with non-polar polymers are unfavourable. There are two main objectives of surface modification on MMT: (1) to expand the interlayer space, allowing large polymer molecules to enter into the clay galleries, and (2) to improve the miscibility of MMT with the polymer to achieve a good dispersion of layered structure within the polymer matrix.

The maleic-anhydride functionalized polypropylene or polyethylene are the most commonly used to improve the interfacial bonding between the clay and respective polymers. Maleated polyethylene (PEgMA)/aminosilane compatibilizer has been very effective for preparing polyethylene-clay nanocomposites (Sanchez-Valdes et al., 2009). Silane grafting is one of methods to functionalize polyolefins, particularly for the preparation of silane-grafted water-

Modification of Thermoplastics with Reactive Silanes and Siloxanes 179

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 thermo-

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

Silicone-based compounds (silicones, silsesquioxanes, silicas, and silicates) usually are used not only as fillers, incorporated in the polymer matrix but also as the flame retardant additives. They are endowed with excellent thermal stability and high heat resistance, with very limited release of toxic gases during thermal decomposition. Several types of silicone polymers were applied as flame retardants in polycarbonates (Iji & Serizawa, 1998). For the PC materials modified with branched methyl- and phenylsiloxanes and end-capped by methyl groups, limiting oxygen index (LOI) increased over 35 %, whereas LOI was about 27 % for pure PC. The effect of content and block size of PDMS on LOI values was investigated for PC-*b*-PDMS copolymers. The PDMS block size influenced the dispersibility of the PDMS in the PC and the moderate PDMS dispersion (i.e. 50 nm mean inclusion size) resulted in high flame retardancy (Nodera & Kanai, 2006). Silica particles "*in situ*" formed by thermal degradation of PDMS mostly remained within the char layer. This highly oxidized char layer has the structure which prevented volatile fuel production and served as

The effect of silica gel structure on the flammability properties of thermoplastics has been investigated by many workers. The effect of pore volume, particle size and surface silanol concentration of silica gel in polypropylene (PP) was studied (Gilman et al., 1999). The performances of various types of silica, silica gel, fumed silica and fused silica as flame retardants in PP and polyethylene oxide were investigated. The fumed silica and silica gel accumulating near the surface acted as a thermal insulation layer and reduced the polymer concentration near the surface in contact with flame. The fused silica did not accumulate near the surface and it is mainly present in the polymer melt layer. The accumulation of silica on the surface of the burned polymer has been also observed in PMMA composites

Nanometric particles in polymer matrices are known to enhance the fire resistance. POSS with general formula (RSiO1.5)8 is an inorganic silica-like nanocage. Eight organic groups located at the corners give possibility for compatibility POSS compounds with organic polymers. These inorganic nanocages are referred to as preceramic compounds. On combustion of such polymer composite, POSS acts as a precursor forming thermally stable ceramic materials at high temperature. The incorporation of POSS in polymers modifies both the viscosity and the mechanical properties of the molten polymer. It also affects the thermal stability and fire performances by reducing the quantity of heat released upon

plastic hybrids possessing low-k or refractive index.

**3.4 Silicones and silica as flame retardant additives** 

unstable materials (Araki & Naka, 2011).

an additional thermal insulator.

(Kashiwagi et al., 2003).

cross-linked polyethylene. Lu et al. (2005) prepared methacryloxypropyltrimethoxysilane (MAPTMS)-grafted PE (PE-*g*-MAPTMS) by melt grafting reaction, and then blend it with organically modified montmorillonite to make PE-*g*-MAPTMS/MMT nanocomposite.
