organic-inorganic hybrid materials: sol-gel reactions...organic-inorganic hybrid materials: sol-gel...

low-bandgap polymers blended with C70-derivative

give photocurrent at 1 mm. Thin Solid Films

511–512:576–580

26. Schokley W, Queisser HJ (1961) Detailed balance

limit of efficiency of p-n junction solar cells. Appl

Phys 32:510–519

27. You J, Duo L, Yoshimura K, Kato T, Ohya K,

Moriarty T, Emery K, Chen C-C, Gao J, Li G, Yang

Y (2013) A polymer tandem solar cell with 10.6 %

power conversion efficiency. Nat Comun

4:1446–1455

28. Nagai H, Segawa H (2004) Energy-storable

dye-sensitized solar cell with a polypyrrole electrode.

Chem Commun 974–975

Organic-Inorganic Hybrid Materials:Sol-Gel Reactions

Takeru Iwamura1,2 and Masato Takasaki2

1Department of Chemistry and Energy

Engineering, Faculty of Engineering,

Tokyo City University, Setagaya–ku,

Tokyo, Japan2Department of Chemistry and Energy

Engineering, Graduate School of Engineering,

Tokyo City University, Setagaya–ku,

Tokyo, Japan

Synonyms

Organic-inorganic nanocomposite materials

Definitions

Organic-inorganic hybrid materials form by

means of the sol-gel reaction of metal alkoxide.

In these hybrids, the organic polymer is dispersed

in the silica gel matrix at the molecular level.

Introduction

Synthesis of organic-inorganic polymer hybrid

material has attracted much attention as a prepa-

ration method for new characteristic materials.

Especially, organic-inorganic hybridization can

be used for the preparation of composite mate-

rials of organic-inorganic materials. In hybridiza-

tion, the sol-gel reaction of alkoxysilanes is the

most typical technique for the synthesis of these

hybrid materials. When organic-inorganic

polymer hybrids are synthesized, the

intermolecular interactions between an organic

polymer and silica gel should be allowed.

Organic-inorganic polymer hybrids have been

elaborated with various intermolecular

interactions such as hydrogen bonding, as well

as ionic, p-p, and CH/p interactions. Meanwhile,

the in situ polymerization method, in which poly-

merization of the organic monomer in the sol-gel

reaction mixture is carried out, is an excellent

method to obtain transparent and homogeneous

organic-inorganic polymer hybrids. This is

because in situ polymerization does not necessar-

ily require strong intermolecular interactions

between an organic polymer and an inorganic

matrix. This entry summarizes methods for

the fundamental synthesis of organic-inorganic

polymer hybrids.

Organic-Inorganic Polymer Hybrids viaHydrogen Bonding Interaction

Generally, the element reactions of a sol-gel pro-

cess are shown in Figure 1. As shown in this

figure, the sol-gel reaction includes two stepwise

reactions: hydrolysis and condensation of metal

alkoxide. Repeating these reactions leads to a

metal oxide. Ordinarily, the sol-gel reaction

involves mild conditions compared with the

usual glass preparation method. Therefore, an

organic polymer can be introduced into an inor-

ganic network (Fig. 1).

Organic-inorganic polymer hybrids can be

synthesized by mixing an organic polymer and

an inorganic oxide resulting from metal alkoxide.

However, organic-inorganic polymer hybrids

cannot be prepared from any combination

between an organic polymer and an inorganic

oxide. To obtain transparent and homogeneous

organic-inorganic polymer hybrids, a physical

Organic-Inorganic Hybrid Materials: Sol-Gel Reactions 1469

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interaction, such as hydrogen bonding interac-

tions between an organic polymer and an inor-

ganic oxide, should be employed. For example, it

is known that the amide carbonyl groups form

strong hydrogen bonds. Consequently, when the

sol-gel reaction is carried out in the presence of an

organic polymer consisting of amide groups, the

organic polymer is incorporated into the three-

dimensional network of silica gel [1]. Concretely,

organic polymers such as poly(2-methyl-2-

oxazoline) (1), poly(N-vinylpyrrolidone) (2), and

poly(N,N-dimethylacrylamide) (3), all of which

have hydrogen-accepting groups, can be used to

synthesize transparent and homogeneous polymer

hybrids using hydrogen bonding interactions

(Fig. 2) [2–7].

Figure 3 shows the formation of a hydrogen

bond between an organic polymer with

hydrogen-accepting groups and an inorganic

oxide resulting from tetramethoxysilane

(TMOS). The hydrogen bonding interactions in

these polymer hybrids are ascertained by FT-IR

spectra in which the carbonyl stretching bands are

shifted to the lower wave number region after the

formation of the polymer hybrids.

Organic-Inorganic Polymer Hybrids viaIonic Interactions

Ionic interactions such as the physical interaction

between an anion and a cation can be used. For

example, partially sulfonated polystyrene is uti-

lized as a starting organic polymer. In the pres-

ence of this polymer, the sol-gel reaction of a

mixture of (3-aminopropyl)trimethoxysilane

(APTMOS) and TMOS is carried out to obtain

organic-inorganic polymer hybrids (Fig. 4). The

resulting polymer hybrids become optically

transparent and homogeneous [8].

Organic-Inorganic Polymer Hybrids viap-p Interactions

The p-p interaction is a useful physical interaction

to obtain organic-inorganic polymer hybrids.

When polymer hybrids are synthesized by using

a hydrophobic organic polymer, this physical

interaction is extremely important. The principle

of this method is based upon an interaction

between the organic polymer and inorganic

Organic-InorganicHybrid Materials: Sol-GelReactions, Fig. 1 Sol-gel

reaction of alkoxysilane

Organic-Inorganic Hybrid Materials: Sol-Gel Reactions, Fig. 2 Organic polymers having accepting groups (With

kind permission from Springer Science and Business Media [1])

1470 Organic-Inorganic Hybrid Materials: Sol-Gel Reactions

components via p-p interactions. For example,

phenyltrimethoxysilane (PhTMOS) can be used

as a starting material for this method (Fig. 5).

As an organic polymer, polystyrene is employed.

Therefore, polystyrene and PhTMOS gel polymer

hybrids are synthesized using a sol-gel reaction of

PhTMOS [9]. Usually, the phase-separated com-

posite is obtained from polystyrene and silica gel

due to poor compatibility between polystyrene

and silica gel. However, transparent polymer

hybrids can be prepared by using polystyrene

and PhTMOS as a starting silicate. The p-p

interactions of the phenyl groups between poly-

styrene and silica gel having phenyl groups lead to

a nanometer-level dispersion of polystyrene in

silica gel. In another example, transparent polymer

hybrids can be obtained from acrylate polymer

having triphenylimidazole moieties and

PhTMOS [10]. Compared with a starting organic

polymer, a 10 % weight loss temperature (Td10) is

shifted to a higher temperature in the polymer

hybrids prepared from acrylate polymer having

triphenylimidazole moieties and PhTMOS via

p-p interactions.

Organic-Inorganic Hybrid Materials: Sol-Gel Reactions, Fig. 4 Ionic interactions between sulfonated polystyrene

and inorganic matrix resulting from APTMOS and TMOS

Organic-InorganicHybrid Materials: Sol-GelReactions,Fig. 3 Hydrogen bonding

interactions between poly

(2-methyl-2-oxazoline) and

silica (With kind

permission from Springer

Science and Business

Media [1])


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Organic-Inorganic Polymer Hybrids viaCH/p Interactions

In many cases, strong intermolecular interactions

such as hydrogen bonding interactions or ionic

interactions are utilized for the preparation of

organic-inorganic polymer hybrids since hydro-

philic polymers such as poly(vinyl alcohol)

(PVA), poly(vinylpyrrolidone) (PVP), and poly

(2-methyl-2-oxazoline) (POZO) are applied for

hybridization. However, these methods are not

applicable to hybridization using hydrophobic

organic polymers. When polymer hybrids are syn-

thesized by using a hydrophobic organic polymer,

the p-p interactions are important physical inter-

actions. Additionally, CH/p interactions play an

important role in the dispersion of a hydrophobic

organic polymer in the silica gel. This method

consists of an interaction between the hydrophobic

organic polymer and inorganic components via

CH/p interactions. As a typical example,

PhTMOS as a starting silicate and poly(vinyl chlo-

ride) (PVC) as a hydrophobic organic polymer are

employed (Fig. 6). The sol-gel reaction of

PhTMOS is carried out in the presence of PVC

having activated CH groups. Transparent and

homogeneous polymer hybrids are obtained

when arylalkoxysilane is used as the starting

alkoxysilane. The dispersity in the resulting poly-

mer hybrids can be confirmed by scanning elec-

tron microscopy (SEM) observations. When

organic-inorganic polymer hybrids are prepared

Organic-Inorganic Hybrid Materials: Sol-Gel Reac-tions, Fig. 5 p-p interactions between polystyrene and

an inorganic matrix resulting from PhTMOS (Reproduced

from Ref. [9] with permission of The Royal Society of

Chemistry)

Organic-Inorganic Hybrid Materials: Sol-Gel Reactions, Fig. 6 CH/p interactions between PVC and inorganic

matrix resulting from PhTMOS


Organic-Inorganic Hybrid Materials: Sol-Gel Reac-tions, Fig. 7 CH/p interactions between PVC and

octaphenetyl-POSS (Reprinted from Progress in Organic

Coatings, 64, Takeru Iwamura, Kaoru Adachi, Masato

Sakaguchi, Yoshiki Chujo, Synthesis of organic-inorganic

polymer hybrids from poly(vinyl chloride) and polyhedral

oligomeric silsesquioxane via CH/p interaction, 124–127,

Copyright (2009), with permission from Elsevier)

Organic-Inorganic Hybrid Materials: Sol-Gel Reactions, Fig. 8 In situ hydrolytic synthesis of PVA/silica hybrid

(With permission from Ref. [13])


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from PhTMOS, silica domains cannot be recog-

nized at a microlevel. Moreover, the CH/p inter-

actions in these polymer hybrids are supported by

FT-IR spectra in which the CH stretching bands

are shifted to a lower wave number region after the

formation of these hybrids. Therefore, in the case

of the organic-inorganic polymer hybrids prepared

from PVC and PhTMOS, CH/p interactions are

quite effective for the synthesis of homogeneous

polymer hybrids of polymers having active CH

groups and silica gel [11].

In another example, transparent polymer

hybrids are obtained from PVC and polyhedral

oligomeric silsesquioxane (POSS) as an inor-

ganic component (Fig. 7). Organic-inorganic

polymer hybrids can be synthesized by using

weak intermolecular interactions such as CH/pinteractions between the CH groups of PVC and

the organic functional groups introduced into the

cage-like POSS (octaphenyl-POSS) [12].

In Situ Hydrolysis Method

There are cases when organic-inorganic polymer

hybrids cannot be obtained since the

intermolecular interactions between an organic

polymer and silica gel are weak. When PVA is

employed as an organic polymer in hybridization,

aggregation of the polymer arises due to interac-

tion among hydroxyl groups in the organic com-

ponent, which results in phase separation.

Consequently, heterogeneous materials are

obtained. However, when poly(vinyl acetate)

(PVAc) is utilized as a starting organic polymer,

the functional groups of PVAc generate hydroxyl

Organic-Inorganic Hybrid Materials: Sol-Gel Reactions, Fig. 9 In situ radical polymerization during formation of

silica from TMOS (With kind permission from Springer Science and Business Media [14])


groups effectively via a hydrolysis reaction with

an acid catalyst in alcohol solvents by ester

exchange. In this reaction mixture, the sol-gel

reaction of TMOS is carried out to obtain the

organic-inorganic polymer hybrids at the

same time (Fig. 8). The resulting polymer

hybrids become optically transparent and

homogeneous [13].

In Situ Polymerization Method

The in situ polymerization method is useful for

the synthesis of polymer hybrids starting from

organic polymers without a high affinity for the

silica matrix. For instance, homogeneous poly-

styrene and silica gel polymer hybrids can be

prepared by this method which can be applied to

vinyl monomers that have a poor affinity for the

silica matrix. A styrene monomer was introduced

into a sol-gel reaction mixture of TMOS,

and radical polymerization was initiated by

2,20-azodiisobutyronitrile (AIBN), while the

sol-gel reaction of TMOS proceeded to form a

silica gel (Fig. 9) [14]. Homogeneity can be con-

firmed quantitatively by measuring the porosity

of charred hybrids using nitrogen porosimetry.

Polystyrene is dispersed at the nanometer scale

in the silica matrix.

Summary

Organic-inorganic polymer hybrids are expected

to have many possibilities as new composite

materials. From the viewpoint of polymer

hybrid preparation, many kinds of organic poly-

mers are applicable to hybridization by using

various intermolecular interactions. Use of

intermolecular interactions may have some

advantages in the preparation process. It can be

incorporated into a preformed organic

polymer without modifying the polymers. From

an environmental science point of view, the

effective use of existing polymers is very

significant.

Related Entries

▶Bioinorganic Hybrid Materials

▶Clay Nanohybrid Materials

References

1. Chujo Y, Saegusa T (1992) Organic polymer hybrids

with silica gel formed bymeans of the sol-gel method.

Adv Polym Sci 100:11–29

2. Chujo Y, Ihara E, Kure S, Saegusa T (1993) Synthesis

of triethoxysilyl-terminated polyoxazolines and their

cohydrolysis polymerization with tetraethoxysilane.

Macromolecules 26:5681–5686

3. Saegusa T, Chujo Y (1990)An organic/inorganic hybrid

polymer. J Macromol Sci A27:1603–1612

4. Chujo Y, Ihara E, Kure S, Suzuki K, Saegusa T (1991)

Block copolymer of 2-methyl-2-oxazoline with silica

gel an organic-inorganic hybrid polymer. Makromol

Chem Macromol Symp 42(43):303–312

5. Chujo Y (1996) Organic-inorganic polymer hybrids.

Polym Mater Encycl 6:4793–4798

6. Saegusa T, Chujo Y (1991) Macromolecular engi-

neering on the basis of the polymerization of

2-oxazolines. Makromol Chem Macromol Symp

51:1–10

7. Saegusa T, Chujo Y (1992)Organic-inorganic polymer

hybrids. Makromol Chem Macromol Symp 64:1–9

8. Tamaki R, Chujo Y (1999) Synthesis of polystyrene

and silica gel polymer hybrids utilizing ionic interac-

tions. Chem Mater 11:1719–1726

9. Tamaki R, Samura K, Chujo Y (1998) Synthesis of

polystyrene and silica gel polymer hybrids via p-pinteractions. Chem Commun 10:1131–1132

10. (a) Takasaki M, Iwamura T (2013) Synthesis of

organic-inorganic polymer hybrids from acrylate

polymer having a triphenylimidazole moiety via p-pinteractions. Polym Prepr Jpn 62:2262; (b) Takasaki

M, Hiroki K, Iwamura T (2015) Synthesis of organic-

inorganic polymer hybrids from acrylate polymer

having a triphenylimidazole moiety via p–p interac-

tions. Polm Bull DOI: 10.1007/s00289-014-1297-9

11. Iwamura T, Adachi K, Chujo Y (2004) Synthesis of

poly(vinyl chloride) and silica gel polymer hybrids

via CH/p interaction. Polym J 11:871–877

12. Iwamura T, Adachi K, Chujo Y (2009) Synthesis of

organic-inorganic polymer hybrids from poly(vinyl

chloride) and polyhedral oligomeric silsesquioxane

via CH/p interaction. Prog Org Coat 64:124–127

13. Tamaki R, Chujo Y (1998) Synthesis of poly(vinyl

alcohol)/silica gel polymer hybrids by in-situ hydro-

lysis method. Appl Organomet Chem 12:755–763

14. Tamaki R, Naka K, Chujo Y (1997) Synthesis of

polystyrene/silica gel polymer hybrids by in-situ

polymerization method. Polym Bull 39:303–310


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