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Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2012, Article ID 453821, 2 pagesdoi:10.1155/2012/453821

Editorial

Silsesquioxanes: Recent Advancement and Novel Applications

Yoshiro Kaneko,1 E. Bryan Coughlin,2 Takahiro Gunji,3 Maki Itoh,4

Kimihiro Matsukawa,5 and Kensuke Naka6

1 Department of Chemistry, Biotechnology, and Chemical Engineering, Graduate School of Science and Engineering,Kagoshima University, Kagoshima, Kagoshima 890-0065, Japan

2 Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA 01003, USA3 Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, Noda,Chiba 278-8510, Japan

4 Electronics Solutions S&T, Dow Corning, Ichihara, Chiba 299-0108, Japan5 Electronic Material Research Division, Osaka Municipal Technical Research Institute, Osaka, Osaka 536-8553, Japan6 Department of Chemistry and Materials Technology, Graduate School of Science and Technology, Kyoto Institute of Technology,Kyoto, Kyoto 606-8585, Japan

Correspondence should be addressed to Yoshiro Kaneko, [email protected] Maki Itoh, [email protected]

Received 6 November 2012; Accepted 6 November 2012

Copyright © 2012 Yoshiro Kaneko et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

Among the products in silicone industry, silicone oils or elas-tomers are based on linear polysiloxanes mainly consisting ofD (R2SiO2/2) unit, which is the predominant material in thisindustry mostly as polydimethylsiloxane. In contrast, siliconeresins are network polymers consisting mainly of T (RSiO3/2)and Q (SiO4/2) units. Silsesquioxanes are one class of siliconeresins that consist only of the T unit. The first commer-cialization of silicones started with silicone resins consistingprimarily of silsesquioxanes for electrical insulation at hightemperatures, in an effort to develop materials much morethermally stable and tougher than plastics but more flexiblethan glass [1]. Development research was started in the 1930sin Corning Glass Works and General Electric Company onthe basis of academic work by Kipping. The research work atCorning Glass Works, led by Hyde, and scale-up productionof the raw materials at Dow Chemical resulted in formationof Dow Corning in 1943. General Electric, where Patnodeand Rochow were acting as pioneers, started commercialproduction of silicones in 1946 [2].

Most of the industrial silicone resin materials can beclassified either into a DT type, which consists of D and Tunits, and an MQ type, which comprise M (R3SiO1/2) andQ units [3]. Silsesquioxanes could be considered as one of

the DT silicone reins in which the content of the D unit iszero. In other words, T units without other components canform a material that we can call a silicone resin. Anothercharacteristic of silsesquioxane is the defined structureslike cages, known as polyhedral oligomeric silsesquioxanes(POSSs), which is drawing attentions both from academiaand industry. Linear polymers could be characterized mostlyby molecular weight and molecular weight distribution.However, the trifunctional nature of silsesquioxanes allowsto form a variety of structures from oligomeric cages toladder-like structures to three-dimensional network struc-tures based on the ring structures. This could open upthe possibility of creating unmet properties by structuralcontrol.

Silicones, including silsesquioxanes, are characterizedwith their high thermal/photo stability, electric insula-tion and so on. Compared with silica, silsesquioxanes orsilicone resins can provide additional features includinglower k, flowability, flexibility, functionality, and interactionwith organic molecules from the combination of siloxanebackbone and organic substitution. Combination of thesecharacteristics and the numerous possibility of structuralpermutations provide the unique attributes of silsesquioxane

2 International Journal of Polymer Science

materials. This special issue highlights the recent significantprogress in silsesquioxanes and their novel applications.

This special issue contains four review papers andeight research articles. One research article, “A syntheticroute to quaternary pyridinium salt-functionalized silsesquiox-anes,” describes synthesis of POSS derivatives having apendant quaternized 4-(2-ethyl)pyridyl group aiming forpotential antimicrobial property. The possible benefit ofusing POSS is its thermal stability and the spacing of thefunctionality by the cubic octamers. A 4-(2-ethyl)pyridinePOSS derivative was prepared by reacting the correspondingtrichlorosilane either directly with cyclohexyl-substituted[RSiO3/2]4[RSi(OH)O2/2]3 or after converting the SiOH toSiOLi. Another characteristic of such defined cage struc-tures is entrapment of gas molecules, cations, or anions.Computer simulation for the insertion reaction of variousguest species for Ti-POSS, [HTiO3/2]n, n = 8 and 10, isdiscussed in “A theoretical study of the insertion of atomsand ions into titanosilsequioxane (Ti-POSS) in comparisonwith POSS” in comparison with that for Si-POSS, exploringthe similarity and difference between Ti-POSS and Si-POSS.Presence of cage compounds in products by the hydrolyticpolycondensation of methyltrichlorosilane in excess water isclarified in “Characterization and some insights into the reac-tion chemistry of polymethylsilsesquioxane or methyl siliconeresins”. An experimental evidence that such cage moleculesare formed by siloxane bond rearrangement from moleculesof similar molecular weight rather than simple condensationof precursor molecules is presented. The presence of suchcage molecules in industrial DT type silicone resins is alsodescribed. Preparation of block copolymers of methacrylateshaving POSS and ferrocene in the side chain by anionic poly-merization is described in “Iron oxide arrays prepared fromferrocene- and silsesquioxane-containing block copolymers.”The materials showed microphase-separated nanostructures,and the array is expected to be a promising catalytic materialfor the creation of carbon nanotube thin films.

Another form of defined structure for silsesquioxane is aladder structure. Proven ladder structure of silsesquioxanescan be found in those synthesized by stepwise reactions.The first nonacyclic ladder silsesquioxanes with isopropylsubstituent are reported in “Nonacyclic ladder silsesquioxanesand spectral features of ladder polysilsesquioxanes”, as formedby the reaction of bicyclic silanol with tricyclic tetrachloride.A review paper, “Preparation of ionic silsesquioxanes with reg-ular structures and their hybridization,” describes the prepa-ration of ladder-like polysilsesquioxanes by self-organizationof ammonium salt, for which anion exchange behavioris investigated. In this review, control of conformationalstructures of the polysilsesquioxanes by the introduction ofchiral moieties is also reported.

Various polysilsesquioxanes including hybrids aiming forspecific functions are presented. Polysilsesquioxanes bearingethoxysulfonyl groups in side chains were prepared for aproton-conductive film, by the hydrolytic polycondensationof 4-(2-methyl-3-triethoxysilylpropoxy)benzenesulfonate asdiscussed in “Synthesis and properties of polysilsesquioxaneshaving ethoxysulfonyl group as a side chain.” Polymeth-ylsilsesquioxane-based organic-inorganic hybrid materials

for gate insulating layer in organic thin film transistors(TFTs) are reviewed in “Polysilsesquioxanes for gate insulatingmaterials of organic thin-film transistors,” referring to the pos-sibility for flexible TFTs. Water-soluble polysilsesquioxanes,including hydroxyl-functional and cationic silsesquioxanes,are reviewed including the hybrids of SiO1.5/SiO2 andRSiO1.5/TiO2 and stimuli-responsive materials in “Designand synthesis of functional silsesquioxane-based hybrids byhydrolytic condensation of bulky triethoxysilanes.” Hybridnanoparticles with other metal oxides are also reported forpoly-3-aminopropyl-silsiesquioxane and zirconia having theestimated refractive index of 1.66, which can form highlytransparent water dispersion as discussed in “Sol-gel prepara-tion of highly water-dispersible silsesquioxane/zirconium oxidehybrid nanoparticles.”

The last set of materials is so-called bridged silsesquiox-anes. Ethylene-bridged polysilsesquioxane gels with hierar-chical macropores and mesopores are prepared by com-bining the micellar templating in nanometer-scale with thepolymerization-induced phase separation in micrometer-scale for well defined mesoporous structures as described in“Evolution of mesopores in monolithic macroporous ethylene-bridged polysilsesquioxane gels incorporated with nonionicsurfactant.” Synthesis and properties of oligo-thiophenebridged polysilsesquioxanes are reviewed in “Synthesis of anovel family of polysilsesquioxanes having oligothiophenes withwell-defined structures.” The polymers anchored on SiO2 orITO substrates showed excellent mechanical hardness basedon the three-dimensional siloxane network structure withchemical linkage between the polymer and the surface of themetal-oxide substrates.

Acknowledgment

The editors are grateful to the contributing authors andreviewers for their efforts in compiling this special issue.

Yoshiro KanekoE. Bryan Coughlin

Takahiro GunjiMaki Itoh

Kimihiro MatsukawaKensuke Naka

References

[1] E. L. Warrick, “Years of firsts,” in The Recollections of a DowCorning Pioneer, chapter 1, pp. 1–45, McGraw-Hill, New York,NY, USA, 1990.

[2] E. G. Rochow, Silicon and Silicones, Springer, Berlin, Germany,1987.

[3] R. H. Baney, M. Itoh, A. Sakakibara, and T. Suzuki,“Silsesquioxanes,” Chemical Reviews, vol. 95, no. 5, pp. 1409–1430, 1995.

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