The term "Inorganic/Organic Hybrid Material" is normally associated with polymers prepared in part by a sol-gel process. The sol-gel process, in this case, is meant to describe polymerization of a soluble metal alkoxide. The polymerization typically involves a series of hydrolysis and condensation reactions with the generation of alcohol and water as reaction by-products. Some of the metal alkoxides used in the preparation of inorganic/organic hybrid materials are tetraethoxysilane, tetramethoxysilane, tetraisopropoxytitanium(IV), tetrapropoxyzirconium(IV) and tributoxyaluminum.(2) The organic nature of the inorganic/organic hybrid material is usually incorporated into the network by the use of an organo-functional silane. However, this is not a rule, as will be seen shortly. The organo- functional silane, which is commonly referred to as a silane coupling agent, is available with a wide variety of reactive end groups. Thus, the reactions used to combine the inorganic and organic moieties are quite diverse. A few examples available in the literature are free radical vinyl polymerizations, hydrosilylation reactions, and condensation reactions.

There are basically four general methods of preparing the inorganic/organic hybrid materials and, associated with them, at least three different particular sub-headings or names. Each will be described briefly in terms of their process and associated nomenclature system. The first process to be described here involves the use of a silane coupling agent which is initially polymerized with a metal alkoxide by the sol-gel process. The resultant system is subsequently blended with reactive monomer(s) and appropriate catalysts for a secondary polymerization reaction which produces a monolithic network. The sub-headings of materials prepared in this manner were known as ORMOSILs for organically modified silanes.

However, in the last year these materials have been referred to as the ORMOCERs,(3) possibly to reflect their more ceramic-like properties following thermal post-cures. An example of the nomenclature associated with these materials is represented by the following: (C6H5)2SiO/MeViSiO/SiO2=32.5:65:2.5 (molar ratio). This nomenclature reflects the complex structure of these inorganic/organic materials. The structures of the three monomers are depicted in Figure 1. The first term in the nomenclature refers to the diphenyldiethoxysilane monomer. The second term refers to methylvinyldiethoxysilane and the last term represents the structural form of tetraethoxysilane following complete hydrolysis and condensation. The molar ratio of the three reactive components is given by the numbers.

Another class of the inorganic/organic hybrid materials, which are referred to in the literature as CERAMERs,(4) are monolithic networks prepared exclusively by a sol-gel process. The reactive components are soluble metal alkoxides and an oligomer or polymer with an alkoxysilane functionality. The oligomers can be functionalized through a reaction of end groups, such as hydroxyls or amines, with the reactive organic group of a silane coupling agent such as (3-isocyanatopropyl)triethoxysilane. Another example of functionalized oligomers used to prepare CERAMERs is silanol terminated poly(dimethylsiloxane) which is illustrated in Figure 2. An alternative IUPAC name (5) for the silanol terminated poly(dimethylsiloxane), which is based on a constitutional repeating unit, is (a-hydro-w-hydroxypoly[oxy(dimethylsilylene)]. The use of various metal alkoxides and oligomers (polymers) led to a unique nomenclature system for the CERAMERs which is listed in Table 1.(6) The designation assigned to tetraisopropoxytitanium(IV) is TiOPr. The brevity of this designation was meant to maintain a uniform system for the CERAMERS. It was especially useful for systems which were also prepared with chelated metal alkoxides (7) and various catalysts,(8) which complicated the nomenclature of the CERAMERs even more. The abbreviation PTMO designates the oligomer of poly(tetramethylene oxide) or a-hydro-w-hydroxypoly(oxytetramethylene) (IUPAC name) functionalized with triethoxysilane.

The third process involves the formation of an inorganic phase by the sol-gel process within an existing network. This has been accomplished by the addition of the metal alkoxide along with an appropriate acid or base catalyst.(9) Another method of in situ formation of silica particles involves the addition of the metal alkoxide to a network which contains the acid catalyst as a functional group of the, polymer backbone, i.e., perfluorosulfonic acid membranes.(10) There has been no particular nomenclature system associated with these materials.

The fourth general process for producing the inorganic/organic hybrid materials begins with the production of a xerogel.(11,12) The xerogel is prepared by sintering, at a sufficiently high temperature (ca. greater than 600ƒC), a polymer produced by the sol-gel polymerization of a metal alkoxide. A reactive monomer(s) such as methyl methacrylate is then allowed to diffuse into the pores of the xerogel and then polymerized by appropriate methods. These materials have not been included in or assigned to any particular sub-heading of the inorganic/organic hybrid material "nomenclature."

In summary, the materials that fall into the either appropriate or inappropriate classification of inorganic/organic hybrid materials represent a diverse group. The intent of this Nomenclature Note was to present the current nomenclature associated with these materials. It is hoped that these Nomenclature Notes will assist in the development of and improvement of the polymer nomenclature system.

REFERENCES

1. W. V. Metanomski, Polym. Prepr., 1991, 32(1), 655.
2. IUPAC, "Nomenclature of Inorganic Chemistry" (The Red Book), G. J. Leigh (ed.), Blackwell, Oxford, 1990.
3. H. Schmidt and H. Wolter, J. Non-Cryst. Solids, 1990, 121, 428.
4. G. L. Wilkes, B. Orier, and H.-H. Huang, Polym. Prepr., 1985, 26(2), 300.
5. IUPAC, "Compendium of Macromolecular Nomenclature" (The Purple Book), W. V. Metanomsld (ed.), Blackwell, Oxford, 1991.
6. H. Huang, R. H. Glaser, and G. L. Wilkes, in "Inorganic and Organometallic Polymers", M. Zeldin, K. J. Wynne, and H. R. Allcock (eds.), ACS Symposium Series No. 360; ACS, Washington, D.C., 1988, 354.
7. B. Wang, A. B. Brennan, H.-H. Huang, and G. L. Wilkes, J. Macromol. Sci., Chem., 1990, A27(12), 1449.
8. A. B. Brennan and G. L. Wilkes, Polymer, 1991, 32(4), 733.
9. J. E. Mark, Y.-P. Ning, C.-Y. Jiang, M.-Y. Tang, and W. C. Roth, Polymer, 1985, 26, 2069.
10. K. A. Mauritz and R. M. Warren, Macromolecules, 1989, 22, 1730.
11. L. C. Klein and G. J. Garvey, J. Non-Cryst. Solids, 1982, 48, 97.
12. E. J. A. Pope, M. Asami, and J. D. Mackenzie, J. Mater. Res., 1989, 4(4), 1018.

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