Polymeric metal alkoxides fall into two main classes: oxo-bridged, which can be regarded as partially hydrolyzed metal alkoxides, and alkoxide-bridged which can be regarded as organo-diester alkoxides. Both classes have the advantages of high metal content and low volatility.
Polymeric metal alkoxides are used primarily as curing agents for 2-part RTVs and in the preparation of binders and coatings including investment casting resins and zinc-rich paints. The latter applications can be considered as special examples of sol-gel technology. Sol-gel is a method for preparing specialty metal oxide glasses and ceramics by hydrolyzing a chemical precursor or mixture of chemical precursors that pass sequentially through a solution state and a gel state before being dehydrated to a glass or ceramic.
Preparation of metal oxides by the sol-gel route proceeds through three basic steps:
1) partial hydrolysis of metal alkoxides to form reactive monomers;
2) the polycondensation of these monomers to form colloid-like oligomers (sol formation);
3) additional hydrolysis to promote polymerization and cross-linking leading to a 3-dimensional matrix (gel formation).
Although presented sequentially, these reactions occur simultaneously after the initial processing stage.
Monomer formation (partial hydrolysis)
Sol formation (polycondensation)
As polymerization and crosslinking progress, the viscosity of the sol gradually increases until the sol-gel transition point is reached. At this point the viscosity abruptly increases and gelation occurs. Further increases in crosslinking are promoted by drying and other dehydration methods. Maximum density is achieved in a process called densification in which the isolated gel is heated above its glass transition temperature. The densification rate and transition (sintering) temperature are influenced primarily by the morphology and composition of the gel.
METAL ALKOXIDES AND DIKETONATES
Bradley, D. C.; Mehrotra, R. C.; Gaur, D. P. Metal Alkoxides, Acadmeic Press, 1978.
Mehrotra, R. C.; Bohra, R.; Gaur, D. P. “Metal Diketonates and Allied Derivatives” Academic Press, 1978.
SOL-GEL TECHNOLOGY
Brinker, C. J.; Scherer, G. W. Sol-Gel Science, Academic Press, 1990.
Brinker, C. J.; Clark, D. E.; Ulrich, D. R. Better Ceramics Through Chemistry, (Materials Research Society Proceedings 32), Elsevier, 1984.
Brinker, C. J.; Clark, D. E.; Ulrich, D. R. Better Ceramics Through Chemistry II, III, IV (IV add’l ed. B. J. Zelinski) (Materials Research Society
Proceedings 73, 121, 180) Mat’l. Res. Soc., 1984, 1988, 1990.
Hench, L. L.; Ulrich, D. R. Ultrastructure Processing of Ceramics, Glasses and Composites, Wiley, 1984.
Hench, L. L.; Ulrich, D. R. Science of Ceramid Processing, Wiley, 1986.
Klein, L. C. Sol-Gel Technology for Thin Fillms, Fibers, Preforms, and Electronics, Noyes, 1988.
Polymeric Metal Alkoxides
| Product Code | Name | Metal Content | Viscosity (cSt) | Unit MW | Density | CAS | Comments |
|---|---|---|---|---|---|---|---|
| PSI-021 | poly(diethoxysiloxane) | 20.5-21.5% Si (40-42% SiO2 equivalent) | 3-5 | 134.20 | 1.05-1.07 | [68412-37-3] | crosslinker for two-component condensation cure (silanol) RTVs TSCA |
| PSI-023 | poly(diethoxysiloxane) | 23.0-23.5% Si (48-52% SiO2 equivalent) | 20-35 | 134.20 | 1.12-1.15 | [68412-37-3] | base for zinc-rich paints TSCA |
| PSI-026 | poly(dimethoxysiloxane) | 26.0-27.0% Si | 6-9 | 106.15 | 1.14-1.16 | [25498-02-6] | highest SiO2 content precursor for sol-gel TSCA |
| PSIAL-007 | diethoxysiloxane-s-butylaluminate copolymer | 7.5-8.5% Al 6.6-7.6% Si | -- | -- | 0.90-1.00 | [68959-06-8] | sol-gel intermediate for aluminum silicates (J. Boilot in “Better Ceramics Through Chemistry III, p121) TSCA |
| PSITI-019 | diethoxysiloxane-ethyltitanate copolymer | 19.1-19.6% Si 2.1-2.3% Ti | 10-20 | -- | -- | -- | employed in formation of titania-silica aerogels. (Miller, J.; et al. J. Mater. Chem. 1995, 5, 1795.) |
| PSIPO-019 | diethoxysiloxane-ethylphosphate copolymer | 19.1-19.6% Si 1.4-1.5% P | 8-12 | 1.09-1.11 | [51960-53-3] | hygroscopic R.I. 1.400 |
|
| PAN-040 | poly(antimony ethylene glycoxide) | 39.8-40.4% Sb | solid | 303.55 | -- | catalyst for transesterification TSCA |
|
| PTI-023 | poly(dibutyltitanate) | 22.0-23.0% Ti | 3,200-3,500 | 210.10 | 1.07-1.10 | [9022-96-2] | stabilized with ~5% ethylene glycol TSCA |
| PTI-008 | poly(octyleneglycol-titanate) | 7.5-7.6% Ti | 1,700 | 482.54 | 1.035 | [5575-43-9] | contains ~5% free 2-ethyl-1,3-hexanediol, oligomeric flashpoint: 50 °C |