Silicone resin

Silicone resin with R = CH₃, H or OH

Silicone resins are a type of silicone material which is formed by branched, cage-like oligosiloxanes with the general formula of R_nSiX_mO_y, where R is a non reactive substituent, usually Methyl (Me) or Phenyl (Ph), and X is a functional group Hydrogen (H), Hydroxyl group (OH), Chlorine (Cl) or Alkoxy group (OR). These groups are further condensed in many applications, to give highly crosslinked, insoluble polysiloxane networks.^[1]

When R is methyl, the four possible functional siloxane monomeric units are described as follows:^[2]

• "M" stands for Me₃SiO,
• "D" for Me₂SiO₂,
• "T" for MeSiO₃ and
• "Q" for SiO₄.

Note that a network of only Q groups becomes fused quartz.

The most abundant silicone resins are built of D and T units (DT resins) or from M and Q units (MQ resins), however many other combinations (MDT, MTQ, QDT) are also used in industry.

Silicone resins represent a broad range of products. Materials of molecular weight in the range of 1000–10,000 are very useful in pressure-sensitive adhesives, silicone rubbers, coatings and additives.^[3][4]

Silicone resins are prepared by hydrolytic condensation of various silicone precursors. In early processes of preparation of silicone resins sodium silicate and various chlorosilanes were used as starting materials. Although the starting materials were the least expensive ones (something typical for industry), structural control of the product was very difficult. More recently, a less reactive tetraethoxysilane - (TEOS) or ethyl polysilicate and various disiloxanes are used as starting materials.^[1]

Microbial deterioration

The algae Stichococcus bacillaris, and certain fungal species have been seen to colonize silcone resins used at archaeological sites.^[5]

References

1. S.J. Clarson, J.A. Semlyen, Siloxane Polymers, Prentice Hall, New Jersey (1993).
2. Dow Corning nomenclature of silicon resins
3. List of silicone resins produced by Dow Corning
4. Database of silicon resins produced by Momentive Performance Materials (formerly GE Silicones)
5. Francesca Cappitelli; Claudia Sorlini (2008). "Microorganisms Attack Synthetic Polymers in Items Representing Our Cultural Heritage". Applied and Environmental Microbiology. 74. PMC 2227722.