The key difference between polysiloxane and polydimethylsiloxane is that polysiloxane has silicon atoms attached to two oxygen atoms and two alkyl groups, whereas polydimethylsiloxane has silicon atoms attached to two oxygen atoms and two methyl groups.
Both polysiloxane and polydimethylsiloxane are important silicone polymer materials. They have different chemical and physical properties as well as different applications.
CONTENTS
1. Overview and Key Difference
2. What is Polysiloxane
3. What is Polydimethylsiloxane
4. Side by Side Comparison – Polysiloxane vs Polydimethylsiloxane in Tabular Form
5. Summary
What is Polysiloxane?
Polysiloxane or silicone is a polymer material containing many siloxane functional groups throughout its structure. It is named as polysiloxane due to the presence of a high number of siloxane repeating units. It is a synthetic polymer that does not naturally occur. Polysiloxane contains a backbone, consisting of Si-O bonds. Moreover, there are side chains attached to this backbone.
Figure 01: Silicone is Useful as a Sealing Material
Usually, the polysiloxane is considered as an inorganic polymer because it has no carbon in its backbone. Since the bond between Si-O is more strong, the backbone is very stronger than carbon-containing backbones. Due to the same reason, this material is highly resistant to heat.
Typically, silicone is resistant to heat and other liquid solvents. It is a rubber-like material and is mainly used as a sealant material. The applications of polysiloxane include using it as a sealant, lubricant, adhesive, medicine, cooking utensils, thermal and electrical insulation, etc.
What is Polydimethylsiloxane?
Polydimethylsiloxane is a type of silicone where the backbone of the polymer contains silicon and oxygen atoms including two methyl groups attached to the silicon atoms. This material is the most commonly used siloxane polymer due to its unusual flow properties. It is an optically clear material with inert, toxic and non-flammable properties.
All the repeating units of polydimethylsiloxane have two methyl groups attached to the silicon atom. The silicon atom is bonded to two oxygen atoms in its backbone. Industrially, this polymer material can be made from dimethyldichlorosilane.
Figure 02 Chemical Structure of Polydimethylsiloxane
Polydimethylsiloxane is a hydrophobic material. Therefore, solid samples of this polymer do not allow aqueous solvents to infiltrate and swell the material. This makes this material useful in combination with water and alcoholic solvents without undergoing any deformation.
When considering the applications of polydimethylsiloxane, it is commonly used as a surfactant and as an antifoaming agent. Also, it has applications in hydraulic fluids and related applications. Moreover, we can use it as a stamp resin and in the synthesis of gecko adhesion.
What is the Difference Between Polysiloxane and Polydimethylsiloxane?
The key difference between polysiloxane and polydimethylsiloxane is that polysiloxane has silicon atoms attached with two oxygen atoms and two alkyl groups, whereas polydimethylsiloxane has silicon atoms attached with two oxygen atoms and two methyl groups. Moreover, when considering the production of these polymers, synthesis of polysiloxane depends on the type of alkyl group attached to the silicon atom; e.g. hydrolysis of dimethyldichlorosilane if alkyl group is methyl. For polydimethylsiloxane production, we can produce it from dimethyldichlorosilane in the presence of water and HCl.
Below infographic shows more information on the difference between polysiloxane and polydimethylsiloxane.
Summary – Polysiloxane vs Polydimethylsiloxane
Both polysiloxane and polydimethylsiloxane are important silicone polymer materials. They have different chemical and physical properties as well as different applications. The key difference between polysiloxane and polydimethylsiloxane is that polysiloxane has silicon atoms attached to two oxygen atoms and two alkyl groups, whereas polydimethylsiloxane has silicon atoms attached to two oxygen atoms and two methyl groups.
Reference:
1. “Silicone.” Wikipedia, Wikimedia Foundation, 16 Apr. 2020, Available here.
2. “Polydimethylsiloxane.” Polydimethylsiloxane – an Overview | ScienceDirect Topics, Available here.
3. “Polydimethylsiloxane.” Wikipedia, Wikimedia Foundation, 16 Apr. 2020, Available here.
Image Courtesy:
1. “Silicone-Sealant-1001U_43333-480×360” By Emilian Robert Vicol (CC BY 2.0) via Flickr
2. “PmdsStructure” By Smokefoot – Own work (Public Domain) via Commons Wikimedia