Ask an Expert: Polydimethylsiloxane (PDMS)

Post by HowardE » Fri Dec 11, 2015 4:46 pm

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When discussing Polydimethylsiloxane (PDMS), it's crucial to understand that this silicone oil is widely used in various industries. For those unfamiliar, PDMS is a silicon-based organic polymer that is notably used in manufacturing and has a range of applications due to its unique properties of flexibility, stability, and resistance to environmental factors.

To find specific products involving PDMS, one might look at sites like Amazon to check for items directly associated with silicone oil. If you can't find precisely what you're looking for, providing more detailed information about your needs will help experts assist you better.

If you want to learn more, please visit our website Polydimethylsiloxane Silicone Oil.

Depolymerization of Polydimethylsiloxane

I am interested in converting polydimethylsiloxane (PDMS) back to its monomer form, dimethylsiloxane. This process is part of my project to create Silly Putty using boric acid for polymerization.

Seeking Pure Dimethylsiloxane

An alternative I am considering is finding over-the-counter sources of pure dimethylsiloxane. PDMS is available in DOT 5 brake fluid, which also includes a purple dye (dissipates at 180°C) and a small amount of tributyl phosphate.

Hi there,

Unfortunately, the specific compound you're looking for doesn't exist in isolation. Silly Putty is typically formed from silanol-chain stopped PDMS. The process involves thoroughly mixing or milling this polymer with an organoborate or boric acid and heating it to about 160°C.

Another method involves reacting diethoxydimethylsilane with boric acid in the presence of HCl and EtOH, then hydrolyzing to achieve the desired properties. However, under cold and neutral pH conditions, this same starting material can yield dimethylsilanediol.

It sounds like an exciting experiment, but it comes with challenges. The PDMS in brake fluid may not have the correct silanol chain-stopped end groups needed for the reaction to proceed as expected.

If more suitable sources of silicone oils such as dimethicone or cyclomethicone are available, these can be viable alternatives. These components are readily found in many consumer products, particularly in cosmetics and personal care items.

Thanks for your reply. While trying a procedure to create silicone oil from dichlorodimethylsilane and 5% boric acid at 180°C, I found an issue. Although the mixture dissolved completely at room temperature and 180°C, there was no thickening. This indicates a potential problem with obtaining the right silanol chain-stopped polymer from the brake fluid.

If someone is looking to break down silicone oils from consumer products or lab reagents, one might use hot NaOH solution.

Depolymerization Challenges

Finding a source of silanol-stopped PDMS or a single type of PDMS compound in products like brake fluid might be necessary. From there, you could potentially depolymerize it back to a useful starting material.

Understanding these complex chemical reactions is essential for anyone looking to work with PDMS and its depolymerization. The intricate details, such as ensuring the correct end groups are present or finding pure sources, can significantly impact your project's success.