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MS polymer (or "mastic") look like silicone. It also comes in a tube, looks the same when it's liquid. Here are the difference I found with silicone caulk:

  • it's looks a bit less flexible when cured (looks like hard rubbery plastic).

  • it's more expensive (3x) but it doesn't dry at all like silicone (I sealed it with the provided cap, and used it several (very hot) weeks later without any problem).

  • It's much more pleasant to use:

  • it's odorless (no solvent, it cures with [water from the] air)

  • it doesn't stick on fingers like silicone (wiping the finger with tissue is enough to get rid of it).

  • it takes much more time to cure (depending of the quantity you use, you can easily work with it during 10-30 minutes: for several cm3 I was wondering if it'll ever cure).

  • I have seen on this video that unlike silicone, mastic has a non-staining property: it doesn't contain "oil", which could trap some dust and dirty its support.

But what are the other differences? Do both contain silicone? For what would you use one, but not the other?

(Chemistry based answers are also welcomed: I hesitated to post it in the stack chemistry)

  • It would help to know the context of what application/function you are planning to use this material for. And possibly what delivery mechanisms / containers of product you are scoping out. – DaveM Sep 4 at 12:33
  • Thanks for your input, I updated my question concerning the delivery mechanisms (comes in a tube like silicone caulk). Concerning the application, it depend of the answer of my question! (My question is global, I'm just curious to know what could be done with it). For what I saw, It fills holes perfectly, feels like a hard rubbery plastic (seems harder than silicone caulk). It might be possible to mold stuff with it. – JinSnow Sep 5 at 8:38
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The "MS" stands for "Modified Silicone" (although some people think it should be "mostly silicone"), so yes, they both contain silicone.

A "polymer" just means a substance that has a molecular level bond with something else. So "MS Polymer" mastic is silicone sealant that is made with additional materials that change its properties. That's why it has different properties.

As to why they charge 2x more, the answer is the same as it is for anything;

"Because they can..."

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I found some information about it:

What is it exactly?

MS Polymer™ is a water- and solvent-free, clear, odourless solution and liquid at room temperature. It has low volatility and a low Tg. When it comes into contact with a catalyst and water, a crosslinked matrix is formed, providing good heat and chemical resistance.

MS Polymer stands for “modified silicone”, although it is not entirely silicone-based. It has a polyether backbone with reactive silyl functionality (telechelic).There are 2 kinds: a dimethoxysilyl (DMS) with 2 reactive groups (each side) on it and a trimethoxysilyl (TMS) with 3 reactive groups on it, making it a faster curing system than the DMS type. The TMS polymer is a newer version which creates a more strongly crosslinked matrix during curing in order to make harder and stronger material.

The biggest difference with products common in the PSA and tapes world is that crosslinking occurs through moisture-curing. So by addition of a catalyst and subsequent contact with water, MS Polymer™ will start crosslinking and form a matrix structure. Besides the functionality, which can be altered by using either DMS or more reactive TMS, the polyether backbone can also be tuned by varying molecular-weight and branching. The polymer is telechelic, having 2 ends, but also a single-end version can be used as a kind of plasticiser. The product range includes a high-strength grade, meaning that the functional groups are even denser, creating even harder or higher-strength material. A mixture of polymers can be used to make many different kinds of products.

What can you do with it?

This add another adventage to the list above:

  • It's an adhesive.

MS Polymer™ is mainly utilised in the adhesives and sealants world where it is a more common technology. (In contrast, silicone is not actually an adhesive, its adhesive qualities tend to break down much sooner than those of an actual adhesive *.) Its applications include sealants and adhesives for construction, automotive and DIY, such as waterproofing, glazing and insulating.

The polymer is also fairly to very compatible with many rubbers, acrylics, resins and additives. In other words, it is very compatible with many components currently used in PSAs to make a tape.

Some important questions remains:

  • is it as resistant than silicone ? (which can bear impressive amount of heat)

  • does it have the same lifespan?

source

If it wasn't more expensive than silicone, I would personaly use it instead since it's much better to use.

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