Vinyltrimethoxysilane (VTMS), CAS 2768-02-7, is a colourless transparent vinyl-functional silane monomer used as the crosslinking graft monomer in silane-cured polyethylene and as a coupling agent for mineral fillers in polyolefins and coatings. It is supplied at purity 99.0% min, colour (Pt/Co) max 30, specific gravity 0.970 +/- 0.005 at 20 deg C and refractive index n25D 1.3930 +/- 0.0050. PolyBlueChem supplies it in drums and IBCs with per-batch COA and SDS.
Specifications
| Property | Specification |
|---|---|
| Appearance | Colourless transparent liquid |
| Colour (Pt/Co) | Max 30 |
| Purity (%) | Min 99.0 |
| Specific gravity (20 deg C, g/cm3) | 0.970 +/- 0.005 |
| Refractive index (n25D) | 1.3930 +/- 0.0050 |
| Packaging | 200 kg drum; 1000 kg IBC on request |
Basic Information
| Chemical name | Vinyltrimethoxysilane (ethenyltrimethoxysilane) |
| Abbreviation | VTMS, VTMO, vinyl trimethoxy silane |
| CAS number | 2768-02-7 |
| Chemical class | Vinyl-functional organosilane; trialkoxysilane coupling agent |
| Reactive groups | Vinyl (free-radical grafting) plus three hydrolysable methoxy groups (condensation) |
| Appearance | Colourless transparent liquid |
| Colour (Pt/Co) | Max 30 |
| Purity | Min 99.0% |
| Specific gravity (20 deg C) | 0.970 +/- 0.005 g/cm3 |
| Refractive index (n25D) | 1.3930 +/- 0.0050 |
Two Reactive Ends, Two Jobs
VTMS carries two chemically different handles on the same small molecule, and that is the whole reason it is used:
- The vinyl group takes part in free-radical reactions – it grafts onto polyethylene in the presence of a peroxide, and it copolymerises with vinyl acetate, acrylates and other vinyl monomers.
- The three methoxy groups hydrolyse to silanol groups in the presence of water, and then condense with each other or with surface hydroxyls to form siloxane bonds.
Put both together and you get the silane crosslinking process: the vinyl end is grafted into the polymer chain, the methoxy ends later condense between chains, and an otherwise thermoplastic polyethylene becomes a crosslinked network.
Typical Applications
- Silane-cured polyethylene for wire and cable – insulation and sheathing crosslinked in a warm water bath rather than by peroxide or irradiation.
- Crosslinked PE pipe and tubing – hot-water pipe where crosslinking gives creep resistance at temperature.
- Filler surface treatment – silica, glass fibre, talc, mica, aluminium hydroxide and magnesium hydroxide, improving dispersion and mechanical bonding in polyolefins.
- Adhesion promotion – coatings, adhesives and sealants on mineral or metallic substrates; also as a primer component.
- Vinyl silane copolymers – EVA and acrylic systems where pendant trimethoxysilyl groups provide moisture-cure or adhesion.
- Building blocks – synthesis of vinyl-functional silicones, silicone resins and other organosilanes.
Processing Notes
| Point | Guidance |
|---|---|
| Moisture | Keep dry and sealed. Methoxy groups hydrolyse on contact with water, forming silanol oligomers that reduce grafting efficiency and can gel the product |
| Grafting | Free-radical grafting onto PE uses a peroxide initiator at typical extrusion temperatures; the vinyl group is the reactive site |
| Catalyst | The later condensation step needs a silanol condensation catalyst (typically an organotin compound in a separate masterbatch, kept apart from the silane before use) |
| By-product | Hydrolysis releases methanol – ventilate extruder feed and curing areas accordingly |
| Storage | Ambient, dry, away from acids, bases and oxidisers; keep containers closed because atmospheric moisture is enough to start hydrolysis |
| Identity check | Refractive index 1.3930 and specific gravity 0.970 are fast incoming checks before running a full assay |
Packaging, Storage and Documentation
Supplied in 200 kg steel or HDPE drums with dry, sealed closures; 1000 kg IBC available on request. Store under dry conditions, away from direct sunlight and heat, and use within the shelf life stated on the COA – silane drums that have been opened repeatedly show rising viscosity from partial hydrolysis. Each batch ships with a COA covering appearance, colour, assay, specific gravity and refractive index; SDS is available in English. Transport classification and packaging for export are confirmed per shipment.
Related reading
- Vinyltrimethoxysilane (VTMS): properties, production and applications
- VTMS in silane-crosslinked PE for wire and cable
- Choosing a silane coupling agent: vinyl vs amino vs epoxy vs methacryloxy
FAQ
What is the CAS number of vinyltrimethoxysilane? CAS 2768-02-7.
Why does the product have a colour specification? Colour (Pt/Co) max 30 is a practical indicator of purity and of hydrolysis or oxidation during storage; darker lots graft less efficiently.
Can it be used in one-step and two-step crosslinking? Yes – it is the standard monomer for both the two-step Sioplas process (graft masterbatch plus catalyst masterbatch) and the one-step Monosil process.
How should it be stored? Sealed, dry, ambient. Atmospheric moisture hydrolyses the methoxy groups, so partial drums should be used first and re-sealed immediately.
Contact PolyBlueChem for specifications, samples and quotations.
