The benefits of activates silanes are:
- High speed reactivity
- Improvements in adhesion
- Higher mechanical bond strength (flexural, tensile, and impact)
- Moisture activation not required prior to deposition
Applications include:
- Primers for fiber-optic cladding
- Coupling agent for light-cure acrylic nanocomposites
- Adhesion promoter for high-speed UV cure systems, particularly acrylated urethanes
Compared to conventional silanes, SIVATETM silanes:
- Radcure: UV, EB, visible light
- React at high speed (seconds compared to hours)
- Do not require moisture or hydrolysis to initiate surface reactivity
- React with a greater variety of substrates
- Inhibit moisture initiated crack propagation on vitreous surfaces
SIVATE™ A200 (SIA0200.A1) can be used in adhesion promotion applications between inorganic materials, particularly vitreous substrates with radical-cure resins when applied on a 100% actives basis as a primer or incorporated at a 0.5-2.0% level with low water content UV curable resins. Photoinitiators should be “hydroxyl-free.” The silane or blended silane-resin combination must be stored in sealed containers under dry conditions until use. Within seconds of application initial bonding is formed with surface in an “A-stage.” After exposure to moisture, the bond strengthens over several hours, depending on conditions, to achieve ultimate “B-stage” bond strength (moisture cure stage).
Activation of silanes is effected by combining a cyclic azasilane with an acrylate-functional silane. The cyclic azasilane reacts with a wider variety of hydroxyl groups with reaction speeds more than 100 times faster than the base silane, providing instant adhesion. Once reacted with the substrate, the cyclic azasilane forms a secondary amine that catalyzes the moisture-initiated condensation reactions of the balance of the silane components, establishing maximum bond strength.
Adhesion and bonding proceeds with a wider variety of substrates. In contrast to conventional silanes, SIVATE™ activated silanes react with newly formed glass surfaces, reducing crack propagation associated with moisture adsorption.
- Density: 1.03 g/mL
- pH value (1:1 in water): ~10
- Viscosity: 2-3 cSt
- Flashpoint: > 65 °C (> 150 °F)
A200 Activating Silane
A200 Base Silane
The reaction of activated silanes is driven by the thermodynamically favored formation of a silicon-oxygen bond, and is > 85% complete in less than 15 seconds, reacting with more than three times as many hydroxyl groups as the conventional ethoxysilane achieves in 1 hour. Once the ring is opened, the secondary amine promotes the condensation of silanols formed from the base silane component with the substrate, more than doubling the kinetics of reactivity for hydrolytic deposition.
A200 Mechanism
DRIFT spectra monitoring the disappearance of the terminal hydroxyl peak over exposure time as the terminal hydroxyls react with a cyclic azasilane
A200 reaction kinetics of the activated silane with an acrylate polymer
Reaction kinetics of the activated silane with an acrylate polymer.
* Conventional silane moisture-induced hydrolysis.
**Room temperature with relative humidity of 55-80%.
| Time (h) | Conventional silane *(ambient**) | Activated silane (ambient**) | Activated silane (50 °C) |
|---|---|---|---|
| 1 | 0 | 14 | 24 |
| 2 | 0 | 14 | 41 |
| 4 | 0.5 | 26 | 69 |
| 24 | 2.5 | 97 | 100 |
| 96 | 11 | 100 | 100 |