Silicone vs MS Polymer Sealants

When engineers require a highly elastic, UV-resistant sealant that bonds without primers, the choice almost always narrows down to Silicone or Modified Silane (MS) Polymer.

Because MS Polymers were chemically engineered to mimic the best properties of silicones (specifically their UV resistance and primerless adhesion) without carrying over their notorious drawbacks (lack of paintability and contamination risk), they are often viewed as direct competitors.

This guide compares these two advanced chemistries to help you specify the right sealant for your manufacturing environment.

Chemical Overview

Silicone (Polysiloxane)

Built on a purely inorganic silicon-oxygen (Si-O) backbone.

• Strengths: The highest temperature resistance of any elastomer, absolute immunity to UV degradation, and excellent electrical insulation.
• Weaknesses: Cannot be painted, tears relatively easily, and poses a massive contamination risk in environments where paints or coatings are applied.

MS Polymer (Silane Modified Polymer)

Built on an organic polyether backbone, but terminated with reactive silane groups (similar to silicone).

• Strengths: Highly paintable (even wet-on-wet), excellent UV resistance, isocyanate-free, and poses zero contamination risk to paint lines.
• Weaknesses: Cannot match silicone’s extreme high-temperature resistance; continuous submersion performance can be inferior to specialized silicones.

Decision Matrix: Silicone vs MS Polymer

Key Engineering Considerations

1. The Paintability Problem

The single largest differentiating factor between these technologies is how they interact with coatings.

• Silicone surface tension is extremely low. If you attempt to paint over a silicone sealant, the paint will immediately bead up and separate (a defect known as “fish-eyeing”). If color matching is required, the silicone must be custom-pigmented at the factory.
• MS Polymers are highly paintable. They can be painted over with water-based and solvent-based automotive paints, often immediately after application (“wet-on-wet”). This is why MS Polymers dominate the commercial vehicle, bus, and rail industries where exterior seams must be painted to match the bodywork.

2. The Contamination Risk

Uncured silicone oils have a tendency to migrate. If silicone is used anywhere in a facility, microscopic amounts can travel through the HVAC system, via operator hands, or on tooling. If these traces land on a metal panel headed for a paint booth, they will cause catastrophic coating failures. For this reason, many automotive OEMs and aerospace facilities run strict “silicone-free” manufacturing lines. In these environments, MS Polymer is the only viable alternative for UV-stable elastic sealing.

3. Extreme Temperature Environments

If the application involves extreme heat, MS Polymers drop out of the race. The organic polyether backbone of an MS Polymer will begin to degrade under continuous exposure above 100°C. Silicone remains highly elastomeric at 200°C, making it the standard for Form-In-Place Gaskets (FIPG) in automotive engines, aerospace heat shields, and electronics potting in high-heat modules.

4. Mechanical Tear Strength

While both are highly flexible, MS Polymers generally possess higher tear resistance than standard silicones. If a silicone bead sustains a small cut from debris or mechanical impact, that tear can propagate easily under cyclic stress. MS Polymers are tougher and resist tear propagation more effectively, making them better suited for areas subject to physical impact or abrasion.

Conclusion

Choose Silicone when:

• The continuous operating temperature exceeds 100°C.
• You are potting high-voltage electronics and require perfect dielectric stability.
• The application is strictly unpainted and will never require future coating.

Choose MS Polymer when:

• The sealant must be painted.
• The manufacturing facility operates a paint line and cannot risk silicone contamination.
• You require a tougher, more tear-resistant bond for dynamic exterior environments (like commercial vehicle roof seams).

For assistance in auditing your current sealing process or validating an MS Polymer alternative to your current silicone system, contact the ParaGlu engineering team.

Industry Standards & References

• ASTM C920: Standard Specification for Elastomeric Joint Sealants.
• IEC 61215: Terrestrial photovoltaic (PV) modules - Design qualification and type approval.