What is MS sealant? How does it differ from silicone sealant? Here are the answers!

People often ask: What is MS sealant? How exactly does it differ from silicone sealant?
1. Chemical Structure and Preparation of MS Sealant
In fact, "MS" stands for "modified silicone" (specifically, silane-modified polyether). It is a type of prepolymer featuring a polyether backbone and hydrolyzable siloxane end-groups; its molecular structure is shown in the figure below.

To prepare the aforementioned prepolymer, the critical step is first to synthesize a high-molecular-weight diallyl polyether polyol. Subsequently, a silane-modified polyether (MS) resin is produced through a hydrosilylation reaction between methyldimethoxysilane (MDMS) and the high-molecular-weight diallyl polyether polyol in the presence of a catalyst, as illustrated in the figure below:

2. Curing Mechanism of MS Sealant
The curing mechanism of one-component MS sealant is moisture-curing, similar to that of one-component silicone sealant. At room temperature, driven by the combined action of moisture and a catalyst, the siloxane groups at the ends of the polymer chains first undergo hydrolysis to form silanol groups (Si-OH). Subsequently, condensation reactions occur—either between two Si-OH groups or between an Si-OH group and an Si-OR group—releasing water or alcohol and forming Si-O-Si linkages; this results in molecular cross-linking that creates an elastomer with a three-dimensional network structure.

3. Characteristics of MS Sealants
Based on its molecular structure, the polymer backbone of MS sealant differs significantly from that of silicone sealant; it represents a new generation of construction sealants developed after polysulfide, silicone, and polyurethane sealants.
Polysulfide sealants are gradually falling out of industrial use due to slow low-temperature curing, a tendency to age and harden, poor durability, and a strong, pungent odor.

Polyurethane sealants (primarily used in industrial applications) are characterized by high strength, tear resistance, flexibility, abrasion resistance, puncture resistance, and resistance to oil and chemical corrosion. However, conventional polyurethane sealants often contain free isocyanates, which emit irritating odors during application and pose health risks; furthermore, the release of carbon dioxide during curing can lead to bubble formation, compromising both the sealant's appearance and its mechanical properties.

Silicone sealants (which comprise the majority of glazing and curtain wall sealants on the market) offer rapid curing, bubble-free performance, strong adhesion to non-porous surfaces, excellent resistance to heat, humidity, and aging, and good storage stability. However, they suffer from low tear strength and poor puncture resistance; additionally, the sealant layer is prone to oily exudation that can stain concrete, stone, and other decorative materials, resulting in poor aesthetics and an inability to be painted over.
MS sealant combines most of the advantages of silicone and polyurethane sealants, offering outstanding overall performance:
1) Broad substrate adhesion: Due to the low surface energy and high permeability of silyl-terminated polyethers, the material exhibits excellent wetting capabilities on most inorganic, metal, and plastic substrates, resulting in strong adhesion.

2) Environmental friendliness: Silane-modified polyethers feature a long-chain structure with silyloxy-terminated polyether groups; unlike polyurethane sealants, they do not contain toxic isocyanate groups or free isocyanates. With low viscosity and excellent workability, they do not require organic solvents to adjust processing characteristics, resulting in very low Volatile Organic Compound (VOC) content.

3) Paintability: Standard silicone sealants cannot be painted or colored after application—colors must be custom-formulated beforehand—whereas silane-modified polyether sealants can be painted, offering superior paintability.

4) Superior stain resistance compared to silicone: They do not exude oily molecules that stain building surfaces or joints, thereby maintaining the building's aesthetic appeal over the long term. In contrast, silicone sealants can exude small molecules that combine with rainwater and dust to form stubborn stains on the building's exterior.

5) Superior weather resistance compared to polyurethane: The material's three-dimensional cross-linked network structure is composed of Si-O-Si chemical bonds and flexible polyether segments. The Si-O-Si bonds provide excellent aging and weather resistance, while the flexible polyether segments impart good flexibility and high elongation.