Hybrid Sealants have started gaining more and more presence in the market nowadays as it can be formulated to provide best properties of two or more polymeric families being used and to limit their own inherent weaknesses.
Silyl modified polyethers or MS Polymers are the ones which have been gaining more attention in the hybrid sealant and adhesive family. In addition to their high performance properties, these sealants are achieving popularity due to their solvent-free and isocyanate-free nature and due to their formulation versatility that allows the customization of viscosity and early strength development for various applications.These MS polymers can withstand the most stringent requirements for high performance bonding and elasticity under severe aging and UV weathering conditions without weathering or yellowing when subjected to extended UV light exposure. After 24 hours, MS Polymers can be painted with any industrial paint or lacquer system.
The structure of an MS polymer consists of a polyether backbone and silane terminal functionality. MS polymer is prepared from high molecular weight polypropylene oxide. It is end-capped with allyl groups, followed by hdrosilylation to produce a polyether end-capped with methyldimethoxysilane groups.
MS polymers offer a low viscosity in the range of 8,000-12,000 cps despite their high molecular weight. The viscosity is relatively stable throughout a wide range of temperatures. As a result, compounding is generally easy and simple. The table below compares the performance of silicone rubber, polyurethane, and MS sealants. Compared with the other two types of sealants, MS sealants have well balanced properties and performance. Some of the unique properties of MS sealants are:
- Environmental friendliness (solvent-free and isocyanate-free)
- Low temperature gunnability: The viscosity of MS sealants is less dependent on temperature changes
- Storage stability: Shelf life is excellent although sealant must be protected from moisture
- Weather resistance and durability: MS sealant shows no cracking, splitting, discoloration or adhesion failure after seven years of testing in desert climate
- Stain resistance: MS sealants do not stain as some silicone sealants do because of low molecular weight siliconmaterials that bleed from the surface of sealed joints
- Paintability: MS sealants provide good paint ability unlike silicone sealants
- Adhesion: MS sealants provide adhesion to various substrates including metals, plastics, wood and ceramics.