Based on WACKER’s Alpha³ technology, these novel polymers can be formulated into tin-free sealants and adhesives that are highly elastic and achieve a low modulus of elasticity. Such properties are desirable in the construction sector and, reportedly, a first in the adhesives and sealants world. Tin-free assembly adhesives are yet another area of application that can benefit from these products. With these polymers, property profiles are now possible that comparable binders fail to provide.

Like a conventional alpha-silane-terminated polymer, the combination of the two silane-terminated polyethers does not require a tin catalyst for curing. During crosslinking, the highly reactive alpha end literally pulls in the gamma end into the swifter curing process, which generally displays slower reactivity. After crosslinking, GENIOSIL^® STP-E 140 and GENIOSIL^® STP-E 340 are highly elastic. Application tests show that the silane-terminated polyethers adhere to a wide range of varying substrates.

Both binders can be processed into creep-resistant, fast-curing adhesives. They also facilitate the production of low-modulus sealants. These are flexible and, even without the application of much force, retain elasticity. Moreover, they also exhibit good elastic recovery, i.e. they return to their original length after exposure to prolonged elongation – a combination of properties that is unusual for conventional alpha-silanes.

The two binders differ in terms of viscosity. At 10,000 millipascal seconds, GENIOSIL STP-E 140 is more fluid-like than GENIOSIL STP-E 340, which has a viscosity of 30,000 millipascal seconds. This makes it easier to tailor the finished product to meet the requirements of the relevant application.

Adhesive and sealant formulators can process GENIOSIL STP E 140 and GENIOSIL STP-E 340 in a similar fashion as conventional silane-terminated polyethers. Even formulations without solvents and plasticizers are possible. Incompatibilities with ester-based additives are eliminated, as the polymers crosslink without a tin catalyst. This increases the scope for novel formulation developments and improves the storage stability of the formulated finished product.

Both binders can be blended with all GENIOSIL silane-terminated polyethers. It is thus possible to tailor the crosslinking rate, skin-over time, and the mechanical and elastic properties of the finished products to precisely meet the requirements of the end user. The new silane-terminated polyethers therefore can now address a diverse range of tin-free formulated adhesives and sealants.

Adhesives and sealants based on GENIOSIL STP-E 140 and GENIOSIL STP-E 340 can be processed and applied without any need to change existing mixing or processing methods. Particularly the craftsman will benefit from the characteristic ease in handling such hybrid products.

Learn more about these binders, which will be showcased at the European Coatings Show, at www.wacker.com.