Silane-Terminated Polymers for Flexible and Elastic Sealants and Adhesives

GENIOSIL® XM 20 – an alpha-silane-terminated polyether that allows the formulation of plasticizer-free adhesives with extremely high elasticity

The new grades can be used as binders in adhesives and sealants, where they can modify the mechanical properties, in particular impacting modulus. This allows adhesives and sealants manufacturers to compound without the need of conventional plasticizers. In plasticizer-free adhesives, the new grades additionally enhance the bonding properties. In low-modulus sealants, they ensure high elastic recovery. As a result, GENIOSIL® XM opens up applications in the adhesives and sealants sector that had previously been unaccessible to silane-crosslinking polymers.

The new grades complement the portfolio of silane-terminated polyethers that the Munich-based chemical group markets under its GENIOSIL® brand. As all silane-terminated polymers, GENIOSIL® XM cures at room temperature under the influence of atmospheric humidity via silane crosslinking. In contrast to the other polymers, GENIOSIL® XM 20 and GENIOSIL® XM 25 only have one silane group at one of their chain ends, meaning they are crosslinkable only at that end.

GENIOSIL® XM can be blended with other silane-terminated polymers in the desired ratio. On curing, the new polymers are firmly integrated into the resulting three-dimensional polymer network, reducing the crosslink density. This leads to a relatively wide-meshed network.

GENIOSIL® XM thereby modifies the elasticity of the cured material, resulting in a low modulus system with high elastic recovery. When stretched or compressed, it behaves like a soft spring. In formulations of silane-terminated polymers, the two new grades thus act as reactive plasticizers. Since they do not alter the mechanical strength of the cured material, they can replace conventional plasticizers. This affords manufacturers of sealants and adhesives the freedom to formulate plasticizer-free products.

The two GENIOSIL® XM grades not only adhere to concrete, wood, aluminum and glass, but also to low-energy surfaces such as polyvinyl chloride (PVC), polystyrene (PS) and cured ethylene propylene diene monomer (EPDM) rubber without prior pretreatment of these substrates.

The Adhesive Specialist: GENIOSIL® XM 20

GENIOSIL® XM 20 is an alpha-silane-terminated polyether. This grade opens the door to plasticizer-free adhesives with extremely high elasticity. At the same time, these possess high ultimate strength and also adhere well to difficult substrates. Furthermore, the product can extend skin-over time. This provides the user with sufficient adhesive tooling time. Typical applications include wood-flooring adhesives and all-round adhesive sealants.

The Sealant Specialist: GENIOSIL® XM 25

GENIOSIL® XM 25 allows the formulation of low-modulus sealants with exceptionally high elastic recovery

GENIOSIL® XM 25, a gamma-silane-terminated polyether, allows the formulation of low-modulus sealants with exceptionally high elastic recovery. Should sealant manufacturers use this grade as a co-binder, low-modulus construction sealants that exceed ISO 11600 specifications are possible. Potential applications include sealants for expansion joints in buildings made of industrially prefabricated concrete parts and for connection joints between window frames and walls.

Toolbox for Adhesives and Sealants Manufacturers

WACKER offers various silane-terminated polyethers that have been designed as binders for adhesive and sealant manufacture. They can be blended with each other acting either as the main binder or as a co-binder. This allows formulators to use the product portfolio like a toolbox to adjust the desired final properties of given products. Both gamma- and alpha-silane-terminated polyethers are available.

Within this portfolio, the hybrid polymers of the GENIOSIL® STP-E product line constitute the standard. They cover a wide range of demanding adhesive and sealant applications. GENIOSIL® XB is ideal for the manufacture of powerful and tough adhesives which make strong bonds possible. If, on the other hand, exceptionally strong yet elastic adhesives need to be formulated, polymers of the GENIOSIL® XT range are the binders of choice. GENIOSIL® XM is suitable for low-modulus sealants or flexible, highly elastic adhesive sealants with virtually universal adhesion.