Silane-modified organic polymers have been around for more than 40 years, and have proliferated in the coatings, adhesives, sealants and elastomers (CASE) industry over the past 20 years. When used in adhesives, sealants, or coatings applications, silyl-terminated polyurethanes (STPUs) and silyl-terminated polyethers (STPEs) offer a number of advantages over other common reactive polymers, such as polyurethanes and silicones. Silylated polymer formulations are free of unreacted isocyanates, are generally solvent- and odor-free, do not generate carbon dioxide or exhibit the subsequent foaming during cure, can be made compatible with super-applied water-based coatings, and do not stain porous substrates.
However, silylated polyethers and polyurethanes present unique formulating challenges. A typical silane-functional organic polymer features relatively high molecular weight polyether segments terminating in di- or trifunctional alkoxy caps. This polymer morphology places much of the stress experienced by the cured matrix on the highly crosslinked polymer termini, as opposed to the polyether backbone. Further contributing to this crosslink density are the supplementary silanes found in most sealant and adhesive formulations.