ABSTRACT
Over the past 2 to 3 decades, sealants have continued to grow in sophistication as customers’ needs have become ever more demanding. The development of new hybrid polymers has spawned a range of new sealant types as varied as their applications. In simplistic terms, hybrids combine the backbone (polymer) of one sealant family with the reactive groups (functionality) of another sealant type. Thus, hybrid sealants are not based on a blend of two polymers (although sometimes the term hybrid is also incorrectly used for such compositions), but rather on polymers with new molecular structures that combine features of the two parent polymer families. In biology, a hybrid is dened as an organism produced by crossing (interbreeding) two phenotypically dissimilar parents, usually with the intent of achieving particular traits of interest. Hybrid sealant technology achieves a marriage of two or more sealant types, with the resulting hybrid offspring receiving key properties from each of its parents, in much the same way as dominant parental phenotypes show up in a biological offspring. For instance, one parent (owing to its polymer type) may contribute to a hybrid’s paintability, whereas the other parent (due to its functionality) may contribute to a hybrid’s environmental friendliness. Figure 10.1 illustrates this merging of properties using the example of silane-modied polyurethane sealants. However, as in real life, the hybrid offspring inherits not just the positive traits of its parents but also some of the negative ones, which implies that for silane-modied polyurethane sealants much research and development efforts were required to overcome the typical polyurethane attribute of poor extrusion behavior at low temperature.
