Pressure-sensitive adhesives represent one of the most important commercial applications of block copolymers. The large-strain tensile properties of these soft adhesive materials play a dominant role in determining their adhesive properties. In many cases changes in the polymer architecture significantly affect the large-strain properties and the resultant adhesive performance, with little or no effect on the linear viscoelastic properties. In this Perspective we provide several examples, using model systems based on diblock, triblock, tetrablock, and star-block copolymers of polystyrene and polyisoprene.

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Chewing gum provides an excellent everyday example of viscoelastic behavior, and understanding its rheological properties is important for application purposes. Here, we compare the rheological behavior of selected commercial chewing gums and bubble gums. Small amplitude oscillatory shear, shear creep, and steady shear demonstrated that both chewing and bubble gums behave like power-law critical gels in the linear regime. Nonlinear viscoelastic behavior was investigated using large amplitude oscillatory shear, shear creep, and start-up flows (in shear and uniaxial extension). Bubble gums showed more pronounced strain hardening and greater stresses to break in start-up of steady uniaxial extension than chewing gums. We argue that this combination of rheological signatures is sufficient to provide a new robust definition of chewing gum that is independent of specific molecular composition. There are potentially many different formulations and design routes that can achieve this distinctive rheological fingerprint.