Polymer/polymer interfaces reinforced with block copolymers or grafted
chains can fail by the pull-out of these chains. A number of constitu
tive models have been proposed in the literature to describe the pull-
out of a single chain. In this paper, we use these models to construct
a continuum theory of a weak interface, and we study the stability of
such an interface subjected to a homogeneous deformation. We show tht
if the perturbation contains a Fourier component with wavelength exce
eding wa critical value Lambda(c), then the homogeneous deformation is
unstable. The dependence of Lambda(c), on the geometry, the stiffness
of the material outside the interface, and the pull-out models is der
ived. We also study the stress field near the tip of a preexisting int
erface crack using the different pull-out models.