Polymers designed to form layered structures
(e.g. alternating glassy and rubbery layers in the
block copolymers studied) may undergo homogeneous
plastic deformation even without forming
any localized zones. This behavior endows ductility
to polymers otherwise brittle in the bulk state
(e.g. polystyrene). The mechanism of homogeneous
plastic deformation of PS lamellae (thin PS layers)
together with adjacent PB lamellae can be described
by a new deformation mechanism, called thin layer
yielding [10], schematically represented in Fig. 20.
This effect appears if the thickness of PS layers lies
below a critical value Dcrit. The critical thickness is
comparable to the maximum craze fibril thickness in
polystyrene homopolymer, i.e. in the range of 20 nm.
The difference between the craze fibril yielding in PS
and the yielding of the PS lamellae lies in the fact that
the craze fibrils stretch between microvoids, while