Roos, A. and Creton, C. (2005) "Effect of the presence of Diblock Copolymer on the Non Linear Elastic and Viscoelastic Properties of Elastomeric Triblock Copolymers"
The mechanical properties of blends of triblock and diblock copolymers of polystyrene(PS)
and polyisoprene(PI) containing 15wt% PS have been investigated with tensile
tests, relaxation tests, dynamic mechanical tests and hysteresis tests. The
properties of binary triblock/diblock blends have been investigated in parallel
with those of the same blends diluted with 60 wt% of a low molecular weight
but high Tg solvent, miscible with the PI component but not with the PS domains.
Both binary and ternary blends show a nonlinear elastic behavior at large strains,
which can be analyzed with rubber elasticity models, and a pronounced nonlinear
viscoelastic behavior at intermediate strains. The analysis of the viscoelastic
behavior beyond the linear regime shows that the proportion of PI blocks effectively
bridging two PS domains, controls the deformation of the blends at large strains,
while the small and intermediate strain behavior is controlled by the density
of entanglements in the rubbery component and by the relaxation of the PI block
of the PS-PI diblock. Both of these nonlinear features depend on the diblock/triblock
ratio in the blend and will have direct consequences on more complex properties
such as fracture or adhesive debonding.