Rubber-toughened cycloolefin copolymers

The influence of polystyrene-block-poly(ethene-co-but-1-ene)-block-polystyrene (SEBS) on the mechanical properties of metallocene-based cycloolefin copolymers (COC) was studied. COC is an amorphous polymer with very high stiffness and yield stress, but poor impact strength. With increasing SEBS volume fraction the notched impact strength is increasing. Low-molecular-weight SEBS (M-w = 90000 g mol(-1)) is more effective as impact modifier than high-molecular-weight SEBS (M-w = 272000 g mol(-1)). This is due to smaller particle size obtained when dispersing low-molecular-weight SEBS. With reduced particle size the amount of particles and, consequently, the probability of initiation of micromechanical processes, such as crazes, is increasing. The stiffness and yield stress of COC are decreasing with increasing SEBS volume fraction, due to low stiffness and tensile strength of SEBS. Addition of ultrahigh-molecular-weight polyethene (UHMWPE) does not improve the stiffness/toughness balance.