  Using Brownian dynamics, we simulate the fracture of polymer interfaces
reinforced by diblock connector chains. We find that for short chains the
interface fracture toughness depends linearly on the degree of polymerization
$N$ of the connector chains, while for longer chains the dependence becomes
$N^{3/2}$. Based on the geometry of initial chain configuration, we propose a
scaling argument that accounts for both short and long chain limits and
crossover between them.
