File Name : figures2.tif

Caption : schematic of discrete state model for dynamics of the chain ends. each state (green circle) corresponds to a particular chain end separation ($r_i$), and has a specific time-scale for fracture ($\tau_i$). transition rates between states ($k_i^\pm$) are defined by eq.~\ref{eqn:ki}. for calculations of first passage time to a given end separation (fig.~2b), the fracture state and all $r_i$ below a particular cutoff $r^*$ are removed from the model.