This paper addresses two fundamental issues: (1) the connection between block copolymer polydispersity (as measured by a polydisperisty index (PDI)) and pattern LER/ LWR limits and (2) the connection between block copolymer χN value and pattern LER/LWR limits. In this work, we have used coarse grained molecular dynamics (MD) simulations of BCP DSA to study the effect of block copolymer PDI on DSA properties including LER/LWR and patterning capability. It is observed that as PDI increases from 1 to values of ∼1.3, there is little effect on pattern LER/LWR, and as PDI increases above ∼1.3 the LER/LWR increases slowly with increasing PDI. This suggests that LER/LWR concerns are not a major determinant in terms of specifying block copolymer PDI requirements for DSA processes. Concerning χN and LER/LWR, there is a sharp increase in roughness for χN<30. Because of the sharp increase at such low χN values, it is unlikely that BCP DSA processes for semiconductor manufacturing will be able to operate at low χN values even though microphase separation still occurs at these low χN values.