Is there any relation between MWD and ESCR(chemical resistance)?

Are your ESCR measurements made at constant Strain (deformation) or at constant Stress (force)? In general, a lower MWD polymer will have slightly higher crytallinity (unless a low MW fraction acts as a crystallization promoter), and the higher crystallinity leads to better resistance to solvents. But, higher crystallinity usually means higher modulus, and ESCR measurements made at constant strain may lead one to conclude that the polymer with higher crytallinity (and higher modulus) has the lower ESCR.

Ernie

ESCR of PE is very complicated. In general density is the most important parameter. For polymers made with the same catalyst system the lower density polymer will generally have the better ESCR. High MW molecules are good for ESCR because they can act as tie chains to hold the lamella together. Lots of low MW material is bad as it weakens the structure. There is a classic paper by Howard. published in 1959 ( cant recall the journal but I have a copy at work) that talks about the effect of molecular structure. He does an interesting experiment where he removes the low MW fraction of a polymer by solvent extraction and improves ESCR from a few hours to a couple of months. Where the short chain branches are is also very critical. For best ESCR you want the branches to be in the high MW fraction. Some catalyst technologies can selectively put the short chain branches in the high MW end, others have no such control. hope this helps terry