Inherent Viscosity vs Molecular Weight
Inherent Viscosity (IV) is a viscometric method for measuring molecular size. IV is based on the flow time of a polymer solution through a narrow capillary relative to the flow time of the pure solvent through the capillary. The units of IV are typically reported in deciliters per gram (dL/g). IV is simple and inexpensive to obtain and reproducible between different laboratories.
Gel Permeation Chromatography (GPC) is a chromatographic method for measuring molecular size. The molecular size can be expressed as molecular weight (MW) obtained from calibration with a standard polymer such as polystyrene. MWs obtained by GPC are very method-dependent and are much less reproducible between laboratories.
These six plots are empirical correlations between IV and MW measured for six polymer compositions produced by Durect Corporation. The IV data for the 50:50 poly(DL-lactide-co-glycolide) and 65:35 poly(DL-lactide-co-glycolide) were obtained in hexafluoroisopropanol (HFIP). The IV data for the four remaining polymer compositions were obtained in chloroform. All GPC data for these plots were obtained in chloroform using polystyrene calibration standards. It is important to note that these are empirical correlations between IVs and MWs. MWs obtained under conditions different from those use in our laboratory may not match the correlation shown here.