Method of inverse gas chromatography (IGC) has been used for the physicochemical characterization of polymers for more than two decades . In this method the polymeric stationary phase could be characterized by using probe molecules . The retention volume of probe is a measure of the polymer-probe interaction and show changes in the polymer structure at melting point or glass transition temperature . Crystallinity of high-density polyethylenes (HOPE) of Poliran and Irapol from Iranian petrochemical companies was studied . The effects of the flow rates and the sample size on peak retention volume were investigated . Modified techniques for measurement of flow rate and coating were used . Retention diagram and degree of crystallinity were determined for a sample of low-density polyethylene and the results were compared with those obtained for HDPE . Experimental data of crystallinity and melting points showed that the Iranian HDPE is a polymer with suitable engineering properties
