Polybutene-1 (PB-1) and its random copolymers are important high-end polyolefin materials widely used in the field of hot water piping,films and so on.PB-1 is typical polymorphic material showing three different crystalline modifications.Among them,only metastable form Ⅱ (with 11/3 helix) and stable form Ⅰ (with 3/1 helix) are of practical importance.PB-1 crystallizes normally into form Ⅱ when being cooled down from the molten state which then transforms into stable form Ⅰ spontaneously accompanied by a shrinkage of the crystalline unit cell.