PROPYLENE ELASTOMER

The novel propylene elastomer according to the invention contains (1) units derived from propylene in amounts of 50 to 95 % by mol and units derived from 1-butene in amounts of 5 to 50 % by mol, and has (2) triad tacticity (mm fraction), determined by the 13C-NMR spectrum (hexachlorobutadiene solution, based on tetramethylsilane), of not less than 90 %, (3) an intrinsic viscosity (in decalin at 135 .degree.C) of 0.1 to 12 dl/g, (4) a molecular weight distribution (Mw/Mn) of not more than 3 and (5) a randomness parameter B value of 1.0 to 1.5, preferably 1.0 to 1.3. In addition, the elastomer desirably has properties that (6) the elastomer has a melting point Tm of 60 to 140 .degree.C, and the melting point Tm and a 1-butene constituent unit content M (% by mol) in the elastomer satisfy the relation -2.6M + 130 .ltoreq. Tm .ltoreq. -2.3M + 155, and (7) a crystallinity C of the elastomer measured by X-ray diffractometry and the 1-butene constituent unit content M (a by mol) satisfy the relation C .gtoreq. -1.5M + 75. Such propylene elastomer is excellent in rigidity, heat resistance, scratch resistance, transparency, heat sealing properties and blocking resistance. The propylene elastomer can be prepared using a specific transition metal compound catalyst.