The present invention provides a propylene / 1-
butene random
copolymer (PBR) having excellent flexibility,
impact resistance,
heat resistance and low-temperature heat-seal properties, a
polypropylene composition containg the
copolymer, a sheet, film or stretched film comprising the composition and a
composite film having a layer of the composition. The propylene / 1-
butene random
copolymer contains 60 to 90 mol % of propylene units and 10 to 40 mol % of 1-
butene units and has a triad isotacticity of not less than 85% and not more than 97.5%, a molecular
weight distribution (Mw / Mn) of from 1 to 3, an
intrinsic viscosity of from 0.1 to 12 dl / g, a
melting point (Tm) of from 40 to 120° C., and satisfies the following relation 146 exp(−0.022M)≧Tm≧125 exp(−0.032M) wherein Tm represents a
melting point and M (mol %) represents a content of 1-butene constituent units. The invention, further, provides a
transition metal compound useful as an
olefin polymerization catalyst and an
olefin polymerization catalyst containing the
transition metal compound. The
transition metal compound is represented by the following formula (2a): wherein each of R1 and R3 is
hydrogen, R2 and R4 are selected from a
hydrocarbon group and
silicon-containing group, R5 to R13 are selected from
hydrogen, a
hydrocarbon group and
silicon-containing group, and adjacent
substituent groups R5 to R12 may be linked to form a ring. R14 is an
aryl group, and R13 and R14 may be linked to form a ring. M is a Group 4 transition
metal, Y is a
carbon atom, Q is
halogen, etc, and j is an integer of 1 to 4.