Patent ID: 8017705

Claim:
A process for producing a syndiotactic propylene polymer having a syndiotactic pentad fraction (rrrr fraction), as measured by 13 C-NMR, of at least 85%, a melting point (Tm), as measured by DSC, of from 145° C. to 170° C., and an intrinsic viscosity [η] of 0.1 to 10 dl/g, wherein said process comprises a step (P 1 ) of solution polymerizing, without deposition of polymers, propylene singly or propylene and at least one monomer selected from ethylene and an α-olefin having 4 to 10 carbon atoms at a polymerization temperature (T R ) of from 30° C. to 250° C. in an inert hydrocarbon solvent, which contains at least one hydrocarbon selected from aliphatic hydrocarbons and alicyclic hydrocarbons, in the presence of an olefin polymerization catalyst which comprises; (A) a bridged metallocene compound represented by the following formula (I), and (B) at least one compound selected from (b-1) an organoaluminum oxy compound, (b-2) a compound capable of forming an ion pair by reacting with the metallocene compound (A), and (b-3) an organoaluminum compound in which M is a titanium atom, a zirconium atom or a hafnium atom, Q is selected from a halogen atom, a hydrocarbon group, an anion ligand and a neutral ligand coordinatable with a lone electron pair, j is an integer of 1 to 4, R a and R b may be identically or differently a single nuclear or polynuclear hydrocarbon residue capable of forming a sandwich structure together with M, Y is a carbon atom or a silicon atom, and R c and R d may be the same or different from each other, is selected from hydrogen, a hydrocarbon group and a silicon atom-containing group and further may be bonded to each other to form a ring, wherein the equilibrium melting temperature T M ([K]), which is calculated from the melting point T m ([K]) of the syndiotactic propylene polymer solubility parameter δ 1 ([MPa) 1/2 ]) of the inert solvent, molar volume of the solvent V 1 ([cm 3 /mol]) and the volume fraction v 2 ([−]) of the syndiotactic propylene polymer, and the polymerization temperature T R ([K]) satisfy the following formula (Eq-1) T M −T R ≦45° C. (Eq-1) and said process further comprises, following the polymerization step (P 1 ), a post-treatment step (P 2 ) of optionally heating a polymer solution (S) discharged from the polymerization step to the temperature not lower than the polymerization temperature and not higher than 250° C., and then carrying out flash procedure at a pressure in a flash vessel of from 0.00 to 0.5 MPa·G thereby distilling off the solvent and the monomer.