Propylene homopolymer having high melt strength and preparation method thereof

A process for preparing propylene homopolymer with high melt strength, comprising carrying out a propylene homopolymerization reaction of two stages in two tubular loop reactors connected in series, wherein

• the first stage comprises carrying out the propylene homopolymerization reaction in the presence of Ziegler-Natta catalyst, under a polymerization temperature of 50-100° C. with a hydrogen content less than or equal to 300 ppmV, and controlling the MFR of the polymer obtained within a range of 0.01-0.3 g/10 min, and said Ziegler-Natta catalyst being composed of the following components:
• (1) a solid catalyst component with magnesium, titanium, halogen and internal electron donor as the main components;
• (2) an organic aluminum component;
• and (3) dicyclopentyl dimethoxy silane, wherein the weight ratio of component (1) to component (2), based on the ratio of titanium to aluminum, is 1:10-500, and the weight ratio of component (2) to component (3) is 10-150:1;
• and
• the second stage comprises adding, based on the resulting material from the first stage, tetraethoxy silane in the presence of hydrogen to further carry out the propylene homopolymerization, and the amount of tetraethoxy silane is determined according to the amount of the organic aluminum component added in the first stage, so that the weight ratio of the tetraethoxy silane to the organic aluminum is 1:1-0;
• and
• controlling the MFR of the polymer finally obtained within a range of 0.2-10 g/10 min.

A propylene homopolymer with high melt strength, comprising the following features:

• (1) the MFR is 0.2-10 g/10 min at 230° C. with a load of 2.16 kg;
• (2) the molecular weight distribution Mw/Mn is 6-20;
• (3) the content of the fraction with a molecular weight higher than 5,000,000 is higher than or equal to 0.8 wt %;
• and
• (4) Mz+1/Mn is higher than or equal to 70.

A propylene homopolymer with high melt strength, comprising the following features:

• (1) MFR is 1.6-6 g/10 min at 230 t with a load of 2.16 kg;
• (2) the molecular weight distribution Mw/Mn is 6-20;
• (3) the content of the fraction with a molecular weight higher than 5,000,000 is higher than or equal to 1.0 wt %;
• (4) the Mz+1/Mn is higher than or equal to 80;
• (5) the content of the fraction with a molecular weight less than 50,000 is higher than or equal to 17.5 wt % and less than or equal to 30 wt %;
• (6) the polymer dispersity index PI is 9.0-16.0.