Continuous process for preparation of highly rigid propylene-ethylene block copolymers

A continuous process for preparation of highly rigid propylene-ethylene block copolymers comprising the steps of:

• (1) continuously feeding propylene, optionally containing up to 5% of ethylene by weight, to a catalyst in a first stage polymerization (FS) to prepare 60 to 95% of a propylene block based on the total weight of the final copolymer, provided that the melt flow rate (MFR) of the propylene block is controlled to give the relationship:
• 0.1.ltoreq.Log (MFR(maximum)/MFR(minimum)) .ltoreq.1, wherein the catalyst comprises:
• (A) a solid catalyst comprising titanium, magnesium, a halogen and a polyvalent carboxylic acid ester,
• (B) an organic aluminum compound, and
• (C) an organic silicon component of the formula R.sup.4.sub.x R.sup.5.sub.y Si(OR.sup.6).sub.z, wherein R.sup.4 and R.sup.6 are hydrocarbon groups, R.sup.5 is a hydrocarbon group, or a hydrocarbon group containing one or more heteroatom selected from the group consisting of oxygen, nitrogen, phosphorus, or silicon and x+y+z=4, 0.ltoreq.x.ltoreq.2, 1.ltoreq.y.ltoreq.3 and 1.ltoreq.z.ltoreq.3;
• (2) continuously feeding (i) a glycol compound in an amount of from 1 to 100 of the glycol compound/Ti (mole/atom) based on the titanium in the solid catalyst (A) and (ii) ethylene, containing 1-10% propylene by weight, to the first stage polymerization of step (1) to prepare 5 to 40% of an ethylene block based on the total weight of the final copolymer in a second stage polymerization (SS), wherein the glycol compound has the formula R.sup.1 --(O--CH.sub.2 --C(R.sup.3)H--).sub.n --OR.sup.2, wherein n is 3.ltoreq.n.ltoreq.100, R.sup.1 and R.sup.2 are hydrogen atoms, or a monovalent organic group of 1 to 20 carbon atoms, or a monovalent organic group of 1 to 20 carbon atoms containing one or more heteroatom of oxygen, nitrogen, phosphorus, sulfur, or silicon, wherein R.sup.1 and R.sup.2 may be identical or different and R.sup.3 is a hydrogen atom or a monovalent organic group having from 1 to 5 carbon atoms.