Microtacticity distribution of polypropylenes prepared with heterogeneous Ziegler-Natta catalysts

Abstract

Polypropylenes produced with various heterogeneous titanium-based Ziegler-Natta catalysts were fractionated by solvent extraction technique. The infrared analysis of the fractions indicates the presence of a crystalline syndiotactic sequence, soluble in xylene at 20"C, and boiling hexane soluble fractions of all samples examined. Highly syndiotactic polypropylene (proportion of rrrr pentad is 0,50), comparable in syndiotacticity to the syndiotactic polymer prepared at -78 "C with a homogeneous vanadium catalyst, was separated from the xylenesoluble fraction of the polymer prepared with the system TiC13-AI(C,H,),C1 by means of elution column fractionation. The steric irregularities are mainly rrrm and rrmr (ratio = I : I),suggesting that the propagation is controlled mainly by end-groups. Chemical inversions, i. e., head-to-head or tail-to-tail linkages of propylene units, are practically absent, though they are seen in syndiotactic polypropylenes prepared with vanadium catalysts.

Microstructural heterogeneities of the cyclopolymer of 1,5-hexadiene obtained by stopped-flow and conventional methods: correlation to plural active sites for polypropene on MgCl2-supported Ziegler catalyst

“…TREF analysis of polypropene prepared with MgCl 2 -supported catalysts has been already reported by many research groups [1][2][3][4][5][6]33) . Kakugo et al pointed out that there exists a bimodal tacticity distribution between 93% and 98% in the pentad level in fractions eluted above 100 8C for the polymer with a catalyst system involving an electron donor, suggesting that at least two types of active species are present in the system 1) .…”

“…Kakugo et al pointed out that there exists a bimodal tacticity distribution between 93% and 98% in the pentad level in fractions eluted above 100 8C for the polymer with a catalyst system involving an electron donor, suggesting that at least two types of active species are present in the system 1) . Furthermore, Kioka et al demonstrated that polypropenes have a broad and continuous distribution of tacticity and the addition of an electron donor drastically reduces the amount of atactic and low isotactic polypropene, resulting in a very sharp tacticity distribution 6) .…”

“…Recently, many reports have been published on the temperature rising elution fractionation (TREF) analysis of various polyolefins, such as polypropene [1][2][3][4][5][6] , polyethene 7) , poly(1-octene) 8) , propene-butene copolymer 9) , ethene-1-hexene copolymer 10) , impact polypropene copolymer 11) , impact-resistant polypropene alloy 12) , etheneFull Paper: Microstructural heterogeneities of cyclopolymers of 1,5-hexadiene and polypropenes obtained by stopped-flow and conventional slurry polymerization methods were investigated by means of temperature rising elution fractionation (TREF) analysis. Both the cyclopolymer and polypropene obtained by the stopped-flow method showed two main peaks in the TREF profiles.…”

Temperature Rising Elution Fractionation of Polypropylenes Produced by Heterogeneous Ziegler-Natta Catalysts Containing Different Internal Donors

“…The existence of more than one isospecific active site agrees with the results of Kakugo. 10 Since internal electron donors influence the tacticity distributions of PPs, one may conclude that internal electron donors can convert aspecific active sites into two isospecific active sites and internal electron donors are present in the environment of isospecific active sites. However, the conversion of aspecific active sites into isospecific ones varies with the internal electron donor.…”

Effect of Ester Compounds on Stereospecificity in Methacrylate Polymerization with t-Butyllithium/Bis(2,6-di-t-butylphenoxy)methylaluminum

“…2 , 3 Ester compounds, as weak Lewis bases, have also been used in ionic polymerization systems as the third initiator component. Cationic polymerization of isobutyl vinyl ether (IBVE) with !BVE-acetic acid adduct/EtAICl 2 in the presence of ester additive, such as ethyl acetate and ethyl benzoate, proceeds in a living manner, while in the absence of the Lewis base neither living nor long-lived propagating species are formed under the same conditions.…”