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

Abstract

ABSTRACT:Ethyl benzoate (EB), bis(2-ethyl hexyl) sebacate (BEHS), di-n-butyl phthalate (DNBP), and bis(2-ethyl hexyl) phthalate (BEHP) were employed as internal electron donors of heterogeneous Ziegler-Natta catalysts and the obtained polypropylene (PP) samples were fractionated by temperature rising elution fractionation (TREF). The influence of different internal donors on the tacticity distributions of PPs was compared. PPs have narrower tacticity distributions with aromatic esters. Based on TREF results, different interactions of internal donor, which may depend on their structures, were proposed. The effects of internal donors on microstructure of the fractions, especially the first fractions, were examined.KEY WORDS Polypropylene / Ziegler-Natta Catalyst / Internal Donor / Fractionation /Characterization / Electron donors are key components of Ti-based heterogeneous catalysts for propylene polymerization and have been the subject of many researches. 1 It is well known that MgClrsupported Ziegler-Natta catalysts underwent two development stages using aromatic monoester and aromatic diester as internal electron donor, respectively. 2 Aromatic diester is found to show better performance than aromatic monoester. The differences between aromatic monoester and diester have been studied by many authors. 3 -5 Yang found that diester could interact with TiCl 4 , while monoester could not interact with TiC1 4 . 3 Sacchi discovered that monoester poisoned active sites which produce a prevailingly syndiotactic first propylene insertion and/or transformed them into isospecific ones. Diester had not such an effect. Thus, they concluded that diester and monoester interact with the nonstereospecific sites in different ways. 4 Soga proposed a model to explain the difference of mono-and diester, in which monoester was presumed to be extracted by AlEt 3 more easily than diester. 5 In this paper, some MgC1 2 -supported Ziegler-Natta catalysts employing different ester compounds (including mono-and diesters) as internal electron donors were prepared. The polypropylene (PP) samples obtained from these catalysts were fractionated with temperature rising elution fractionation (TREF) and the influence of different internal donors on the tacticity of PPs was investigated. Based on TREF results, different interactions of these internal donors with active sites were compared. EXPERIMENT AL Preparation of the CatalystThe preparation of MgC1 2 -supported catalysts is described in ref 6. Under N 2 atmosphere, 1 gram of anhydrous MgC1 2 and 6 ml BuOH were added to 50 ml n-octane. This suspension was heated to 80°C and stirred until MgCl 2 was dissolved. The solution was then heated at 100°C for 2 hours after 50 ml TiCl 4 was introduced. The resulting solid product was separated by filtration and washed with n-octane. Internal electron donors (if needed) was added and stirred for 2 hours. The suspension was washed and 50ml TiC1 4 was added again. After 2 hours, filtration and washing were repeated. Polymerization of PropylenePolymerizati...

Crystallization Rates of Matched Fractions of MgCl2-Supported Ziegler Natta and Metallocene Isotactic Poly(Propylene)s. 1. The Role of Chain Microstructure

“…Modified Busico Three-State Statistical Model. The defected pentads and heptads observed by 13 C NMR for the ZN-iPP fractions and the parent ZN-iPP are listed in [7][8][9][10][11][22][23][24][25][26] we notice a nonnegligible concentration of purely syndiotactic sequences (rrrrrr) in all the ZN fractions, including the fraction with the highest molar mass. In addition, stereoerrors of the type, rmrrrm or rmrrrr are also not detected.…”

“…[11][12][13][14][22][23] TREF 14,22 and solvent gradient extraction [11][12][13] led to fractions of increasing isotacticity and increasing molar mass, a result that clearly indicated a nonuniform interchain composition of defects. They also observed that most of the fractions contained syndiotactic rrrr pentads and, as in other works, [7][8][9][10][11][12][13][24][25][26] it was proposed that some of the propagation errors were "blocky" in nature.…”

Isoselectivity Distribution of Isospecific Centers in Supported Titanium‐Based Ziegler‐Natta Catalysts

“…[16,17] This technique reveals even minor differences in stereoregularities of polymers prepared with similar catalysts. [9,10,[18][19][20] Earlier Tref analysis of the ''isotactic'' fractions of poly(propylene) (the fractions insoluble in o-xylene at 95 8C) prepared with several catalysts of the type TiCl 4 / MgCl 2 /internal electron donor has shown that these fracions differ quite substantially in stereoregularity depending on the type of the internal donor as well as the type of the external electron donor, which is used in combination with AlEt 3 as a part of a cocatalyst mixture. [9,10] This paper describes in detail the quantitative aspects of the distribution of isospecific centers in these catalysts.…”

Temperature Rising Elution Fractionation and Crystallization Analysis Fractionation

“…Fractionation by TREF of polypropylene followed by GPC and NMR analysis has been described by Mingozzi 98 and Xu et al 100,101 Preparative fractionation by TREF of propylene copolymers have been reported by Usami, 94 Kakugo et al, 96 Abiru et al 102 and Feng et al 103 …”