Article pubs.acs.org/Macromolecules
Nanostructured Polyethylene Reactor Blends with Tailored Trimodal Molar Mass Distributions as Melt-Processable All-Polymer Composites Markus Stürzel,† Timo Hees,† Markus Enders,§ Yi Thomann,† Hannes Blattmann,† and Rolf Mülhaupt*,†,‡ †
Freiburg Materials Research Center (FMF) and Institute for Macromolecular Chemistry, University of Freiburg, Stefan-Meier-Str. 21, D-79104 Freiburg, Germany ‡ Sustainability Center Freiburg, Ecker-Strasse 4, D-79104 Freiburg, Germany § Institute for Inorganic Chemistry, University of Heidelberg, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany ABSTRACT: Tailoring trimodal polyethylene (PE) molar mass distributions by means of ethylene polymerization on three-site catalysts, supported on functionalized graphene (FG), enables nanophase separation during polymerization and melt processing, paralleled by PE self-reinforcement. Typically, FG/MAO-supported three-site catalysts combine bis(iminopyridyl)chromium trichloride (CrBIP), producing PE wax having high crystallization rate, and quinolylcyclopentadienylchromium dichloride (CrQCp), forming in situ ultrahigh molecular weight PE (UHMWPE) nanostructures, with bis(iminopyridyl)iron dichloride (FeBIP) or bis(tert-butyl cyclopentadienyl)zirconium (ZrCp), respectively, producing HDPE with variable intermediate molar mass. During injection molding, the formation of shish-kebab fiber-like extended-chain UHMWPE structures, as verified by SEM, AFM, and DSC, account for effective self-reinforcement. Only in the presence of high UHMWPE content, PE wax, usually an unwanted byproduct in HDPE synthesis, functions as a built-in processing aid and enables the incorporation of much higher UHMWPE contents (30 wt %) than previously thought to be tolerable in injection molding. Whereas the incorporation of UHMWPE/PE wax blends improves stiffness and strength, the simultaneous FG dispersion accounts for substantially higher impact strength.
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INTRODUCTION Polyolefins are hydrocarbon polymers which are industrially produced in solvent-free, highly energy- and resource-efficient catalytic olefin polymerization by exploiting fossil as well as renewable resources. On heating above 400 °C, thermal degradation occurs and converts polyolefin wastes back into oil and gas in essentially quantitative yields; therefore, they exhibit high, oil-like energy content in combustion similar to that of crude oil. Today, polyolefins such as polypropylene are the clear leaders in both life cycle assessment and world polymer production.1−3 Among polyolefins, high-density polyethylene (HDPE) is well-known to meet the demands of diversified applications ranging from pipes to artificial hips and battery separators.4 Moreover, ultrahigh molecular weight PE (UHMWPE), aligned by gel spinning, produces ultrastrong fibers like Dyneema,5 which exhibit superior strength with respect to steel fibers. In sharp contrast, today’s PE injection molding fails to orient PE, gives much lower stiffness, and does not tolerate UHMWPE, owing to the massive viscosity build-up associated with UHMWPE entanglement. Attempts to prepare self-reinforced PE by melt blending HDPE with commercial micron-sized UHMWPE powders have failed since micrometersized UHMWPE does not melt during the short residence time typical for extrusion and injection molding.6 Furthermore, © XXXX American Chemical Society
UHMWPE nanoparticles are not yet commercially available. Since organic nanoparticles exhibit an extremely high surface accompanied by the high specific resistance known for nonmetal particles, electrostatic discharges occur and trigger explosions when such dust-like organic particles are exposed to air. Hence, current HDPE matrix reinforcement does not use UHMWPE nanoparticles and requires the incorporation of alien fibers and fillers. In view of improving performance and lowering weight without sacrificing facile recycling, it is highly desirable to produce “all-polyolefin composites”, in which polyolefins are reinforced by in situ formed fiber-like extended chain polyolefin structures.7 Today, self-reinforcement of polyolefins is achieved by costly processing technologies, for example, hot compaction of stretched tapes or lamination of fabrics.8,9 Already in 1975, Capiati and Porter proposed the concept of “one polymer composite” made from PE by reinforcing the PE matrix with a PE of different morphology such as extended-chain PE fibrils, bonded to the PE matrix by transcrystallization.10 Following pioneering advances of Ehrenstein and co-workers,11 who Received: June 30, 2016 Revised: October 4, 2016
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DOI: 10.1021/acs.macromol.6b01407 Macromolecules XXXX, XXX, XXX−XXX
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weight ratio of the individual PE fractions without affecting their individual molar mass.33−35 Furthermore, owing to the close proximity of adjacent sites, nanophase-separated UHMWPE is formed during polymerization, which is unavailable by conventional melt compounding. Rastogi and Chadwick et al. have tailored bimodal PE containing higher UHMWPE content on two-site catalysts, prepared by cosupporting quinolylindenyl−chromium with FeBIP single site catalysts on MgCl2/AlEtn(OEt)3−n. However, only by drawing of compression-molded HDPE/UHMWPE reactor blends with high UHMWPE content, shear-induced formation of UHMWPE shish-kebab structures was achieved by oriented crystallization. 36 Among various single-site catalysts, quinolylcyclopentadienyl−chromium complexes (CrQCp), pioneered by Enders, enabled the in situ formation of UHMWPE, the molar mass of which is unaffected by most other metal alkyls.37,38 Co-supporting CrQCp together with FeBIP on mesoporous silica and functionalized graphene produced HDPE/UHMWPE reactor blends, which were melt-processable by classical injection molding with an UHMWPE content up to 20 wt %.39 For further improvement of PE self-reinforcement it is highly desirable to increase the UHMWPE content well above 20 wt % without impairing injection molding and short cycle times. To date, such high UHMWPE content has been thought to be impractical in classical injection molding.6 Herein we report on tailoring PE reactor blends with trimodal molar mass distributions as self-reinforced PE (“allpolymer composites”) having significantly higher extendedchain UHMWPE content. Particularly, the question is addressed how the PE wax content, serving as built-in processing aid, the average molar mass of HDPE, and the FG content influenced UHMWPE nanostructure formation during polymerization and during classical injection molding at 210 °C. Albeit many groups have successfully employed graphenesupported single-site catalysts to disperse graphene in PE by polymerization filling, most graphene/PE nanocomposites are rendered brittle by increasing the graphene content even at low graphene incorporation. Therefore, another objective of our research is to improve toughness/stiffness balance by simultaneous graphene dispersion and UHMWPE nanostructure formation.
created shish-kebab PE by means of injection molding using special convergent dies and low processing temperatures close to the HDPE melting temperature, several processing strategies have emerged for achieving polymer self-reinforcement.12−16 However, in addition to the rather narrow processing window, prolonged cycle times are rather problematic with respect to the industrial applications of self-reinforcement.17 Melt manipulations such as dynamic packing injection molding (DPIM)18,19 or controlled solvent evaporation20 afford selfreinforcement at the expense of reduced resource- and ecoefficiency as compared to classical injection-molded polyolefins.2 The flow-induced oriented crystallization of UHMWPE/ HDPE blends, produced by ethylene polymerization and subsequent in situ formation of UHMWPE shish-kebab fiber structures during melt processing, is economically and ecologically highly advantageous. As verified by studies on UHMWPE/HDPE model blends, prepared by solution blending, UHMWPE having low crystallization rate is elongated during melt-processing or drawing to form shish, whereas lower molar mass HDPE, having much larger crystallization rate, is nucleated by extended-chain UHMWPE to produce kebab.21 However, owing to their high melt viscosities, state-of-the-art PE reactor blends contain just a few weight-percent UHMWPE, which is insufficient to reinforce the PE matrix.6 In conventional HDPE/UHMWPE reactor blends, produced in reactor cascades by varying the hydrogen content, the UHMWPE chains serve as “tie molecules” bonding together PE crystal lamellas and thus substantially improving PE pipe fatigue resistance.22 Albeit successful catalyst and process development has enabled to substantially increase the UHMWPE content by ethylene polymerization in cascade reactors, the resulting reactor blends are processable only by compression molding. Alternatively, annealing PE under high pressure enables the transition from folded-chain-crystal to extended-chain-crystal morphology.24−27 However, the latter process is not practical in classical injection molding. Few attempts have been directed toward catalyst-mediated UHMWPE fiber formation during polymerization. In mesoscopic shape replication fiber-like supports were used as templates to induce the in situ formation of UHMWPE fibers.28−31 By immobilizing catalysts in tubular pores and ethylene polymerization in a confined environment, referred to as extrusion polymerization, Aida and co-workers produced extended-chain PE fibers.32 In a similar extrusion polymerization process, Soares et al. obtained UHMWPE fibers by ethylene polymerization on Cp2TiCl2 supported on tailored mesoporous silica.25 However, at present, both mesoscopic shape replication and extrusion polymerization have still limited potential for their implementation in industrial ethylene polymerization processes and production of all-polyolefin composite, processed by classical injection molding. Instead of prefabricating in situ UHMWPE (nano) fibers, embedded in the HDPE matrix, a more industrially viable strategy aims at tailoring self-reinforcing HDPE/UHMWPE reactor blends. They are readily produced in a single reactor by designing multisite catalyst containing different sites producing UHMWPE, HDPE, and PE wax without sacrificing the singlesite nature of the individual catalysts. In advanced multisite catalysts, the independent ethylene polymerization on different sites affords unprecedented MWD control. While the choice of the single-site component determines the molar mass of the individual PE fractions, their molar mixing ratio governs the
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EXPERIMENTAL SECTION
Materials and General Considerations. All reactions involving air- and moisture-sensitive compounds were carried out under a dry argon atmosphere using standard Schlenk techniques. Ethylene (3.0) and argon (5.0) were supplied by Messer Griesheim and used without further purification. Toluene (anhydrous), n-heptane (anhydrous), trimethylaluminum (TMA, 2 M in n-heptane), xylene (mixture of isomers, ≥96%), and triisobutylaluminum (TiBAl, 1 M in n-hexane) were purchased from Sigma-Aldrich. Toluene and n-heptane were further purified using a Vacuum Atmospheres Co. solvent purifier. Bis(tert-butylcyclopentadienyl)zirconium dichloride (ZrCp) was purchased from MCAT Konstanz and was used as received. CrBIP and FeBIP were synthesized by literature procedures and supplied by Scheuermann and Xalter from our group.40,41 The catalyst, dichloroη5-(3,4,5-trimethyl-1-(8-quinolyl)-2-trimethylsilyl-cyclopentadienyl)chromium(III) (CrQCp), was synthesized in the group of Enders by Mark, University of Heidelberg, following procedures previously reported.38 MAO, purchased from Sigma-Aldrich, had an Al content of 4.65 wt % in toluene and was stored under a dry argon atmosphere in a glovebox (MBraun MB 150B-G-II). FG was synthesized from graphite using a modified Hummers method to obtain GO, which was thermally reduced by rapid heating (750 °C) under an N2 atmosphere B
DOI: 10.1021/acs.macromol.6b01407 Macromolecules XXXX, XXX, XXX−XXX
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Figure 1. Types of the single-site precatalysts used as components of FG-supported three-site catalysts producing tailored UHMWPE/HDPE/PE wax reactor blends with variable HDPE molar mass (2 and 3 in series A and B). to produce FG nanosheets exhibiting an average surface of 600 m2 g−1 and a hydroxyl concentration of 0.15 mmol g−1.42,43 Catalyst Preparation and Olefin Polymerization. The FGsupported catalyst was prepared by heating FG for 2 h in vacuum at 110 °C. Then the FG was dispersed in n-heptane (10 mg mL−1) and sonicated for 40 min. The MAO cocatalyst in toluene (10 wt %) was added and stirred vigorously (10 min), and then the mixture was sonicated for 20 min. CrQCp in toluene (0.1 mg mL−1) was added with a syringe, and the mixture was stirred for 5 min. After that the catalysts for the HDPE fraction (FeBIP or ZCp) and wax fraction (CrBIP) were consecutively added and stirred for 5 min each. Prior to their injection, catalyst precursors containing BIP ligands were pretreated with TMA (10 equiv). The thus-activated catalyst was transferred into the reactor, and the polymerization was started. Ethylene polymerizations were carried out in a 200 mL double-jacket steel reactor equipped with a mechanical stirrer and connected to a thermostat. Then dry n-heptane (80 mL) and triisobutylaluminum (TiBAl, 0.5 mL 1 M in n-hexane) as a scavenger were added to the reactor. Typically, the ethylene pressure was kept constant at 5 bar, the temperature at 40 °C, and the stirring speed at 1000 rpm. Polymerization was stopped by venting and pouring the slurry into acidified methanol. The polymer was filtered off, washed, and dried for 16 h at 65 °C under reduced pressure to constant weight. Polymerizations for online kinetic measurements were carried out in a 600 mL Büchi steel autoclave equipped with a mechanical stirrer and a software interface. The reactor, previously charged with n-heptane (280 mL) and TiBAl (2.0 mmol), was saturated three times with ethylene at 40 °C before polymerization was started by addition of the catalyst. Scale-up reactions were carried out using a 2 L Büchi steel autoclave having similar properties. The reactions were done in 600 mL of n-heptane. Polymer Characterization. The Mw and MWD of the polymers were determined using a PL-220 chromatograph (Polymer Laboratories) equipped with a differential refractive index (DRI) detector and a differential viscometer 210 R (Viscotek). Polyethylene was defined as UHMWPE if its Mw exceeded 106 g mol−1 and denoted PE wax, if the molecular weight was below 5000 g mol−1. The measurements were performed at 150 °C with three PLgel Olexis columns, and 1,2,4-trichlorobenzene (Merck) stabilized with 0.2 wt % 2,6-di-tert-butyl-(4-methylphenol) (Aldrich) was used as a solvent at a flow rate of 1.0 mL min−1. Columns were calibrated using 12 polyethylene samples with a narrow MWD defining universal calibration. Melting points and the overall thermal behavior of the neat polymer were determined by differential scanning calorimetry
using a DSC 6200 from Seiko Instruments. The polymer was heated from room temperature to 200 °C, kept at this temperature for 5 min, cooled to −70 °C, and then heated again to 200 °C. The heating rate was kept constant at 10 K min−1. TEM microscopy was performed with a LEO EM 912 Omega device and SEM microscopy with a Quanta 250 FEG. The tensile modulus of the nanocomposites was measured with a Zwick model Z005 (DIN EN ISO 527). IZOD notched impact strength tests were performed at a Zwick pendulum according to DIN EN ISO 180. Polymer Processing. The obtained reactor blends were processed by twin-screw mini-extrusion (DSM Xplore 5 mL Compounder, 200 °C, 100 rpm, 2 min), followed by injection molding (DSM Xplore 5.5 mL laboratory injection molding, 210 °C, 9 bar, 40 °C mold) to prepare tensile and Izod impact strength test specimens. Samples for TEM and SEM microscopy were prepared by compression molding at 200 °C and a pressure of 5 bar forming disks with a thickness of 1 mm and a diameter of 25 mm. All polymers were stabilized prior to processing with Irganox 1010 and Irgafos P168 (1:1 w:w, 0.1 wt %) by dispersing the polymer powder in acetone followed by ultrasonication (15 min) and removal of the volatile compounds under reduced pressure.
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RESULTS AND DISCUSSION In order to examine how PE wax incorporation, HDPE molar mass, and in situ dispersion of functionalized graphene (FG) nanosheets influence PE self-reinforcement during classical PE injection molding, we tailored UHMWPE/HDPE/PE wax reactor blends by ethylene polymerization on three-site catalysts, supported on FG. Typically, FG was prepared by thermal reduction of graphite oxide and tethered with methylaluminoxane (MAO) in order to coimmobilize three different types of single-site catalysts, which are displayed in Figure 1. The molar masses of PE wax, HDPE, and UHMWPE was controlled by the choice of the single-site catalyst type, whereas their molar mixing ratio governed the reactor blend composition without affecting the molar masses of the individual PE fractions. The PE wax fraction (Mw = 1 kg mol−1) was varied by cosupporting CrBIP (see Figure 1), whereas the amount of UHMWPE (Mw = 3000 kg mol−1) was independently varied by cosupporting various amounts of C
DOI: 10.1021/acs.macromol.6b01407 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules Table 1. Comparison of MAO-Activated Homogeneous and FG-Supported FeBIP and ZrCp Catalystsa
a
catalyst
c (μmol L−1)
FeBIP FeBIP ZrCp ZrCp
10.1 10.1 24.7 24.7
FG support (mg) 150 150
solvent
Al:M
activity (g mmol−1 h−1)
Mw (kg mol−1)
Mw/Mn
toluene heptane toluene heptane
2000:1 600:1 2000:1 600:1
1000 20000 2900 5800
72 200 250 1600
36 8.3 2.4 2.6
Polymerization conditions: Vpol = 100 mL, TiBAL = 0.5 mmol, tpolym = 60 min, pethylene = 5 bar, Tpolym = 40 °C.
Figure 2. Comparison of MWDs for HDPE produced on homogeneous and FG-supported FeBIP (left) and ZrCp (right) catalysts, as measured by high temperature SEC in 1,2,4-trichlorobenzene at 150 °C.
Table 2. Comparison of Ethylene Polymerization on FG/MAO-Supported Single-, Two-, and Three-Site Catalysts Combining CrQCp with CrBIP and FeBIPa catalyst activity (g mmol−1 h−1)
a b
entry
CrBIP (μmol L−1)
1 2 3 4 5 6 7
6.3
FeBIP (μmol L−1)
CrQCp (μmol L−1)
2.0 0.8 6.3 6.3 6.3
2.0 2.0 2.0
0.8 0.8 0.8
exptl 6000 26200 14000 9900 6900 16300 9300
calcdb
Mw (kg mol−1)
Mw/Mn
10900 6900 22700 11100
1.2 260 3900 244 690 361 230
1.9 8.6 2.3 55 770 9.4 11
Polymerization conditions: Vn‑heptane = 300 mL, pethylene = 5 bar, tpolym = 120 min, MAO = 150:1, Tpolym = 40 °C, FG = 150 mg, TiBAl = 2 mmol. See eq 1.
systems were supported on FG without further purification by washing, there was no indication for leaching. It should be noted that leaching would form homogeneous catalysts producing PE powders with different morphology accompanied by severe reactor fouling. This was not observed. Influence of the FG Support on FeBIP and ZrCp Single-Site Catalysts. As listed in Table 1, ethylene was polymerized in toluene on homogeneous MAO-activated FeBIP and ZrCp and compared with ethylene polymerization on FG/MAO-supported FeBIP and ZrCp to elucidate the influence of the FG support. For both FG-supported FeBIP and ZrCp catalysts, the immobilization of the single-site catalysts on FG/MAO afforded markedly higher catalyst activities and also higher HDPE molar masses. As is apparent from the SEC traces displayed in Figure 2, homogeneous MAO/FeBIP produced bimodal MWDs, most likely accounted for by self-supporting when HDPE precipitated during polymerization.
CrQCp (see Figure 1). HDPE with variable intermediate molar mass was incorporated into the PE reactor blends by cosupporting either FeBIP (see Figure 1, series A) or bis(tertbutylcyclopentadienyl)zirconium dichloride (ZrCp, see Figure 1, series B) as the third catalyst component. For achieving a controlled incorporation of HDPE with molar mass varying between that of PE wax and UHMWPE, it was important to understand how the FG-support affects ethylene polymerization on FeBIP and ZrCp single-site catalysts. Only robust three-site catalysts, in which the molar ratio of the catalysts exclusively affects the PE wax/UHMWPE/HDPE weight ratio instead of the molar mass of the three individual PE fractions, meet the demands of process control in reactor blend formation. In order to elucidate the role of HDPE molar mass, trimodal PE reactor blends containing the same PE wax and UHMWPE fractions but different HDPE with low molar mass of Mw = 200 kg mol−1 (PE reactor blend series A) or higher molar mass of Mw = 1600 kg mol−1 (PE reactor blends series B) were compared. Albeit all three different catalyst D
DOI: 10.1021/acs.macromol.6b01407 Macromolecules XXXX, XXX, XXX−XXX
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CrQCp, producing UHMWPE, was combined with the other catalyst components. Most likely, this is accounted for by diffusion limitation encountered in the presence of UHMWPE. As a function of the catalyst precursor types and their mixing ratio, the two- and three-site catalysts afforded broad MWDs with catalyst-mediated variation of the PE wax, HDPE, and UHMWPE (see Table 3). Typically, the reactor blend compositions were varied from 0 to 30 wt % UHMWPE, from 0 to 48 wt % PE wax, and from 0 and 2.1 wt % FG. Since the PE reactor blend compositions depended on the catalyst component mixing ratio, it was possible to independently tailor the content of individual components without affecting their individual average molar mass. This remarkable precision in designing MWDs is unparalleled by earlier multisite catalyst generations, many of which have failed to meet the demands of industrial process control owing to the rather complex interplay of catalyst components. Hence, raising the CrQCp content from 9.5 to 30 mol % increased the UHMWPE content from 15 to 30 wt % (see Figure 4 and also Table 3, entries 5−7), while the absolute amount of CrBIP and FeBIP was kept constant. Regarding the case that both CrBIP and CrQCp were kept constant (cf. Table 3, entries 2−5), the content of HDPE increased with increasing FeBIP content. As a consequence, controlled HDPE and UHMWPE incorporation enabled the precise tailoring of MWDs as displayed in Figure 4. The obtained correleations between HDPE and FeBIP contents and between UHMWPE and CrQCp contents are displayed in Figure 5 according to their entries in Table 3. Moreover, ethylene polymerization on multisite catalysts having similar contents of the individual catalysts components (69 mol % CrBIP, 5 mol % FeBIP, and 17 mol % CrQCp) enabled to vary FG content from 0.1 to 2.1 wt % without affecting the UHMWPE/HDPE/PE wax weight ratio. All samples listed in Table 4 were melt-processable by classical injection molding at 210 °C using a twin-screw miniextruder and a microinjection molding device. It should be noted that injection molding of PE reactor blends containing 30 wt % UHMWPE was thought to be impossible, since UHMWPE dissolved only up to 3 wt % in classical HDPE blends as reported by Boscoletto et al.6 The mechanical properties of PE reactor blends such as tensile strength, stiffness, and toughness, as listed in Table 4, were determined as a function of UHMWPE, HDPE, PE wax, and FG contents, varied via the three-site catalyst compositions. The highest Young’s modulus of 5.1 GPa (see entry 7, Table 4) was observed for the highest UHMWPE content of 30 wt % in conjunction with high PE wax content of 48 wt %. Furthermore, the role of the UHMWPE/PE wax weight ratio, governed by the CrQCp/CrBIP molar ratio in the three-site catalyst, was examined in more detail. Large amounts of PE wax (79 wt %) at low content of UHMWPE (8.7 wt %) impaired processing, caused massive emission and odor problems, and adversely affected the toughness/stiffness balance (see entry 4, Table 4). For low UHMWPE content, the variation of PE wax failed to significantly improve mechanical properties. In fact, for conventional HDPE in the absence of UHMWPE, PE wax represents a highly undesirable byproduct and would never qualify as processing aid. In sharp contrast, the increasing PE wax addition, resulting from ethylene polymerization on CrBIP sites, combined with an increasing amount of UHMWPE,
In contrast, the FG/MAO-supported FeBIP produced HDPE with unimodal MWD and higher molar mass of 200 kg mol−1, which is very similar to that of the high molar mass fraction of HDPE obtained with homogeneous MAO/FeBIP. Unlike FG/ MAO-supported FeBIP, however, immobilization of ZrCp on FG/MAO accounts for a massive increase of HDPE molar mass from 250 to 1600 kg mol−1 without affecting the narrow polydispersity. This increase of molar mass typical for ZrCp is in accord with similar observations reported by Park et al., who supported Cp2ZrCl2 and Cp2TiCl2 on n-doped graphene nanoplatelets.23 According to their hypothesis, π−π interactions between FG and the single-site catalysts are supposed to account for increased HDPE molar mass. Hence, using either FG/MAO-supported FeBIP or ZrCp, the average molar mass of the HDPE fraction in reactor blends can be set to 200 kg mol−1 (series A) or 1600 kg mol−1 (series B) with an unimodal MWD. Role of UHMWPE, FG, and FG Contents (PE Reactor Blend Series A). Tailored reactor blends with bi- and trimodal MWDs and HDPE molar mass of 200 kg mol−1 (series A) were prepared on FG-supported two- and three-site catalysts combining FeBIP with CrQCp and CrBIP. As is apparent from the polymerization data listed in Table 2 and polymerization kinetics displayed in Figure 3, the combinations of the different single-site catalysts afforded highly active and robust multisite catalysts for ethylene polymerization.
Figure 3. Comparison of polymerization kinetics for FG/MAOsupported single-, two-, and three-site catalysts combining CrBIP, FeBIP, and CrQCp.
Interestingly, while the FG-supported CrBIP single-site catalyst exhibited rather low activity, the combination of CrBIP with CrQCp and FeBIP markedly increased catalyst activity of the corresponding two- and three-site catalysts. However, the opposite was observed for FeBIP, which gave much lower catalyst activity when combined with the other two catalyst components. Assuming independent ethylene polymerization on the different sites, one can calculate the expected activities for two- and three-site catalysts, taking into account the activities of the corresponding single site catalyst; the site content and their mixing ratio (see eq 1). activity [g mol−1 h−1] = x(CrBIP) + y(FeBIP) + z(CrQCp) (1)
Clearly, the real catalyst activities were lower with respect to the calculated ones. This deviation was more pronounced when E
DOI: 10.1021/acs.macromol.6b01407 Macromolecules XXXX, XXX, XXX−XXX
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Table 3. Scale-Up of PE Reactor Blends by Ethylene Polymerization on FG/MAO-Supported CrBIP/FeBIP/CrQCp Three-Site Catalystsa entry
CrBIP (μmol L−1)
FeBIP (μmol L−1)
CrQCp (μmol L−1)
time (min)
activity (g mmol−1 h−1)
Mwb (kg mol−1)
Mw/Mn
PE waxb (wt %)
UHMWPE (wt %)
FGc (wt %)
1 2 3 4 5 6 7 8d 9d 10d
6.3 6.3 6.3 6.3 6.3 6.3 12.6 7.9 6.3
2.0 2.0 1.3 0.7 1.0 1.0 1.0 2.6 1.7 1.3
0.8 0.8 0.8 0.8 1.6 3.2 3.2 1.9 1.6
120 120 120 120 120 120 120 240 180 110
26200 9300 15300 16900 14900 16200 14400 3100 5000 6800
270 230 650 400 470 570 1125 660 780 570
8.6 10 197 389 202 247 780 212 195 147
