influence of organoboron compounds on ethylene polymerization using cp2zrcl2/mao as catalyst system

Research ArticleInfluence of Organoboron Compounds on EthylenePolymerization Using Cp2ZrCl2MAO as Catalyst System

Luis Alexandro Valencia Loacutepez1 Francisco Javier Enriacutequez-Medrano1

Ricardo Mendoza Carrizales1 Florentino Soriano Corral1

Adali Castantildeeda Facio2 and Ramoacuten Enrique Diacuteaz de Leoacuten Goacutemez1

1 Centro de Investigacion en Quımica Aplicada Boulevard Enrique Reyna Hermosillo No 140 Col San Jose de los Cerritos25294 Saltillo COAH Mexico

2 Facultad de Ciencias Quımicas Universidad Autonoma de Coahuila Boulevard V Carranza sn 25280 Saltillo COAH Mexico

Correspondence should be addressed to Ramon Enrique Dıaz de Leon Gomez ramondiazdeleonciqaedumx

Received 6 February 2014 Revised 28 May 2014 Accepted 28 June 2014 Published 15 July 2014

Academic Editor Ali Akbar Entezami

Copyright copy 2014 Luis Alexandro Valencia Lopez et al This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Organoboron compounds of nonionic and ionic nature tris(pentafluorophenyl)borane and NN-dimethylaniliniumtetra(pentafluorophenyl)borate were evaluated to act in conjunction with MAO as activators on ethylene polymerizationby using the catalyst Cp

2ZrCl2 A decrease on the catalytic activity was observed in both cases in relation with a reference

polyethylene which was synthesized in absence of any organoboron compound An increase on the crystallinity degree andmolecular weight as well as an improvement in thermal and dynamic-mechanical properties was observed in polyethylenessynthetized in presence of tris(pentafluorophenyl)borane A low density polyethylene with improved thermal stability wasobtained when NN-dimethylanilinium tetra(pentafluorophenyl)borate was employed as activator

1 Introduction

Due to the increasing current demand of polyethylene (PE)since the last decades some strategies have been developedin order to reduce the production costs and the quantityof impurities in the final products as well as improve thefinal properties of the obtained polymers One of thesestrategies has been the use of organoboron compounds asactivators of metallocene catalysts [1ndash3] since these com-pounds have proved to have the capacity of producinghighly active catalysts systems for ethylene polymerizationand in low molar ratios Boron compound (B)Zirconiumcatalyst (Zr) (between 01ndash5) in comparison with alkyl-aluminumswhich commonly require fixedmolar ratios alkyl-aluminumZr between 1000 and 15000 [4ndash7] Nonethelessone disadvantage of these compounds as cocatalysts is theirnoncapacity of alkylating halide metallocene catalysts suchas Cp

2ZrCl2 therefore for using these compounds on these

kinds of systems a necessity of being combined with an

alkyl-aluminum such as MAO is required where besidesof alkylating the Zr catalyst acts as scavenger during thepolymerization however in the literature there is very fewinformation reported about the influence wielded on the finalproperties of thematerials by using amixture of organoboroncompound andMAO and specifically depending on the ionicnature of the organoboron compound

As it was previously exposed organoboron compoundscan be classified according to their ionic nature in nonionicor ionic compounds [8ndash10] where nonionic are constitutedby an only species (mainly tris(pentafluorophenyl)borane)[11 12] which abstracts one of the methyl groups of thecatalyst leading to the formation of two ionic species an ldquoacti-vatedrdquo cationic metallocene ([Cp

2ZrCH

3]+) which proceed

to be coordinated by an ethylene molecule beginning thepolymerization and an anionic boron compound of generalformula [CH

3B(C6F5)3]minus Nonetheless even though these

kinds of compounds have been referred as ldquoan ideal boron-based Lewis acidrdquo because of their acid strength and stability

Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2014 Article ID 519203 8 pageshttpdxdoiorg1011552014519203

2 International Journal of Polymer Science

it has been suggested that the catalyst reactivity is mildlydecreased by a persistent interaction between the previouslyabstracted methyl group and the transition metal atom

On the other hand ionic compounds are constitutedin an ion-pair configuration where the cationic species(commonly anilinium or carbonium) takes the functionof activating the alkylated active sites while the anionicspecies (tetra(pentafluorophenyl)borate) prevent the interac-tion between the abstracted methyl and the Zr center (1)therefore the catalytic activity is better Consider

Cp2Zr(CH

3)2+ [C6H5NH(CH

3)2]+

[B (C6F5)4]minus

997888rarr [Cp2ZrCH

3]+

[B(C6F5)4]minus

+ C6H5NH(CH

3)3

(1)

This work is focused on the use of one of each kindof organoboron compound according to their ionic natureas activators of the halide catalyst Cp

2ZrCl2by employing

a reduced amount of MAO to act as alkylating agent andscavenger besides activating in a synergistic way with theorganoboron compound at a fixed molar relation of MAOB= 20 MAOZr = 100 Furthermore another material inwhich no boron compound was employed was synthesizedas reference material A complete characterization of thesynthesized PE was carried out in order to elucidate theinfluence of the B on the ethylene polymerization and thefinal properties of the obtained polymers

2 Materials and Methods

21 Reactants and Manipulations All manipulations werecarried out under inert atmosphere using a dual vacuum-argon line and standard Schlenk techniques or in a glovebox Toluene was twice distilled from sodium and benzo-phenone under argon atmosphere before use Bis(cyclope-ntadienyl)zirconium (IV) dichloride (Cp

2ZrCl2 98) and

methylaluminoxane (MAO 10wt- in toluene) were purc-hased from Aldrich and were used as received Tris(pentaflu-orophenyl)borane (B(C

6F5)3 95) and NN-dimethylani-

linium tetra(pentafluorophenyl)borate ([C6H5N(CH

3)2H]+

[B(C6F5)4]minus 98) were supplied by Strem Chemicals and

they were used as received as well Polymer-grade ethylenewas purchased from Praxair and it was purified by passing itthrough 3-4 A activated molecular sieves

22 Ethylene Polymerization All polymerizations were per-formed in a 1 L stainless steel Parr reactor through thefollowing procedure several vacuum-argon cycles at 80∘Cwere carried out in order to purify the reactor Then itwas cooled to room temperature and filled with 150mLof distilled toluene under argon atmosphere The reactorstirring system was set at 100 rpm and it was heated to 50∘CThe catalyst system was fed into the reactor as follows (i)solution comprising MAO + B prepared in toluene at 5 wt-by stirring during two hours under inert atmosphere (ii)catalyst solution at 37 wt- in toluene prepared under inertatmosphere The molar ratios MAOZr and BZr were 100and 5 respectively The polymerization started by adding

the monomer at a continuous flow All experiments wereperformed at an ethylene pressure of 1 bar during 1 hour

The polymerization reaction was terminated by the clo-sure of the ethylene feeding and finally by adding an acidified(10 of hydrochloric acid) methanol solution The obtainedpolymerwas filtered off washedwithmethanol and vacuum-dried

23 Characterization Density was measured as describedin the ASTM D4052-11 standard test method for densityMolecular weight distributions (MWD) were determinedby size exclusion chromatography (SEC) using an Alliancechromatograph (GPC V-2000) equipped with two on-linedetectors a differential viscometer and a differential refrac-tometer The calibration was executed under polystyrenestandards using 124-trichlorobencene as eluent measure-ments were performed at a flow rate of 1mLmin at 140∘CDifferential scanning calorimeter (DSC) thermograms wereobtained by means of a TA instrument DSC 2920 at a heatingrate of 10∘Cmin under inert atmosphere Each sample washeated twice in order to eliminate the thermal historyThermogravimetric analyses (TGA) were performed usinga TA-Q500 apparatus in which the samples were heated to10∘Cmin under nitrogen atmosphere and at a flow rate of50mLmin Thermograms were recorded from 30 to 600∘CWide-angle X-ray diffraction (WAXD) measurements werecarried out in a Siemens D5000 diffractometer with a Ni-filtered CuK120572 radiation generator (wave length of 15406 A)Patterns were recorded from 5 to 35∘ (in 2120579) with 5 sec perstep Transmission electronmicroscopy (TEM) analyses wereperformed on a TITAN 80ndash300 kV Samples were preparedemploying a cryogenic ultramicrotome Leica Ultracut atminus125∘C and a cut rate of 2mmmin The sample slices werestained using ruthenium tetroxide (RuO

4) steam to contrast

amorphous and crystalline phases Dynamic mechanicalanalyses (DMA) were measured in a TA Instrument inflexural mode at a frequency of 01 Hz and a temperaturerange from minus103 to 103∘C During the measurement theheating rate was 5∘Cmin and the amplitude was 05mmThesample test specimens were prepared in a LMM LaboratoryMixing Molder from Dynisco Instruments at 180∘C and60 rpm

3 Results and Discussion

Theeffect of B on the final product properties was determinedby evaluating two different compounds one of each kind ofionic nature and using as referencematerial a synthesized PEin which only MAO was used as activator at a fixed molarratio of MAOZr = 100 and BZr = 5 Table 1 shows thecatalytic activity density and molecular weight (Mw) of thesynthesized PE

31 Catalytic Activity It is noticeable how the addition ofB either of ionic or nonionic nature significantly decre-ased the catalytic activity in the way that by incorpora-ting tris(pentafluorophenyl)borane (B1) into the reactionsystem (PE-2) the catalytic activity diminished in 4236and in 7279 by adding NN-dimethylanilinium

International Journal of Polymer Science 3

Table 1 Catalytic activity density and molecular weight results

Sample Organoboron compound(B) Nature

Catalyticactivity

(KgPEmolZr)

Density(gcm3)

Mw(Kgmol) PDI

PE-1 None (reference) mdash 12325 0970 8395 27

PE-2 B(C6F5)3(B1) Nonionic 6734 0974 11618 43

PE-3 [C6H5N(CH3)2H]+[B(C6F5)4]minus (B2) Ionic 3331 0925 20776 52

Zr = 01283mmol molar ratio MAOZr = 100 BZr = 5 toluene = 141mol polymerization temperature = 50∘C and pressure = 1 bar

tetra(pentafluorophenyl)borate (B2) (PE-3) this behavioris attributed to reactions that could have taken placeduring the aging time between MAO and B giving BR

3

and AlR3minusx(C6F5)x which subsequently would react with

the catalyst species leading to unstable species of the kindCp2ZrMe(120583-Me)Al(C

6F5)3which rapidly decomposes to

Cp2ZrMe(C

6F5) as it has been previously reported in the

literature [12 13]

32 Molecular Weight Distribution It is well known that themolecular weight (Mw) andMWDdepend fundamentally onchain transfer reactions which are responsible of deactivatingthe catalyst active sites predominating the chain transferreaction to aluminum as well as 120573-elimination and trans-ference to monomer The influence wielded by the employedB on the Mw and polydispersity index (PDI) is presented inTable 1

As it can be appreciated that the Mw increased by addingboth of B from 8395 Kgmol (PE-1) to 11618 Kgmol inthe case of B1 (PE-2) and to 20776Kgmol in the caseof B2 (PE-3) however this behavior was expected becauseof the reduced concentration of active sites which leadto the formation of less polymer chains but of higherMw

As it can be observed in Figure 1 a multimodal behaviorwas exhibited by all PE samples which suggest the presenceof more than one family of active centers during the poly-merization [14] supporting the assumption that the differentkinetic behavior of the existing catalyst sites controls thepolymerization kinetics For this reason in order to get anapproximate notion of this behavior the obtained MWDwere deconvoluted using informatics software However itis important to note that while the information acquiredis useful there is no guarantee that is exactly the numberof families of active sites Nevertheless this technique isinteresting to understand how the different families of activesites are carrying out the polymerization with or without B inthe reaction medium

It can be appreciated that MWD of PE-1 (in which onlyMAO was used as activator) presents two families of activecenters one of them is associated with MAO and anotherone is related to the presence of trimethylaluminum (TMA)which is the reagent utilized in the synthesis of MAO andwhich remains present in about 30 of the total contentof MAO solution [15 16] Supported by the deconvolutedgraphs it is suggested that TMA can act as activator of

the catalyst nonetheless it acts in a lesser extent thanMAO

By adding both of B into the polymerization system thepresence of a third family of active centers was observed (seeFigures 3(b) and 3(c)) attributed to the active centers whichwere activated by B however they were presented in a lesserextent (1097 and 678 for PE-2 and PE-3 resp)

33 Density The density of a material reflects its branchingdegree malleability and hardness therefore it is determinantin the type of application in which can be submitted Table 1shows the influence wielded on the density of materials byadding B into the catalyst system

Taking into account the density values presented inTable 1 it can be appreciated that in the synthesized PE inwhich B1 was added into the reaction system (PE-2) as wellas the reference polymer (PE-1) values of 0974 and 0970were obtained respectively thus thematerials correspond tohigh density polyethylenes as expected by using this kind ofcatalysts however by employing B2 a density value of 0925was obtained which indicates that a low density polyethylenewas produced

34 Crystallinity Degree The crystallinity degree of a PEsample can be determined by a variety of methods each ofwhich measures a different property that is then related tothe level of crystallinity via a particular set of assumptionsIdeally more than one method of determination shouldbe used In this work the determination of crystallinitywas measured according to density heat fusion and X-rayscattering Determination of crystallinity degree fromdensityrests on two simple assumptions (i) PE samples consist in atwo-phase morphology and (ii) the density of each phase isuniform within the sample and consistent from one sampleto another According to this the crystallinity degree of asample can be readily determined by its density if densitiesof the crystalline and disordered regions are known just as(2) shows

119883119863=1120588 minus 1120588120572

1120588119888 minus 1120588120572times 100 (2)

where 120588 is the material density 120588120572 is the density of a PEcompletely amorphous (0853 gcm3) and 120588119888 is the densityof a PE completely crystalline (10 gcm3) [17]


9172

PE-1

827

10

08

06

04

02

00

30 35 40 45 50 55 60 65

Log M

dwd

LogM

(a)

PE-2

5672

32301097

08

07

06

05

04

03

02

01

00

30 35 40 45 50 55 60 65

Log M

dwd

LogM

(b)

PE-3

4449

4871

678

Log M

dwd

LogM

07

06

05

04

03

02

01

00

30 35 40 45 50 55 60 65 70

(c)

Figure 1 Deconvoluted MWD of PE-1 PE-2 and PE-3

On the other hand for determining the crystallinitydegree according to the heat fusion it was calculated bymeansof the ratio between the melting enthalpy (the area betweenthe measured curve and the baseline in the region of thepeak) and the melting enthalpy of a completely crystalline PE(69 calg) [17]

Moreover measurement of crystallinity degree by meansof X-ray diffraction is based in the fact that X-ray scatteringoccurs from both the crystalline and the noncrystallinemate-rial illuminated with X-rays being the difference betweenthe two types of scattering the ordering of the material thusby deconvoluting the amorphous from crystalline scatteringit is possible to determine the ratio of intensity from thecrystalline peaks (at an angular orientation (2120579) of 215∘ and240∘) corresponding to the crystallographic planes of 110and 200 respectively in the orthorhombic structure [18 19]to the sum of the crystalline and amorphous intensities (3)and in this way to obtain a reliable value of crystallinity degree

of the material The deconvoluted spectra of synthesized PEare presented in Figure 2 Consider

119883119863=

119868crystalline119868crystalline + 119868amorphous

lowast 100 (3)

The crystallinity of the obtained PE is shown in Table 2It is appreciated that the results obtained by each techniquediffer from each other however the obtained value by densityis the most accurate according to the reported in literature[20] By adding B1 into the reaction system the crystallinityincreased in 208 (taking as reference the value obtained bydensity) in comparison with PE-1 while by incorporating theB2 (PE-3) the crystallinity degree decreased in 2973 Thisbehavior is suggested to be induced by the presence of chainbranches as well a higher Mw that inhibit the movement ofthe polymer chains preventing their ordering thus causing adisordered lamellar structure arrangement of these materials


Table 2 Crystallinity degree

Sample Organoboron compound Crystallinity degreeBy density () By DSC () By X-ray ()

PE-1 None (reference) 8262 6995 6811PE-2 B1 8470 7102 6872PE-3 B2 5289 5849 5149

PE-1

5 10 15 20 25 30 35

PE-2

Crystalline

5 10 15 20 25 30 35

Amorphous

PE-3

5 10 15 20 25 30 35

2120579 (deg)

2120579 (deg)

2120579 (deg)

Figure 2 Deconvoluted diffractograms of the synthesized PEs

and a lower crystallinity degree Nevertheless in order tocorroborate these lamellar arrangements TEM analyses werecarried out (Figures 3) where it can be observed that thelamellar structure of the reference polymer (PE-1) as wellas PE-2 (using B1) is mostly ordered while by using B2 thelamellar structure is more dispersed

35 Thermal Analyses DSC thermograms of the synthetizedPE are shown in Figure 4 An increase in themelt temperaturewas noticed by the addition of B1 and B2 which is attributedto the increment in Mw that led to an increase of the tensionbetween the lamellas and therefore a higher thermal energywas required to melt the crystalline structure of materials

Through TGA analysis (Figure 5) the influence wieldedby the B on the thermal stability was determined It can

Table 3 TGA results

Sample Organoboroncompound

Temperature of5 weight loss

(∘C)


(∘C)

PE-1 None (reference) 34104 38975PE-2 B1 39319 42071PE-3 B2 38094 41990

be noticed that in all the cases a slightly weight losswas presented at low temperatures (lt275∘C) which canbe attributed to an oligomeric degradation Later a moresignificant weight loss was exhibited corresponding to thebreakdown of polymer chains bonds either in the mainpolymer chains or in branches However by employing Bthe temperature decomposition range was shifted to highesttemperatures (from 300 to 400∘C approximately) thus inorder to have a better appreciation of this improvement inthe thermal stability Table 3 shows the temperatures inwhichthe 5 and 10 of weight loss were presented It can be noticeda significant difference between the reference material (PE-1) and the PE in which B1 was added for instance PE-1 lost10 of weight at 38975∘C while at a very similar temperaturethe PE synthesized with B1 only presented a 5 loss weightas well as PE-3 which presented a similar behavior In otherwords the addition of B improves the thermal stability of PEdue to the higher molecular weight obtained in their polymerchains

36 Dynamic-Mechanical Analysis DMA analyses were onlyperformed to PE-1 and PE-2 since these materials presentedsignificant differences on their catalytic activity morphologyand thermal stability Storage and loss modulus as a functionof the temperature is presented respectively in Figure 6Two main transitions corresponding to different movementsin the molecular structure were detected One of thesetransitions which took place at around minus100∘C (120574 transition)is originated by the rotational motion of 4 to 6 methylenegroups at the polymer chains in the amorphous phase ofPE in addition to the reorientation of chain ends within thecrystalline and amorphous phases [21]The another identifiedtransition (120572 transition) was presented at temperatures near50∘C and corresponds to a premelting transition that isoriginated by the movement of the chains inside the crystals

It can be appreciated that by adding B1 the materialpresented higher values of storage modulus as well as of both


PE-1 PE-2 PE-3

Figure 3 TEM images of PE-1 PE-2 and PE-3

Table 4 DMA results

Sample Organoboron compound Storage modulus (MPa) Loss modulus (MPa) Transition temperature (∘C)120574 transition 120572 transition 120574 transition 120572 transition 120574 transition 120572 transition

PE-1 None (Reference) 4523 2019 292 200 minus11063 4272PE-2 B1 7059 2919 424 225 minus10767 4797

Temperature (∘C)

13349∘C

13153∘C

13148∘C

PE-1

PE-2

PE-3

0 20 40 60 80 100 120 140 160

Figure 4 DSC thermograms of PE-1 PE-2 and PE-3

120574 and 120572 transitions which is shown in Table 4 in a wide rangeof temperatures which can be attributed to the increase inMw of the polymer chains

Finally it is important to mention that polymers thatpresent relevant loss transitions at temperatures below minus50∘Ctend to exhibit good impact strength This is because themolecular motion is directly associated with the toughnessFor this reason knowing that the 120574 transition in PE-2 ishigher than in PE-1 it can be predicted that by adding B1 themechanic performance improves

100

90

80

70

100 200 300 400 500

Wei

ght (

)

Temperature (∘C)PE-1PE-2PE-3

Figure 5 TGAThermograms of PE-1 PE-2 and PE-3

4 Conclusions

The addition of organoboron compounds of ionic and noni-onic nature on the ethylene polymerization using Cp

2ZrCl2

MAO as catalyst system promoted a partial deactivation ofthe catalyst causing a reduction on the catalytic activityhowever the properties of the obtained polyethylenes weremostly improved Tris(pentafluorophenyl)borane allowedthe synthesis of a material with higher molecular weightand better thermal properties than the correspondingpolyethylene obtained in absence of this organoboron


450

400

350

300

250

200

150

100

50

0

minus150 minus100 minus50 0 50 100 150

PE-1PE-2

Temperature (∘C)

Stor

age m

odul

us (M

Pa)

(a)

times103

11

10

9

8

7

6

5

4

3

2

1

0

minus1

PE-1PE-2

Loss

mod

ulus

(MPa

)


Temperature (∘C)

(b)

Figure 6 Storage and loss modulus as a function of temperature for PE-1 and PE-2

compound however the crystallinity degree was notconsiderably affected On the other hand NN-dimethy-lanilinium tetra(pentafluorophenyl)borate of ionic natureconsiderably decreased the catalytic activity in comparisonwith the reference polyethylene nonetheless the thermalstability was improved This organoboron compound produ-ced a low density polyethylene in contrast to the nonionicorganoboron compound that produced a high densitypolyethylene

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors thank to Jose Diaz Elizondo Jesus CepedaUriel Pena Teresa Rodriguez GuadalupeMendez and JudithCabello for their technical support

References

[1] J Zhou S J Lancaster D A Walker S Beck M Thornton-Pett andM Bochmann ldquoSynthesis structures and reactivity ofweakly coordinating anions with delocalized borate structurethe assessment of anion effects in metallocene polymerizationcatalystsrdquo Journal of the American Chemical Society vol 123 no2 pp 223ndash237 2001

[2] S W Ewart M J Sarsfield D Jeremic T L Tremblay E FWilliams and M C Baird ldquoEthylene and propylene polymer-ization by a series of highly electrophilic chiral monocyclopen-tadienyltitanium catalystsrdquo Organometallics vol 17 no 8 pp1502ndash1510 1998

[3] M H Hannant J A Wright S J Lancaster D L Hughes PN Horton and M Bochmann ldquoThe synthesis of new weaklycoordinating diborate anions anion stability as a function oflinker structure and steric bulkrdquo Dalton Transactions no 20pp 2415ndash2426 2006

[4] A Hajizadeh and K Sobhanmanesh ldquoEffects of polymerizationparameters on activity of ethylenepropylene copolymerizationusing CP

2ZrCl2MAO catalyst systemrdquo Iranian Polymer Jour-

nal vol 13 no 3 pp 179ndash187 2004[5] M Ahmadi R Jamjah M Nekoomanesh G Zohuri and H

Arabi ldquoInvestigation of ethylene polymerization using solubleCp 2ZrCl

2MAO catalytic system via response surface method-

ologyrdquo Iranian Polymer Journal vol 16 no 2 pp 133ndash140 2007[6] S Srinivasa Reddy K Radhakrishnan and S Sivaram ldquoMethy-

laluminoxane synthesis characterization and catalysis of ethy-lene polymerizationrdquo Polymer Bulletin vol 36 no 2 pp 165ndash171 1996

[7] W Kaminsky ldquoDiscovery of methylaluminoxane as cocatalystfor olefin polymerizationrdquo Macromolecules vol 45 no 8 pp3289ndash3297 2012

[8] X Yang C L Stern and T J Marks ldquoCationic zirconoceneolefin polymerization catalysts based on the Organo-Lewis acidtris(pentafluorophenyl)borane A synthetic structural solutiondynamic and polymerization catalytic studyrdquo Journal of theAmerican Chemical Society vol 116 no 22 pp 10015ndash100311994

[9] X Yang C L Stern and T J Marks ldquoldquoCation-likerdquo homoge-neous olefin polymerization catalysts based upon zirconocenealkyls and tris (pentafluoropnenyl) boranerdquo Journal of theAmerican Chemical Society vol 113 no 9 pp 3623ndash3625 1991

[10] W E Piers and T Chivers ldquoPentafluorophenylboranes Fromobscurity to applicationsrdquoChemical Society Reviews vol 26 no5 pp 345ndash354 1997

[11] WMichiels andAMunoz-Escalona ldquoMixed cocatalyst systemsin metallocene ethylene polymerizationrdquoMacromolecular Sym-posia vol 97 pp 171ndash183 1997


[12] J N Pedeutour K RadhakrishnanH Cramail andADeffieuxldquoReactivity of metallocene catalysts for olefin polymerizationinfluence of activator nature and structurerdquo MacromolecularRapid Communications vol 22 pp 1095ndash1123 2001

[13] M Watanabi C N McMahon C J Harlan and A R BarronldquoReaction of trimethylaluminumwith [(119905Bu)Al(120583

3-O)]6 hybrid

tert-butylmethylalumoxanes as cocatalysts for olefin polymer-izationrdquo Organometallics vol 20 no 3 pp 460ndash467 2001

[14] V F Tisse C Boisson F Prades and T F L McKenna ldquoAsystematic study of the kinetics of polymerisation of ethyleneusing supported metallocene catalystsrdquo Chemical EngineeringJournal vol 157 no 1 pp 194ndash203 2010

[15] J N Pedeutour K RadhakrishnanH Cramail andADeffieuxldquoUse of ldquoTMA-depletedrdquo MAO for the activation of zirco-nocenes in olefin polymerizationrdquo Journal of Molecular Catal-ysis A Chemical vol 185 no 1-2 pp 119ndash125 2002

[16] D W Imhoff L S Simeral S A Sangokoya and J H PeelldquoCharacterization ofmethylaluminoxanes anddetermination oftrimethylaluminum using proton NMRrdquo Organometallics vol17 no 10 pp 1941ndash1945 1998

[17] A J Peacock Handbook of Polyethylene Structures PropertiesandApplications chapter 5MarcelDeckerNewYorkNYUSA2000

[18] T Furukawa H Sato Y Kita et al ldquoMolecular structurecrystallinity and morphology of polyethylenepolypropyleneblends studied by Raman mapping scanning electron micro-scopy wide angle X-ray diffraction and differential scanningcalorimetryrdquoPolymer Journal vol 38 no 11 pp 1127ndash1136 2006

[19] W Du W Zhong Y Lin L Shen and Q Du ldquoSpace chargedistribution and crystalline structure in polyethylene blendedwith EVOHrdquo European Polymer Journal vol 40 no 8 pp 1987ndash1995 2004

[20] A J Peacock Handbook of Polyethylene Structures Propertiesand Applications chapter 6 Marcel Dekker 2000

[21] M Sethi N K Gupta and A K Srivastava ldquoDynamic mechan-ical analysis of polyethylene and ethylene vinylacetate copoly-mer blends irradiated by electron beamrdquo Journal of AppliedPolymer Science vol 86 no 10 pp 2429ndash2434 2002

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it has been suggested that the catalyst reactivity is mildlydecreased by a persistent interaction between the previouslyabstracted methyl group and the transition metal atom

On the other hand ionic compounds are constitutedin an ion-pair configuration where the cationic species(commonly anilinium or carbonium) takes the functionof activating the alkylated active sites while the anionicspecies (tetra(pentafluorophenyl)borate) prevent the interac-tion between the abstracted methyl and the Zr center (1)therefore the catalytic activity is better Consider

Cp2Zr(CH

3)2+ [C6H5NH(CH

3)2]+

[B (C6F5)4]minus

997888rarr [Cp2ZrCH

3]+

[B(C6F5)4]minus

+ C6H5NH(CH

3)3

(1)

This work is focused on the use of one of each kindof organoboron compound according to their ionic natureas activators of the halide catalyst Cp

2ZrCl2by employing

a reduced amount of MAO to act as alkylating agent andscavenger besides activating in a synergistic way with theorganoboron compound at a fixed molar relation of MAOB= 20 MAOZr = 100 Furthermore another material inwhich no boron compound was employed was synthesizedas reference material A complete characterization of thesynthesized PE was carried out in order to elucidate theinfluence of the B on the ethylene polymerization and thefinal properties of the obtained polymers

2 Materials and Methods

21 Reactants and Manipulations All manipulations werecarried out under inert atmosphere using a dual vacuum-argon line and standard Schlenk techniques or in a glovebox Toluene was twice distilled from sodium and benzo-phenone under argon atmosphere before use Bis(cyclope-ntadienyl)zirconium (IV) dichloride (Cp

2ZrCl2 98) and

methylaluminoxane (MAO 10wt- in toluene) were purc-hased from Aldrich and were used as received Tris(pentaflu-orophenyl)borane (B(C

6F5)3 95) and NN-dimethylani-

linium tetra(pentafluorophenyl)borate ([C6H5N(CH

3)2H]+

[B(C6F5)4]minus 98) were supplied by Strem Chemicals and

they were used as received as well Polymer-grade ethylenewas purchased from Praxair and it was purified by passing itthrough 3-4 A activated molecular sieves

22 Ethylene Polymerization All polymerizations were per-formed in a 1 L stainless steel Parr reactor through thefollowing procedure several vacuum-argon cycles at 80∘Cwere carried out in order to purify the reactor Then itwas cooled to room temperature and filled with 150mLof distilled toluene under argon atmosphere The reactorstirring system was set at 100 rpm and it was heated to 50∘CThe catalyst system was fed into the reactor as follows (i)solution comprising MAO + B prepared in toluene at 5 wt-by stirring during two hours under inert atmosphere (ii)catalyst solution at 37 wt- in toluene prepared under inertatmosphere The molar ratios MAOZr and BZr were 100and 5 respectively The polymerization started by adding

the monomer at a continuous flow All experiments wereperformed at an ethylene pressure of 1 bar during 1 hour

The polymerization reaction was terminated by the clo-sure of the ethylene feeding and finally by adding an acidified(10 of hydrochloric acid) methanol solution The obtainedpolymerwas filtered off washedwithmethanol and vacuum-dried

23 Characterization Density was measured as describedin the ASTM D4052-11 standard test method for densityMolecular weight distributions (MWD) were determinedby size exclusion chromatography (SEC) using an Alliancechromatograph (GPC V-2000) equipped with two on-linedetectors a differential viscometer and a differential refrac-tometer The calibration was executed under polystyrenestandards using 124-trichlorobencene as eluent measure-ments were performed at a flow rate of 1mLmin at 140∘CDifferential scanning calorimeter (DSC) thermograms wereobtained by means of a TA instrument DSC 2920 at a heatingrate of 10∘Cmin under inert atmosphere Each sample washeated twice in order to eliminate the thermal historyThermogravimetric analyses (TGA) were performed usinga TA-Q500 apparatus in which the samples were heated to10∘Cmin under nitrogen atmosphere and at a flow rate of50mLmin Thermograms were recorded from 30 to 600∘CWide-angle X-ray diffraction (WAXD) measurements werecarried out in a Siemens D5000 diffractometer with a Ni-filtered CuK120572 radiation generator (wave length of 15406 A)Patterns were recorded from 5 to 35∘ (in 2120579) with 5 sec perstep Transmission electronmicroscopy (TEM) analyses wereperformed on a TITAN 80ndash300 kV Samples were preparedemploying a cryogenic ultramicrotome Leica Ultracut atminus125∘C and a cut rate of 2mmmin The sample slices werestained using ruthenium tetroxide (RuO

4) steam to contrast

amorphous and crystalline phases Dynamic mechanicalanalyses (DMA) were measured in a TA Instrument inflexural mode at a frequency of 01 Hz and a temperaturerange from minus103 to 103∘C During the measurement theheating rate was 5∘Cmin and the amplitude was 05mmThesample test specimens were prepared in a LMM LaboratoryMixing Molder from Dynisco Instruments at 180∘C and60 rpm

3 Results and Discussion

Theeffect of B on the final product properties was determinedby evaluating two different compounds one of each kind ofionic nature and using as referencematerial a synthesized PEin which only MAO was used as activator at a fixed molarratio of MAOZr = 100 and BZr = 5 Table 1 shows thecatalytic activity density and molecular weight (Mw) of thesynthesized PE

31 Catalytic Activity It is noticeable how the addition ofB either of ionic or nonionic nature significantly decre-ased the catalytic activity in the way that by incorpora-ting tris(pentafluorophenyl)borane (B1) into the reactionsystem (PE-2) the catalytic activity diminished in 4236and in 7279 by adding NN-dimethylanilinium




Catalyticactivity

(KgPEmolZr)

Density(gcm3)

Mw(Kgmol) PDI


PE-2 B(C6F5)3(B1) Nonionic 6734 0974 11618 43




3




Cp2ZrMe(C


literature [12 13]










119883119863=1120588 minus 1120588120572

1120588119888 minus 1120588120572times 100 (2)



9172

PE-1

827

10

08

06

04

02

00

30 35 40 45 50 55 60 65

Log M

dwd

LogM

(a)

PE-2

5672

32301097

08

07

06

05

04

03

02

01

00

30 35 40 45 50 55 60 65

Log M

dwd

LogM

(b)

PE-3

4449

4871

678

Log M

dwd

LogM

07

06

05

04

03

02

01

00

30 35 40 45 50 55 60 65 70

(c)





119883119863=


lowast 100 (3)






PE-1

5 10 15 20 25 30 35

PE-2

Crystalline

5 10 15 20 25 30 35

Amorphous

PE-3

5 10 15 20 25 30 35

2120579 (deg)

2120579 (deg)

2120579 (deg)





Table 3 TGA results



(∘C)


(∘C)






PE-1 PE-2 PE-3


Table 4 DMA results



Temperature (∘C)

13349∘C

13153∘C

13148∘C

PE-1

PE-2

PE-3

0 20 40 60 80 100 120 140 160




100

90

80

70

100 200 300 400 500

Wei

ght (

)



4 Conclusions


2ZrCl2



450

400

350

300

250

200

150

100

50

0


PE-1PE-2

Temperature (∘C)

Stor

age m

odul

us (M

Pa)

(a)

times103

11

10

9

8

7

6

5

4

3

2

1

0

minus1

PE-1PE-2

Loss

mod

ulus

(MPa

)


Temperature (∘C)

(b)





Acknowledgments


References



















3-O)]6 hybrid

















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Catalyticactivity

(KgPEmolZr)

Density(gcm3)

Mw(Kgmol) PDI


PE-2 B(C6F5)3(B1) Nonionic 6734 0974 11618 43




3




Cp2ZrMe(C


literature [12 13]










119883119863=1120588 minus 1120588120572

1120588119888 minus 1120588120572times 100 (2)



9172

PE-1

827

10

08

06

04

02

00

30 35 40 45 50 55 60 65

Log M

dwd

LogM

(a)

PE-2

5672

32301097

08

07

06

05

04

03

02

01

00

30 35 40 45 50 55 60 65

Log M

dwd

LogM

(b)

PE-3

4449

4871

678

Log M

dwd

LogM

07

06

05

04

03

02

01

00

30 35 40 45 50 55 60 65 70

(c)





119883119863=


lowast 100 (3)






PE-1

5 10 15 20 25 30 35

PE-2

Crystalline

5 10 15 20 25 30 35

Amorphous

PE-3

5 10 15 20 25 30 35

2120579 (deg)

2120579 (deg)

2120579 (deg)





Table 3 TGA results



(∘C)


(∘C)






PE-1 PE-2 PE-3


Table 4 DMA results



Temperature (∘C)

13349∘C

13153∘C

13148∘C

PE-1

PE-2

PE-3

0 20 40 60 80 100 120 140 160




100

90

80

70

100 200 300 400 500

Wei

ght (

)



4 Conclusions


2ZrCl2



450

400

350

300

250

200

150

100

50

0


PE-1PE-2

Temperature (∘C)

Stor

age m

odul

us (M

Pa)

(a)

times103

11

10

9

8

7

6

5

4

3

2

1

0

minus1

PE-1PE-2

Loss

mod

ulus

(MPa

)


Temperature (∘C)

(b)





Acknowledgments


References



















3-O)]6 hybrid

















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




9172

PE-1

827

10

08

06

04

02

00

30 35 40 45 50 55 60 65

Log M

dwd

LogM

(a)

PE-2

5672

32301097

08

07

06

05

04

03

02

01

00

30 35 40 45 50 55 60 65

Log M

dwd

LogM

(b)

PE-3

4449

4871

678

Log M

dwd

LogM

07

06

05

04

03

02

01

00

30 35 40 45 50 55 60 65 70

(c)





119883119863=


lowast 100 (3)






PE-1

5 10 15 20 25 30 35

PE-2

Crystalline

5 10 15 20 25 30 35

Amorphous

PE-3

5 10 15 20 25 30 35

2120579 (deg)

2120579 (deg)

2120579 (deg)





Table 3 TGA results



(∘C)


(∘C)






PE-1 PE-2 PE-3


Table 4 DMA results



Temperature (∘C)

13349∘C

13153∘C

13148∘C

PE-1

PE-2

PE-3

0 20 40 60 80 100 120 140 160




100

90

80

70

100 200 300 400 500

Wei

ght (

)



4 Conclusions


2ZrCl2



450

400

350

300

250

200

150

100

50

0


PE-1PE-2

Temperature (∘C)

Stor

age m

odul

us (M

Pa)

(a)

times103

11

10

9

8

7

6

5

4

3

2

1

0

minus1

PE-1PE-2

Loss

mod

ulus

(MPa

)


Temperature (∘C)

(b)





Acknowledgments


References



















3-O)]6 hybrid

















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







PE-1

5 10 15 20 25 30 35

PE-2

Crystalline

5 10 15 20 25 30 35

Amorphous

PE-3

5 10 15 20 25 30 35

2120579 (deg)

2120579 (deg)

2120579 (deg)





Table 3 TGA results



(∘C)


(∘C)






PE-1 PE-2 PE-3


Table 4 DMA results



Temperature (∘C)

13349∘C

13153∘C

13148∘C

PE-1

PE-2

PE-3

0 20 40 60 80 100 120 140 160




100

90

80

70

100 200 300 400 500

Wei

ght (

)



4 Conclusions


2ZrCl2



450

400

350

300

250

200

150

100

50

0


PE-1PE-2

Temperature (∘C)

Stor

age m

odul

us (M

Pa)

(a)

times103

11

10

9

8

7

6

5

4

3

2

1

0

minus1

PE-1PE-2

Loss

mod

ulus

(MPa

)


Temperature (∘C)

(b)





Acknowledgments


References



















3-O)]6 hybrid

















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




PE-1 PE-2 PE-3


Table 4 DMA results



Temperature (∘C)

13349∘C

13153∘C

13148∘C

PE-1

PE-2

PE-3

0 20 40 60 80 100 120 140 160




100

90

80

70

100 200 300 400 500

Wei

ght (

)



4 Conclusions


2ZrCl2



450

400

350

300

250

200

150

100

50

0


PE-1PE-2

Temperature (∘C)

Stor

age m

odul

us (M

Pa)

(a)

times103

11

10

9

8

7

6

5

4

3

2

1

0

minus1

PE-1PE-2

Loss

mod

ulus

(MPa

)


Temperature (∘C)

(b)





Acknowledgments


References



















3-O)]6 hybrid

















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




450

400

350

300

250

200

150

100

50

0


PE-1PE-2

Temperature (∘C)

Stor

age m

odul

us (M

Pa)

(a)

times103

11

10

9

8

7

6

5

4

3

2

1

0

minus1

PE-1PE-2

Loss

mod

ulus

(MPa

)


Temperature (∘C)

(b)





Acknowledgments


References



















3-O)]6 hybrid

















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






3-O)]6 hybrid

















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



influence of organoboron compounds on ethylene polymerization using cp2zrcl2/mao as catalyst system

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