synthesis of propylene/1-butene copolymers in liquid pool and gas-phase processes: a comparative...

Available online at www.sciencedirect.comEUROPEAN

European Polymer Journal 44 (2008) 1102–1113

www.elsevier.com/locate/europolj

POLYMERJOURNAL

Synthesis of propylene/1-butene copolymers in liquid pooland gas-phase processes: A comparative analysis

Fabricio Machado a,b,*, Enrique Luis Lima b, Jose Carlos Pinto b,Timothy F. McKenna a,1

a LCPP-CNRS/ESCPE-Lyon, 43 Blvd du 11 Novembre 1918, Bat 308F, BP 2077, 69616 Villeurbanne Cedex, Franceb Programa de Engenharia Quımica/COPPE, Universidade Federal do Rio de Janeiro, Cidade Universitaria, CP 68502,

Rio de Janeiro 21945-970, RJ, Brazil

Received 14 November 2007; received in revised form 22 January 2008; accepted 24 January 2008Available online 9 February 2008

Abstract

Batch liquid pool and semibatch gas-phase polymerizations were performed with high-activity Ziegler–Natta catalyststo evaluate the effect of 1-butene on the crystallinity, the melt temperature and the average molecular weights of the final 1-butene/propylene copolymers and alloys. According to the obtained results, 1-butene can be significantly incorporated intothe polymer chain over the whole range of copolymer compositions in both gas and liquid-phases, leading to the decreaseof the melting temperature of the copolymer resins. On the other hand, the properties of the polymer alloys seem to be lesssensitive to 1-butene incorporation, indicating the development of a distinct 1-butene phase. The average molecularweights, the polydispersities and the reactivity ratios are quite different in the liquid pool and gas-phase processes, indicat-ing that sorption/ diffusion effects may exert an important role during the copolymerization. The obtained reactivity ratiosin the gas-phase are close to 1, while the reactivity ratios of propylene are systematically higher than the reactivity ratios of1-butene in the liquid pool process. Polymer materials with large molecular weights and good particle morphology can beobtained in all analyzed cases, indicating that development of propylene/1-butene copolymer grades is indeed possible inboth liquid pool and gas-phase processes.� 2008 Elsevier Ltd. All rights reserved.

Keywords: Propylene/1-butene copolymers; Liquid pool, gas-phase and sequential polymerizations; Ziegler–Natta catalysts; Deconvo-lution of molecular weight distributions

0014-3057/$ - see front matter � 2008 Elsevier Ltd. All rights reserved

doi:10.1016/j.eurpolymj.2008.01.040

* Corresponding author. Present address: Nova Petroquımica,Rua Hidrogenio, 1404, Polo Petroquımico, CEP: 42810-000Camac�ari, BA, Brazil. Tel.: +55 71 3797 3709; fax: +55 71 36322206.

E-mail address: [email protected](F. Machado).

1 Present address: Department of Chemical Engineering,Queen’s University, 19 Division Street, Kingston, ON, CanadaK7L 3N6.

1. Introduction

The appropriate choice of comonomers can allowfor drastic modification of the properties of homo-polymer resins, leading to considerable improve-ment of product performance. In propylenepolymerizations, comonomers can be used for mod-ification of a number of important end-use proper-ties, such as hardness, tensile strength, stiffness,

.

mailto:[email protected]

F. Machado et al. / European Polymer Journal 44 (2008) 1102–1113 1103

density, melt point, impact strength and transpar-ency of the final polymer resin.

It is well known that the melting point and thecrystallinity of isotactic polypropylene-based poly-mers are lowered by incorporation of comonomerunits. According to Arnold et al. [1], propene/1-butene copolymers (CPP1B) obtained with heter-ogeneous Ziegler–Natta catalysts may present veryinteresting properties for a large number of distinctapplications. For instance, propene/1-butene ran-dom copolymers can be used for development ofspecial film applications, which require printingand metallization for improvement of the aestheticsof the final products. In this particular case, CPP1Bmay be regarded as very promising materials,because of the lower sensibility to the surface treat-ment [2]. In addition, the incorporation of 1-buteneinto the copolymer chains leads to decrease of themelting and the sealing initiation temperatures ofthe polymer film, which is advantageous when lowerprocessing temperatures are required.

Liquid pool polymerizations are extensively usedin industrial practice for production of polypropyl-ene resins because of the higher polymerizationrates and easier separation and purification of thefinal polymer material. Gas-phase polymerizationsalso constitute very competitive industrial processes,because process constraints related to liquid viscos-ity and solubility in the liquid-phase can be elimi-nated. The absence of solvent treatment alsoreduces plant operation costs very significantly [3].For these reasons, both liquid pool and gas-phasepolymerizations based on a high-activity Ziegler–Natta catalyst system can be used successfully toproduce propylene resins with different propertiesand copolymer compositions [4,5].

Compared to propylene and ethylene homopoly-merizations and to ethylene/a-olefin copolymeriza-tions, there are relatively few studies in the openliterature about the synthesis of propylene/1-butenecopolymers. Among available published studies,most investigated polymerizations in suspensionsof heptane, hexane or toluene [6–11], although somefew studies regard polymerizations performed inbulk [12,13] and in gas-phase [14]. These studiesshow that, depending on the features of the Zie-gler–Natta catalyst system (for example, type ofexternal and internal donors, catalyst carriers, iso-specificity of the catalyst sites, etc.), both randomand block copolymers can be obtained.

There are also few studies in the open literatureconcerning the synthesis of propylene alloys via

sequential polymerization [15–26]. More important,these works are essentially focused upon the synthe-sis of polypropylene-based materials, where poly-ethylene and/or poly(ethylene-co-polypropylene)constitute the second phase. To the best of ourknowledge, the work developed by Cecchin et al.[27] is the only one that presents experimental datafor propylene/1-butene alloys produced in sequen-tial polymerizations. However, 1-butene was usedin this case only to provide information about themechanism of polypropylene growth over MgCl2/TiCl4 catalyst system, so that no information wasprovided about the quality of the final polymerproducts.

Recently, Machado et al. [28–30] developed afamily of random polypropylene/1-butene copoly-mer grades for gas-phase and bulk processesintended for packaging and film applications. Itwas shown for the first time that it is possible to pro-duce propylene/1-butene random copolymers insemibatch gas-phase polymerizations using high-activity Ziegler–Natta catalysts [28]. It was alsoshown that 1-butene can be incorporated into thepolymer chain over the whole range of copolymercompositions during liquid pool polymerizations[29]. It was observed in both cases that 1-butene isincorporated at random into the polymer chains athigh polymerization rates, resulting in polymermaterials with lower melting temperatures. It wasalso shown that the microstructure of the resultingpolymer chains can be controlled through adjust-ment of the propylene and hydrogen partial pres-sures. Machado et al. [30] also synthesized a newfamily of polypropylene/1-butene alloys throughin situ sequential two-stage polymerizations, usinga high-activity MgCl2/Ziegler–Natta catalyst. Inthe first stage, liquid pool propylene polymeriza-tions were carried out in batch mode, while 1-butenewas polymerized inside the polypropylene matrix ingas-phase in semibatch mode during the secondpolymerization stage. It was shown that it is possi-ble to incorporate 1-butene in the polypropylenematrix in polymerizations performed at low pres-sures, indicating that polypropylene/1-butene alloyscan also be prepared in situ for future applicationsas high-performance structured materials.

In this paper, the results obtained by Machadoand coworkers are reviewed and compared. Themain objective here is presenting a critical evaluationof the main differences observed among the distinctanalyzed polymerization processes and obtainedpolymer products. In addition, new analytical and

1104 F. Machado et al. / European Polymer Journal 44 (2008) 1102–1113

characterization results are also presented for thepropylene/1-butene copolymer products obtainedhere.

2. Chemicals, experimental procedure and analyses

2.1. Chemicals

Propylene with minimum purity of 99.5%, 1-butene with minimum of purity 99.0% and hydro-gen with minimum purity of 99.9% were purchasedfrom AGA S/A (Rio de Janeiro, Brazil). Heptane(VETEC, Rio de Janeiro, Brazil) was used for prep-aration of cocatalyst solution and catalyst systemslurry after pre-treatment on 3 A molecular sieves(purchased from Spectrum Chemical, USA). Thetriethylaluminum (TEA) cocatalyst was providedby Akzo Nobel, Sao Paulo, Brazil. Polymerizationgrade cyclohexyl-methyl-dimethoxysilane(DMMCHS), kindly supplied by Suzano Petroquı-mica, was used as external electron donor. Nitrogenpurchased from AGA S/A (Rio de Janeiro, Brazil),with minimum purity of 99.0%, was used to keep thereaction environment free of oxygen. The gases usedin the reaction were used after purification in succes-sive beds of copper catalysts and 3 A molecularsieves. Unless otherwise stated, chemicals were usedas received, without additional purification. A com-mercial MgCl2-supported TiCl4 catalyst, with cata-lyst titanium content of 3.0 wt.% containingdiisobutyl phthalate (DIBP) as internal donor, wasused to perform the polymerizations. Suzano Petro-quımica kindly provided the catalyst samples. Thereader is encouraged to read the original referencesfor additional information.

3. Experimental procedure

3.1. Liquid pool polymerizations

Bulk polymerizations were carried out in a 450-mL mini bench top PARR 4562 reactor at 60 �C.The system was kept under isothermal conditionsand constant agitation of 500 rpm. Gas feed lineswere equipped with Brooks mass flow meters(model 5860 i). The reaction temperature and thegas feed flow rates were monitored in line with amicrocomputer equipped with an AD/DA dataacquisition system PCI-1710 (Advantech Brazil,Sao Paulo – SP). The software ADPol 2.0 was usedfor data acquisition [31]. The 1-butene content ofthe feed was varied in the range of 0–100%, while

the cocatalyst and catalyst concentrations were keptconstant and equal, respectively, to 1 mg of TEA/5 g of monomer and 1 mg of catalyst/25 g of mono-mer. Detailed description of reactor apparatus ispresented by Machado et al. [29].

3.2. Gas-phase polymerizations

Gas-phase polymerizations were carried out insemibatch mode. The system was kept under iso-thermal conditions and constant agitation of270 rpm. The reactor used was a 2.5 L thermostat-ted turbosphere stainless steel reactor, equippedwith injection valves for the catalyst and comono-mer feeds. Polymerizations were performed with20 mg of commercial MgCl2-supported TiCl4 cata-lyst and 10 mg of DMMCHS. The 1-butene contentwas varied in the range of 0–15 mol%, while theTEA/DMMCHS mole ratio was kept equal to 40.The experimental setup used to carry out the poly-merization reactions was similar to the onedescribed by Machado et al. [28] and Kittilsen andMcKenna [42], and the reader is referred to thesepublications for a more detailed description of theprotocol.

3.3. Sequential polymerizations

Sequential polymerizations were carried out in a1000 mL moveable PARR 4531 reactor equippedwith a PARR 4842 temperature controller. The sys-tem was kept under isothermal conditions and con-stant agitation of 500 rpm. Gas feed lines wereequipped with Kobold MAS-4010 mass flow meters,which provided real time flowrate data. The reac-tion temperature and the gas feed flowrates weremonitored in line with a microcomputer equippedwith an AD/DA data acquisition system AdvantechPCI-1710. The software ADPol 2.0 was used fordata acquisition [31]. In the experimental runs, thecatalyst/DMMCHS weight ratio ðRCAT=EDÞ wasvaried within the range of 1.8–2.3. In the first stage,liquid pool propylene polymerizations were carriedout in batch mode. In the second stage, 1-butenewas polymerized into the polypropylene matrix insemibatch mode in gas-phase. The experimentalsetup used to carry out the sequential polymeriza-tions was similar to the one described by Machadoet al. [29,30] and the reader is referred to this publi-cation for detailed information.


3.4. Analyses

The weight-average molecular weight and theMWD of the polymers were measured on a WatersAlliance GPCV 2000. The system was equippedwith a refractometer, a viscometer and WatersStyragel HT2 and HT6E gel columns. Analyseswere performed at 150 �C using trichlorobenzeneas solvent. Copolymer composition was determinedby liquid 13C NMR in a Bruker DRX 400 spectrom-eter, operating at 100.6 MHz and equipped withprobes of 5 mm. The 13C NMR copolymer spectrawere obtained at 90 �C. Typical accumulationsincluded 70� flip angle and 4.44 s recycle time. Sam-ples were dissolved in tetrachloroethylene and ben-zene-d6 (2/1 v/v). The melting temperature wasdetermined by DSC measurements in a Pyris 1 cal-orimeter at heating rates of 5 �C/min. Surface mor-phology of polymer particles was determined usingscanning electron microscopy (SEM). The imageswere recorded with a S800 Hitachi microscope oper-ating at accelerating voltages of 15 keV.

4. Results and discussion

Polymer composition was determined by 13CNMR through quantitative analysis of the charac-teristic peaks of the group CH2. Fig. 1 shows thecharacteristic CH2 peak placed at 46–47.1 ppm forpolypropylene, at 40–40.1 ppm for poly(1-butene)and 43–43.6 for polypropylene/1-butene copolymer.

The 1-butene content of the copolymer, the num-ber average sequence lengths and the reactivity ratiowere determined from the dyad distributions byusing standard relationships [32,33]. Number aver-age sequence lengths could also be determined fromthe dyad distributions and used to characterize themolecular microstructure of polymer materialsthrough the following relationships [32]:

�nB ¼½BB� þ 0:5½BP�

0:5½BP� and �nP ¼½PP� þ 0:5½BP�

0:5½BP� ð1Þ

The dyad sequence distribution was also used forthe calculation of the reactivity ratio products, ex-pressed in accordance with the following equation[33]:

r1 � r2 ¼ 4½PP�½BB�½BP�2

ð2Þ

The reactivity ratios of propylene (r1) and of 1-bu-tene (r2) can be expressed as [33]

r1 ¼ 2½PP�W½BP � and r2 ¼ 2

½BB�½BP�W ð3Þ

where W is the ratio between 1-butene and propyl-ene concentrations in the feed. P denotes propyleneand B denotes 1-butene monomer units.

Table 1 and Fig. 2 show how the incorporationof 1-butene (I¼C4

Þ depends on the initial monomerfeed composition (X¼C4

Þ. It can be observed that 1-butene is significantly incorporated into the polymerchains over the entire range of feed compositionsemployed in the liquid pool and the gas-phase poly-merization processes.

According to the results presented in Table 1,the kinetics of the polymerization are not affectedby the increasing 1-butene concentration, when the1-butene concentration in the medium is relativelysmall (up to 10 wt.%). The reactivity ratios of bothmonomers change slightly and polymerizations rateare not significantly different when the 1-butenecontent increases. In the particular case of the gas-phase propylene/1-butene polymerizations, bothreactivity ratios are very close to 1. This was verysurprising, because olefins of larger molecularweights are believed to react at lower rates.

The distinct reactivity ratios obtained during theliquid pool and the gas-phase polymerizations per-formed with the same catalyst indicate that masstransfer effects (sorption and/or diffusion) shouldplay an important role during the reaction. As amatter of fact, the solubility of 1-butene into thecopolymer matrix is favored in the gas-phase withrespect to propylene because of its larger molecularweight and lower vapor pressure. These effects areexpected to be minimized in the liquid-phasebecause of the much more significant swelling ofthe polymer phase and the much larger density ofthe bulk monomer phase. This seems to indicatethat the higher solubility of 1-butene in the polymermatrix in the gas-phase compensates its intrinsicallylower reactivity, leading to reactivity ratios that areclose to 1.

This behavior changes when the concentration of1-butene in the reaction medium is higher than10 wt.% in the liquid-phase. As shown in Table 1for liquid pool polymerizations, the propylene reac-tivity ratios increase linearly, while the 1-butenereactivity ratios tend to go through a maximumand decrease slowly to a value around 0.50. Again,this is probably related to the preferential swell-ing and higher diffusivity of propylene into thecopolymer matrix. This also reflects the higher

8

7

6

ppm

50 45 40 35 30 25 20 15 10 5

8

7

6

5

4

3

2

1

47 46 45 44 43 42 41 40

Fig. 1. Typical 13C NMR spectrum of propylene/1-butene copolymers.

Table 1Copolymer composition and average sequence lengths of propylene-based polymers

Run T (�C) P (Bar) X¼C4(wt.%) I¼C4

(wt.%) �nB �nP r1 r2 r1 � r2

Liquid pool polymerizationa

LP00 60 25.4 0 0.00 – – – – –LP01 60 24.5 5 4.28 1.01 30.12 1.15 0.24 0.28LP02 60 23.6 10 6.25 1.02 20.01 1.58 0.24 0.38LP03 70 26.6 20 13.16 1.20 10.56 2.39 0.80 1.91LP04 60 16.5 50 33.73 1.53 4.00 2.25 0.70 1.58LP05 60 9.38 90 82.68 5.12 1.43 2.91 0.61 1.78LP06 60 8.49 95 89.82 8.29 1.25 3.62 0.51 1.85LP07 60 7.60 100 100 – – – – –

Gas-phase polymerizationb

GF00 60 4 0 0.00 – – – – –GF01 60 4 5 4.30 1.1 23.5 1.18 1.13 1.34GF02 60 4 10 8.20 1.1 12.4 1.27 0.94 1.19GF03 40 4 15 11.90 1.2 8.6 1.34 0.94 1.26

a The TEA/catalyst weight ratio was kept equal to 5. The polymerizations were performed without hydrogen.b The TEA/catalyst weight ratio was kept equal to 15. The hydrogen concentration was kept equal to 3 mol%.


intrinsic reactivity of propylene molecules, whencompared to the 1-butene monomer. Therefore,the comparative analysis of reactivity ratiosobtained for the different reaction systems shows

that the intrinsic kinetic behavior of propylene/1-butene copolymerizations cannot be investigatedwithout the support of good thermodynamicanalysis.

0 10 20 30 40 50 60 70 80 90 100

0

20

40

60

80

100

Liquid Pool Gas-Phase

Feed Composition of 1-Butene (wt-%)

1-B

uten

e C

ompo

sitio

n in

the

Cop

olym

er (

wt-

%)

0

8

16

24

32 n1 : Liquid Pool

n1 : Gas-Phase

n2 : Liquid Pool

n2 : Gas-Phase

Ave

rage

Seq

uenc

eL

engt

hs

0

1

2

3

4

5 r1 : Gas-Phase

r2 : Gas-Phase

r1 .r2 : Gas-Phase

r1 : Liquid Pool

r2 : Liquid Pool

r1 .r2 : Liquid Pool

Rea

ctiv

ity R

atio

s

Fig. 2. Copolymer composition, average sequence lengths andreactivity ratios of propylene-based polymers.

SP01 SP02 SP03 SP04 SP05303132333435363738

PP

Dya

d D

istr

ibut

ion

(mol

-%)

Experiment Code

SP01 SP02 SP03 SP04 SP050.0

0.1

0.2

0.3

0.4

0.5

BB

Dya

d D

istr

ibut

ion

(mol

-%)

Fig. 3. Dyad distribution for propylene/1-butene copolymers.


According to Table 1, the product of the reactiv-ity ratios (r1 � r2) for samples obtained from liquidpool experiments increase with the 1-butene contentof the copolymer chain. This indicates that devia-tion from ideal random copolymerizations and rela-tive increase of 1-butene incorporation can beobserved when the 1-butene content increases. Thescenario is very different in the gas-phase, whereconditions resemble the ideal copolymerization,where all reactivity ratios are very similar to 1. Thismeans that liquid pool polymerizations give birth tolonger monomer blocks in the polymer chain thatthe corresponding gas-phase polymerizations. Thisalso means that liquid pool polymerizations aremore sensitive to changes of the feed conditionsthan gas-phase polymerizations, because feedchanges can also cause significant changes of reac-tivity ratios because of sorption/diffusion effects.

The reactivity ratios and the number averagesequence lengths of the polymeric material obtainedfrom sequential polymerizations cannot be evalu-ated from the dyad distributions by using standard

relationships [32,33]. Polymer samples obtainedfrom this process were polymer alloys, not realcopolymers, because of the experimental procedureadopted to perform the polymerizations [30]. Asthe reactions were started in the absence of propyl-ene in the second stage of the polymerization, BPdyad sequences were not observed in the final poly-mer chains. This confirmed the production of 1-butene homopolymer chains in the gas-phase duringthe second polymerization stage. Therefore, poly(1-butene) can be produced both during liquid pooland gas-phase polymerizations, which encouragesthe development of future poly(1-butene) grades.Fig. 3 illustrates the dyad sequences obtainedthrough 13C NMR of the final polymer samples. Itcan be observed that PP dyad sequences are presentin higher concentrations than BB dyad sequences,given the lower amounts of produced poly(1-butene).

Fig. 4 illustrates the triads distributions (PBP,PBB and BBB) [34–37], as determined from theCH signal peaks of 1-butene placed at 35.05–35.10 ppm. As can be observed, the triad concentra-tions are proportional to the content of 1-butene inthe copolymer chain, independent of the used poly-merization process. The triads/I¼C4

ratio is obtainedin the range of 0.18–0.30 for the liquid pool poly-merization, of 0.25–0.66 for the sequential polymer-ization and of 1.05–1.21 for the semibatch gas-phaseprocess, indicating that the formation of triads isfavored in the gas-phase polymerization process,as illustrated in Fig. 4. Therefore, it seems clear thatthe incorporation of 1-butene is favored in the gas-phase, when compared to the results obtained forthe liquid pool polymerizations. As 1-butene vaporpressures are not very low at typical reaction

LP01LP02

LP03LP04

LP05LP06

GF01GF02

GF03SP01

SP02SP03

SP04SP05

0.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

Tri

ad D

istr

ibut

ion

(mol

-%)

Experiment Code

Fig. 4. Triad distribution for propylene/1-butene copolymers.

150

155

160

165

170

Gas-Phase Liquid Pool Sequential Process

empe

ratu

re (

° C)


temperatures, the use of 1-butene in monomer feedlines for production of new copolymer grades ingas-phase polypropylene facilities seems to beencouraging.

The fraction of atactic polymer, soluble in hotxylene (XS) was determined through extractionsvia Soxhlet technique with boiling xylene, stabilizedwith BHT to avoid oxidative degradation, for 3 hand vacuum dried at 100 �C. Table 2 shows theresults obtained to the XS. It is observed that theXS value is directly correlated with 1-butene contentin the final copolymer. As a consequence, the poly-mer solubility in xylene increases with the incorpo-ration of 1-butene in the polymeric chain.

According to Table 1 (Run 06), the r1/r2 ratio isabout 7, which indicates that the produced copoly-mers do not present a homogeneous chemical com-position in reactions performed in batch modebecause of the preferential polymerization of pro-pylene, leading to the formation of copolymer richin propylene in the beginning of the polymerizationand very rich in 1-butene at the end of the polymer-ization. The isotactic index obtained for pure poly-propylene is higher than the one obtained for purepoly(1-butene), as shown in Table 2. In the particu-lar case of copolymer material with a high contentof 1-butene, it is expected that the contribution of

Table 2Xylene soluble in propylene-based polymers in liquid poolpolymerizations

Run LP00 LP01 LP02 LP06 LP07

I¼C4(wt.%) 0.00 4.28 6.25 89.82 100.00

XS (wt.%) 2.32 3.16 5.46 12.41 4.17

1-butene for the formation of copolymeric chainin the beginning of the reaction be more importantfor determination of the isotactic index than thepropylene incorporation at the end of thepolymerization.

Fig. 5 illustrates the influence of the 1-butenecontent on melting temperature and crystallinityof propylene-based polymers. It can be observedthat a small increase of the 1-butene content maylead to very significant reduction of the melting tem-perature of the copolymer when compared to themelting temperature of the propylene homopoly-mer. The crystallinity of propylene-based polymersis also influenced by the 1-butene incorporation verysignificantly, probably because of the regular per-turbations of the geometrical structure of the poly-mer chains. (The incorporation of comonomerunits into a homopolymer chain and reduction ofcrystallinity can also contribute to an increase ofpolymer transparency.) Depending on the 1-butenecontent, the melting temperature of the randomcopolymer can be 30 �C lower than the melting tem-perature of the polypropylene homopolymer, whichis very significant for development of new film appli-cations. Surprisingly, the melting temperatures ofthe polymer samples obtained from the two-stagepolymerization processes do not change much andare even slightly higher than the ones obtained forpolypropylene. This seems to confirm once morethat poly(1-butene) is produced in gas-phase dur-ing the second stage of the polymerization. In addi-tion, the formation of different crystalline structureof the propylene-based polymer in both liquid pooland gas-phase processes should be taken intoconsideration.

0 2 4 6 8 10 12 14130

135

140

145

Mel

ting

T

1-Butene Content (mol-%)

Fig. 5. Effect of 1-butene content on the melting temperature.


It is well known that supported Ziegler–Nattacatalysts present multiple catalyst sites, which maylead to development of multimodal distributionsof final molecular properties of polymer materials,such as chain size and chain composition. Fig. 6 pre-sents typical DSC thermograms obtained for poly-mer samples produced in the distinct analyzedprocesses.

It is well known that the incorporation of como-nomer units into a homopolymer chain leads tosmall structural imperfections, allowing for decreas-ing of the melting point and the crystallinity of iso-tactic polypropylene-based polymers. Depending onthe extent of the structural changes in the polymerchain, different patterns can be observed for theshape of DSC curve. As one can observe, bimodalcurves can be obtained in many of the samples. Thisclearly indicates that the polymer material is nothomogeneous and that polymer chains with distinctcomposition are produced both in the gas-phase andin the liquid-phase polymerizations. In general, thebimodal behavior seems to be more pronouncedfor the copolymer materials obtained in the liquidpool polymerization process, which can also berelated to the more pronounced variation of reactiv-ity ratios observed for increasing 1-butene feed com-positions. Therefore, detailed kinetic understandingof the analyzed copolymerizations can only be per-formed if the multi-site nature of the catalyst istaken into consideration. This is beyond the scopeof this text and will not be performed here becausethe comonomer composition distribution dependson several factors, such as the nature of the catalystsystem, the polymerization conditions, the polymer-ization process, the monomer reactivities, etc.

100 110 120 130 140 150 160 170 18023

24

25

26

27

28

29

30

31

χ (%) = 31.39

χ (%) = 34.34

Liquid Pool: Run LP03 Gas-Phase: Run GF03 Sequential Process: Run SP02

Hea

t Flo

w (

mW

)

Temperature (°C)

χ (%) = 45.69

Fig. 6. Typical DSC curves of the propylene/1-butene samples.

Deconvolution of molecular weight distributions(MWDs) has been extensively employed for obtain-ing information about the polymerization kineticsand interpretation of the main features of catalystsystems. The MWDs can generally be described asthe summation of the Schulz–Flory distributions[38].

W i ¼XNS

j¼1

ajwi;j ð4Þ

where NS is the number of active sites, aj is the massfraction of polymer produced by the individual cat-alyst site j an wi,j is the weight Schulz–Flory [39] dis-tributions given as

wi;j ¼ ið1� qjÞ2qi�1

j ð5Þ

The propagation probability (q) is represented as

q ¼ KPMKPM þ

PkKTk X k

ð6Þ

where M and X are monomer and chain transferagent concentrations, KP and KT are the kinetic con-stants for propagation and transfer to the chaintransfer agents.

Fig. 7 illustrates MWD obtained from GPC anal-yses that were deconvoluted into different Flory–Schulz distributions. Depending on the sample, itcan be observed that up to five Flory-distributionsmay be necessary to describe the GPC data of thepolymer samples. In the particular case of Fig. 7B(sample obtained from liquid pool polymerization),only four sites are required to describe the MWD.The estimated model parameters are presented inTable 3. Weight-average molecular weights (MwÞpredicted by the deconvoluted Schulz–Flory distri-butions agree very well with the Mw obtained fromthe GPC measurements (see Fig. 7 and Table 3).Shapes of the MWDs are significantly differentbecause the different active sites respond distinctlyto the reaction conditions (the reaction temperatureand the 1-butene content). For this reason, the Mws

and the as predicted by the individual Schulz–Florydistributions are significantly different, as shown inTable 3.

The analysis of molecular weight distributionsindicates that the average molecular weights andthe polydispersities can be quite different for poly-mer samples obtained in the different processesand different conditions, as shown in Tables 2 and3. The reader is encouraged to refer to the originalreferences [28–30] for detailed analysis of molecular

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.00.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9 GPC Data All Sites Individual Sites

dwt/d

[Log

(M)]

Log(Mw)

Log(Mw)3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7


dwt/d

[Log

(M)]

3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.00.0

0.1

0.2

0.3

0.4

0.5


dwt/d

[Log

(M)]

Log(Mw)

Fig. 7. Deconvolution of MWD into Schulz–Flory distributions: (A) gas-phase: GF03 – I¼C4(wt.%) = 11.90; (B) liquid pool: LP03 – I¼C4

(wt.%) = 13.16; (C) sequential polymerization, SP02 – I¼C4(wt.%) = 1.59.

Table 3Deconvolution of MWD into Schulz–Flory distributions

Process Mw Error (%) Site a q Mw

GPC Schulz–Flory

Gas-phase (Run GF03) 105,923 103,986 1.83 I 0.051 0.9996 594,479II 0.081 0.9737 7923III 0.174 0.9989 196,760IV 0.324 0.9938 33,639V 0.370 0.9972 75,379

Liquid pool (Run LP03) 237,871 226,193 4.91 I 0.113 0.9998 876,910II 0.144 0.9941 35,344III 0.322 0.9992 264,155IV 0.421 0.9976 87,779

Sequential (Run SP02) 549,454 577,772 5.15 I 0.109 0.9942 35,685II 0.130 0.9999 2,379,187III 0.248 0.9997 713,942IV 0.254 0.9976 87,945V 0.260 0.9992 250,741



weight distributions of all polymer samples. How-ever, it is important to say that, despite the multi-site nature of the catalyst, obtained MWD’s donot present multimodal behavior. Nevertheless,molecular weight distributions are usually verybroad and present large polydispersities in all cases(larger than 4). It is also interesting to observe thatmolecular weights of commercial interest areobtained in all cases, although molecular weight dis-tributions are shifted towards larger molecularweights when polymerizations are performed inthe liquid-phase. This is to be expected, given themuch larger monomer concentrations in theliquid-phase. Table 4 shows, however, that hydro-gen exerts a pronounced effect on the molecularweight distribution and can be used for control pur-poses, as usual.

Surface morphology of polymer particles wasdetermined using SEM. Images were recorded ataccelerating voltages of 15 keV. Fig. 8 shows the

Table 4Polymer composition and average molecular weight in sequential polym

Run Temperature (�C) RCAT=ED (w/w) H2 (mo

Stage Ia Stage IIb

SP00 70 – 1.87 0.38SP01 70 70 1.80 0.34SP02 70 70 1.83 0.00SP03 70 60 1.84 0.00SP04 70 60 1.84 0.38SP05 70 60 1.75 0.38

a First stage pressure equal to 31 bars. The TEA/catalyst weight ratiob Second stage pressure equal to 1 bar g.

Fig. 8. Morphology of polymer particles: (A) gas-phas

surface morphology of typical polymer particles.Polymer particles with good morphology can beobtained in gas-phase, liquid pool and sequentialprocesses. The morphological control of polymerparticles is desired because of problems associatedto process viability and reduction of plant operationcosts. Generally, it is desired that polymer particlespresent regular shape because the absence of finesprevents reactor fouling problems and undesirablefluidization effects. It can be observed that polymerparticles grow uniformly in all cases, leading to for-mation of polymer material with good morphologi-cal features in the whole range of analyzedexperimental conditions. This probably means thatheat and temperature effects associated with over-heating and melting of polymer particles did notoccur at the analyzed process conditions. As theemployed catalyst is provided as a solid suspensionin a mineral oil, it is possible that the inert materialcontributes with the reduction of local reaction rates

erizations

l%) I¼C4(wt.%) Mn (g/mol) Mw (g/mol) PDI

0.00 73,781 538,293 7.301.06 141,440 566,295 4.001.59 77,707 549,454 7.070.67 77,926 538,471 6.910.80 80,395 570,449 7.100.27 76,936 463,605 6.03

was kept equal to 5.

e; (B) liquid pool; (C) sequential polymerization.


during particle breakup, allowing for more uniformcatalyst fragmentation and production of particleswith good morphology [40,41].

5. Conclusions

A family of propylene/1-butene copolymergrades can be successfully developed for processesintended for packaging and film applications. Poly-propylene/1-butene in-reactor alloy can also be suc-cessfully developed for applications as high-performance structured materials. It was observedthat 1-butene can be successfully incorporated intopolypropylene chains at high polymerization ratesand low 1-butene partial pressures, resulting inpolymer materials with lower melting and sealinginitiation temperatures. It is possible to incorporate1-butene upon the polypropylene matrix at randomin liquid pool and gas-phase polymerizations andsequentially through combination of liquid pooland gas-phase polymerization processes.

The average molecular weights, the polydisper-sity index and the reactivity ratios are quite differentin the analyzed processes. The reactivity ratios areclose to 1 and essentially constant in the gas-phase,while it depends significantly on the 1-butene com-position in the liquid-phase. The obtained resultsindicate that 1-butene solubilization in the polymermatrix seems to be favored in the gas-phase process,which partially compensates for its lower reactivi-ties, as observed in the liquid-phase. The multi-sitenature of the Ziegler–Natta catalysts leads to pro-duction of materials with heterogeneous composi-tions and broad molecular weights. Gas-phasematerials are more homogeneous and present lowermolecular weights. However, all analyzed processescan produce molecular weights of commercial inter-est in the whole range of 1-butene compositions.Polymer particles with good morphology can beobtained in gas-phase, liquid pool and sequentialprocesses, without significant formation of finesand particle sticking.

Acknowledgements

The authors thank Coordenac�ao de Aperfeic�oa-mento de Pessoal de Nıvel Superior (CAPES, Bra-zilian Agency, Project No. BEX 2813/03-3),Conselho Nacional de Desenvolvimento Cientıficoe Tecnologico (CNPq) and UCBL-1 for providingscholarships and research funds. The authors thank

Suzano Petroquımica for providing technicalsupport.

References

[1] Arnold M, Henschke O, Knorr J. Copolymerization ofpropene and higher a-olefins with the metallocene catalystEt[Ind]2HfCl2/methylaluminoxane. Macromol Chem Phys1996;197:563.

[2] Marega C, Marigo A, Saini R, Ferrari P. The influence ofthermal treatment and processing on the structure andmorphology of poly(propylene-ran-1-butene) copolymers.Polym Int 2001;50(4):442–8.

[3] Xie T, McAuley KB, Hsu JCC, Bacon DW. Modelingmolecular weight development of gas-phase a-olefin copo-lymerization. AIChE J 1995;41(5):1251.

[4] Dotson NA, Galvan R, Laurence RL, Tirrel M. Polymer-ization process modeling. New York: VCH Publishers.;1996.

[5] Lieberman RB, Lenoir RT. Manufacturing. In: Moore EP,editor. Polypropylene Handbook Polymerization Character-ization Properties Processing Applications. New York: Han-ser Publishers; 1996. p. 287–302.

[6] Kissin YV, Beach DL. A kinetic method of reactivity ratiomeasurement in olefin co-polymerization with Ziegler–Nattacatalysts. J Polym Sci Part A Polym Chem 1983;21(4):1065–74.

[7] Locatelli P, Sacchi MC, Tritto I, Zannoni G. Propene–1-butene copolymerization with a heterogeneous Ziegler–Natta catalyst – inhomogeneity of isotactic active-sites.Makromol Chem Rapid Commun 1988;9(8):575–80.

[8] Kakugo M, Miyatake T, Mizunuma K, Kawai Y. Charac-teristics of ethylene–propylene and propylene–1-butenecopolymerization over TiCl31/3AlCl3–Al(C2H5)2Cl. Macro-molecules 1988;21(8):2309–13.

[9] Sacchi MC, Shan CJ, Forlini F, Tritto I, Locatelli P. Effectof internal and external Lewis-bases on propene/1-butenecopolymerization with MgCl2-supported Ziegler–Natta cat-alysts. Makromol Chem Rapid Commun 1993;14(4):231–8.

[10] Xu J, Feng L, Yang S, Yang Y, Kong X. Influence ofelectron donors on the tacticity and the compositiondistribution of propylene–butene copolymers produced bysupported Ziegler–Natta catalysts. Macromolecules1997;30(25):7655–60.

[11] Abiru T, Mizuno A, Weigand F. Microstructural charac-terization of propylene–butene-1 copolymer using tempera-ture rising elution fractionation. J Appl Polym Sci1998;68(9):1493–501.

[12] Collina G, Noristi L, Stewart CA. Propene-co-butenerandom copolymers synthesized with superactive Ziegler–Natta catalyst. J Mol Catal A Chem 1995;99(3):161–5.

[13] Machado F, Santos RTP, Nele M, Crossetti GL, Melo PA,Lima EL, et al. Bulk copolymerization of propylene/1-butene using a high-activity Ziegler–Natta catalyst. Deche-ma Monographs 2004;138:267–73.

[14] Oliva L, Serio MD, Peduto N, Santacesaria E. Chainpropagation rate constants for gas-phase polymerization ofpropene and 1-butene with Ziegler–Natta catalysts. Macro-mol Chem Phys 1994;195(1):211–6.

[15] Fu Z, Xu J, Zhang Y, Fan Z. Chain structure andmechanical properties of polyethylene/polypropylene/


poly(ethylene-co-propylene) in-reactor alloys synthesizedwith a spherical Ziegler–Natta catalyst by gas-phase poly-merization. J Appl Polym Sci 2005;97(2):640–7.

[16] Xu J, Feng L, Yang S, Wu Y, Yang Y, Kong X. Separationand identification of ethylene–propylene block copolymer.Polymer 1997;38(17):4381–5.

[17] Xu J, Fu Z, Fan Z, Feng L. Temperature rising elutionfractionation of PP/PE alloy and thermal behavior of thefractions. Eur Polym J 2002;38:1739–43.

[18] Zhang X, Olley RH, Huang B, Bassett DC. Characterizationof propylene/ethylene copolymers sequentially polymerizedwith catalyst system d-TiCl3/Et2AlCl. Polym Int1997;43:45–54.

[19] Hongjun C, Xiaolie L, Xiangxu C, Dezhu M, Jianmin W,Hongsheng T. Structure and properties of impact copolymerpolypropylene II. Phase structure and crystalline morphol-ogy. J Appl Polym Sci 1999;71:103–13.

[20] Hongjun C, Xiaolie L, Dezhu M, Jianmin W, Hongsheng T.Structure and properties of impact copolymer polypropyleneI. Chain structure. J Appl Polym Sci 1999;71:93–101.

[21] Fu Z, Fan Z, Zhang Y, Xu J. Chain structure of polyeth-ylene/polypropylene in-reactor alloy synthesized in gasphase with spherical Ziegler–Natta catalyst. Polym Int2004;53(8):1169–75.

[22] Xu J, Jin W, Fu Z, Fan Z. Composition distributions ofdifferent particles of a polypropylene/poly(ethylene-co-pro-pylene) in situ alloy analyzed by temperature-rising elutionfractionation. J Appl Polym Sci 2005;98(1):243–6.

[23] Mckenna TF, Bouzid D, Matsunami S, Sugano T.Evolution of particle morphology during polymerisationof high impact polypropylene. Polym React Eng2003;11(2):177–97.

[24] Bouzid D, McKenna TF. Improving impact poly(propylene)morphology and production: selective poisoning of catalystsurface sites and the use of antistatic agents. MacromolChem Phys 2006;207:13–9.

[25] Xu J, Linxian Feng. Characterization of microstructure ofpolypropylene alloys. Polym Int 1998;47(4):433–8.

[26] Fan ZQ, Zhang YQ, Xu JT, Wang HT, Feng LX. Structureand properties of polypropylene/poly(ethylene-co-propyl-ene) in-situ blends synthesized by spherical Ziegler–Nattacatalyst. Polymer 2001;42:5559–66.

[27] Cecchin G, Marchetti E, Baruzzi G. On the mechanism ofpolypropene growth over MgCl2/TiCl4 catalyst system.Macromol Chem Phys 2001;202(10):1987–94.

[28] Machado F, Lima EL, Pinto JC, McKenna TF. Synthesis ofpropylene/1-butene copolymers with Ziegler–Natta catalyst

in gas-phase copolymerizations, 1. Kinetics and macromo-lecular properties. Macromol Chem Phys 2005;206:2333–41.

[29] Machado F, Melo PA, Nele M, Lima EL, Pinto JC. Liquidpool copolymerization of propylene/1-butene with a MgCl2-supported Ziegler–Natta catalyst. Macromol Mater Eng2006;291:540–51.

[30] Machado F, Lima EL, Pinto JC, McKenna TF. In-situpreparation of polypropylene/1-butene alloys using aMgCl2-supported Ziegler–Natta catalyst. Eur Polym J2008;44(4):1130–9.

[31] Machado F, Lenzi MK, Software para Aquisic�ao de Dadosde Reac�oes de Polimerizac�ao. ADPol versao 2.0: Manual doUsuario, PEQ/COPPE/UFRJ, Rio de Janeiro; 2003.

[32] Randall JC. A 13C NMR determination of the comonomersequence distributions in propylene–butene-1 copolymers.Macromolecules 1978;11(3):592–7.

[33] Uozumi T, Soga K. Copolymerization of olefins withKaminsky-Sinn-type catalysts. Die Makromol Chem1992;193(4):823–31.

[34] Fisch MH, Dannenberg JJ. Propylene incorporation in 1-butene copolymers by carbon-13 nuclear magnetic resonancespectrometry. Anal Chem 1977;49(9):1405–8.

[35] Zhang Y-D, Gou Q-Q, Wang J, Wu C-J, Qiao J-L. C-13NMR, GPC, and DSC study on a propylene–ethylene–1-butene terpolymer fractionated by temperature rising elutionfractionation. Polym J 2003;35(7):551–9.

[36] Zhang Y-D. Monomer sequence distributions in propylene–1-butene random copolymers. Macromolecules2004;37:2471–7.

[37] Zhang Y. Monomer sequence characterization of propyl-ene–1-olefin copolymers by carbon-13 NMR spectroscopy.Polymer 2004;45:2651–6.

[38] Nele M, Pinto JC. Molecular-weight multimodality ofmultiple flory distributions. Macromol Theory Simul2002;11:293–307.

[39] Flory PJ. Molecular size distribution in linear condensationpolymers. J Am Chem Soc 1936;58(10):1877–85.

[40] Merquior DM, Lima EL, Pinto JC. Modeling of particlefragmentation in heterogeneous olefin polymerization reac-tions, 2. A Two Phase Model. Macromol Mater Eng2005;290(6):511–24.

[41] Merquior DM, Lima EL, Pinto JC. Modeling of particlefragmentation in heterogeneous olefin polymerization reac-tions. Polym React Eng 2003;11(2):133–54.

[42] Kittilsen P, McKenna TF. Study of the kinetics, masstransfer, and particle morphology in the production of high-impact polypropylene. J Appl Polym Sci 2001;82(5):1047–60.

synthesis of propylene/1-butene copolymers in liquid pool and gas-phase processes: a comparative...

Documents