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Morphological Stability of the Initially Formed
Polymer Particles in Stopped‑Flow Propylene
Polymerization

Author(s)Thang, Vu Quoc; Taniike, Toshiaki; Umemori,Masaki; Ikeya, Mitsuhiro; Hiraoka, Yuichi;
Terano, Minoru

Citation

Journal of Materials Life Society, 22(1): 30‑34

Issue Date

2010‑02

Type

Journal Article

Text version

publisher

URL

http://hdl.handle.net/10119/9168

RightsCopyright (C) 2010 マテリアルライフ学会. Vu QuocThang, Toshiaki Taniike, Masaki Umemori,
Mitsuhiro Ikeya, Yuichi Hiraoka, Minoru Terano,
Journal of Materials Life Society, 22(1), 2010,30‑34.

Description

Japan Advanced Institute of Science and Technology?T 1) 7 }v717~~~t (Materiaru Raifu Gakkaishi), 22 [1J 30~34 (Feb. 2010)

Original Paper)Morphological Stability of the Initially Formed Polymer Particles
in Stopped-Flow Propylene Polymerization
Vu Quoe THANG*1*2, Toshiaki TANIIKE**l, Masaki UMEMORI*l, Mitsuhiro lKEYA*l,Yuiehi HlRAOKA*l, Minoru TERANO*l(Received October 8, 2009, Accepted November 24,2009)
Abstract
The morphological stability of initially formed polymer particles against air was improved in order to study the initial morphology
development with Zigler-Natta catalyst olefin polymerization. The stopped-flow polymerization technique was applied tosynthesize initial polymer particles in combination with various quenching and stabilizing procedures. When polymerizing
particles were quenched with cold heptane maintained at -65°C under N2 or CO 2, the exposure of the formed particles to air caused
the fast formation of cracks on the surface, leading to serious reformation of the particle shape. However, when the particles werequenched with cold heptane under CO 2 and washed with heptane containing an appropriate amount oftetrahydrofuran, the particle
morphology was significantly stabilized which hardly changed even after 1 h exposure to air. The established stabilizing procedure
is highly useful for various characterizations of the initially formed particles.
Keywords: Morphological stability, Polyolefins, Ziegler-Natta catalyst, Stopped-flow polymerization

early stage of polymerization, the particles are mechanically

1. Introduction

weakest to be easily broken by the force from the formed
polymer and/or the heat attack. Therefore the initial morph-The worldwide polyolefin (PO) production in 2008 was

ological development is the key step for the final polymer

about 110 million tons and is speculated to steadily grow inparticle morphology. The huge impact of the initial stage not

the long future. Because of this huge capacity, the reaction

only on the final particle morphology but also on the wholeengineering aspects of the PO production with heterogene-

polymerization behaviors has invoked a great attention fromous catalysts such as Ziegler-Natta, Phillips and supported

both the academic and the industrial points of view.

metallocene are of great importance. Especially, the polymer

The stopped-flow (SF) technique (Fig. 1) explained in de-particle morphology strongly affects the plant operation andtails in the experimental part has been widely recognized toprocessing step. A failure of morphological control in a plant

be one of the most useful tools for the study of the veryleads to a number of serious troubles such as fouling, sheet-initial stage of olefin polymerization3),4). However, the SFing, and broadening residence-time distribution. It is recog-technique has been rarely applied to the investigation ofnized that the morphology of polymer particles is mainly

the morphological development because the conventional

determined by that of the original catalyst particles as well as

quenching procedure in the SF polymerization completely

the way how the particles developl),2). Especially, at the very

destroys the particle morphology. Another serious problem in* Corresponding author

the study of the initial particle morphology is that a large*1 School of Materials Science, Japan Advance Institute ofamount of the catalyst and cocatalyst remaining in the initial-

Science and Technology, 1-1 Asahidai, Nomi, Ishikawa, 9231292 Japan*2 Institute of Chemistry, Vietnam Academy of Science andTechnology, 18- Hoang Quoc Viet stress, Cau Giay, Ha Noi,Vietnam

30

ly formed polymer/catalyst particles readily react with moisture in air, leading to the rapid destruction of the particle
morphology.

The establishment of a way to improve the?T 1) 7 }v71 7~~~,t 2010:{f 2 fjVu Quoe TRANG, Toshiaki TANIIKE, Masaki UMEMORI, Mitsuhiro IKEYA, Yuiehi RIRAOKA, Minoru TERANOSF polymerization and stabilization
The initial polymer/catalyst particles were synthesized bythe stopped-flow technique illustrated in Fig. 1, in which catalyst slurry and cocatalyst solution saturated with propylene
gas at 1 atm were contained in the separate special glassvessels. The downstream flask contained a quenching agent.
The polymerization was conducted for 0.5 s, for which only

Polymerization

0.1 g of polypropylene was formed per 1 g of the catalyst. In
this study, we set up three new quenching and stabilizing
procedures instead of the conventional acidic ethanol:i) Heptane of 200 ml at - 65°C was used to significantly
decelerate the polymerization under the N2 atmosphere. After

MeOH + liq. NI

settling the mixture between the polymerization slurry andquenching heptane, the upper solvent was removed and thenFig. 1 Scheme of the stopped-flow polymerization

the remaining solid particles were washed with 100 ml heptane
to remove unreacting components.
ii) A similar quenching and washing procedure to i) wasmorphological stability of the initially formed particles underapplied under CO 2 rather than under N 2. CO 2 can kill theair must be highly valuable for various kinds of ex-situ

polymerization by cleaving the metal-alkyl bonds.

characterizations of the particles such as microscope ob-iii) A similar procedure to ii) was conducted except theservation, spectroscopic analysis, porosity measurement, etc.

addition of THF in the washing step as a morphologicalIn this study, we have successfully established a new quench-stabilizer, where the THF /Ti molar ratio was optimized to being and stabilizing procedure for the SF polymerization, which200.

effectively quenched the polymerization reaction and sig-

After removing the upper solvent, the particles were dried bynificantly improved the morphological stability of the initiallyN2 flow for 2 h. The detailed information about polymerization

formed polymer/catalyst particles under air.

and stabilization conditions is summarized in Table 1.
Scanning electron microscopy (SEM)

2. Experimental

The morphological stability of the initially formed polymer particles under air was examined by Hitachi S-41 00 Scan-Materials

ning Electron Microscope. The samples for SEM were pre-N 2, CO2, propylene (donated by Japan Polypropylene Co.),

pared in a glove bag under the N2 atmosphere, then transferredethanol (EtOH) and anhydrous tetrahydrofuran (THF) of

to a deposition device (Hitachi E-1 030 Ion Sputter) for the Pt-

research grade were used without further purification. Tri-

Pd coating, and finally transferred to the SEM chamber. The

isobutylaluminium (TiBA, donated by Tosoh FineChem Co.),two transfer processes were conducted under air for 90 s,

diisobuthylphthalate (DBP), spherical Mg(OEt)2 and titani-

which was the shortest exposure time in this study. In addition,

umtetrachloride (TiCI4) were used as delivered. Heptane of

the samples were intentionally exposed to air for 1 h before

research grade was used as solvent after passing through athe SEM observation, with an assumption that 1 h might becolumn of 4A molecular sieve and bubbling with dry N2

the maximum exposure time required for possible character-overnight.

izations.

The catalyst used in this study was the spherical Mg(OEt)2based catalyst, which is one of the most advanced industrial
olefin polymerization catalysts, prepared from the sphericalMg(OEt)2 basically according to the procedure in Ref. 5.

Diffuse reflectance infrared fourier transform spectroscopy (DRIFTS)
The surface states of the SF particles, especially the state of
THF on the particle surface, were examined by DRIFT spectrausing a JASCO FT/IR-6100 spectrometer in the N2 atmosphere.

Materiaru Raifu Gakkaishi, VoL22, No.1

31

Morphological Stability of the Initially Formed Polymer Particles in Stopped-Flow Propylene Polymerization

Table 1. Applied quenching and washing conditions

Run no.

Quenching step 1

Washing step

1-65°C heptane under N2

Heptane under N2 at r.t.

2-65°C heptane under CO 2

Heptane under CO 2 at r.t.

3-65°C heptane under CO 2

Heptane under CO 2 containing THF(THF/Ti=200/1)

All spectra were recorded by a MCT detector with a nominal
resolution of 4 cm -I.

As shown in Fig. 3, the SF polymer/catalyst particles could
experience two stages of damages caused by the exposure to
air : the fast crack formation on the particle surface and the3. Results and discussion

slow morphological change to result in a popcorn shape. The
mechanism of the particle stabilization by CO2 and THF isThe morphology of the original catalyst is shown in Fig. 2.

addressed as follows.

The catalyst particle is dense and spherical with an average

It is evident that after the SF polymerization the initiallydiameter of ca. 28.0,um. From the higher magnification image

formed particles are mainly composed of the catalyst com-(Fig. 2B), it is clearly seen that the catalyst particle has a roughponents, TiCI4/MgCh/DBP and TiBA with a small amountand grain-like surface.

of formed polymer (polymer yield 0.1 g/g-cat.). The compo-The morphology of the initial polymer/catalyst particles,nents other than DBP and the formed polymer are moisture-

which was prepared with the three different quenching pro-sensitive materials. TiBA and TiCl4 intensively react withcedures and then exposed to air for 90 s or for 1 h, is shown inmoisture according to the reactions (1) and (2), respectively.

Fig. 3. For the first quenching procedure, the initially formed

These reactions produce a huge amount of heat and gases,

polymer/catalyst particles were not stable. Many big cracks

which rapidly cause the cracks on the particle surface (Fig.

appeared on the particle surface after 90 s and the particles

3A and 3B). On the other hand, MgCh reacts with moistureturned to a popcorn shape after 1 h under air (Fig. 3A and 3A',

more mildly to make the MgCh' (H20)6 adduct through therespectively). When CO 2 was applied for the quenching agent,

reaction (3). This reaction accompanies the reformation ofthe

the polymer particles became more stable : after 90 s of theparticle morphology, which might be a driving force of theexposure, the cracks still appeared but became much smaller

cracks, and slowly swells the whole particle, leading to the(Fig.3B). However, the particle morphology severely changed

expansion of the cracks and finally to the popcone or molten

after the longer exposure time of 1 h (the cracks became much

shape (Fig. 3A' and 3B').

bigger in Fig. 3B'). With the third quenching procedure, when

Fresh heptane can wash out the mobile or only weakly

THF was added in the washing step as a stabilizer, the particles

bound TiBA from the SF particles. CO 2 can readily insert into

were perfectly stabilized for both the short and long exposure

metal-alkyl bonds to form the metal-ester bonds (the reactiontime. The particle morphology hardly changed even after 1 h(4)). The reaction helps to quench the polymerization more

under air (Fig. 3C and 3C').

effectively. Moreover, they can partly prevent the fast for-Fig.2 Catalyst morphology. B is the magnification of the rectangular area in A32

Vu Quoe THANG, Toshiaki TANIIKE, Masaki UMEMORI, Mitsuhiro IKEYA, Yuiehi HIRAOKA, Minoru TERANO

Fig. 3 A (A'), B (B'), and C (C') are SEM images of the polymer/catalyst particles respectively
quenched and washed with the procedures i), ii) and iii), and then followed by the exposure
to air for 90 s (1 h).

mati on of the cracks (compare Fig. 3A and 3B) because themetal-ester bonds are quite inert to moisture.

THF cancordinate to both TiCl4 and MgCb according to the raections(5) and (6), respectively. The resulting complex, TiCI4 ' (THF)2
must be mobile enough to be removed by the washing step

No.2

with heptane, while THF is considered to chemisorb on theNo.1

MgCb surface to significantly slow down the formation of theMgCb' (H20)6 adduct. Thus, THF is believed to stabilize theinitially formed polymer particles by decelerating both thefast and slow reactions. The existance ofTHF on the particle

Catalyst
3000

surface in the SF samples was confirmed by DRIFT in Fig. 4,
where only the spectra for Run 3 exhibited the peak at 1025
cm- 1 assigned as the symmetric stretching vibration of the2000

1000

Wavenumber/cm-1

Fig. 4 DRIFT spectra of the fresh catalyst and theSF samples

C-O-C group ofTHF. The ester band ofR-CO-OM was not
visible in the presence of the dominant amount of DBP withMgCb+6H2O~

MgCb' (H2O)6

two ester groups per molecule.

M-R+C0 2~

R-CO-OM(M: Al orTi)

(3)
(4)

AIR3+3H20~

AI(OH)3+3RH+Q(1)

TiCl4 + 2THF~

TiCI4 ' (THF)2(5)

TiCI4 +2H20~

Ti0 2+4HCI +Q(2)

MgCb Surf. + X THF~

MgCb ad. (THF)x(6)

Materiaru Raifu Gakkaishi, Vo1.22, No.133

Morphological Stability of the Initially Formed Polymer Particles in Stopped-Flow Propylene Polymerization

Co., Toho Titanium Co., and Tosho FineChem Co. for their

4. Conclusionkind supports. Y.Q.T. thanks for the scholarship of The Ministry of Education and Training (MOET) by the Vietnamese

The morphology of the initially formed polymer/catalyst

government.

particles were successfully stabilized against air by a newquenching procedure in the stopped-flow propylene poly-Referencesmerization. Cold heptane and CO 2 effectively freezed andquenched the polymerization, while THF worked as a morphological stabilizer by protecting the particle surface fromthe moisture. The results of this study are highly meaningful
for the future morphological study at the very early stage ofpolyolefin polymerization, which contributes to the development of new catalyst with highly controlled catalyst andpolymer morphologies.

1) Moore, E.P. : "Polypropylene Handbook", Hanser (1996),
Chapter 22) Kakugo, M., Sadatoshi, H., Sakai, 1., Yokoyama, M.

Macromolecules, 22, 3172 (1989)
3) Keii, T., Terano, M., Kimura, K., Ishii, K. : Macromol.

Rapid Commun., 8, 583 (1987)
4) Liu, B., Matsuoka, H., Terano, M. : Macromol. RapidCommun., 22, 1 (2001)

Acknowledgement

5) Dashti,A., Ramazani,A., Hiraoka, Y., Kim, S. Y., Taniike,T., Terano, M. : Polym. Int., 58,40 (2001)
The authors thank for Japan Polypropylene Co., Yuki Gosei

34?j- 1) 7 )v717

2010 ~ 2}j