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Cationic Polymerization of Isobutylene and C4 Mixed Feed Using Complexes of Lewis Acids with Ethers: A Comparative Study

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The cationic polymerization of C4 mixed feed and isobutylene co-initiated by AlCl3×OⁱPt2, ⁱBuAlCl2×nOⁱPr2, and [emim]Cl-FeCl3×nOⁱPr2 ([emim]Cl: 1-ethyl-3-methylimidazolium chloride) has been investigated. AlCl3×OⁱPr2 co-initiated cationic polymerization of C4 mixed feed proceeds at a lower rate than polymerization of isobutylene affording polymers with higher molecular weight. Complexes of ⁱBuAlCl2 with diisopropyl ether of different compositions are more suitable co-initiators than AlCl3×OⁱPr2 for the synthesis of highly reactive polyisobutylene (HR PIB) from C4 mixed feed due to their higher activity in the polymerization as well as possibility to prepare polyisobutylenes with lower molecular weight and higher content of exo-olefin end groups. However, ⁱBuAlCl2 needs activating via addition of external water (initiator) and/or interaction with salts hydrates in order to increase the reaction rate and the saturated monomer conversion. [Emim]Cl-FeCl3/ⁱPr2O is a quite promising catalyst for the preparation of HR PIB with high exo-olefin end group content (> 80%) and relatively low polydispersity (Mw/Mn < 2.8) via cationic polymerization of C4 mixed feed. The sonication of reaction mixture in case of using [emim]Cl-FeCl3 allowed increasing the reaction rate and decreasing the molecular weight.
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https://doi.org/10.1007/s10118-019-2290-4
Chinese J. Polym. Sci.
Cationic Polymerization of Isobutylene and C4 Mixed Feed Using
Complexes of Lewis Acids with Ethers: A Comparative Study
DmitriyI.Shimana,IvanA.Bereziankoa,b,IrinaV.Vasilenkoa,andSergeiV.Kostjuka,b,c*
aResearch Institute for Physical Chemical Problems of the Belarusian State University, 14 Leningradskaya St., Minsk 220006, Belarus
bDepartment of Chemistry, Belarusian State University, 14 Leningradskaya st., Minsk 220006, Belarus
cSechenov First Moscow State Medical University, Institute for Regenerative Medicine, 8-2 Trubetskaya st., Moscow 119991, Russia
Abstract Thecationic polymerizationofC4mixedfeedandisobutyleneco-initiatedbyAlCl3×OiPr2,iBuAlCl2×nOiPr2,and[emim]Cl-
FeCl3×nOiPr2([emim]Cl:1-ethyl-3-methylimidazoliumchloride)hasbeeninvestigated.AlCl3×OiPr2co-initiatedcationicpolymerization
of C4 mixed feed proceeds at a lower rate than polymerization of isobutylene affording polymers with higher molecular weight.
ComplexesofiBuAlCl2withdiisopropyletherofdifferentcompositionsaremoresuitableco-initiatorsthanAlCl3×OiPr2forthesynthesis
ofhighlyreactivepolyisobutylene(HRPIB)fromC4mixedfeedduetotheirhigheractivityinthepolymerizationaswellaspossibilityto
preparepolyisobutyleneswithlowermolecular weightand highercontentofexo-olefinendgroups.However,iBuAlCl2needsactivating
via addition of external water (initiator) and/or interaction with salts hydrates in order to increase the reaction rate and the saturated
monomerconversion.[Emim]Cl-FeCl3/iPr2OisaquitepromisingcatalystforthepreparationofHRPIBwithhigh exo-olefinend group
content(>80%)andrelativelylowpolydispersity(Mw/Mn<2.8)viacationicpolymerizationofC4mixedfeed.Thesonicationofreaction
mixtureincaseofusing[emim]Cl-FeCl3allowedincreasingthereactionrateanddecreasingthemolecularweight.
Keywords Cationicpolymerization;Isobutylene;C4mixedfeed;Highlyreactivepolyisobutylene
Citation: Shiman,D.I.;Berezianko,I.A.;Vasilenko,I. V.;Kostjuk,S.V.CationicpolymerizationofisobutyleneandC4mixedfeedusingcomplexesof
Lewisacidswithethers:Acomparativestudy.Chinese J. Polym. Sci.https://doi.org/10.1007/s10118-019-2290-4
INTRODUCTION
Highlyreactive polyisobutylene (HR PIB),a low molecular
weight polyisobutylene bearing mainly exo-olefin terminal
group, is used as a precursor in the preparation of ashless
dispersants for fuel and motor oil.[1] Among different cata-
lyticsystems for thesynthesisofHRPIBdiscovered during
the last decade,[28] the use of complexes of AlCl3 with
ethers,whichwasindependentlyreportedin2010byKostjuk
et al.[9]andWuet al.[10],ismorepromisingduetotheirlow
costas well as high activityand regioselectivity at ambient
conditions. Since this discovery, the complexes of other
metal halides such as FeCl3,[1115] GaCl3,[13] TiCl4,[16,17]
HfCl4,[18] and WCl4[18] with ethers/alcohols were shown to
be suitable for the synthesis of HR PIB. Although these
complexes displayed high activity towards cationic poly-
merization of isobutylene (IB) in polar solvents[2,3,911] or
toluene,[19,20] their activity and regioselectivity significantly
reduced in non-polar hydrocarbons due to their poor solu-
bility.[13,18,21] The solubility issue was addressed by using
complexesof alkylaluminum dichlorides with ethers, which
are fully soluble in n-hexane and other non-polar sol-
vents.[2230] These new initiating systems, under optimized
conditions, induced fast cationic polymerization of isobuty-
lene at high temperature (0−20 °C) and monomer concen-
tration(up to 5mol·L–1)toaffordHRPIB with desiredlow
molecular weight (Mn < 2500 g·mol–1) and high content of
exo-olefin end groups (> 80%).[2230] However, the poly-
dispersity of obtained PIBs was typically high (Mw/Mn =
3−5), which is detrimental for the application.[1] The poly-
dispersitycanbeimproved (Mw/Mn = 2.3−3.5) by using the
mixture of two ethers of different basicities and steric
structures(diethylanddiisopropylethers)insteadofiPr2O[31]
or micromixing conditions.[32] Very recently, we demonst-
ratedthatchlorometallateacidicionicliquidsinthepresence
ofethersinitiatedthecationicpolymerizationofIBaffording
HR PIB with relatively low polydispersity (Mw/Mn = 2.0−
3.0).[33,34]Thiswasmade possible due to the heterogeneous
natureofpolymerizationprocess, whichproceedsatthepar-
ticleinterface.[33,34]
Cationic polymerization of C4 mixed feed is used at the
industrial scale for production of conventional poly-
isobutylene,i.e. low molecular weight polyisobutylene with
internal tri- and tetra-substituted olefinic end groups.[1,2,3]
Therefore, the polymerization of C4 mixed feed to yield
polyisobutylene with high content of exo-olefin end groups
is challenging. Despite the huge progress achieved in the
synthesisof HRPIBfromneat isobutyleneusingcomplexes
*Correspondingauthor:E-mailkostjuks@bsu.byorkostjuks@rambler.ru
Invitedarticleforspecialissueof"IonicPolymerization"
ReceivedJanuary15, 2019; Accepted May 9, 2019; Published online June
25,2019
Chinese Journal of
POLYMER SCIENCE ARTICLE
©ChineseChemicalSociety
InstituteofChemistry,ChineseAcademyofSciences www.cjps.org
Springer-VerlagGmbHGermany,partofSpringerNature2019 link.springer.com
ofLewis acidswithethersas catalysts,[2,3,2234] considerably
less attention has been paid to polymerization of C4 mixed
feed.[16,28,35,36]Mostofexamplesreportingthecationicpoly-
merizationofC4mixedfeeddealwithapplicationofthefirst
generation of catalysts, namely complexes of metal halides
withethers.[16,28,35,36]Ontheotherhand,onlylimitedinform-
ationisavailable in the literature regarding to the polymeri-
zationofC4 mixed feed co-initiated by complexesofalkyl-
aluminum dichlorides[28,37] and little data was about the
activityof acidic ionic liquids/ethers systemstowards poly-
merizationofC4mixedfeed.
Industrial C4 mixed feed used in this work along with
isobutylene (45.7 wt%) contains significant amount of 1-
butene (24.1 wt%) and 2-butenes (16.7 wt% cis and trans
isomers) (see experimental section for precise composition
ofC4mixedfeed).Sincetheseolefinsmayactaschaintrans-
fer agents or even terminate the polymerization,[37,38] de-
tailedstudy of thecationicpolymerizationofC4mixed feed
isrequired. The aim ofthis study is toestimatethe activity
andregioselectivityofabove-mentionedthreegenerationsof
catalysts for the synthesis of HR PIB, i.e. complexes with
ethersofmetalhalides,alkylaluminumdichlorides,andacid-
ic ionic liquids, in the cationic polymerization of C4 mixed
feed. The similarities and differences in the polymerization
behaviorofC4mixedfeedandneatisobutylenewillbedis-
cussedandtheoptimumcatalyticsystemforthepolymeriza-
tionofC4mixedfeedwillbefinallyselected.
EXPERIMENTAL
Materials
Isobutylene(Aldrich,99%)wasdriedinthegaseousstateby
passing through a column packed with drierite. C4 mixed
feed containing 45.7 wt% isobutylene, 24.1 wt% 1-butene,
10.0 wt% trans-2-butene, 6.7 wt% cis-2-butene, 10.0 wt%
n-butane,3.4wt%isobutane,andtracesof1,3-butadieneand
methylcyclopropane was purified similarly to isobutylene.
n-Hexane (Sigma-Aldrich, > 95%) and CH2Cl2 (Sigma-
Aldrich,>99.5%)were treated with sulphuric acid,washed
with aqueous sodium bicarbonate, dried over CaCl2, and
distilled twice from CaH2 under an inert atmosphere. Di-
isopropyl ether (iPr2O, Fluka, ≥ 98.5%) and diethyl ether
(Sigma-Aldrich,99%)weredistilledoverCaH2underargon.
1-Ethyl-3-methylimidazolium chloride ([emim]Cl, Sigma-
Aldrich, ≥ 95%) was dried in vacuum for 5 h before use.
AlCl3(Sigma-Aldrich,99.999%),iBu3Al(1mol·L–1solution
inhexanes,Sigma-Aldrich),FeCl3(Sigma-Aldrich,>97%),
CDCl3 (Euriso-top®), ethanol (Sigma-Aldrich, > 96%), and
tetrahydrofuran (anhydrous, Sigma-Aldrich, ≥ 99.9%) were
usedasreceived.ComplexofAlCl3withiPr2O(as1mol·L–1
solution in CH2Cl2) was synthesized following the recipe
described in Ref. [21]. Isobutylaluminum dichloride (iBu-
AlCl2)wasobtainedbymixingAlCl3andBu3AlClsolutions
ina2:1molarratioatroomtemperatureaccordingprocedure
described in Ref. [28]. The pre-activation of iBuAlCl2 was
performed in the presence of required amounts of MgSO4·
7H2O (15 mol% of H2O to iBuAlCl2) as described in Ref.
[31]. [Emim]Cl-FeCl3 was obtained by simple mixing of
requiredamounts of [emim]ClandFeCl3under argon atmo-
sphereaccordingtoaproceduredescribedintheliterature.[34]
Instrumentation
Size exclusion chromatography (SEC) was performed on a
Ultimate 3000 Thermo Scientific apparatus with Agilent
PLgel 5 μm MIXED-C column (300 × 7.5 mm) and one
precolumn(PLgel5μmguard50×7.5mm)thermostatedat
30 °C. The detection was achieved by differential refracto-
meter (thermostated at 35 °C). Tetrahydrofuran (THF) was
eluted at a flow rate of 1.0 mL·min–1. The calculation of
molar mass and polydispersity was carried out using poly-
styrene standards (Polymer Labs, Germany). 1H-NMR (500
MHz)spectra wererecordedinCDCl3at 25°ConaBruker
AC-500 spectrometer calibrated relative to the residual sol-
vent resonance. The sonication was performed using Elma-
sonic S30H ultrasonic batch (ultrasonic power: 80 W;
ultrasoundfrequency:37kHz).
Polymerization Procedures
Thepolymerization reactionswerecarriedout inglasstubes
equipped with a cold finger condenser under argon atmo-
sphereattemperaturesfrom–20°Cto10°C.Asanexample
ofatypicalprocedure,polymerizationof C4mixedfeedwas
initiated by adding 9.6 mL of C4 mixed feed to a mixture
(totalvolume0.58mL)consistingofsolutionsofdiisopropyl
ether(0.15mL,1 mol·L–1inhexane),6μL (3.3×10–4mol)
of deionized H2O, and pre-activated iBuAlCl2 (0.38 mL,
1mol·L–1).Afterapredeterminedtime,ca.2mLofaqueous
ammonia (25%) was poured into the glass reactor to term-
inate the polymerization. The quenched reaction mixtures
weredilutedbyn-hexane andfiltered,evaporatedtodryness
under reduced pressure, and dried in vacuum (≤ 60 °C) to
give the product polymers. Monomer conversions were de-
terminedgravimetrically.
RESULTS AND DISCUSSION
AlCl3 × OiPr2 as Catalyst
Equimolar complex of AlCl3 with diisopropyl ether was
selectedforthecomparativestudyofcationicpolymerization
of IB and C4 mixed feed as one of the most active
representativesofthefirstgenerationcatalysts(complexesof
metal halides with ethers) for the synthesis of HR
PIB.[2,3,921] The cationic polymerization of C4 mixed feed
co-initiated by AlCl3×OiPr2 proceeded at a considerably
lower rate in comparison with the polymerization of IB
affording polymers with higher molecular weight and exo-
olefin end group content (runs 1 and 2 in Table 1). Since
adventitious water acts as the initiator in these experiments
and the solubility of H2O in IB/n-hexane mixture and C4
mixedfeed maybedifferent,we theninvestigatedtheeffect
of adding external H2O on the cationic polymerization of
these two monomers. The addition of H2O allowed to
increase the monomer conversion for the polymerization of
C4 mixed feed, although the reaction rate was still lower
than that of IB polymerization (runs 3 and 4 in Table 1).
However, cationic polymerization of C4 mixed feed using
H2O/AlCl3×OiPr2initiatingsystemresultedinpolymerswith
considerablyhighermolecular weight than it isrequired for
practicalapplication (Mn 2300g·mol–1).[1] As we showed
2Shiman, D. I. et al./Chinese J. Polym. Sci.
https://doi.org/10.1007/s10118-019-2290-4
earlier,[1921] the reaction temperature is a powerful tool in
controlling the molecular weight during AlCl3×ether co-
initiated isobutylene polymerization. Indeed, the increase
of temperature from –20 °C to 0 °C resulted in some low-
ering of Mn of polymers obtained from C4 mixed feed up
to 4370 g·mol–1, which is about two times higher than that
ofthepolyisobutylenesynthesizedfromneatIB(Table1).
Insummary,AlCl3×OiPr2co-initiatedcationicpolymeriz-
ationofC4mixedfeedproceededatalowerratethanpoly-
merizationofisobutylene and afforded polymerswithhigh-
ermolecularweightandexo-olefinendgroupcontentaswell
as lower polydispersity. The systematically observed lower
conversionandhigherMninthecaseofC4mixedfeedpoly-
merizationcanbe explained by end-capping ofthe growing
polyisobutylene chains by 1-butene that can lead to slow-
downor termination of polymerization.[37]1H-NMRspectra
oftheHRPIBsynthesizedfromneatIBandC4mixedfeed
aresimilarandindependentofthecatalystusedforpolymer-
ization(Fig.1)indicatingveryloworno incorporationof1-
buteneor other olefins into polymerchain.Thesimilarcon-
clusionwas made by Wu et al.throughthecomparisonbet-
ween13C-NMR spectra of commercial HR PIB (Glissopal®
1000) and HR PIB prepared from C4 mixed feed.[35,36]
On the other hand, a very weak signal was observed in an
olefinic part of spectrum at 5.39 ppm (Fig. 2a), which cor-
respondstotheolefinic endgroupformedafter1-butenead-
dition to polyisobutylene macrocation followed by proton
elimination.[37] Therefore, 1-butene may copolymerize with
IB,butitscontentinapolymerchainisratherlow tobede-
tectedbyNMR.
iBuAlCl2 × nOiPr2 as Catalyst
The cationic polymerization of both C4 mixed feed and IB
co-initiated by iBuAlCl2×0.8OiPr2 terminated at low mono-
mer conversions (runs 1 and 2 in Table 2) due to low con-
centration of adventitious H2O in the system as well as
consumptionoftwomoleculesofH2Ofor the generation of
oneproton in the initiation stage.[28] On theother hand, the
molecularweight ofpolyisobutylenessynthesizedfrom both
C4mixedfeedand IB in the presence of iBuAlCl2×0.8OiPr2
wasmuch lower thanthose obtained withAlCl3×OiPr2 (see
Tables1and2).TheadditionofexternalH2O(33mmol·L–1)
led to the significant increase of monomer conversion and
lowering of Mn for the polymerization of C4 mixed feed
(Table2).
ItshouldbenotedherethatthemodeofH2Oadditioninto
to the system hardly affected the monomer conversion but
Table 1CationicpolymerizationofC4mixedfeedandisobutyleneinthepresenceofAlCl3×OiPr2asco-initiatora
Run M Time(min) Initiator(mmol·L–1)T(°C) Conv.b
(%) Mn(g·mol–1)Mw/Mn
Endgroupdistribution(mol%)
exo endo+tri tetra
1 IB 10 −c–20 70 5950 3.8 71 12 17
2C430 −c–20 28 10800 2.9 82 11 7
3 IB 10 H2O–20 77 2280 4.4 68 13 19
4С430 H2O–20 64 6570 2.7 75 10 16
5 IB 10 −c0 57 2950 2.7 71 12 17
6С430 −c0 42 4370 2.4 73 11 16
a[AlCl3×OiPr2]=22mmol·L–1;[IB]=[C4]=5.2 mol·L–1;[H2O]=30 mmol·L–1;bWithrespecttoisobutylenecontentinthecaseofC4mixedfeedpoly-
merization;cAdventitiouswateractedasinitiator
g
n
b
a
n
g
b
c
h
i
j
n
n
n
nm
n
d
e
f
d,e
c
a
ih
A
123456
δ (ppm)
h
n
b
g
d,e
c
ai
B
123456
δ (ppm)
Fig. 1Typical 1H-NMRspectraofHRPIB synthesizedfrom(A)
IB(run1,Table2)and(B)C4mixedfeed(run8,Table2)
Cl
n
n
n
b
b
a + a
a
a
6.0 5.8 5.6 5.4 5.2 5.0 4.8 4.6 4.4 4.2 4.0 3.8
A
B
C
δ (ppm)
Fig. 2  Olefinic part of 1H-NMR spectra of HR PIB synthesized
fromC4mixedfeedusing(A)AlCl3×OiPr2,(B)iBuAlCl2×0.8OiPr2,
and(C)[emim]Cl-FeCl3/0.5iPr2Oasco-initiators
Shiman, D. I. et al./Chinese J. Polym. Sci. 3
https://doi.org/10.1007/s10118-019-2290-4
influencedsignificantlytheexo-olefinendgroupcontent.In-
deed, when water was introduced into system after some
timesincetheadditionofco-initiator(iBuAlCl2),thehigher
amountofexo-olefinend groupcouldbeobtained(runs 5−8
in Table 2). In contrast, the addition of H2O before the co-
initiator resulted in polyisobutylenes with lower content of
exo-olefin terminal group (runs 3 and 4, Table 2). Import-
antly,theoptimaltimeofH2Oadditionintothesystemwas3
and10minafterthebeginningofreactionforthepolymeriz-
ationof IB and C4mixed feed, respectively (Table2). This
observationisconsistentwiththelowerreactionrate(lower
rateofconsumptionofH2Ofor theinitiation)forthecation-
icpolymerization of C4 mixed feedin comparison with IB.
Therefore, the delayed addition of H2O is required because
excessH2Ocoulddeactivatethecatalyst.
Despite the significant increase of monomer conversion
aftertheadditionofexternalH2Oasinitiatorintothesystem,
theconversion was below 80% and70% for the iBuAlCl2×
0.8OiPr2-co-initiated cationic polymerization of IB and C4
mixedfeed,respectively.Therefore,inorder to increase the
polymer yield, it was proposed to add the initiator (H2O)
with several shots in the course of polymerization. Indeed,
theaddition ofH2Ointotwo shots(after3 and7minfor IB
andafter3 and 15 min forC4 mixed feed) afforded desired
low molecular weight HR PIB (Mn < 2800 g·mol–1) with
highexo-olefin end group content(> 80%) inhigh yield (≥
89%) (Table 3). The observed higher molecular weight of
HRPIB prepared from C4 mixed feed thantheonesynthes-
izedfromIBcanbeexplainedbylowerpolymerizationtem-
peratureintheformercase(seeTable3).
Another approach to increase the activity of iBuAlCl2 in
thesynthesis ofHRPIB,whichwas developedbyus,[31]in-
volves the pre-activation of co-initiator by its interaction
with salts hydrates. As shown in Table 4 and in our earlier
report,[31]thepre-activatedcatalystrequiredloweramountof
ether in comparison with non-pre-activated one (Tables 2
and3)toretainhighfunctionalityatthechainend.However,
for the cationic polymerization of isobutylene, the optimal
ratioofiPr2OtoiBuAlCl2was0.4,whileforthepolymeriza-
tion of C4 mixed feed, high exo-olefin end group content
couldbeobservedonlyatiPr2O/iBuAlCl2=0.5(Table4).At
thisratio, HR PIBwithdesiredlowmolecular weight (Mn
2000 g·mol–1) but with relatively high polydispersity (Mw/
Mn~4)canbeobtainedinahighyield(≥90%)in10minby
thecationic polymerization ofC4mixedfeedwith H2O/iBu-
AlCl2×0.5OiPr2initiatingsystem(run4,Table4).
The polydispersity of HR PIB prepared from C4 mixed,
similarlytothatofpolyisobutylenesynthesizedfromneatIB,
canbeimprovedbyusingthemixtureoftwoethersofdiffer-
entstericstructuresandbasicitiesinsteadofdiisopropyleth-
er(seeruns5and6inTable4).
To summarize, complexes of iBuAlCl2 with diisopropyl
ether were more suitable co-initiators than AlCl3×OiPr2 for
the synthesis of HR PIB from C4 mixed feed due to their
higheractivityinpolymerizationaswellaspossibilitytopre-
parepolyisobutyleneswithlowermolecularweightandhigh-
ercontentof exo-olefin end groups(seeTables 14). How-
ever,iBuAlCl2requiredactivationinordertoincreasethere-
action rate and the saturated monomer conversion. Among
differentwaysofcatalystactivation(additionofexternalwa-
ter(initiator)inoneortwoshots, reaction of iBuAlCl2 with
salts hydrates), the pre-activation of iBuAlCl2 by salts hy-
drateisthemost promisingapproachduetoits efficiency(≥
90% of monomer conversion in 10 min) and simplicity. In
Table 2CationicpolymerizationofC4mixedfeedandisobutyleneinthepresenceofiBuAlCl2×0.8OiPr2asco-initiatora
Run M Time(min) Conv.b(%) Mn(g·mol–1)Mw/Mn
Endgroupdistribution(mol%)
exo endo+tri tetra coupled
1cIB 10 36 1470 3.9 91 3 4 2
2cC430 24 2600 4.2 86 7 6 1
3dIB 30 78 1900 3.7 80 9 11 <1
4dC430 70 1450 4.4 79 10 9 2
5e,f IB 20 74 1230 3.4 88 4 3 5
6e,f C430 30 930 6.9 91 3 0 6
7e,g IB 20 64 1260 3.4 90 4 3 3
8e,g C430 64 1280 5.3 81 11 8 <1
a[iBuAlCl2]=22mmol·L–1;[iPr2O]=18mmol·L–1;[IB]=[C4]=5.2mol·L–1;[H2O]added =33mmol·L–1;T=10°C;bWithrespecttoisobutylenecontentin
thecaseofC4mixedfeedpolymerization;cAdventitiouswateractedasinitiator;dPolymerizationwasinitiatedbytheadditionofiBuAlCl2tothereaction
mixture;eThesequenceforcomponentsaddition:C4,iPr2O,iBuAlCl2,H2O,andn-hexane,iPr2O,iBuAlCl2,IB,H2OforthepolymerizationofC4mixedfeed
andIB,respectively;fH2Oaddedafter3minsincethebeginningofthepolymerization;gH2Oaddedafter10minsincethebeginningofthepolymerization
Table 3EffectofH2Oadditionon cationicpolymerization ofC4 mixedfeedandisobutyleneinthepresenceofiBuAlCl2×0.6OiPr2 asco-
initiatora
Run M H2Oadditionb(min) Time(min) T(°C) Conv.c(%) Mn(g·mol–1)Mw/Mn
Endgroupdistribution(mol%)
exo endo+tri tetra coupled
1 IB 3+3 10 10 89 1900 3.6 80 9 11 <1
2 IB 3+7 30 10 93 1380 4.1 83 9 8 <1
3C43+3 10 0 50 2680 3.9 89 8 0 3
4C43+15 30 0 89 2790 4.3 81 11 7 1
a[iBuAlCl2]=38mmol·L–1;[iPr2O]=23mmol·L–1;[IB]=[C4]=5.2mol·L–1;[H2O]1=[H2O]2=15mmol·L–1.Thesequenceforcomponentsaddition:C4,
iPr2O,iBuAlCl2,H2O,andn-hexane,iPr2O,iBuAlCl2,IB,H2OforthepolymerizationofC4mixedfeedandIB,respectively;bTimeofH2Ointroductionsince
thebeginningofpolymerization;cWithrespecttoisobutylenecontentinthecaseofC4mixedfeedpolymerization
4Shiman, D. I. et al./Chinese J. Polym. Sci.
https://doi.org/10.1007/s10118-019-2290-4
addition,pre-activated catalyst can bestored up to1 month
withoutanylossinactivity.ItshouldbenotedthatHRPIBs
preparedfrom C4 mixed feedusingiBuAlCl2asa co-initiat-
orweretypicallycharacterizedbyhigherpolydispersitythan
those synthesized from IB (Tables 24). Finally, HR PIBs
synthesized from C4 mixed feed using H2O/iBuAlCl2×
0.5OiPr2 initiating system did not contain any significant
amountofotherolefininamainchain,whileveryweaksig-
nalat5.39ppm(Fig.2b)indicatesthatend-cappingofpoly-
isobutylenemacrocationsby1-buteneoccurred(Fig.2b).
Ionic Liquids as Catalysts
It was recently demonstrated that acidic imidazole-based
ionicliquids(ILs),especially[emim]Cl-FeCl3([emim]Cl: 1-
ethyl-3-methylimidazolium chloride), in the presence of di-
isopropyletherareveryefficientcatalystsforthepreparation
ofHR PIBwithrelativelylow polydispersity (Mw/Mn<3.0)
from neat IB.[33,34] This catalytic system was tested for the
first time in the cationic polymerization of C4 mixed feed
(Table 5). Note that in all experiments the ionic liquid was
dispersed in n-hexane before C4 mixed feed addition;
therefore,theconcentrationofmonomerwas3.8mol·L–1.
AccordingtoTable 5, [emim]Cl-FeCl3 eitherin the pres-
ence or in the absence of iPr2O showed approximately two
times lower activity in the cationic polymerization of C4
mixed feed as compared to polymerization of isobutylene.
Interestingly, [emim]Cl-FeCl3 allowed to synthesize PIB
withquite highexo-olefinendgroup contentfromC4mixed
feedevenwithouttheadditionofetherintothesystem(runs
1 and 2, Table 5). Several key differences in the polymeri-
zation behavior of IB and C4 mixed feed can be seen in
Table5. Firstly,thehighmonomer conversionwasobtained
for IB polymerization at [IL] = 33 mmol·L–1, while in the
caseof C4mixedfeedpolymerization, the higherconcentra-
tionofionicliquidwasrequired(comparerun5withrun6in
Table 5). Secondly, the relatively high molecular weight
polymers were formed during [emim]Cl-FeCl3-co-initiated
cationicpolymerizationofC4mixedfeedathigh co-initiator
concentrationsascomparedtothepolymerizationofIB(runs
5−9 in Table 5). On the other hand, independently of the
natureofmonomer used (IB or C4 mixed feed), all synthes-
izedpolymerswerecharacterized by relatively low polydis-
persity(Mw/Mn<2.8)duetotheheterogeneousnatureofthe
polymerizationprocess.[33,34]
Takingintoaccounttheheterogeneousnatureofthepoly-
merizationandpoordispergationof [emim]Cl-FeCl3innon-
polarn-hexaneor n-hexane/monomer mixture, sonication of
reactionmixturebeforemonomeradditionwasapplied. Ac-
cordingtothedatapresentedinTable 6, sonication resulted
insignificantincreasesofmonomerconversion,especiallyin
thecase of C4 mixed feed cationic polymerization.Another
positive effect of sonication is the reduction of molecular
weight of HR PIB prepared from C4 mixed feed (see runs
3−5inTable6).Ontheotherhand,thesonicationdidnotin-
fluence the polydispersity of HR PIB but led to some de-
creaseofexo-olefinendgroupcontent.
The comparison between the olefinic part of 1H-NMR
spectrum of HR PIB prepared from C4 mixed feed using
[emim]Cl-FeCl3 as catalyst (Fig. 2c) and the spectra of HR
PIB synthesized with AlCl3×OiPr2 (Fig. 2a) and iBuAlCl2×
Table 4 EffectofiBuAlCl2pre-activationoncationicpolymerizationofC4mixedfeed andisobutyleneinthepresenceofiBuAlCl2asco-
initiatora
Run M OiPr2/iBuAlCl2(mol/mol) T(°C) Conv.b(%) Mn(g·mol–1)Mw/Mn
Endgroupdistribution(mol%)
exo endo+tri tetra coupled
1 IB 0.4 10 94 1210 3.7 80 9 9 1
2C40.4 0 96 5230 3.6 66 18 16 0
3 IB 0.5 10 86 1420 3.7 81 7 8 4
4C40.5 0 90 2050 4.2 72 15 11 2
5c,d IB 0.5 10 94 1190 2.6 82 6 10 2
6c,d C40.5 0 96 1180 3.3 80 10 8 2
a[iBuAlCl2]=38mmol·L–1;[IB]=[C4]=5.2mol·L–1;[H2O]added=33mmol·L–1;time:10min.Co-initiatorwaspre-activatedbyMgSO4·7H2O(15mol%of
H2OtoiBuAlCl2).Thesequenceforcomponentsaddition:H2O,iPr2O,iBuAlCl2,C4,andn-hexane,iPr2O,H2O, iBuAlCl2,IBforthe polymerizationofC4
mixedfeedandIB,respectively;bWithrespecttoisobutylenecontentinthecaseofC4mixedfeedpolymerization;cEquimolarmixtureofiPr2OandEt2Owas
usedinsteadofiPr2O;dReactiontime:30min
Table 5CationicpolymerizationofC4mixedfeedandisobutyleneusing[emim]Cl-FeCl3asco-initiatorat0°Ca
Run M IL(mmol·L–1) Conv.b(%) Mn(g·mol–1)Mw/Mn
Endgroupdistribution(mol%)
exo endo+tri tetra PIBCl coupled
1cIB 22 27 5400 3.8 53 20 19 7 1
2cC422 18 5800 3.5 74 16 7 3 0
3 IB 22 18 1700 2.2 84 7 3 4 2
4C422 19 1700 2.7 82 8 5 2 3
5 IB 33 71 1630 2.6 84 8 6 1 1
6C433 24 2200 2.8 86 5 4 4 1
7 IB 44 95 1800 2.5 87 8 3 1 1
8C444 68 3900 2.6 81 9 7 3 0
9dC444 88 3700 2.6 75 10 9 4 2
a[IB]=5.2mol·L–1;[C4]=3.8mol·L–1;[iPr2O]=11mmol·L–1;time:30min;bWithrespecttoisobutylenecontentinthecaseofC4mixedfeedpolymeri-
zation;cWithouttheadditionofiPr2O;dReactiontime:60min
Shiman, D. I. et al./Chinese J. Polym. Sci. 5
https://doi.org/10.1007/s10118-019-2290-4
0.8OiPr2(Fig.2b)revealstheappearanceofanewsignalat
3.9ppminadditionto thesignalat 5.39ppm.Thisnewsig-
nal corresponds to the methine proton of CHCl group,
which was formed after PIB+ capping with 1-butene fol-
lowedbyirreversibletermination via ion pair collapse.[37] It
shouldbe noted thatthissignalis much moreintensivethan
the signal at 5.39 ppm, which corresponds to olefinic pro-
tonsofinternaldoublebondatthechainendformeddueto
1-butene addition followed by β-H abstraction. These data
allowedforexplainingthemuchloweractivityof[emim]Cl-
FeCl3 in cationic polymerization of C4 mixed feed in com-
parison with IB as well as the necessity to use quite high
concentrationsof ionic liquidsto reach high monomer con-
versions.Indeed,theformationofCHClgroupledtoirre-
versible termination and, in turn, to the decrease of active
species concentration. On the other hand, the formation of
olefinicendgroupaftercappingofPIB+with1-buteneresul-
tedinregenerationofactivecenter andtherefore,didnotin-
fluencetheconcentrationofactivespecies.
Insummary,[emim]Cl-FeCl3isaquitepromisingcatalyst
forthe preparation ofHR PIB with the high exo-olefin end
group content (> 80%) and relatively low polydispersity
(Mw/Mn<2.8)viacationicpolymerizationofC4mixedfeed.
However, due to the irreversible termination after end-cap-
ping of PIB+ with 1-butene, a relatively high concentration
ofionicliquidcatalystwasrequiredtoachievethehighreac-
tion rate and monomer conversion. This limitation of using
[emim]Cl-FeCl3forthepolymerizationofC4mixedfeedcan
beovercomeby sonication of reaction mixturebefore poly-
merization.The sonication allowed to decrease the molecu-
lar weight of HR PIB synthesized from C4 mixed feed as
well.
CONCLUSIONS
Three generations of catalysts, namely the complexes of
AlCl3,iBuAlCl2,and[emim]Cl-FeCl3withdiisopropylether,
forthesynthesisofhighlyreactivepolyisobutylene from C4
mixed feed were tested in this work. The key difference in
thepolymerizationbehaviorofC4mixedfeedascomparedto
IB is the lower activity of all above-mentioned catalytic
systems, which can be connected with the end-capping of
PIB+by1-butene that led to thedecreaseofpolymerization
rate.Anotherdifferenceisthesystematically highermolecu-
larweight of polyisobutylenes obtained fromC4mixedfeed
in comparison with those prepared from IB. Among the
catalystsstudied,iBuAlCl2pre-activatedbyMgSO4·7H2Oin
thepresenceof equimolar mixture of iPr2OandEt2O repre-
sentsthemostpromisingcatalystforthesynthesisofHRPIB
from C4 mixed feed. This catalytic system induced fast
cationicpolymerization of C4 mixed feed(> 90% of mono-
merconversionin10min)toaffordHRPIBwithdesiredlow
molecularweight(Mn~1200g·mol–1)aswellasreasonable
functionality(exo-olefinendgroupcontentof80%)andpoly-
dispersity(Mw/Mn=3.3).Acidicionicliquidsinconjunction
withiPr2OcouldbeconsideredasanalternativetoiBuAlCl2-
basedinitiating systemforthecationic polymerizationofC4
mixed feed. Although [emim]Cl-FeCl3-co-initiated cationic
polymerizationof C4 mixed feedwas slower in comparison
withiBuAlCl2-based initiatingsystem,it resultedinHRPIB
withlowerpolydispersity(Mw/Mn=2.5).
ACKNOWLEDGMENTS
ThisworkwasfinanciallysupportedbyBASFSE.
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Table 6EffectofsonicationofthereactionmixtureonthecationicpolymerizationofC4mixedfeedandisobutyleneusing[emim]Cl-FeCl3
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Run M SonicationbConv.c(%) Mn(g·mol–1)Mw/Mn
Endgroupdistribution(mol%)
exo endo+tri tetra PIBCl coupled
1 IB NO 71 1630 2.6 84 8 6 1 1
2 IB YES 93 1830 2.4 81 10 8 1 0
3C4NO 24 2200 2.8 86 5 4 3 2
4C4YES 51 2200 2.8 82 6 5 4 3
5dC4YES 78 2500 2.5 81 7 7 3 2
a[IB]=5.2mol·L–1;[C4]=3.8mol·L–1;[emimCl-FeCl3]=33mmol·L–1;[iPr2O]=11mmol·L–1;time:30min;bn-hexane/ILmixturesonicatedfor3min;
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https://doi.org/10.1007/s10118-019-2290-4
... The many Lewis acid compounds that have been tested to produce PIB materials, especially in the last two decades, illustrate the efforts that are still being made to select more efficient and viable alternatives to replace the more conventional catalysts in these processes [68,71,72,[78][79][80]. Generically, the development of new catalysts pursues the combination of high activity and selectivity, cost reduction, easy handling and possible operation at mild conditions [59,65,76,81]. ...
... Water is a peculiar additive that has been used as co-catalyst in isobutylene polymerizations because of its many known advantages, such as low cost and non-toxicity [81,86,95,[103][104][105]. In the field of HR-PIB, the use of water has been extensively investigated [43,45,71,106]. ...
... As AlCl 3 complexes usually present poor solubility in nonpolar solvents due to the strong acidity, the use of these catalysts usually demands the use of solvent mixtures, higher initiator concentrations and high monomer concentrations [62,86,116]. However, GaCl 3 or FeCl 3 complexes can be used to produce HR-PIB grades in nonpolar solvents [80,81,103,117]. ...
Article
Full-text available
Polyisobutylenes (PIB) constitute a versatile family of polymer materials that have been used mainly as fuel and lubricant additives. Particularly, the current commercial demand for highly reactive polyisobutylene (HR-PIB) products motivates the development of new processes and procedures to produce PIBs with high polymer yields, narrow molar mass distributions and high vinyl contents. For this reason, a bibliometric survey is presented here to map and discuss important technical aspects and technological trends in the field of solution cationic polymerization of isobutylenes. It is shown that investigations in this field are concentrated mainly on developed countries and that industrial initiatives indicate high commercial interest and significant investments in the field. It is also shown that use of catalyst systems based on AlCl3 and ether cocatalysts can be very beneficial for PIB and HR-PIB manufacture. Finally, it is shown that investigations search for cheaper and environmentally friendly catalysts and solvents that can be employed at moderate temperatures, particularly for the production of HR-PIB.
... Polyisobutene (PIB) and butyl rubber (IIR) with a unique set of properties such as excellent air-barrier performance, good flex fatigue and vibration damping etc. have found numerous commercial applications, rubbers, sealants, lubricants, and oil additives. Commercially, PIB and IIR are synthesized by means of cationic polymerization with inorganic Lewis acid initiators in chloromethane [1][2][3] and high-molecular-weight products require costly cryogenic temperatures of about À 100 to À 90 � C. This kind of industrial process leads to seriously environment taxing. ...
... For instance, zirconocene compounds (Cp 2 ZrMe 2 , Cp* 2 ZrMe 2 or [Cp' 2 ZrH(μ-H)] 2 ) activated by B(C 6 F 5 ) 3 or [Ph 3 C][B(C 6 F 5 ) 4 ] exhibited good catalytic performance for IB polymerization even at temperature up to À 30 � C [12,13]. On the other hand, Bochmann and coworkers reported that the cationic organoaluminum compound [Cp 2 Al][B(C 6 F 5 ) 3 Me] was a highly active initiator for IB polymerization, which readily gave high molecular weight PIB of 3.2 � 10 5 g/mol with molecular weight distribution of 1.8 in CH 2 Cl 2 at -30 � C [5]. Interestingly, changing the Cp (C 5 H 5 ) ligand to bulkier Cp rings C 5 Me 4 H and C 5 Me 5 really depressed the polymerization activity and even led to be completely inactive [14]. ...
... As reported previously, the reaction of well-defined rare-earth metal dialkyl complexes with one equivalent of organoborate [Ph 3 4 ] afforded the electronically unsaturated cationic rare-earth metal alkyl species, which could behave as an excellent catalyst for coordination polymerization process [28,29]. Herein, the half-sandwich scandium complex 1a, activated by one equivalent of [Ph 3 C][B(C 6 F 5 ) 4 ], was used to initiate IB cationic polymerization at À 30 � C in a toluene solution and gave high molecular weight polyisobutene (PIB) (M w ¼ 13.8 � 10 4 g/mol) with molecular weight distribution of 1.85 in a yield of 76% (Table 1, run 1). ...
... It should be also noted that preactivated i BuAlCl 2 in conjunction with H 2 O as an initiator showed good activity and regioselectivity toward cationic polymerization of C 4 mixed feed providing HR PIB in high yield (>95% in 10 min), low molecular weight (M n $1200 Da) and acceptable polydispersity ( -D$3.0). [33] 2.2.2. t BuCl/EtAlCl 2 /bis(2-chloroethyl) ether initiating system Another soluble in n-hexane initiating system for the synthesis of HR PIB was developed by Faust et al., who proposed to use the complex of ethylaluminium dichloride with bis(2-chloroethyl) ether (CEE) in conjunction with t BuCl as an initiator. ...
... The negative effect of the nucleophilic impurities could be neutralized either by the addition of FeCl 3 or H 2 O (using wet hexane as reaction medium). [38] It should be also noted that t BuCl/EtAlCl 2 ÂCEE initiating system, similarly to H 2 O/ i BuAlCl 2 /O i Pr 2 system, [33] could be used for the synthesis of HR PIB from C 4 mixed olefin feed. [39] In addition, this initiating system also displayed improved efficiency toward synthesis of HR PIB under micromixing conditions. ...
Article
In this article, the current state and future perspectives in the application of complexes of Lewis acids with ethers in the synthesis of highly reactive polyisobutylene (HR PIB) were critically reviewed. The complexes of metal halides with ethers showed good activity and regioselectivity in the synthesis of HR PIB only in polar solvents due to their poor solubility in hydrocarbons. In strong contrast, HR PIB with high exo-olefin end group content was synthesized in non-polar n-hexane using fully soluble in hydrocarbons complexes of alkylaluminum dichlorides as catalysts. The further improvement in the synthesis of HR PIB was achieved using heterogeneous catalysts (acidic ionic liquids or liquid coordination complexes), which provides polyisobutylenes with high exo-olefin end group content in conjunction with low polydispersity.
Article
Background Because methyl tert‐butyl ether (referred to as MTBE) is harmful to the environment, MTBE is limited in China. To avoid the waste of isobutylene as MTBE raw material and improve the utilisation rate of isobutylene in mixed C4 fraction, the supported Fe(NO3)3/β molecular sieve catalysts with different active components were prepared by equal volume impregnation method. The catalysts were analysed by XRD, TG, NH3‐TPD, BET and SEM, and the catalytic performance of catalysts with mixed C4 fractions as raw materials and different active component loadings for selective oligomerisation of isobutylene was investigated in a fixed bed reactor. Results The results show that when the active component loading is 6 %, the reaction temperature is 60 °C, the reaction pressure is 1 MPa, and the reaction space velocity is 1.5 h‐1, the catalyst has the best catalytic performance. Conclusion The conversion rate of isobutylene is over 90 %, the selectivity of C8 olefin is about 80 %, and there is almost no loss of n‐butene. This article is protected by copyright. All rights reserved.
Article
A number of acidic liquid coordination complexes (LCC) based on phosphorus-containing electron donors such as tri-n-octylphosphine oxide (POct3O), triphenylphosphine oxide (PPh3O) or triphenylphoshine (PPh3), and Lewis acids (AlCl3, FeCl3, TiCl4) have been synthesized and tested as catalysts of cationic polymerization of isobutylene. Among different LCCs studied, POct3O–AlCl3 and POct3O–FeCl3 (χ(MCl3)=0.60) in combination with bis(2-chloroethyl)ether (CE) and ⁱPr2O, respectively, showed best results in terms of monomer conversion, exo-olefin end group content and polydispersity. POct3O–AlCl3/CE catalytic system afforded highly reactive polyisobutylene (HR PIB) with high exo-olefin end group content (75–90%) and low polydispersity (Đ≤2.0) in high yield (70 – 90%) at 20 °C and high monomer concentration ([IB]=5.2 M) in n-hexane, although the number-average molecular weight (Mn=2.500–3.500 g mol–1) is slightly higher than required for application. POct3O–FeCl3/ⁱPr2O catalytic system showed higher activity and regioselectivity in the cationic polymerization of isobutylene as compared to POct3O–AlCl3/CE giving desired low molecular weight HR PIB (Mn=1500 g mol⁻¹, Đ=2.1, Fn(exo)=91%) in quantitative yield at lower catalyst concentration (22 mM for POct3O–FeCl3 vs. 44 mM for POct3O–AlCl3) at room temperature.
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The effect of different initiators (tert-butyl chloride (t-BuCl) and 2-chloro-2-phenylpropane (CumCl) on the cationic polymerization of isobutylene co-initiated by acidic chloroferrate imidazole-based ionic liquid emimCl-FeCl3 (emimCl: 1-ethyl-3-methylimidazolium chloride, molar fraction of FeCl3 (χ(FeCl3)) ≥ 0.6) in the presence of diisopropyl ether at 0 °C and [IB] = 5.2 M has been investigated. Generally, the use of all above-mentioned initiators results in increase of the monomer conversion from 30% to 60% as well as in decrease of molecular weight from 2500 g mol⁻¹ to 1100 g mol⁻¹ and polydispersity from 2.6 to 1.7, respectively, but does not influence the content of exo-olefin end group. It was demonstrated that CumCl does not initiated directly the polymerization at 0 °C or −20 °C, rather, it decomposed with the formation of the proton, a true initiator of the polymerization. It was also found that addition of small amounts (1% by volume) of benzene or its derivatives into the polymerization system leads to further increase of the monomer conversion (>90%). The rate of isobutylene polymerization depends on basicity of aromatic compounds added and increases in the following order: benzene < toluene ≈ mesitylene.
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Catalytic chain transfer polymerization (CCTP) of isobutylene in the presence of alcohol as an exo-enhancer with tert-butyl chloride/ethylaluminum dichloride (EADC)·bis(2-chloroethyl) ether (CEE) has been investigated in hexanes at 0 °C. Increasing exo-olefin content was observed with increasing steric bulkiness of the alkyl group of the alcohol, i.e., tert-butyl > isopropyl > methyl. Here, we report that tert-butanol (t-BuOH) is an excellent exo-enhancer compared to other tert-alcohols such as tert-amyl alcohol (AmOH), 2-methyl-2-pentanol (MPOH), and 3-ethyl-3-pentanol (EPOH). The aromatic tert-alcohol cumyl alcohol was not an exo-enhancer but acted as an initiator. In the reaction of EADC.CEE and t-BuOH, t-butoxyaluminum dichloride (t-BuOAlCl2) was formed, which is the real exo-enhancer and is not stable at room temperature. Molecular weights were virtually unchanged in the presence t-BuOAlCl2 with [t-BuOAlCl2]:[EADC.CEE] < 0.5, and exo-olefin content increased ∼15% relative to polymerization in the absence of t-BuOAlCl2. This is presumably due to stabilization of the cation by t-BuOAlCl2 which slows isomerization of the PIB⁺. Stabilization of the cation was confirmed by ¹H NMR and UV–vis spectroscopy at 0 °C by adding t-BuOAlCl2 to the diphenylmethyl cation, a representative stable cation. The rate constant of chain transfer (ktr) was determined to be 2 × 10⁸ L mol–1 s–1 at 0 °C, which is not affected by t-BuOAlCl2. Addition of an exo-enhancer is especially important for polymerization at CSTR conditions at low steady state monomer concentrations. This is the first report identifying the role of alcohols in CCTP and opens new vistas in the synthesis of highly reactive polyisobutylene.
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Cationic polymerization of isobutylene (IB) in the presence of other C4 olefins, 1-butene (B1), cis-2-butene (C2B), and 1,3-butadiene (BD) using the ethylaluminum dichloride (EADC)·bis(2-chloroethyl) ether (CEE) complex in conjunction with tert-butyl chloride (t-BuCl) as initiator in hexanes at 0 °C has been investigated. The reactivity ratio of IB rIB = 1100 was determined for copolymerization of IB and B1 at low conversions, using product compositions obtained from inverse gated ¹³C NMR analysis. The reactivity ratio of B1 rB1 = 1 was deduced from theoretical considerations. At low B1 incorporation levels, exo-olefin contents remained high in the copolymers, and the molecular weights were virtually unchanged relative to the experiments with IB alone [Banerjee, S.; Macromolecules2015, 48, 5474]. Close to linear first-order plots of ln{[M]0/[M]} versus time were obtained ([M]0 and [M] are IB concentrations at time t = 0 and t, respectively) when the copolymerization was carried out with [IB] > 2 M. This is because propagation rate increases with increasing [IB] while termination (ion collapse/sec-alkyloxonium ion formation) is independent of [IB]. The formation of polyisobutylene (PIB) sec-alkyloxonium ion after B1 incorporation was confirmed by ¹H NMR spectroscopy and GC-MS analysis by adding EADC·CEE to a mixture of B1 and 2-chloro-2,4,4-trimethylpentane (TMPCl), a model for the PIB chain end, at 0 °C in cyclohexane-d12. Olefin formation and ion collapse to TMP-B1-Cl from TMP⁺-capped B1 were observed by quenching the sec-alkyloxonium ion with methanol at 0 °C. These results are important to understand the mechanism of commercially important highly reactive polyisobutylene (HRPIB) synthesis using mixed C4 olefin feeds.
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In this work, a micromixing module was utilized in the polymerization of isobutylene (IB) initiated by tert-butyl chloride (t-BuCl) and catalyzed by ethylaluminum dichloride (EADC)/bis(2-chloroethyl)ether (CEE) complex for the synthesis of highly reactive polyisobutylene (HRPIB). Better micromixing performance resulted in HRPIB with narrower molecular weight distribution, where the PDI could be decreased from 3.5 without micromixing module to 2.5 or less. The polymerization rate also increased while the molecular weight and content of exo-olefin end groups of HRPIBs could be adjusted conveniently by the ratio of CEE to EADC and monomer concentration. A dynamic mechanism was proposed to explain the effects of micromixing on the enhanced HRPIB synthesis.
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The cationic polymerization of isobutylene (IB) was systematically studied in 1-N-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]) ionic liquid at −10 °C. Different initiation systems, including titanium tetrachloride, boron trichloride, and ethylaluminum sesquichloride, were considered in [Bmim][PF6] for IB polymerization. The effects of solvent polarity and anion/cation structure on the initiation systems and carbocation active center were simulated by density functional theory in combination with conductor-like screening model. A highly reactive polyisobutylene (HR PIB) with a high exo-olefin end group content (>80%) was synthesized using H2O/TiCl4 initiation system in [Bmim][PF6] ionic liquid. Polymerization proceeded at the interface of ionic liquid particles in a mild exothermic manner and [PF6]⁻ anions promoted ionization of the initiation system and stabilized the carbocation active center. A possible mechanism for HR PIB synthesis was proposed and the microstructure of ionic liquids were considered.
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A number of imidazole-based acidic (χ(LA)≥0.6) ionic liquids (RmimCl-LA, where R = Et or Bu, LA = AlCl3, AlBr3, ⁱBuAlCl2, FeCl3, GaCl3, and BBr3) has been synthesized and their activity in cationic polymerization of isobutylene has been assessed. Among different ionic liquids tested here, emimCl-AlCl3, emimCl-FeCl3 and emimCl-GaCl3 showed the best results in terms of monomer conversion, exo-olefin end group content and polydispersity. It was shown that reaction rate depended strongly on the rate of partial hydrolysis of corresponding ionic liquid and increased in the following order: emimCl-FeCl3<emimCl-GaCl3<emimCl-AlCl3. It was demonstrated that emimCl-FeCl3 is the most promising catalyst for the synthesis of HR PIB with desired low molecular weight (Mn < 2500 g mol⁻¹) and polydispersity (Mw/Mn < 2.5) and high content of exo-olefin end groups (>85%). However, due to poor dispergation of emimCl-FeCl3 in n-hexane as well as its high stability toward hydrolysis, the catalyst aging and/or sonication of reaction mixture is required in order to provide acceptable polymerization rate.
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Fast polymerization of isobutylene (IB) initiated by tert-butyl chloride using ethylaluminum dichloride�bis(2-chloroethyl) ether complex (T. Rajasekhar, J. Emert, R. Faust, Polym. Chem. 2017, 8, 2852) was drastically slowed down in the presence of impurities, such as propionic acid, acetone, methanol, and acetonitrile. The effect of impurities on the polymerization rate was neutralized by using two different approaches. First, addition of a small amount of iron trichloride (FeCl3) scavenged the impurity and formed an insoluble FeCl3�impurity complex in hexanes. The polymerization rate and exo-olefin content were virtually identical to that obtained in the absence of impurities. Heterogeneous phase scavenger (FeCl3) exhibited better performance than homogenous phase scavengers. In the second approach, conducting the polymerization in wet hexanes, the fast polymerization of IB was retained in the presence of impurities with a slight decrease in exo-olefin content. 1H NMR studies suggest that nucleophilic impurities are protonated in the presence of water, and thereby neutralized. Mechanistic studies suggest that the rate constant of activation (ka), rate constant of propagation (kp), and rate constant of b-proton elimination (ktr) are not affected by the presence of impurities. To account for the retardation of polymerization in the presence of impurities, delay of proton transfer to monomer in the chain transfer step is proposed.
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The kinetics and mechanism of the polymerization of isobutylene (IB) using ethylaluminum dichloride (EADC)•bis(2-chloroethyl) ether (CEE) complex as catalyst in conjunction with tert-butyl chloride (t-BuCl) as initiator in hexanes at 0 °C have been previously reported.1 In an effort to further study the catalyst performance, we have investigated the polymerization at elevated temperatures. Polymerization rates increased while molecular weights and exo-olefin contents (90-78 %) decreased with increasing temperature. At elevated temperatures the first-order plots are curved upward, suggesting that the formation of the tert-butyloxonium ion is slower at higher temperatures. 1H NMR studies confirmed that the t-butyloxonium ion is stable up to 15 oC but slowly decompose at 20 °C. Linear first order plots were obtained when the polymerization was carried out with tert-butyloxonium ion preformed at 10 °C. The slope of the first order plots that is proportional to the steady state concentration of carbenium ions increased 2, 3 and 4 fold at 10, 15 and 20 °C relative to that at 0 °C. Kinetic parameters of activation-deactivation were determined using model reactions. The rate constant of activation at 0 oC (ka = 3x10-4 s-1) increased 2, 3.4 and 4 fold at 10, 15 and 20 oC, respectively, in line with the rate increases. The deactivation rate constant, kd = 1010 L mol-1 s-1 was at the diffusion-limit.
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The cationic polymerization of isobutylene with H2O/ⁱBu2AlCl and H2O/ⁱBuAlCl2·nOR2 (n = 0-1; R2O = Bu2O, Hex2O, ⁱPr2O) initiating systems in toluene as a solvent at -20 °C has been investigated. The H2O/ⁱBu2AlCl initiating system induced slow cationic polymerization of isobutylene to afford polyisobutylenes with high molecular weight (up to Mn = 55 000 g mol⁻¹) with relatively low polydispersity (Mw/Mn < 2.5) and high exo-olefin end group content (>85%). The introduction of additional water into the system allowed increasing the reaction rate, but almost did not influence the molecular weight and exo-olefin content. The use of stronger Lewis acid ⁱBuAlCl2 results in a significant increase of the intensity of side reactions such as chain transfer to solvent (toluene) and isomerization of the growing macrocations, leading to the formation of ill-defined products. However, the addition of 0.6-1.0 equivalents of ethers to Lewis acid allowed conducting the polymerization in a controlled fashion in terms of chain end functionality. In addition, the molecular weight can be efficiently controlled by either the ether/Lewis acid ratio or the nature of the electron donor additive. Based on the obtained results, the polymerization mechanism, the key features of which are complex formation between Lewis acid and toluene and possible stabilization of active species through their interaction with toluene, was proposed.
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The use of [emim]Cl–AlCl3 in combination with diisopropyl ether allowed us to synthesize highly reactive polyisobutylene with an exceptionally high exo-olefin end group content (≥90%) and a relatively narrow molecular weight distribution (Mw/Mn ≤ 2.0) at a high reaction temperature (0 °C–10 °C) and monomer concentration ([IB] = 5.2 M–7.8 M).
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The cationic polymerization of isobutylene using pre-activated by the wet argon or salts hydrates iBuAlCl2 as catalyst in the presence of diisopropyl ether in n-hexane at 10 °C as a starting temperature and high monomer concentration ([IB] = 5.8 M) has been investigated. It was shown that pre-activated iBuAlCl2 possessed high activity (>90% of monomer conversion in 10 min) and unexpectedly high regioselectivity of β-H abstraction at rather low ether to Lewis acid ratio (iPr2O/iBuAlCl2 = 0.4). The use of pre-activated iBuAlCl2 as a co-initiator leads to formation of more uniform active species that results in narrowing of molecular weight distribution as compared to polyisobutylenes synthesized with non-pre-activated iBuAlCl2. Much better control over polydispersity can be achieved by using of mixture of two ethers of different basicity and steric structure (diethyl and diisopropyl ethers) as additive instead of one (diisopropyl ether) during IB polymerization co-initiated by pre-activated iBuAlCl2. Under optimized conditions ([iBuAlCl2 pre-act.] = 38 mM, [Et2O] = [iPr2O] = 7.6 mM, [H2O] = 0.033 M, time: 15 min), desired low molecular weight (Mn ∼ 1,000 g mol−1) highly reactive polyisobutylenes in high yield (>90%) with high content of exo-olefin end groups (>80%) and relatively low polydispersity (Mw/Mn = 2.4–2.7) were readily synthesized at high reaction temperature (10 °C) and monomer concentration ([IB] = 5.8 M).