Note: Descriptions are shown in the official language in which they were submitted.
CA 02334263 2000-12-04
METHOD FOR PRODUCING HIGHLY REACTIVE POLYISOBUTENES
The present invention relates to a process for preparing highly
reactive polyisobutenes having a terminal vinylidene group
content of more than 80 mold and an average molecular weight of
from 500 to 5000 dalton by cationic polymerization of isobutene
in the liquid phase in the presence of boron trifluoride
complexes at from +40°C to -60°C.
High molecular weight polyisobutenes having molecular weights of
up to several 100,000 dalton have long been known and their
preparation is described, for example, in H. Guterbock:
Polyisobutylen and Mischpolymerisate, pages 77 to 104, Springer,
Berlin 1959. The currently available polyisobutenes having
molecular weights of from 500 to 5000 dalton are prepared with
the aid of Lewis acid catalysts, such as aluminum chloride,
alkylaluminum chlorides or boron trifluoride, and generally have
a terminal double bond (vinylidene group) content of less than
10 mold and a molecular weight distribution (dispersity) between
2 and 5.
A distinction must be made between these conventional
polyisobutenes and the highly reactive polyisobutenes, which
have a high terminal vinylidene group content of preferably
substantially more than 60 mold. Such highly reactive
polyisobutenes have achieved a 10~ share of the market and are
used as intermediates for the preparation of additives for
lubricants and fuels, as described, for example, in
DE-A 27 02 604. For the preparation of these additives,
polyisobutene/maleic anhydride adducts, in particular
polyisobutenylsuccinic anhydrides, are first produced by reacting
predominantly terminal double bonds of the polyisobutene with
malefic anhydride, and said adducts are then reacted with certain
amines to give the finished additive. Since terminal vinylidene
groups are the main reaction sites in the adduct formation with
malefic anhydride (whereas, depending on their position in the
macromolecule, the double bonds present further in the interior
of the macromolecule lead to substantially lower, if any,
conversion without the addition of halogens), the amount of
terminal vinylidene groups in the molecule is the most important
quality criterion for this type of polyisobutene.
The formation of terminal vinylidene groups and the isomerization
of terminal double bonds in the isobutene macromolecules to
internal double bonds are, according to Puskas et al., J. Polymer
OU50/49091 ~ 02334263 2000-12-04
2
Sci.: Symposium No. 56, (1976) 191, based on the concepts shown
in the scheme below.
CH3 5 CH3 CH3 ~~ H2
a~ - H~
R CH2- C- CH2- C ~ R CH2 - C -CHZ-
Y II
H3 Protonation CH3
CH3
CH3
I II
Concerted CH3 CH3
1,3-Methyl 1,2-hydride
group group
shif and
t
2,3-methyl R CH2- CH=
C - C
group
shift
CH3 CH3
III
CH3 CH3 CH3 CH3
CH3
R ' CH2-C-CH2 -C-CH3 R CH2-C- CH-C -H
O O
CH3
H3
IV
V
-H 0 ~ T -H ~ ~ T
3 Double bond isomers 3 Double bond isomers
R~ Polyisobutylene radical
The polyisobutene cation I formed in the course of the
polymerization reaction may be converted into the corresponding
polyisobutene by elimination of a proton. The proton may be
eliminated either from one of the b-methyl groups or from the
internal Y-methylene group. Depending on which of these two
positions the proton is eliminated from, a polyisobutene having a
terminal vinylidene group II or having a trisubstituted double
bond III present close to the end of the molecule is formed.
X050/49091 ~ 02334263 2000-12-04
3
The polyisobutene cation I is relatively unstable and tries to
achieve stability by rearrangement to form more highly
substituted cations. Both 1,3-methyl group shifts to give the
polyisobutene cation IV and successive or concerted 1,2-hydride
group and 2,3-methyl group shifts to give the polyisobutene
cation V may take place. Depending on the position from which the
proton is eliminated, in each case three different polyisobutene
double bond isomers can form from the cations IV and V. However,
it is also possible for the cations IV and V to undergo further
rearrangement, causing the double bond to migrate even further
into the interior of the polyisobutene macromolecule.
All these deprotonations and rearrangements are equilibrium
reactions and therefore reversible, but ultimately the formation
of more stable, more highly substituted cat:ions and hence the
formation of polyisobutenes having an internal double bond with
establishment of a thermodynamic equilibrium is favored. These
deprotonations, protonations and rearrangements are catalyzed by
any traces of acid present in the reaction mixture, but in
particular by the actual Lewis acid catalyst required for
catalyzing the polymerization. The loss of reactivity due to
isomerization can therefore only be counteracted by short
residence times or steric hindrance of the complex anion. Since
only polyisobutenes having terminal vinylidene groups according
to formula II react really efficiently with the malefic anhydride
with adduct formation, polyisobutenes of the formula III have by
comparison substantially lower reactivity and other
polyisobutenes having more highly substituted double bonds are
virtually unreactive toward malefic anhydride, the continued
efforts of many research groups to find improved processes for
the preparation of highly reactive polyisobutenes or
polyisobutenes having higher and higher contents of terminal
double bonds are understandable.
According to DE-A 27 02 604, reactive polyisobutenes having a
terminal double bond content of up to 88% by weight are
obtainable by boron trifluoride-catalyzed polymerization of
isobutene at from -50 to +30°C and residence times of less than
10 minutes. The lowest dispersity found for the polyisobutenes
thus prepared is 1.8.
Polyisobutenes having similarly high terminal double bond
contents, but a narrower molecular weight distribution, are
obtainable by the process described in EP-A 145 235, by
polymerizing isobutene in the presence of a preformed complex of
boron trifluoride and a primary alcohol at from -100 to +50°C and
a contact time of the polymerization reaction of more than
005U/49091 ~ 02334263 2000-12-04
4
8 minutes, the molar ratio of boron trifluoride to the alcohol
being from 0.5:1 to 5:1. This process has the disadvantages that
polyisobutenes having a high terminal double bond content of more
than 80~ can only be obtained at a low isobutene conversion and
that the resulting polyisobutenes are particularly costly to
prepare.
Polyisobutenes having a terminal double bond content of up to
95 mold are said to be available by the gas phase process
described in US-A 3 166 546 and also by the process described in
US-A 3 024 226, in which the catalyst used is a boron
trifluoride/sulfur dioxide gas mixture. These polyisobutenes are
characterized on the basis of infrared spectroscopy results.
However, when the polyisobutenes obtained by these processes were
analyzed by means of 13C nuclear magnetic resonance (13C NMR)
spectroscopy, which is a much more specific and precise method
for detecting terminal double bonds, yet not common at the time
said patent was written, the terminal double bond content found
was only up to 40 mold.
US-A 4 227 027 teaches alkyl transfer reactions catalyzed by
boron trifluoride, the catalysts used being adducts of boron
trifluoride and diols or polyols at from 40 to 120°C. The
polymerization of isobutane by this process using a boron
trifluoride/1,2-butanediol adduct catalyst gave diisobutylene as
the only product. No polyisobutene was formed.
Further quality criteria for polyisobutenes useful for the
abovementioned application are their average molecular weight and
the molecular weight distribution, also called dispersity, of the
macromolecules contained in the polyisobutene. Generally,
polyisobutenes having number average molecular weights (Mn) of
from 500 to 5000 dalton are used as intermediates for the
preparation of the abovementioned lubricant and fuel additives.
But polyisobutenes having molecular weights of from 800 to
3000 dalton, in particular from 1000 to 2500 dalton, are more
effective for this purpose and thus preferred.
The polymerization of isobutene yields polyisobutene products
whose polyisobutene components, i.e. the polyisobutene
macromolecules, have a more or less broad, random molecular
weight distribution with the result that broadening the molecular
weight distribution of these polyisobutenes would lead to an
increasing proportion of polyisobutene macromolecules having
relatively low or relatively high molecular weights which are
more or less unsuitable for the abovementi.oned purpose since they
are relatively ineffective. It is therefore desirable to prepare
~~5~/49091 ~ 02334263 2000-12-04
highly reactive isobutenes having average molecular weights
inside the preferred molecular weight ranges and preferably a
very narrow molecular weight distribution so as to reduce the
proportion of undesired, relatively high molecular weight or
5 relatively low molecular weight polyisobutenes in the resulting
product and thus to improve the quality of the product.
It was attempted to solve this problem by a process described in
US 5,408,018 in which highly reactive polyisobutenes having a
terminal vinylidene group content of more than 80 mold and an
average molecular weight of from 500 to 5000 dalton by cationic
polymerization of isobutene in the liquid phase with the aid of
boron trifluoride as catalyst at from O~C to -60~C are produced by
polymerizing in the presence of secondary alcohols having 3-20
carbon atoms and/or dialkyl ethers having 2-20 carbon atoms. The
dialkyl ethers used are preferably ethers containing at least one
tertiary alkyl group. This process yields very good results,
according to Example 6 of the cited patent, in the presence of a
complex of BF3 with 2-butanol and 2-butyl t.-butyl ether.
It is an object of the present invention to simplify the process
and in particular to reduce the formation of by-products in the
form of tertiary butanol and tertiary organic fluorides, which
increase the solvent purification costs and reduce the polymer
yield.
We have found that this object is achieved by a process for
preparing highly reactive polyisobutenes having a terminal
vinylidene group content of more than 80 mold and an average
molecular weight of from 500 to 5000 dalton by cationic
polymerization of isobutene in the liquid phase in the presence
of a complex comprising boron trifluoride at from +40~C to -60~C,
which comprises polymerizing in the presence of a complex
comprising boron trifluoride and
a) a primary alcohol having 1-20 carbon atoms or a secondary
alcohol having 3-20 carbon atoms, or a mixture of these
alcohols, and
b) an ether containing no tertiary alkyl groups and having the
formula I
Rl-O-R2 I.
amended sheet
0050/49091 ~ 02334263 2000-12-04
6
where R1 and R2 are primary or secondary alkyl groups having
3-10 carbon atoms, with the proviso that at least one of R1 and R2
is a secondary alkyl group.
Pref erred secondary alcohols used are 2-butanol and especially
isopropanol, and preferred ethers used are diisopropyl ether or
di-sec-butyl ether.
For the purposes of the present invention, terminal vinylidene
groups or terminal double bonds are those double bonds whose
position in the polyisobutene macromolecule is described by the
general formula IIa
CH3 8 CH2
R CH2-C-- CH2 a ~ IIa
H3 CH3
where R is the polyisobutylene radical in question. The type and
proportion of the double bonds present in the polyisobutene
prepared according to the invention is determined by 13C NMR
spectroscopy. In the 13C NMR spectrum, the two terminal double
bond carbon atoms indicated by a and ti in formula IIa can be
identified by their peaks at a chemical shift of 114.4 and
143.6 ppm, respectively, and the proportion of terminal double
bonds with regard to other types of double bonds is calculated by
an evaluation of the peak areas in relation to the overall
integral of the olefin peaks.
The number average molecular weight or number average molar mass
used herein is the number average molecular weight Mn which can be
determined, for example, by gel permeation chromatography,
ozonolysis or vapor-pressure osmometry.
The process according to the invention makes it possible to
prepare polyisobutenes having a terminal vinylidene group content
of more than 80 mold, especially more than 90 mold, by cationic
polymerization in the liquid phase of isobutene at from +40 to
-60~C, preferably from -4 to -30~C, more preferably from -10 to
-20~C.
Useful protic complex constituents, which are also referred to as
initiators, include virtually all primary alcohols having 1-20
carbon atoms as well as all secondary alcohols having 3-20 carbon
' 050/49091 ~ 02334263 2000-12-04
7
atoms, i.e. the primary or secondary alcohols may be linear or
branched.
Examples of primary alcohols which can be used according to the
invention are methanol, ethanol, n-propanol, n-butanol,
n-pentanol, n-hexanol, n-heptanol, n-octanol, n-nonanol,
n-decanol, 2-ethylhexanol, 2-propylheptanol., n-undecanol,
n-dodecanol, n-tridecanol, ethylene glycol and n-eicosanol.
Examples of suitable secondary alcohols are: isopropanol,
2-butanol, and also sec-pentanols, sec-hexanols, sec-heptanols,
sec-octanols, sec-nonanols, sec-decanols or. sec-tridecanols.
In addition to monohydric, primary and/or secondary alcohols,
(poly)etherols of ethylene oxide, propene oxide and butene oxide
as well as polytetrahydrofuran may also be used according to the
invention.
Preference is given to using 2-butanol and especially
isopropanol.
The ether containing no tertiary alkyl groups and having the
formula I
Rl-O-R2,
may be any ether in which the groups R1 and/or R2 are derived from
a secondary alcohol and are primary or secondary alkyl groups
having 3-10 carbon atoms, i.e. alkyl groups which are attached to
the ether oxygen atom either as -CH2-R or -CH-(R)2 group, but not
as -C-(R)3 group. Specific examples of R1 a.nd R2 include the
following groups:
isopropyl, 2-butyl, sec-pentyl, hexyl, heptyl and octyl, and for
R2 also methyl, ethyl, propyl, butyl, pentyl and hexyl groups.
Particular preference is given to diisopropyl ether, isopropyl
2-butyl ether and di-2-butyl ether.
The boron trifluoride/ether/alcohol complexes are advantageously
prepared by introducing gaseous boron trifluoride into the ether
and the alcohol in question or preferably into a solution in a
solvent of the ether and the alcohol in question. These complexes
are usually prepared at from -60 to +40~C, preferably at from -20
to +40~C. Although it is also possible to work at lower
temperatures, it is technically more difficult to achieve such
low temperatures. Since the complexing of boron trifluoride with
0050/49091 ~ 02334263 2000-12-04
8
secondary alcohols is exothermic, the reaction mixture is
preferably cooled to maintain it at the desired temperature.
At low temperatures, many of the boron trif:luoride complexes to
be used according to the invention are highly viscous liquids or
even solids. In these cases it is advantageous to generate the
boron trifluoride complexes in a solvent. Examples of suitable
solvents are hydrocarbons, such as pentane, hexane, isooctane, or
halogenated hydrocarbons, such as methylene chloride or
chloroform. It is of course also possible to use solvent
mixtures. Usually, the solubility of boron trifluoride complexes
increases with increasing solvent polarity.
Therefore, when the boron trifluoride complexes to be used
according to the invention are prepared in apolar solvents, such
as the abovementioned hydrocarbons or a polyisobutene solution,
the boron trifluoride complex may exceed the solubility product
and separate out to form an emulsion or suspension. Since the
process according to the invention is catalyzed not only by
catalyst complexes dissolved homogeneously in the reaction medium
but also by catalyst complexes disbursed heterogeneously in the
reaction medium, such catalyst separations are usually not
critical.
The boron trifluoride complexes may be preformed in separate
reactors prior to use in the process according to the invention,
temporarily stored after their formation and metered into the
polymerization reactor as required.
For temporary storage, the solutions of the preformed boron
trifluoride complexes, if desired after dilution with further
solvent, are preferably filled into coolable containers and
stored at generally below O~C until used.
Another, preferred variation comprises generating the boron
trifluoride complexes in situ in the polymerization reactor. This
procedure comprises introducing the alcohol in question and the
ether, if desired together with a solvent and together with the
isobutene, into the polymerization reactor and dispersing the
boron trifluoride in the required amount in this reactant mixture
in which the boron trifluoride reacts with the alcohol and the
ether to give the boron trifluoride complex. The in situ
generation of the boron trifluoride catalyst complex can
advantageously be conducted using isobutene or the reaction
mixture comprising unconverted isobutene and polyisobutene as
solvent instead of an additional solvent. If the reaction mixture
of isobutene comprising polyisobutene is used as a solvent, the
0050/49091 ~ 02334263 2000-12-04
9
isobutene is of course usually not converted completely, and it
is advantageous to choose a partial isobutene conversion of in
general up to 80~, preferably of up to 70~.
The in situ generation of the boron trifluoride complexes in the
preparation of highly reactive polyisobutenes represents (as in
the case of the process of US 5,408,018) a substantial
simplification of the process for their preparation. Among other
things, the investment in terms of equipment is reduced, since
neither reactors for preparing preformed camplexes nor storage
tanks for the preformed complex solutions are required.
It is advantageous to prepare the catalysts comprising boron
trifluoride, secondary alcohol and ether in the molar ratio
intended for the complex to be used in the process according to
the invention, i.e. the molar boron trifluoride/sec-alcohol/ether
ratio is usually not altered after generation of the complex in
question.
The molar ratio of alcohol to ether may vary from 0.01 to 10.
Particular preference is given to a ratio of from 0.02 to 2 and
particularly preferably from 0.2 to 1Ø
The BF3 concentration in the reactor may be significantly higher
than the concentrations customary to date and should be in
general in the range from 0.01 to 1~ by weight, more preferably
from 0.05 to 0.5~ by weight. The molar concentration of the
complexing agents alcohol and ether depends on the BF3
concentration; the molar ratio of the sum of alcohol and ether to
BF3 is more than 1 and less than 2 and is preferably from 1.4 to
2.
The isobutene concentration in the reactor is generally from 0.5
to 60~ by weight, for polyisobutene up to MN = 3000 preferably
from 0.5 to 20~ by weight more preferably below 5~ by weight. The
polymer concentration ranges from 10 to 60~ by weight.
In a preferred embodiment, the BF3/ether complex is first prepared
separately or in the solvent feed to the reactor and then
combined with the alcohol in the complex or solvent feed to the
reactor or in the reactor itself. This makes it possible to
dissipate the energy of complex formation without detrimental
by-product formation during the generation of the alcohol
complex.
0050/49091 ~ 02334263 2000-12-04
The starting material used for the preparation of the boron
trifluoride complexes is advantageously gaseous boron
trifluoride. Although it is possible to use technical grade boron
trifluoride comprising minor amounts of sulfur dioxide and SiF4
5 (purity: 96.5 by weight), it is preferable to use high purity
boron trifluoride (purity: 99.5 by weight).
Thus, the preparation of highly reactive polyisobutenes according
to the invention comprises disbursing the preformed boron
10 trifluoride complex solution or suspension in the isobutene
according to the catalyst requirement or alternatively generating
the catalyst in the isobutene stream comprising alcohol and ether
by introducing gaseous boron trifluoride in situ. Isobutene
feedstocks which may be used in the process of the invention
include pure isobutene and mixtures of isobutene and other
hydrocarbons whose isobutene content should advantageously not be
less than 6~ by weight. Preference is given to using hydrocarbon
mixtures having a high isobutene content and a low butadiene
content, particular preference being given to a pure isobutene
feedstock. This feedstock is convertible as such into
polyisobutene with the aid of the catalyst system according to
the invention in the presence of inert solvents, such as
saturated hydrocarbons, for example butane, pentane, hexane,
isooctane, cyclobutane or cyclopentane, halogenated hydrocarbons,
such as methylene chloride or chloroform, or halocarbons having
suitable melting and boiling points. The isobutene feedstock may
comprise minor amounts of impurities such as water, carboxylic
acids or mineral acids without causing critical yield or
selectivity losses during polymerization. This results in a lower
alcohol/ether consumption which alters the abovementioned molar
ratios in favor of BF3. It is, however, convenient and
advantageous to avoid an accumulation of these impurities in the
system by removing such substances from the isobutene feedstock,
for example by adsorption on solid adsorbents, such as activated
carbon, molecular sieves or ion exchangers.
The isobutene polymerization can be carried out batchwise,
semicontinuously or continuously. It is possible to use
conventional reactors such as tubular reactors, tube bundle
reactors or stirred tanks, but the process according to the
invention is preferably carried out in a loop reactor, i.e. a
tubular or tube bundle reactor with continuous circulation of the
reacting material, where the feed/circulation ratio may generally
vary from 1:1 to 1:1000, preferably from 1:50 to 1:200 v/v. It
will be appreciated that the amount of feed equals the amount of
' U05U/49091 ~ 02334263 2000-12-04
11
reaction effluent after equilibration of the polymerization
reaction.
To avoid high local and steady-state catalyst concentrations in
the polymerization reactor which may give rise to double bond
shifts, it is advantageous to provide for good mixing of all
reactants during their introduction into the reactor both in the
case of preformed catalyst complexes being introduced into the
reactor and in the case of generating the boron trifluoride
complexes in the reactor in situ. It is also advantageous to
generate a turbulent flow of the reaction mixture in the reactor,
which can be achieved, for example, by providing the reactor with
suitable internals such as baffles or by dimensioning the tube
cross sections such that a suitable flow rate is achieved.
The residence time in the reactor of the isobutene to be
polymerized may range from 5 sec to several hours, preference
being given to choosing a residence time of from 1 to 30 minutes,
more preferably from 2 to 20 minutes. The overall reaction rate
depends on the amount, but in particular on the molar ratio, of
the complex used. Virtually any overall reaction rate may be
chosen by varying this ratio. The optimum reaction rate is a
function of the equipment and depends on the dissipation of heat.
Short reaction times are preferred. The boron
trifluoride/alcohol/ether catalyst is usually introduced in an
amount of from 0.05 to 1~ by weight, based on the isobutene or
isobutene/hydrocarbon mixture used.
The polymerization is advantageously carried out at below 20~C,
preferably below O~C. Although isobutene can be polymerized to
give highly reactive polyisobutene at substantially lower
temperatures, the polymerization is generally carried out at from
+40 to -60~C, in particular from -4 to -30«C, particularly
preferably from -10 to -20~C. The polymerization is generally
conducted under atmospheric pressure, although it is also
possible to work under elevated pressure, in particular under the
autogeneous pressure of the reaction system, although this is
usually immaterial to the result of the polymerization. The
polymerization reaction is advantageously conducted under
isothermal conditions and at a constant, steady-state monomer
concentration in the reaction medium. Any steady-state isobutene
concentration may be chosen in principle, but it is advantageous
to choose a monomer concentration of in general from 0.2 to 505
by weight, preferably from 0.2 to 5~ by weight, based on the
total polymerization mixture.
0050/49091 ~ 02334263 2000-12-04
12
Since the polymerization reaction is exothermic, the heat of
polymerization is usually dissipated by a cooling means, which
may be operated, for example, using liquid ammonia as coolant.
Another way to dissipate the heat of polymerization is
evaporative cooling. In this case, the heat. evolved is consumed
by evaporation of the isobutene and/or other volatile
constituents of the isobutene feedstock or the possibly volatile
solvent such as ethane, propane or butane, keeping the
temperature constant. However, a disadvantage is the volatility
of the BF3 complexes which may result in side reactions occurring
in the gas phase.
Any isobutene conversion may be chosen in principle. It will be
appreciated, however, that very low isobutene conversions
jeopardize the economic viability of the process, whereas very
high isobutene conversions of more than 99~ increase the risk of
double bond shifts which makes shorter reaction times, i.e. an
improved dissipation of heat, absolutely necessary. For these
reasons, the isobutene conversion is usually from 20 to 99~, more
preferably from 90 to 98~. Surprisingly, these high isobutene
conversions, when achieved using the catalyst system according to
the invention, result only to a minor extent in double bond
shifts, and the resulting polymer still has a terminal vinylidene
group content of more than 80 mold. For the preparation of a
polyisobutene having a terminal double bond content of more than
90 mold, preference is given (at a 50~ strength by weight
isobutene content of the feed) to an isobutene conversion of up
to 99~, preferably from 90 to 99~, especially from 94 to 99~,
particularly preferably from 96 to 98~.
The reaction effluent is advantageously worked up by introducing
it into a medium which deactivates the polymerization catalyst
and thus terminates the polymerization. Examples of suitable
media include water, alcohols, acetonitrile, ammonia or aqueous
solutions of mineral bases, such as solutions of alkali metal and
alkaline earth metal hydroxides, solutions of carbonates of these
metals and the like.
As part of the continued workup, the polyisobutene is
advantageously subjected to one or more extractions to remove
residual complex - usually washes with methanol or water -
followed by separation by distillation into unconverted
isobutene, solvent, oligomers and polyisobutene. The isobutene,
the solvent and the oligomers may be returned to the
polymerization reactor. The desired polyisobutene is obtained as
bottom product.
' 0050/49091 ~ 02334263 2000-12-04
13
The process of the invention provides an economical way to
prepare highly reactive polyisobutenes which have a terminal
double bond content of more than 80 mold, often even more than
90 mold, at very high selectivities and very high conversions,
and moreover provides polyisobutenes in the. preferred molecular
weight range having narrow molecular weight distributions.
Alternatively, the process of the invention makes it possible to
conduct the polymerization at an elevated temperature or to
increase the reactivity of the polyisobutene produced even
further as compared to the process of US 5,408,018, and it is
easier to separate off the complex owing to its lower solubility.
Example 1
The reactor used was a recycle reactor consisting of a Teflon
tube which had a length of 7.1 m and an internal diameter of 6 mm
and via which 100 1/h of reactor content were circulated by means
of a gear pump. The tube and pump had a capacity of 200 ml. The
Teflon tube and pump head were immersed in a cold bath at -23.8°C
(cryostat). A mixture of 300 g/h of isobutene and 300 g/h of
hexane was dried over a 3 A molecular sieve to a water content of
less than 3 ppm and fed to the recycle reactor through a
capillary which had an internal diameter of 2 mm and was
precooled to -23.8°C. BF3 and isopropanol/diisopropyl ether as
complexing agents were directly introduced into the hexane feed
to the reactor. The BF3 feed was set to 23.5 mmol, and the total
amount of the feed of the mixture of hexane, isopropanol and
diisopropyl ether (15:1:4 ml) was varied until an isobutene
conversion of 92.0 was obtained. The isopropanol feed was
13.6 mmol, and the diisopropyl ether feed was 27.2 mmol, at a
reactor temperature of -18°C. The reactor effluent was washed with
water and worked up by distillation at 230°C/2 mbar. The molecular
weight Mn of the polymer was 1070; the reactivity (vinylidene
double bond content) was 97Ø
Examples 2 - 6:
Example 1 was repeated, except that increasing molar ratios of
ether to alcohol were used. At an isobutene conversion of from 92
to 98~, the amount of BF3 was increased until a molecular weight
of about 1000 as determined by GPC was obtained after workup. The
ether used in Example 7 was di-sec-butyl ether. The results are
summarized in Table 1.
0050/49091
CA 02334263 2000-12-04
14
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