CA2360611C

CA2360611C - Transition metal-free initiator for the preparation of isobutylene-based polymers

Info

Publication number: CA2360611C
Application number: CA 2360611
Authority: CA
Inventors: Michael C. Baird; Rajesh K. Kumar; Mark J. Drewitt; Calvin Tse
Original assignee: Lanxess Inc
Current assignee: Arlanxeo Canada Inc
Priority date: 2001-10-30
Filing date: 2001-10-30
Publication date: 2010-08-17
Anticipated expiration: 2021-10-30
Also published as: RU2004116348A; GB2397822A; JP2005507029A; CA2360611A1; WO2003037940A1; GB2397822B; HK1077308A1; GB0411385D0; CN1610705A; RU2308463C2; CN1294162C

Abstract

There is disclosed a process for polymerizing a cationically polymerizable olefin comprising the step of polymerizing at least one cationically polymerizable olefin, preferably at subatmospheric pressure, in the presence of an initiator system which comprises a Lewis acid and an activator which is a proton source, such as an alcohol, a thiol, a carboxylic acid, a thiocarboxylic acid and the like. The initiator system does not contain a transition-metal compound.

Description

TRANSITION METAL-FREE INITIATOR FOR THE PREPARATION OF
ISOBUTYLENE-BASED POLYMERS
FIELD OF THE INVENTION
The present invention relates to an alternative initiator system for the preparation of isobutylene-based polymers.
BACKGROUND OF THE INVENTION
Cationic polymerization of olefins is known in the art.
Conventionally, cationic polymerization is effected using a catalyst system comprising: (i) a Lewis acid, (ii) a tertiary alkyl initiator molecule containing a halogen, ester, ether, acid or alcohol group, and, optionally, (iii) an electron donor molecule such as ethyl acetate. Such catalysts systems have been used for the so-called "living" and "non-living" carbocationic polymerization of olefins.
Catalyst systems based on halogens and/or alkyl-containing Lewis acids, such as boron trichloride and titanium tetrachloride, use various combinations of the above components and typically have similar process characteristics. For the so-called "living"
polymerization systems, it is conventional for Lewis acid concentrations to exceed the concentration of initiator sites by 16 to 40 times in order to achieve 100 percent conversion in 30 minutes (based upon a degree of polymerization equal to 890) at -75° to -80°C.
In the so-called "non-living" polymerization systems, high molecular weight polyisobutylenes are prepared practically only at low temperatures (-60 to -100°C) and at catalyst concentrations exceeding one catalyst molecule per initiator molecule. In practice, many of these catalyst systems are applicable only in certain narrow temperature regions and concentration profiles.
In recent years, a new class of catalyst systems utilising compatible weakly-coordinating anions in combination with cyclopentadienyl transition metal compounds (also referred to in the art as "metallocenes") has been developed. See, for example, any one of:

published European patent application 0,277,003A;
published European patent application 0,277,004;
United States patent 5,198,401; and published International patent application W092/00333.
The use of ionising compounds not containing an active proton is also known.
See, for example, either of published European patent application 0,426,637A; and published European patent application 0,573,403A.
US 5,448,001 discloses a carbocationic process for the polymerization of isobutylene which utilizes a catalyst system comprising, for example, a metallocene catalyst and a borane.
WO 00/04061 discloses a cationic polymerization process which is conducted at subatmospheric pressure in the presence of a catalyst system such as Cp*TiMe3 (the "initiator") and B(CsF5)3 (the "activator"). Such a system generates a "reactive cation" and a "weakly-coordinating anion". Using such a catalyst system a polymer having desirable molecular weight properties may be produced in higher yields and at higher temperatures than by conventional means, thus lowering capital and operating costs of the plant producing the polymer.
However, the catalysts employed in the above process have a number of disadvantages, including cost and handling issues.
The polymerization of isobutylene with small amounts of isoprene, to produce butyl rubber, presents unique challenges. Specifically, as is well known in the art, this polymerization reaction is highly exothermic and it is necessary to cool the reaction mixture to approximately -95°C in large scale production facilities. This requirement has remained, notwithstanding advances in the art relating to the development of novel reactor designs and/or novel catalyst systems.
It would be desirable to be able to obtain isobutylene-based polymers, and in particular isobutylene-based copolymers, in high yield, at relatively high temperatures (as compared to the methods of the art) under more environmentally-friendly conditions, and in a cost-effective manner. This has not been demonstrated to date.
SUMMARY OF THE INVENTION
We have found that, unexpectedly, polymerization of isobutylene can be effected using an initiator system comprising a Lewis acid and an activator, but which does not contain any transition-metal compound. This initiator system produces polymers having high molecular weights and narrow polydispersity indices in very high yields, at relatively high temperatures. The activator is best characterized as being a proton source. Suitable activators include alcohols, thiols, carboxylic acids, thiocarboxylic acids and the like.
Such a system not only produces a polymer having a high molecular weight and associated narrow molecular weight distribution, but also results in greater monomer conversion. The polymerization is, preferably, carried out at subatmospheric pressure, and has the further advantage that it can be carried out at higher temperatures than previously thought possible.
Further, the reaction can be carried out in solvents which are more environmentally friendly than those of the art.
DETAILED DESCRIPTION OF THE INVENTION
Thus, the present process is directed to the polymerization of isobutylene.
As mentioned hereinabove, the present process is particularly advantageous in the preparation of butyl rubber polymers. The term "butyl rubber" as used throughout this specification is intended to denote polymers prepared by reacting a major portion, e.g., from about 70 to 99.5 parts by weight, usually 85 to 99.5 parts by weight of an isomonoolefin, such as isobutylene, with a minor portion, e.g., about 30 to 0.5 parts by weight, usually 15 to 0.5 parts by weight, of a multiolefin, e.g., a conjugated diolefin, such as isoprene or butadiene, for each 100 weight parts of these monomers reacted.
The isoolefin, in general, is a C4 to Ca compound , e.g., isobutylene, 2-methyl-1-butene, 3-methyl-1-butene, 2-methyl-2-butene and 4-methyl-1-pentene. The preferred monomer mixture for use in the production of butyl rubber comprises isobutylene and isoprene.
Optionally, an additional olefinic termonomer such as styrene, ~ -methylstyrene, p-methylstyrene, chlorostyrene, pentadiene and the like may be incorporated in the butyl rubber polymer. See, for example, any one of:
United States patent 2,631,984;
United States patent 5,162,445; and United States patent 5,886,106.
The present process comprises the use of a cationic polymerization system comprising a Lewis acid and an activator.
The Lewis acid component of the initiator system is a compound of formula (R~ R2R3)M
wherein:
M is selected from the group consisting of B, AI, Ga and In;
R~, R2 and R3 are independently selected bridged or unbridged halide radicals, dialkylamido radicals, alkoxide and aryloxide radicals, hydrocarbyl and substituted-hydrocarbyl radicals, halocarbyl and substituted-halocarbyl radicals and hydrocarbyl and halocarbyl-substituted organometalloid radicals; preferably, not more than one such R
group may be a halide radical;

The activator component of the catalyst system is an alcohol, a thiol, a carboxylic acid, a thiocarboxylic acid or the like. Preferred activators are those having at least 8 carbon atoms, for example nonanol, octadecanol and octadecanoic acid.
In a preferred embodiment M is B, R~ and R2 are the same or different aromatic or substituted-aromatic hydrocarbon radicals containing from about 6 to about 20 carbon atoms and may be linked to each other through a stable bridging group; and R3 is selected from the group consisting of hydride radicals, hydrocarbyl and substituted-hydrocarbyl radicals, halocarbyl and substituted-halocarbyl radicals, hydrocarbyl- and halocarbyl-substituted organometalloid radicals, disubstituted pnictogen radicals, substituted chalcogen radicals and halide radicals.
In a particularly preferred embodiment, R1, R2 and R3 are each a (CsFS) group.
Without wishing to be bound by any particular theory, it is thought that the Lewis acid and the activator together form a bridged species which is thought to have the following structure ((R~ R2R3)nnl2-~zl H+
where Z represents the radical resulting from abstraction of the acidic proton from the activator (for example, if the activator is an alcohol (ROH) Z represents an alkoxy radical (OR)). The proton in this structure is much more acidic than anticipated (by NMR
evidence) and, indeed, can be considered to be "super acidic", at least to the degree that it is acidic enough to initiate polymerisation in the absence of any transition-metal compound.
At least about 0.01 moles of activator is employed per mole of Lewis acid, the maximum amount of activator employed being about 1 mole per mole of Lewis acid. More preferably, the ratio of activator to Lewis acid is in the range of from about 0.1 : 1 to about 1 : 1, even more preferably in the range of from about 0.25 : 1 to about 1 :
1, and still more preferably in the range of from about 0.5 : 1 to about 1 : 1. Most preferably, about 0.5 moles of activator is employed per mole Lewis acid, as this is the theoretical amount of activator required to convert all of the Lewis acid originally present to the bridged species.
It should be noted that when the ratio of activator to Lewis acid is less than this theoretical amount the bridged species will, of course, still be formed (under equilibrium conditions), but in a less than optimal amount.
The present process can be conducted at sub-atmospheric pressure. Preferably, the pressure at which the present process is conducted is less than about 100 kPa, more preferably less than about 90 kPa, even more preferably in the range of from about 0.00001 to about 50 kPa, even more preferably in the range of from about 0.0001 to about 40 kPa, even more preferably in the range of from about 0.0001 to about 30 kPa, most preferably in the range of from about 0.0001 to about 15 kPa.
The present process may be conducted at a temperature higher than about -80°C, preferably at a temperature in the range of from about -80°C to about 25°C, more preferably at a temperature in the range of from about -60°C to about 10°C and, most preferably, at a temperature in the range of from about -40°C to about 0°C.
The use of the initiator system disclosed herein for the preparation of isobutylene-based polymers has some unexpected advantages. The polymers so produced have high molecular weights. This is even true in the case of isobutylene-based copolymers. Usually the introduction of a second monomer (such as isoprene (1P)) results in a copolymer having a molecular weight very much lower than that of a homopolymer produced under the same conditions, but this is not the case here - whilst the molecular weight of the isobutylene copolymer is still less than that of a homopolymer prepared under the same conditions, the drop in molecular weight is, surprisingly, significantly less than would be expected. Further, these polymerisation reactions are very fast and yields are very high, with monomer conversions of 100% being achieved in homopolymerisation reactions.
Similar conversions were achieved in copolymerisations in polar solvents.
Further embodiments of the present invention will be described with reference to the following Examples which are provided for illustrative purposes only and should not be used to limit the scope of the invention.
EXAMPLES
All glassware was dried by heating at 120°C for at least 12 hours before being assembled. Nitrogen was purified by passing sequentially over heated BASF
catalyst and molecular sieves. Dichloromethane was dried by refluxing over calcium hydride under argon, toluene by refluxing over sodium-benzophenone under argon, and both solvents were freshly distilled and then freeze-pump-thaw degassed prior to use. When necessary, solvents were stored over activated molecular sieves under argon.
The diene monomer isoprene (1P) was purified by passing through a column to remove p-tertbutylcatechol, titrated with n-BuLi (1.6 M solution in hexanes) and distilled under vacuum prior to use. This was then stored at -30 deg.C in a nitrogen-filled dry box.
Isobutylene (1B) was purified by passing through two molecular sieve columns and condensed into a graduated finger immersed in liquid nitrogen. The IB was allowed to melt, the volume noted (~8 to 24 mL) and then refrozen by immersing in the liquid nitrogen bath. The system was evacuated to 10-3 torr, the IB finger isolated and the system placed under a nitrogen atmosphere.
All activators were distilled under argon before use.
A mixture of Lewis acid (for example, B(C6F5)3, usually 25 mg, 0.05 mmol, sublimed), and octadecanoic acid (usually 13 mg, 0.06 mmol, sublimed) both in 5 mL of solvent, were added and frozen in liquid nitrogen sequentially, giving an initiator to monomer ratio of approximately 1:1500. The solution of initiator and IB was brought to the desired temperature (using a cooling bath at -30 deg.C) prior to the addition of the IB.
In some Examples an amount of diene equivalent to ~1 - 3 mole% of the amount of IB was added to the IB finger prior to the condensation of the IB, this being done in a nitrogen-filled dry box.

Solutions of the olefins) and initiator system were generally stirred under a static vacuum and at the predetermined cooling bath temperature (by "static vacuum", it is meant that the system was closed at this point and the pressure essentially was the vapour pressure of the remaining IB and solvent at the reaction temperature). When dichloromethane was used as the solvent copious amounts of polymeric materials generally began to precipitate after about 15 - 90 seconds after the IB/IP
introduction.
When toluene was the solvent a viscous solution was formed and stirring was maintained.
Reactions were terminated after approximately 1 hour by precipitation into methanol (greater than 1 L). The precipitated material was dissolved in hexanes and the solvent flashed off under reduced pressure. The solid white polymer so obtained was dried to constant weight.
Table 1 shows the results of a series of isobutylene homopolymerisation reactions.
Table 2 shows the results of a series of isobutylene/isoprene copolymerization reactions using octadecanoic acid.
Table 3 shows the results of a series of isobutylene/isoprene copolymerization reactions using a variety of different acids.

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. " w The results support the conclusion that conducting the polymerization of isobutylene at sub-atmospheric pressure using the initiator system disclosed herein results in the production of a polymer having a high Mw in the absence of any transition-metal compound.
Similarly, the results support the conclusion that conducting the co-polymerization of isobutylene/isoprene under similar conditions sometimes results in the production of a copolymer having a higher Mw when compared to conducting the polymerization (or copolymerization) of isobutylene in the absence of the activator.
The above embodiments of the disclosed invention detail experiments which were carried out at subatmospheric pressure. Without intending to be bound by any particular theory, it is thought that carrying out the reactions at subatmospheric pressure results in the reaction mixtures refluxing, resulting in better mixing and excellent heat transfer within the mixture, thus minimizing the occurrence and/or build-up of "hot-spots", which are known to be detrimental. Thus, any means which would facilitate excellent heat transfer (for example, highly efficient cooling, improved reactor design) is encompassed by the invention disclosed herein.
All publications, patents and patent applications referred to herein are incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety.

Claims

1. A process for polymerizing a cationically polymerizable olefin comprising the step of polymerizing at least one cationically polymerizable olefin in the presence of an initiator system which comprises a Lewis acid having the formula :
(R1R2R3)M
wherein:
M is selected from the group consisting of B, Al, Ga and In;
R1, R2 and R3 are independently selected bridged or unbridged halide radicals, dialkylamido radicals, alkoxide and aryloxide radicals, hydrocarbyl and substituted-hydrocarbyl radicals, halocarbyl and substituted-halocarbyl radicals and hydrocarbyl and halocarbyl-substituted organometalloid radicals ;
and an activator, the activator being a proton source;
with the proviso that the initiator system does not further contain a transition-metal compound.

2. A process according to claim 1 wherein not more than one R group may be a halide radical;

3. A process according to claim 2 wherein M is B.

4. A process according to claim 2 wherein the proton source is selected from the group consisting of an alcohol, a thiol, a carboxylic acid, a thiocarboxylic acid and the like.

5. A process according to claim 2 wherein the reaction is carried out at subatmospheric pressure.

6. A process according to claim 4 wherein the ratio of co-initiator to boron compound is in the range of from about 0.01:1 to about 1:1.

7. A process according to claim 6 wherein the ratio of co-initiator to boron compound is in the range of from about 0.1:1 to about 1:1.

8. A process according to claim 7 wherein the ratio of co-initiator to boron compound is in the range of from about 0.25:1 to about 1:1.

9. A process according to claim 8 wherein the ratio of co-initiator to boron compound is in the range of from about 0.5:1 to about 1:1.

10.A process according to claim 4 wherein the ratio of co-initiator to boron compound is about 0.5:1.

11.A process according to claim 1 wherein R1, R2 and R3 are independently selected aromatic or substituted aromatic hydrocarbon radicals having from about 6 to about 20 carbon atoms, and which may be linked to each other by a table bridging group.

12. A process according to claim 11 wherein R1, R2 and R3 are each a C6F5 group.

13. A process according to claim 2 wherein the co-initiator is a carboxylic acid.

14.A process according to claim 2 wherein the reaction is carried out at a temperature higher than about -100°C.

15.A process according to claim 14 wherein the reaction is carried out at a temperature higher than about -80°C.

16 16.A process according to claim 15 wherein the reaction is carried out at a temperature higher than about -60°C.

17.A process according to claim 2 wherein the subatmospheric pressure is less than about 100kPa.

18.A process according to claim 17 wherein the subatmospheric pressure is less than about 1kPa.

19.A process according to claim 18 wherein the subatmospheric pressure is less than about 0.01kPa.

20.A process according to claim 2 wherein the at least one cationically polymerizable olefin comprises a mixture of isobutylene and isoprene.

21.A process for polymerizing a cationically polymerizable olefin comprising the step of polymerizing at least one cationically polymerizable olefin in the presence of an initiator system which comprises a Lewis acid having the formula:

(R1R2R3)M

wherein:

M is selected from the group consisting of B, Al, Ga and In;
R1, R2 and R3 are independently selected bridged or unbridged halide radicals, dialkylamido radicals, alkoxide and aryloxide radicals, hydrocarbyl and substituted-hydrocarbyl radicals, halocarbyl and substituted-halocarbyl radicals and hydrocarbyl and halocarbyl-substituted organometalloid radicals;

and an activator, the activator being a proton source;

with the proviso that the initiator system does not further contain a transition-metal compound;

the reaction being carried out such that highly efficient cooling of the reaction mixture occurs.

22.A process according to claim 21, wherein not more than one R group may be a halide radical.