WO2003037940A1

WO2003037940A1 - Transition metal-free initiator for the preparation of isobutylene-based polymers

Info

Publication number: WO2003037940A1
Application number: PCT/CA2002/001619
Authority: WO
Inventors: Michael C. Baird; K. Rajesh Kumar; Mark J. Drewitt; Calvin K. W. Tse
Original assignee: Bayer Inc.
Priority date: 2001-10-30
Filing date: 2002-10-28
Publication date: 2003-05-08
Also published as: CN1294162C; RU2004116348A; RU2308463C2; HK1077308A1; CN1610705A; GB0411385D0; GB2397822A; GB2397822B; CA2360611A1; JP2005507029A; CA2360611C

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 "nonliving" 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 EP-A-0 277 003, EP-A-0 277 004, US-A-5, 198,401 , and WO-92/00333-A1. The use of ionising compounds not containing an active proton is also known. See, for example, either of EP-A-0426 637; and EP-A-0 573 403.

US-A-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-A1 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(C₆Fs)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 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 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) at least one Lewis acid having the formula:

(RιR₂R₃)M wherein:

M is selected from the group consisting of B, Al, Ga and In;

R-i, R₂ and R₃ are bridged or unbridged and independently are selected from the group consisting of 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 b) at least one activator, the activator being a proton source; with the proviso that the initiator system does not further contain a transition-metal compound. 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, usually in the range of from 70 to

99.5 parts by weight, preferably 85 to 99.5 parts by weight of an isomonoolefin, such as isobutylene, with a minor portion, usually in the range of 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 Cs 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, one or more additional olefinic monomers such as styrene, α-methylstyrene, p-methylstyrene, chlorostyrene, pentadiene and the like may be incorporated in the butyl rubber polymer.

It is apparent to the skilled in the art that the composition above in this case will have to be adjusted to result in a total of 100%. Preferred compositions are disclosed in US-A- 2,631 ,984, US-A-5,162,445, and US-A-5,886,106 which are incorporated by reference herein with regard to jurisdictions allowing for this procedure.

The Lewis acid component of the initiator system is a compound of formula :

(R₁R₂R₃)M wherein:

M is selected from the group consisting of B, Al, Ga and In, preferably B; Rι, 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 denotes a halide radical;

The activator component of the catalyst system is preferably an alcohol, a thiol, a carboxylic acid, a thiocarboxylic acid or the like. Especially preferred activators are those listed above having at least 8 carbon atoms, for example nonanol, octadecanol and octadecanoic acid.

In a preferred embodiment M is B, Ri and R₂ are the same or different aromatic or substituted-aromatic hydrocarbon radicals containing in the range of from 6 to 20 carbon atoms and may be linked to each other through a stable bridging group (stable meaning that the bridge is not broken during the polymerization); 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 nitrogen radicals, substituted chalcogen radicals and halide radicals.

In a particularly preferred embodiment, R-i, R₂ and R₃ are each a (C_ΘF_S) 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 :

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.

Preferably, at least 0.01 moles of activator is employed per mole of Lewis acid, the maximum amount of activator employed being preferably 1 mole per mole of Lewis acid. More preferably, the ratio of activator to Lewis acid is in the range of from 0.01 : 1 to 1 : 1 , even more preferably in the range of from 0.25 : 1 to 1 : 1 , and still more preferably in the range of from 0.5 : 1 to 1 : 1. Most preferably, 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 100 kPa, more preferably less than 90 kPa, even more preferably in the range of from 0.00001 to 50 kPa, even more preferably in the range of from 0.0001 to 40 kPa, even more preferably in the range of from 0.0001 to 30 kPa, most preferably in the range of from 0.0001 to 15 kPa.

The present process may be conducted at a temperature higher than -100°C, preferably at a temperature in the range of from -80°C to 25°C, more preferably at a temperature in the range of from -60°C to 10°C and, most preferably, at a temperature in the range of from -40°C to 0°C.

The use of the initiator system disclosed herein especially 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 (IP)) 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 (IP) 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 °C in a nitrogen-filled dry box.

Isobutylene (IB) 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 °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 olefin(s) 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.

Table 1 - Homopolymerisation experiments

Unless noted otherwise, all experiments were carried out in 15mL CH₂CI₂ using 60μmoles of initiator, and were run for 1 hour under vacuum at a bath temperature of -30 °C.

Table 2 - Copolymerization experiments using octadecanoic acid

Unless otherwise noted, all experiments were carried out in 15mL CH₃CI using βOμmoles of initiator, and were run for 1 hour under vacuum, at a bath temperature of -30 °C.

a) T = -50°C; b) reaction time 10min.; c) reaction time 15min.; d) 40μmoles Lewis acid; e) reaction time 10min., 40μmoles Lewis acid; f) 20μmoles Lewis acid; g) reaction time 20min.

Table 3 - Copolymerization experiments using various acids

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.

Claims

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) at least one Lewis acid having the formula :

(RιR₂R₃)M wherein: M is selected from the group consisting of B, Al, Ga and In;

R-i, R₂ and R₃ are bridged or unbridged and independently selected from the group consisting of 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 b) at least one 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 is 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.

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 0.01 : 1 to 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 0.5 : 1 to about 1 : 1.

8. A process according to claim 1 wherein Ri, R₂ and R₃ are independently selected aromatic or substituted aromatic hydrocarbon radicals having in the range of from 6 to 20 carbon atoms, and which may be linked to each other by a stable bridging group.

9. A process according to any of claims 1-8 wherein R-i, R₂ and R₃ are each a C₆F₅ group.

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

11. A process according to any of claims 1-10 wherein the reaction is carried out at a temperature higher than-100°C.

12. A process according to any of claims 1-11 wherein the pressure is less than 100kPa.

13. A process according to any of claims 1-12 wherein the at least one cationically polymerizable olefin comprises a mixture of isobutylene and isoprene.