GB1589985A - Method for preparation of conjugated diene butyl rubber in absence of solvent - Google Patents

Description

(54) METHOD FOR PREPARATION OF CONJUGATED DIENE BUTYL RUBBER IN ABSENCE OF SOLVENT (71) We, EXXON RESEARCH AND ENGINEERING COMPANY, a Corporation duly organised and existing under the laws of the State of Delaware, United States of America, of Linden, New Jersey, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it. is to be performed, to be particularly described in and by the following statement: The present invention relates to the dehydrohalogenation of halogenated butyl rubber to prepare conjugated diene butyl rubber, containing randomly distributed sites of olefinic unsaturation in the linear backbone thereof.

The expression "butyl rubber" is used in the rubber industry to describe copolymers made from a polymerization reaction mixture having therein from 70 to 99.5% by wt. of an isoolefin which has 4 to 7 carbon atoms per molecule, e.g., isobutylene, and 30 to 0.5% by wt. of a conjugated multiolefin having from 4 to 14 carbon atoms per molecule, e.g., isoprene. The resulting copolymers contain 85 to 99.5% by wt. of combined isoolefin and 0.5 to 15% of combined multiolefin. The preparation of butyl rubber is described in U.S. Patent 2,356,128.

The polymer backbone of commercial butyl rubber is made up primarily of isobutylene units, with just a few percent of isoprene units. The isoprene units contribute the small amount of unsaturation present in butyl rubber. The basic preparative equation is represented by:

isobutylene isoprene which combine in the presence of Friedel-Crafts catalysts to form:

where n + 1 represents the number of isoolefin units incorporated in the butyl rubber, while m represents the number of olefin units derived from incorporation of the diene present, substantially as randomly distributed units. The conjugated diolefin, isoprene, loses one olefinic linkage upon its essentially random incorporation into the polymer backbone.

Thus, butyl rubber, as presently produced, contains only a small percentage of unsaturation, in the form of the single double bond associated with the isoprene residue which is incorporated more or less randomly throughout the polymer chain.

Halogenated butyl rubber has been developed in recent years and has contributed significantly to the elastomer business. A method of preparing halogenated butyl rubber is described in U.S. Patent No. 3,099,644. Both chlorinated and brominated butyl rubber are well known in the art. The formula for halogenated butyl rubber is representable by:

where n and m have the same values as for butyl rubber, described above, and x represents halogen, though this structure is but one of several which can be formed, depending on the conditions of halogenation, the halogenating agent use, etc.

It has recently been discovered that relatively high molecular weight halogenated butyl rubber could be dehydrohalogenated to produce a butyl rubber containing randomly distributed sites of diolefinic unsaturation. This new butyl rubber has been termed "conjugated diene butyl", hereinafter referred to as CDB, regardless of the structure of the conjugated unsaturation. One method teaches the contacting of a solution of halogenated butyl rubber with: (1) a soluble metal carboxylate, wherein the metal is a metal of Groups Ib, IIb, IVb or VIII of the Periodic Table; (2) a soluble carboxylic acid; and (3) an oxide or hydroxide of a metal of Groups Ia or IIa of the Periodic Table (see U.S. Patent No. 3,775,387). It has also been discovered that halogenated butyl rubber could be dehydrohalogenated to produce CDB by use of soluble zinc phenoxides such as zinc di-(t-butyl phenolate) as the dehydrohalogenating reagent.

Another method is disclosed in U.S. Patent No. 3,852,253 which teaches a heterogeneous process for preparing CDB. This process comprises contacting a solution of halogenated butyl rubber with a strong mineral acid salt of a metal of Groups IIa or IIb of the Periodic Table.

According to this invention a copolymer consisting of from 85 to 99.5% by wt. of a C4 to C7 isoolefin combined with 15 to 0.5 % by wt. of a Cq to C14 conjugated diolefin, containing randomly distributed sites of conjugated diene unsaturation is prepared by a process comprising either contacting a mixture of a halogenated butyl rubber with a salt of a metal of Group IIa or IIb of the Periodic Table of the Elements in an internal mixer reactor or heating in a mould said mixture, said contacting of said heating being in the absence of solvent and at a temperature of from 100"C to 200"C for a time sufficient to dehydrohalogenate at least partially the halogenated butyl rubber. In this specification we are referring to the Periodic Table appearing in Notes on the Use of the Classification Key of Abridgments of Patent Specifications. Since the amount of dehydrohalogenation obtainable depends on the temperature and the dehydrohalogenating agent concentration, conditions can be found under which the extent of dehydrohalogenation can be carried out at will, thus limiting the number of sites of conjugated unsaturation.

More particularly the invention is directed to at least partially dehydrohalogenating a halogenated butyl rubber comprising 85 to 99.5 percent by weight of an isoolefin having from 4 to 7 carbon atoms per molecule, combined with 15 to 0.5 percent by weight of a conjugated diolefin having from about 4 to 14 carbon atoms per molecule.

The dehydrohalogenation is accomplished by contacting, in reaction zone, said halogenated butyl rubber with a salt of an acid, e.g. the phosphate, sulfate, chloride, nitrate, naphthenate, stearate, tallate or rosinate of calcium or zinc. The minimum weight ratio of rubber to salt is about 100 to 1 (based on residence time) at a temperature of from 100"C. to about 200"C. for a time sufficient to dehydrohalogenate at least partially the halogenated butyl rubber. The resulting rubber, having a reduced halogen content is recovered and is characterized by having randomly distributed sites of conjugated diene unsaturation.

In simplified terms, the process of the present invention comprises dehydrohalogenation in bulk of halogenated butyl rubber to produce a butyl rubber having a reduced halogen content and having conjugated diene groups more or less randomly inserted along its linear backbone.

The product produced by the process of this invention is fully described and claimed in U.S. Patent No. 3,816,371.

Halogenated butyl rubber is commercially available and may be prepared by halogenating butyl rubber in a solution containing 1 to 60 percent by weight of butyl rubber in a substantially inert CsC8 hydrocarbon solvent such as pentane, hexane, heptane, toluene, etc. then contacting this butyl rubber cement with a halogen gas for a period of about 2-25 minutes. The resulting products are a halogenated butyl rubber and a hydrogen halide, wherein the halogenated butyl rubber contains up to one or more halogen atoms per double bond initially present in the copolymer, especially in the case of bromines. This invention is not intended to be limited in any way by the manner in which butyl rubber is halogenated, and both chlorinated and brominated butyl rubber are suitable for use in this invention.

Illustrative of halogenated butyl rubber is Exxon Chemical Chlorobutyl HT-1068 (a chlorinated butyl rubber prepared from a butyl rubber having 1.8 mole percent unsaturation and a viscosity average molecular weight of about 450,000). However, for the purposes of this invention, it is preferred that the butyl rubber starting material have incorporated therein from 0.5 to 6 mole percent of combined diolefin, more preferably 0.5 to 3 percent, e.g. about 2 percent. Butyl rubber generally has a number average molecular weight of 5,000 to 500,000, as determined by membrane osmometry, preferably 80,000 to 250,000, especially 100,000 to 200,000 and a Wijs Iodine No. of about 0.5 to 50, preferably 1 to 15.

In general the process of the present invention may be performed in an internal mixer reactor such as a Z-blade mixer, a Banbury mixer, single or twin-screw extruders and the like, wherein the halogenated butyl rubber is introduced pre-mixed with the dehydrohalogenating agent. In situ mixing is also contemplated. Residence time, contacting temperature, and concentration of the dehydrohalogenating agent would then determine the degree of dehydrohalogenation.

By using the method described herein, CDB may be prepared by contacting halogenated butyl rubber with salt of a Group IIa or IIb metal at a temperature of from 100 to 200"C. Tvpical of the metals of Groups IIa and IIb of the Periodic Table are calcium and zincz The halogenated rubber is first premixed at low temperature with the dehydrohalogenating agents and successively introduced in the preheated internal mixer reactor. Equally excellent results are obtained by mixing the halogenated rubber and the dehydrohalogenating agent directly in the internal mixer reactor either pre-heated or not. Alternatively, the premixed halogenated rubber and dehydrohalogenating agent mixture is heated in a mould. The temperature for the reaction is between 100 and 200"C., with the most preferred temperature in the range of 140 to 1700C.

The reaction period may be for a period of time ranging from 0.1 to 24 hours, depending on the composition of the copolymer (i.e. brominated or chlorinated), amount of dehydrohalogenation agents present in the reaction zone, the level or degree of dehydrochlorination desired, temperature, or any combination of these variables. Preferably the time is in the range of 0.1 to 3 hrs.

Especially suitable for use as dehydrohalogenating agents are the inorganic salts of calcium (e.g., calcium salts of phosphoric, sulfuric, hydrochloric and nitric acids) and the organic salts of zinc (e.g. zinc salts of napthenic, stearic, talloil and rosin acids).

While useful in preparing the compositions of the present invention, potential toxicity problems which could be encountered in practicing the present invention might limit the use of certain metals, such as cadmium and mercury. Tricalcium orthophosphate and zinc naphthenate are the most preferred reagents in the present invention.

The amount of dehydrohalogenating agent suitable for use in the present invention depends upon the residence time of the halogenated butyl rubber at the chosen reaction temperature and upon the degree of dehydrohalogenation desired. The use of dehydrohalogenating agents should preferably be based on a weight ratio that would ensure that 100 parts of rubber would be in contact with a minimum of at least 1 part of salt during the rubber residence either in the reactor or in the mould. Practically speaking this could require the actual use of up to 30 parts of salt per 100 parts of rubber, preferably 3 to 15 parts of salt per 100 parts of rubber. Open reactors such as Z-blade and Banbury mixers should be operated with an inert atmosphere to avoid crosslinking and/or deterioration of the conjugated diene butyl rubber. Single - or twin screw extruders as well as moulds, which operate completely filled with rubber, need not to be connected with inert gas sources.

The predominant structure of CDB, produced by the process of the present invention, is thought to be

where n, m and 1 have the values previously described, though other structures may be present. When the starting halobutyl is a chlorinated butyl rubber the above structure is thought to dominate. However, there may be randomly inserted conjugated diene units having the general structure:

The present invention includes both structures, since their presence depends to a large extent on the starting polymer, rather than on process conditions. Process conditions and reagents used can influence the degree to which the possible geometrical isomers associated with these structures occur in the final conjugated diene product.

The CDB is ready for further use, after baling, dicing or crumbing, as soon as it is discharged from the reactor mixer or from the mould. This method of producing conjugated diene butyl rubber may provide the removal of up to 85-95 % of the halogen present in the halogenated butyl rubber being converted.

The CDB prepared according to the process of this invention may be cured by a variety of methods, e.g., sulfur, sulfur-containing curing agents or polyfunctional dienophiles. Non-limiting examples of polyfunctional dienophiles suitable for use in the present invention are m-phenylene-bis-maleimide, ethylene glycol dimethylacrylate, and trimethylol propane trimethacrylate. Monofunctional dienophiles suitable for further modification of the polymer are cis-2-butene diol, maleic anhydride, acrylic acid and crotonaldehyde. These are merely well known examples. There are many more polyfunctional and monofunctional dienophiles, known in the art that will cure, and modify respectively, the compositions produced by the process of this invention.

The sulfur-containing curing agents are known in the art, and along with sulfur, are useful in curing the compositions produced by this invention.

The CDB prepared according to the process of this invention may also be graft cured by reacting the CDB with at least one free radical polymerizable monomer such as those monomers disclosed in "Appendix A and Appendix B" of the book "Copolymerization" by George E. Ham, Interscience Publishers (1964) on pages 695 to 863, but preferably those monomers with a relatively high boiling point such as indene which boils at 1900C. The graft curing is performed by irradiation or in the presence of at least one free-radical initiator such as organic peroxides, organic hydroperoxides, and azo compounds.

Another method of crosslinking the CDB prepared according to the process of this invention is by introducing ionic crosslinks by reacting the CDB with an ethylenically unsaturated compound such as maleic anhydride, acrylic acid, acrylonitrile, and maleic imide in the presence of a metal hydroxide of a metal selected from Groups I and II of the Periodic Table of the Elements. Preferred is calcium hydroxide.

As described, vulcanization or modification reactions via Diels-Alder adduction with dienophiles are conducted as separate steps from the production of CDB. However, these reactions may be obtained as the dehydrohalogenation reaction is occurring, as encompassed by the present invention, if dienophiles are added to the mixture of halogenated butyl rubber and dehydrohalogenating agents. In this way, dehydrohalogenation and vulcanization or modification are obtained in an one-step process.

A more complete understanding of the present invention can be obtained by reference to the following examples.

EXAMPLE 1 (Comparison).

About 210 grams of a chlorinated butyl rubber (chlorobutyl) HT-1068, manufactured by Exxon Chemical Co), which before chlorination contained about 1.8 mol % unsaturation, was heated in a closed press at 160 C. for 1 hour. After recovery, the rubber was found to be crosslinked and porous as a result of HC1 elimination. The resulting rubber was not soluble in a hydrocarbon solvent such as isooctane.

EXAMPLE 2.

A mix containing 210 grams of a chlorinated butyl rubber, as used in Example 1, and 31 grams of Ca3(POi)2 was prepared on a rubber mill at 70"C. The resulting mix was heated in a closed press at 1600C. for 1 hour. After extracting from the press, the rubber was found not crosslinked and totally soluble in isooctane with evidence of no gel formation. The rubber was found to contain conjugated diene unsaturation via UV analysis (A max at 245 nm).

EXAMPLE 3.

The following composition was prepared on a rubber mill at 70"C.

Chlorobutyl rubber (HT-1066 containing 1.10 wt. % Cl) 100 parts Zinc naphthenate 4 Naphthenic acid 1.5 Calcium oxide 2 Samples of the above composition were placed in a curing press for the time and temperatures set forth in Table I.

TABLE I Dehydrochlorination in Bulk Time, Chlorine, % Cl Mol % Run Temp. Mins. Wt % Loss Diene 1 1400C 15 0.83 23 0.28 2 1400C 30 0.88 20 0.31 3 1400C 60 0.82 25 0.39 4 1700C 15 0.71 35 0.48 5 1700C 45 0.65 41 0.50 6 2000C 7 1/2 0.57 48 0.62 7 2000C 15 crosslinked - - 8 2000C 30 crosslinked - All resulting elastomers (except runs 7 and 8) after the curing press treatment were found to contain conjugated diene unsaturation. Diene content is indicated in column 6 of Table I.

EXAMPLE 4.

The following composition was prepared on a rubber mill at 70"C.

Bromobutyl rubber Polysar X2 containing 1.77 wt. % bromine) 100 parts Zinc Naphthenate 4 Naphthenic acid 1.5 Calcium oxide 2 ('Polysar' is a Registered Trade Mark) Samples of the above composition were placed in a curing press for the time and temperatures set forth in Table II below.

TABLE 11 Dehydrobromination in Bulk Time Bromine % Br Mol % Run Temp. Mins. Wt. % Loss Diene 1 1400C 15 1.33 25 0.29 2 1400C 30 1.29 27 0.33 3 1700C 15 0.97 45 0.43 4 2000C 15 crosslinked - All elastomers after curing press treatment were found to contain conjugated diene unsaturation.

EXAMPLE 5.

The following composition was prepared on a rubber mill at 7C"C.

Chlorobutyl rubber (HT-1066 containing 1.10 wt. % Cl) 100 parts Zinc Naphthenate 4 Naphthenic acid 1.5 Calcium oxide 2 Metaphenylene-bis maleimide 2 Samples of the above composition were placed in a curing press for the time and temperatures set forth in Table III.

TABLE III Dehydrochlorination/Curing in Bulk Time Solvent Swell Data Run Temp. Mins. Mc* & Extractables % 1 1.400C 15 - 31 2 1400C 30 - 11 3 1400C 60 35,000 5.5 4 1700C 15 20,000 2.9 5 1700C 45 16,500 2.9 6 2000C 7 1/2 14,300 2.6 7 2000C 15 14,700 2.8 8 2000C 30 12,500 1.9 *Mc - number average molecular weight between crosslinks via solvent swell determination in cyclohexane.

It will be noted that if all the chlorine atoms of the above composition were used for vulcanization, an Mc of approximately 3,200 would be obtained. Generally, a good cure uses only about 30% of the chlorine atoms.

A comparison between percent dienes formed from Table I and Mc from Table III shows that the diene utilization for crosslinking is much higher than 30%. Most of the diene units of the present invention result in crosslinking.

Claims (9)

WHAT WE CLAIM IS:

1. A process for preparing a copolymer consisting of from 85 to 99.5 51/, by weight of an isoolefin having from 4 to 7 carbon atoms per molecule, combined with 15 to 0.5% by weight of a conjugated diolefin having from 4 to 14 carbon atoms per molecule, containing randomly distributed sites of conjugated diene unsaturation, which comprises either contacting a mixture of a halogenated butyl rubber with a salt of a metal of Group IIa or IIb of the Periodic Table of the Elements in an internal mixer reactor or heating in a mould said mixture, said contacting or said heating being in the absence of solvent and at a temperature of from 100"C to 200 C for a time sufficient to dehydrohalogenate at least partially the halogenated butyl rubber.

2. A process according to claim 1 wherein the temperature of reaction is from 140"C to 1700C.

3. A process according to either of claims 1 and 2 wherein the reaction period is from 0.1 to 24 hours.

4. A process according to any one of the preceding claims wherein the salt is a calcium salt of phosphoric, sulphuric, hydrochloric or nitric acid.

5. A process according to any one of claims 1 to 3 wherein the salt is a zinc salt of naphthenic, stearic, talloil or rosin acid.

6. A process according to any one of the preceding claims wherein the halogenated butyl rubber is chlorobutyl rubber.

7. A process according to any one of claims 1 to 5 wherein the halogenated butyl rubber is derived from a copolymer of isobutylene and isoprene having a numberaverage molecular weight from 5,000 to 500,000.

8. A process for preparing a copolymer according to claim 1 substantially as hereinbefore described with reference to Examples 2 to 5.

9. A copolymer of a Cg to C, isoolefin and a C4 to C14 conjugated diolefin whenever prepared by the process according to any one of the preceding claims.