GB1568613A - Production of unsaturated halogen containing copolymers - Google Patents

Description

(54) PRODUCTION OF UNSATURATED HALOGEN CONTAINING COPOLYMERS (ill) We, ANIC S.P.A., a company organised and existing under the laws of the Italian Republic, of Via M. Stabile 216, Palermo, Italy, 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:- This invention relates to a process for producing a copolymer of isobutene which contains centres of ethylenic unsaturations and halogen atoms.

Already known are isobutene copolymers, which are commercially referred to as "Butyl Rubber" and which contain small percentages of units derived from isoprene statistically distributed along the polymeric chain in order to supply residual centres of unsaturation in the polymer, susceptible of being exploited in the vulcanization processes. These copolymers have found a number of applications by virtue of their imperviousness to gases, resistance to ozone and to oxidizing agents in general, and the high value of the dampening coefficient. A limit to the predictable applications of such products is their low curing speed, even if ultra-accelerators are used, and the impossibility of carrying out miscellaneous curing with them and various unsaturated elastomers, be these latter natural or synthetic (e.g. NR, SER, ER and others). These problems have been partly offset by halogenating such copolymers, which has led to a product known commercially as "Chlorobutyl Rubber", which displays properties which are considerably improved over those of the non-chlorinated starting copolymer. It has been shown in Rubber and Plastic Age, 42, 500, (1961), that the halogenation of isobuteneisoprene copolymers takes place, specifically, on the structural isoprene moiety and is a substitution of an allyl hydrogen atom by a halogen atom, with the evolution of a molecule of an haloid acid. The principal structures which are formed in the macromolecule are:

and in these are present secondary allyl halogen atoms (A, B) or tertiary allyl halogen atoms, which are allegedly responsible for the high reactivity of this elastomer as far as vulcanization is concerned, along with the possibility, in the usual vulcanizing formulae with sulphur, of the formation of a "mixed" lattice having intermolecular bonds of the type -C-S-C-, and -C-O- (these latter being produced by curing with metal oxides).

In our copending British Patent Application No. 32946-76 (Serial No. 1549645) there is described and claimed a process for producing a copolymer, which comprises copolymerizing at least one olefin and at least one polyene having the following general formula:

wherein each of R1, R2, R3, R4, R5, R6, R7 and R8, which are the same or different, is a hydrogen atom or an alkyl, alkenyl or aryl radical containing up to 7 carbon atoms. The isobutene-triene copolymers are of particular interest. The copolymers contain in the polymeric chain a number of highly reactive conjugated double bonds which impart to the copolymer special properties and features. As a result of studying these copolymers, we ascertained that their reactivity in vulcanization reactions can be further enhanced by halogenating such copolymers with, for example, halogens or haloid acids.

Thus, the present invention provides a process for producing a copolymer of isobutene which contains centres of ethylenic unsaturation and halogen atoms, the process comprises halogenating with a halogenating agent a copolymer of isobutene and a linear triene, the copolymer to be halogenated containing cony gated centres of ethylenic unsaturation, and the number of units in the copolymer which are denved from the linear triene being in the amount of from 0.1% to 8% of the number of units in the copolymer which are derived from isobutene. The reaction can take place under extremely mild operating conditions as regards temperature and concentration of the reactants and involves the reduction or, in some cases, the elimination of the conjugated diene system from the starting copolymer. In addition, no undue formation of by-products is experienced during progress of the reaction, the latter being essentially an addition of, say, the halogen or the haloid acid in the 1, 4-positions of the conjugated diene system, the results being the formation of structures of the following type:

The product is not limited to structure (D) or (E) as some of the hydrogen atoms may be substituted by, for example, a methyl radical.

In structure (D), there is a double bond with two adjoining halogen atoms in secondary allyl positions, whereas in structure (E) a double bond is present with a single adjoining halogen atom in a secondary allyl position. The high reactivity of such halogen atoms when being cured with ZnO is well known, but by comparing the structures (D) and (E) above with those which are present in "Chlorobutyl Rubber", a few differences can be seen. In particular, the products of the process of the present invention have no halogen atoms of the tertiary allyl type (C): these latter, owing to the particularly high mobility of the halogen atom, can cause spontaneous thermal degradation phenomena (Rubber and Plastic Age, 42, 500, (1961)). The products of the process of the present invention have a curing speed higher than that of "Chlorobutyl Rubber" and produce vulcanizates having outstanding mechanical and heat-resistance features and which are oxidationresistant.

Preferably in the trienes all three centres of ethylenic unsaturation are conjugated.

Examples of trienes which can be used for the synthesis of the isobutene-triene copolymer are: 1, 3, 5-hexatriene; 1,3,5-heptatriene; 2,4,6-octatriene, and 2,6-dimethyl-2,4,6-octatriene. The amount of triene employed in the synthesis must be such that, in the copolymer, the number of units derived from the triene is from 0.1% to 8% of the number of units derrived from isobutene. The special properties which identify these novel copolymers reside, therefore, both in the structure of the starting copolymer and in the trend of the halogenation reaction, along with the possibility of carrying out such a reaction with haloid acids (which cannot be done in the case of the isobutene-isoprene-copolymers), and in the structure of the halogenated products which can be obtained and their suitability to undergo curing reactions as well.

The fields of use in which the copolymers produced by the process of the present invention can profitably be exploited are for tyres of the tubeless type, inner tubes for tyres, tyre curing bags, i.e. bags used for supporting tyres in a mold during vulcanization, conveyor belts for hot materials, tubes for conveying hot fluids, containers for pharmaceutical products, technical and household sundries (such as gaskets and sponges), and sealing and waterproofing compounds.

Generally, for carrying out the halogenation reaction, a solution of the copolymer is contacted with the halogenating agent (preferably a halogen, or a haloid acid) either in solution or in the gaseous phase.

The reaction media to be adopted include those which are conventionally used for this kind of reaction: more particularly, aliphatic and cycloaliphatic hydrocarbons having up to 12 carbon atoms, the corresponding mono- or polyhalogenated compounds and CS2, it being, however, possible also to work without any solvents by direct inter-action of the halogenating agent with the finely ground polymer.

Particular examples of solvents which can be used are n-pentane, n-hexane, nheptane, methylene dichloride, chloroform, carbon tetrachloride, cyclohexane and methyl-cyclohexane. The reaction is usually carried out in the dark, at a temperature in the range from -80 C and +80"C by employing up to stoichiometrically molar quantities of the halogenating agent relative to the content of conjugated double bonds which are contained in the copolymer. The content of halogen found in the final products is thus variable and generally is in the range from 0.4% to 8%, preferably 0.6% to 4%, on molar percentage basis.

The halogenating agents to be used basically belong to two classes, viz: (I) halogens, interhalogenic compounds or compounds which are capable of behaving as halogenating agents; and (2) haloid acids.

Examples of the first class of compounds are Cl2, Br2, I2, ICI, IBr, SO2CI2, SOCI2, N-bromo-succinimide and N-chloro-succinimide.

Examples of the second class of compounds are HC1, HBr, HI.

Physico-chemical analysis of the polymers was carried out with UV radiations (235 millimicron band attributed to the conjugated double bonds of the type -CH=CH-CH=CH-) and with IR radiations (10.1 micron band attributed to the conjugated double bonds of the trans configuration). The determination of the quantity of the conjugated double bonds has been carried out by UV analysis (R = millimicrons) by employing as the standard compound 2,4-hexadiene trans-trans (E = 24,500).

The halogen content in the copolymer was determined by combustion of the copolymer by the Schöniger method and analysis of the combustion product, as reported in Microchimica Acta, 480, 1961.

The molecular weight of the copolymers was determined on the basis of viscosity measurements carried out in cyclohexane at +300C and employing the following equation: In PMV = 11.98 + 1.452 In [8], where [tl] was determined by extrapolating C 0 O the magnitude 7speJC and PMV is the viscometric molecular weight; x7 is the intrinsic viscosity, 7spec iS the specific viscosity, and C is the concentration in grams/100 ml.

The present invention will now be illustrated by the following Examples 2 to 7, with Example 1 describing the preparation of a typical isobutene-triene copolymer, which is the material subjected to subsequent halogenation reactions; by working with similar procedures, it is possible to prepare the other copolymers which are used as the starting materials in subsequent examples.

Example 1 A tubular glass reactor which had a volume of 300 ml and was fitted with a mechanical stirrer and a thermometric jacket, was first dried and maintained in an atmosphere of dry argon and then was charged with 40 ml of liquid CH3CI, 28.4 grams of isobutene, 40 ml of anhydrous n-heptane and 0.7 ml of 1,3,5-hexatriene (99% purity). The temperature was brought to -750C, whereafter there was slowly introduced 0.4 millimole of AlEtCI2 dissolved in 5 ml of n-heptane over the course of 13 minutes. Concurrently with the addition of the catalyst, there was introduced into polymerizing solution 0.6 additional ml of 1,3,5-hexatriene, diluted with 4 ml of n-heptane, the addition taking place evenly throughout the period of introduction of the catalyst.

The reaction was allowed to proceed for 10 additional minutes by maintaining the temperature of the reaction mixture between -71 0C and -60 C, and an extremely viscous polymeric solution was obtained. The reaction was discontinued by introducing 2 ml of ammoniated CH3OH, the polymer was coagulated in a 50/50 (volume) mixture of methanol and acetone, and then dried in vacuo.

There were thus obtained 8.05 grams of dry polymer (yield = 20.5%), which had [#] equal to 2.01 dl/g (PMv = 420,000) and contained 1.55 molar percent of diene unsaturations as determined by UV analysis.

Example 2 A 300 ml, three-necked flask fitted with a stirring mechanism and kept in the dark, was charged with 100 ml of a solution in n-heptane which contained 6 grams of the copolymer of Example 1. The flask was cooled to OOC, whereafter there were slowly introduced 8 ml of a solution of Cl2 in CCI2 which contained 1.8 millimoles of Cl2, with energetic stirring, over the course of 10 mins. The reaction was allowed to proceed for 10 additional minutes, whereafter the polymeric solution was washed with H2O and coagulated in acetone. The thus obtained polymer was dried in vacuo at a temperature of 50 C overnight, and 5.6 grams of a dry polymer were obtained, which had an intrinsic viscosity in cyclohexane equal to 2.05 dl/g (PMv = 430,000).

UV and IR analyses of the product showed the complete discharge of the conjugated diene unsaturations. The determination of the chlorine content gave a value of 1.63% by weight. This chlorinated polymer was subjected to curing at the temperature of 160 C for variable times, by employing the following vulcanizing formulation: Polymer 100 parts by weight HAF black (N330) 50 " " " MBTS (mercaptobenzothiazole disulphide) I " " " TMTD (tetramethylthiuram disulphide) I " " " Stearic acid 3 AO-2246 (antiox.) 1 ZnO 5 s Sulphur 2 AO-2246 is 2,2-methylene-bis (4-methyl-6-tert-butyl-phenol). HAF black is high abrasion furnace carbon.

The following Table 1 reports the rheometric data and the properties of the vulcanizates produced from the chlorinated polymer described above (Sample A) and from a commercial sample of "Chlorobutyl Rubber" (Sample B), the latter having the following characteristics: Cl = 1.35%, [X7] = 1.95 dl/g TABLE 1 Sample A B Rheometric data (0) MV (00) (N.m) 1.7 1.6 MT (N.m) (000) 5.7 5.8 T2 (min.) 1 min 15 sec 1 min 40 sec T90 (min.) 8 min 9 sec 18 min 30 sec Mechanical properties of the vulcanizates at room temperature for various curing times: A B Time (mins) 15 min 30 min 60 min 15 min 30 min 60 min Mod. 300% (M Pa) 11 11.5 12.5 9.7 10.8 12.4 Tensile (M Pa) 22.1 21.4 20.9 21.9 21.9 20.2 Elongation % at 525 455 450 582 530 500 break Tension set % 4 2 2 5 5 3 NOTE: (O) At 1600C in a Monsanto Model 100 Rheometer, oscillation arc 3 degrees.

Readings taken according to R. W. Wise, G. E. Decker, ASTM Special Technical Publication No. 383 (1965).

(00) Minimum value of Torque (Newton.metre) (000) Maximum value of Torque (Newton.metre) The data of Table 1 indicated that the sample A showed a higher curing speed and better mechanical properties than the commercial copolymer (Sample B).

MPa = Megapascal, SI unit.

Example 3 Following the same general procedure as described in Example 2, a flask was charged, in the dark, with 100 ml of a solution in CHCl3 of 5 grams of a copolymer which had the following properties : % of conjugated double bonds = 0.99; [T] = 2.12 dl/g; and Pom,= 460,000. There was slowly introduced, in the dark, at a temperature of 20"C, 0.95 millimole of Cl2 dissolved in 6 ml of CCl4 over the course of 15 minutes. The chlorinated polymer was collected in the manner described in Example 3, and there were obtained 4.6 grams of dry polymer which had the following properties: % of conjugated double bonds = 0; %Cl (By wt.) = 1.1; [#] = 2.02 dl/g; and PMv = 420,000.

The chlorinated polymer was cured according to the vulcanizing formulation reported in Example 2, and the properties of the vulcanizates, at room temperature, are reported in the following Table 2.

TABLE 2 Properties df the vulcanizate at room temperature for different curing times: Time (minutes) of cure 15 min. 30 min. 60 min.

Modulus at 300% et. (MPa) 7.6 7.8 7.6 Tensile strength (MPa) 20.0 20.5 19.6 Elong. at break % 585 580 590 Tension set, % 8 7 7 The data indicate the formation of satisfactory vulcanizate, even though its properties are below those of the vulcanizate of Sample A of Table l.

Example 4 There were used 100 ml of the same solution of the isobutene-1,3,5-hexatriene copolymer as used in Example 3. Through this solution, cooled to -150C, a gaseous stream of HCl was bubbled over the course of 60 minutes. The temperature of the mixture was allowed to rise to OOC and the reaction was allowed to proceed for 10 additional hours. The polymeric solution was washed with distilled water and the above indicated polymer was coagulated as described above. There were obtained 4.6 grams of a dry polymer having the following properties: % of conj. double bonds, residual : 0.11 % Cl (by wt.) = 0.95 [#] = 2.20 dl/g PMv = 480,000 The chlorinated polymer was cured under the conditions of Example 2 and the properties of the vulcanizates obtained with different curing times and measured at room temperature are reported in the following Table 3.

TABLE 3 Time of cure, min. 15 mins. 30 mins. 50 mins.

Modulus 300% (MPa) 6.8 7.3 7.3 Tensile strength (MPa) 18.3 18.8 19.1 Belong. at break % 655 610 560 Tension set, % 8 Example 5 To a solution of the same copolymer as Example 3 in CHCl3 (5 grams in 100 ml.), cooled to --100C, there were slowly added, with stirring, 3 millimoles of anhydrous HBr dissolved in 6 ml of CCl4. Stirring was continued for 2 hours, after which the temperature of the solution was brought to OOC. The brominated polymer was collected as described in Example 2 and there were obtained 4.7 grams of the polymer which had the following properties: % of residual conjugated double bonds = 0.07; %Br (by wt.) = 2.1; [17] = 2.0 dl/g; and PMV = 420,000.

The sample, subjected to technological tests, gave a vulcanizate having mechanical properties which were akin to those of the previous sample of Example 4, but with higher curing kinetics.

Example 6 There was employed a solution in CHCl3 (5 grams in 100 ml of solution) of an isobutene-2,4,6-octatriene copolymer which had the following properties: % of conjugated double bonds = 1.64.

[17] = 1.90 dUg; and PMV = 390,000.

It has been prepared by a method similar to that described in Example l.

The solution was transferred to a flask, in the dark, at the temperature of 0 C and slowly supplemented with 1.5 millimoles of Br2 dissolved in 4 ml of CCl4, over the course of 20 minutes. There were collected, using the procedure described in Example 2, 4.7 grams of a dry brominated polymer which had the following properties: % of conjugated double bonds = 0; Br % (by wt.) = 3.2; [17i = 1.75 dVg; and PMV = 340,000.

Example 7 Following the same general procedure described in Example l, an isobutene1,3,5-heptatriene copolymer was prepared, which had the following properties: %conjugated double bonds = 1.35: [17] = 2.14 dl/g; and PMV = 480,000.

A solution in CHCl3 containing 5 grams of the copolymer in a volume of 100 ml was placed in a flask, in the dark, and treated at the temperature of 0 C with 1.5 millimoles of SO2Cl2 dissolved in 5 ml of CCl4. The reaction was allowed to proceed for 3 hours, whereafter the polymeric solution was washed with H2O until a neutral reaction was achieved, and the polymer was collected as described in Example 2.

There were obtained 4.6 grams of a dry polymer which had the following properties: % conjugated double bonds = 0.95; Cl % (by wt.) = 1.48; [17] = 1.90 dVg; and PMv = 390,000.

The sample, as cured under the same conditions as for Example 2, has a vulcanization behaviour and technological properties similar to those of Sample A of Example 2.

Claims (13)

1. WHAT WE CLAIM IS: 1. A process for producing a copolymer of isobutene which contains centres of ethylenic unsaturation and halogen atoms, the process comprising halogenating with a halogenating agent a copolymer of isobutene and a linear triene, the copolymer to be halogenated containing conjugated centres of ethylenic unsaturation, and the number of units in the copolymer which are derived from the linear triene being in an amount of from 0.1% to 8% of the number of units in the copolymer which are derived from isobutene.
2. 2. A process according to claim 1, wherein the halogenation is effected with a halogen or haloid acid.
3. 3. A process according to claim 1, wherein the halogenating agent is C12, Br2, 12, ICI, IBr SO2Cl2, SOCl2 or N-bromosuccinimide or N-chlorosuccinimide.
4. 4. A process according to claim 2, wherein the haloid acid is HCl, HBr or HI.
5. 5. A process according to any preceding claim, wherein the temperature at which halogenation is effected is in the range from -80 C to +800 C.
6. 6. A process according to any preceding claim, wherein the quantity of halogenating agent is up to the stoichiometric molar value with respect to the centres of conjugated double bonds in the copolymer.
7. 7. A process according to any preceding claim, wherein the halogenation is such that the halogen content in the end product is in the range from 0.4% to 8% molar.
8. 8. A process according to claim 7, wherein the halogen content in the end product is from 0.6% and 4% molar.
9. 9. A process according to any preceding claim, wherein the halogenation is effected in the presence of a solvent selected from alliphatic and cycloaliphatic hydrocarbons having up to 12 carbon atoms, the corresponding mono- or polyhalogenated derivatives, and carbon disulphide.
10. 10. A process according to any preceding claim, wherein all three centres of ethylenic unsaturation in the triene are conjugated.
11. l l. A process according to any preceding claim, wherein the triene is selected from 1,3,5-hexatriene; 1.3.5-heptatriene; 2,4,6-octatriene, and 2,6-dimethyl-2,4,6octatriene.
12. 12. A process for the production of an unsaturated halogenated copolymer of isobutene, substantially as described in any one of the foregoing Examples 2 to 7.
13. 13. An unsaturated halogenated copolymer of isobutene and a linear triene, whenever produced by the process claimed in any one of the preceding claims.