Claims:1. A process for preparing a halogenated butyl rubber with controlled microstructure having endo isomer content greater than 70 %, said process comprising the following steps:
a. digesting a butyl rubber in an aliphatic fluid medium under agitation with an agitation speed in the range of 100 rpm to 500 rpm for a time period in the range of 8 hours to 10 hours to obtain a dispersion of butyl rubber; and
b. halogenating said dispersion of butyl rubber using at least one halogenating agent at a temperature in the range of 50 oC to 60 oC for a time period in the range of 1 min to 5 min, to obtain the microstructured halogenated butyl rubber comprising endo isomer content greater than 70 %.
2. The process as claimed in claim 1, wherein the Mooney viscosity of said microstructured halogenated butyl rubber is in the range of 10 MU - 50 MU.
3. The process as claimed in claim 1, wherein said step of halogenation is one of bromination or chlorination.
4. The process as claimed in claim 1, wherein the concentration of said halogenating agent is in the range of 4 wt % to 6 wt % with respect to the amount of the butyl rubber.
5. The process as claimed in claim 1, wherein said aliphatic fluid medium is at least one selected from the group consisting of C5 to C10 aliphatic hydrocarbons, typically hexane, heptane, and decane.
6. A process for preparing halogenated butyl rubber ionomers, said process comprising ionomerizing said halogenated butyl rubber with controlled microstructure having endo isomer content greater than 70 % as claimed in claim 1, by using at least one nucleophile to obtain said halogenated butyl rubber ionomers.
7. The process as claimed in claim 6, wherein the amount of said nucleophile is in the range of 1 to 3 molar equivalents based on the total molar amount of halogen present in the halogenated butyl rubber.
8. The process as claimed in claim 6, wherein said nucleophile is at least one selected from nitrogen and phosphorous containing nucleophiles.
9. The process as claimed in claim 6, wherein said nucleophile is at least one of triphenyl phosphine or 2-(methylphenylamino) ethanol. , Description:FIELD
The present disclosure relates to a process for preparing halogenated butyl rubber with a controlled microstructure having endo isomer greater than 70%.
DEFINITIONS
As used in the present disclosure, the following term is generally intended to have the meaning as set forth below, except to the extent that the context in which it is used indicates otherwise.
Microstructure: The term “microstructure” refers to the very small scale structure of a material, and is defined as the structure of a prepared surface of material as revealed by a microscope above 25 X magnification. The microstructure of a material (such as metals, polymers, ceramics or composites) can strongly influence physical properties such as strength, toughness, ductility, hardness, corrosion resistance, high/low temperature behavior or wear resistance.
Endo–exo isomerism: The term “endo-exo isomerism” refers to a special type of stereoisomerism found in organic compounds with a substituent on a bridged ring system. The prefix endo is reserved for the isomer with the substituent located closest, or "syn", to the longest bridge. The prefix Exo is reserved for the isomer with the substituent located farthest, or "anti", to the longest bridge.
Mooney viscosity: The term “Mooney viscosity” refers to a measurement of viscosity of a rubber or compound, determined in a Mooney shearing disk viscometer. Mooney viscosity differentiates between different types and grades of polymers in order to ensure a high processing consistency.
Ionomer: The term “Ionomer” refers to a polymer that comprises repeat units of both electrically neutral repeating units and a fraction of ionized units (usually no more than 15 mole percent) covalently bonded to the polymer backbone as pendant group moieties. Alternatively, ionomers are polymers with bonded ionic species that are used under conditions where the salt groups are in a condensed state.
BACKGROUND
Butyl rubber, also known as poly (isobutylene-co-isoprene) is a random copolymer of isobutylene and isoprene, and is prepared by randomly copolymerizing isobutylene with small amount of isoprene (1-2 mol %), by the slurry process. Butyl rubber has good air impermeability and oxidative stability and thus finds extensive use in inner tube applications. However, butyl rubber has poor curing or vulcanization problems and has compatibility issues with other diene elastomers.
Halogenated butyl rubber or halo butyl rubber is prepared by halogenation of butyl rubber with halogens, such as chlorine and bromine, which facilitates in retaining all the properties of the butyl rubber besides having better and faster curing characteristics as compared to its predecessor. Halogenation of butyl rubber results in formation of exo-methylene allylic halides and endo-halogenated methyl pendants on the poly (isobutylene-co-isoprene) backbone, thus increasing the reactivity towards sulphur and other nucleophiles. The presence of unsaturation in the form of isoprene units in butyl rubber provides means for enhancing useful properties of this important commodity elastomer by incorporation of reactive functionality such as halogens, epoxides, esters, ions by post-polymerization chemical modification of butyl rubber.
By using the conventional process, the exo isomer of butyl rubber is formed in higher quantity and endo isomer of butyl rubber is formed in lower quantity. However, endo isomer of butyl rubber with comparatively higher quantity is desirable which can be used in various applications such as in the preparation of ionomers
There is, therefore, felt a need to develop a simple process for preparing halogenated butyl rubber with controlled microstructure comprising endo isomer greater than 70%..
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a process for preparing a halogenated butyl rubber with a controlled microstructure.
Another object of the present disclosure is to provide a process for preparing a halogenated butyl rubber with controlled microstructure having comparatively high yield.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to a process for preparing a halogenated butyl rubber with controlled microstructure. The process comprises digesting butyl rubber in an aliphatic fluid medium under agitation with agitation speed in the range of 100 rpm to 500 rpm for a time period in the range of 8 hours to 10 hours to obtain a dispersion of butyl rubber. The dispersion of the butyl rubber is halogenated using at least one halogenating agent at a temperature in the range of 50 oC to 60 oC to for a time period in the range of 1 min to 5 min to obtain microstructured halogenated butyl rubber comprising endo-isomer content greater than 70 %. The Mooney viscosity of the microstructured halogenated butyl rubber is in the range from 10 MU to 50 MU.
DETAILED DESCRIPTION
The present disclosure envisages a process for preparing a halogenated butyl rubber with controlled microstructure. The process is described in detail.
Firstly, butyl rubber is digested in an aliphatic fluid medium under agitation with agitation speed in the range of 100 rpm to 500 rpm for a time period in the range of 8 hours to 10 hours to obtain a dispersion of butyl rubber.
The butyl rubber used in accordance with the present disclosure is natural butyl rubber or commercially available butyl rubber. The butyl rubber can be in any form selected from the group consisting of chips, crush, powder, pieces, and the like.
Secondly, the so obtained dispersion of the butyl rubber is halogenated using at least one halogenating agent at a temperature in the range of 50 oC to 60 oC for a time period in the range of 1 min to 5 min to obtain the microstructured halogenated butyl rubber comprising endo isomer content greater than 70 %.
In accordance with the present disclosure, the step of halogenation is one of bromination or chlorination. In one embodiment the halogenating agent is a brominating or chlorinating agent. Typically, the halogenating agent is liquid bromine. The concentration of the halogenating agent is in the range of 4 to 6 wt % with respect to the amount of the butyl rubber. In one embodiment, the halogenating agent can be further diluted with at least one aliphatic fluid medium to obtain a liquid halogenating agent which can be used in the halogenation reaction.
The aliphatic fluid medium is at least one selected from the group consisting of C5 to C10 aliphatic hydrocarbons. In one embodiment, the aliphatic fluid medium used in the process of the present disclosure is anhydrous. Typically, the aliphatic fluid medium is anhydrous hexane, anhydrous heptane and anhydrous decane.
In accordance with the present disclosure, nitrogen gas is passed through the reaction mixture for removing moisture therefrom and attain a moisture free atmosphere.
In one embodiment of the present disclosure, the halogenated butyl rubber after halogenation, is neutralized by using at least one base to obtain neutralized microstructured halogenated butyl rubber. The neutralized microstructured halogenated butyl rubber undergoes coagulation to obtain the microstructured halogenated butyl rubber. In accordance with the present disclosure, the base is selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and the like. In one embodiment, the neutralized halogenated butyl rubber is coagulated in acetone and washed 3-4 times with water, followed by drying to obtain a microstructured halogenated butyl rubber comprising endo isomer greater than 70 %.
In an aspect of the present disclosure the so obtained microstructured halogenated butyl rubber is ionomerised with at least one nucleophile in at least one fluid medium at a predetermined temperature for a predetermined time to obtain the halogenated butyl rubber ionomer. The amount of the nucleophile used in the process of ionomerization can be in the range of 1 to 3 molar equivalents based on the total molar amount of halogen present in the halogenated butyl rubber.
In accordance with the present disclosure the fluid medium can be selected from the group consisting of polar and nonpolar organic solvents. Typically, the fluid medium is toluene.
In accordance with the process of the present disclosure the predetermined temperature is in the range of 85 oC to 110 oC. In an exemplary embodiment, the predetermined temperature is 108 oC.
In accordance with the process of the present disclosure the predetermined time is in the range of 45 minutes to 150 minutes. Typically, the predetermined time is 120 minutes.
The nucleophile is at least one selected from the group consisting of nitrogen and phosphorous containing nucleophiles. Typically, the nucleophile is triphenyl phosphine and 2-(methylphenylamino) ethanol.
Typically, commercial butyl rubber is dispersed in hexane and brominated with liquid bromine from 52-62 oC for 1 - 5 min to obtain a brominated butyl rubber. The brominated butyl rubber after completion of bromination reaction is neutralized with dilute NaOH solution and the brominated butyl rubber is coagulated in acetone and washed few times with water and then dried to constant weight. The bromination is confirmed by 1H solution NMR and bromine content is quantified using XRF (X-ray fluorescence) analysis. The brominated butyl rubber is further functionalized to generate quaternary nitrogen/phosphorus ionomeric moieties on the bromobutyl elastomer backbone.
The brominated butyl rubber is quaternized/ionomerised with triphenyl phosphine in toluene at 85-110 oC for a time period ranging from 30 minutes to two hours, to obtain the desired ionomer content. The quaternization can be confirmed by 1H & 31P solution NMR analysis. All the products are characterized for their respective functionalization and microstructure. The process for preparing the halogenated butyl rubber ionomers having quaternary pendants directly synthesized from brominated butyl rubber in accordance with the present disclosure is economic and simple.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
Experimental details:
Experiment 1: Process for preparation of brominated butyl rubber with controlled microstructure in accordance with the present disclosure
Experiment 1a:
In a 500 mL glass reactor, 50g commercial butyl rubber was completely dispersed in hexane (12-14 wt% solution) to obtain a mixture. The mixture was heated to 60 oC under stirring and maintained for 1 minute to obtain a resultant mixture. The so obtained resultant mixture was brominated with 2 gm of liquid bromine (4 wt % in respect of butyl rubber) at 60 oC for 3 minutes. After the addition of bromine was completed, the reaction was continued for 1 min, followed by complete neutralization with NaOH solution (base solution- typically 1.1g/100 g of butyl rubber), and washed with water to obtain neutralized brominated butyl rubber. The rubber product was coagulated with 150 ml acetone and dried to a constant weight in a vacuum oven to obtain porous matrix/microstructured brominated butyl rubber.
The microstructure of the product was determined using 1H NMR spectroscopy (CDCl3) and the results are provided in table 1.
Experiment 1b
A similar experiment as that of experiment 1a was performed under identical experimental conditions at 55 oC. The microstructure of the product was determined using 1H NMR spectroscopy (CDCl3) and the results are provided in table 1.
Experiment 1c
A similar experiment as that of experiment 1a was performed under identical experimental conditions at 58 oC. The microstructure of the product was determined using 1H NMR spectroscopy (CDCl3) and the results are provided in table 1.

Experiment 1d
A similar experiment as that of experiment 1a was performed under identical experimental conditions at 52 oC. The microstructure of the product was determined using 1H NMR spectroscopy (CDCl3) and the results are provided in table 1.
Experiment 1e
In a 500 mL glass reactor 50g commercial butyl rubber was dispersed in hexane completely followed by addition of water to bring the solution to 90% hexane and 10% water mixture. Bromination was carried out with liquid bromine at 55 oC for 5 minutes. After the addition of bromine was completed, the reaction was continued for a desired time, followed by neutralization with a base solution and washing with water. The rubber product was coagulated and dried to a constant weight in a vacuum oven. The microstructure of the product was determined using 1H NMR spectroscopy (CDCl3) and the results are provided in table 1.
Experiment 1f
A similar experiment as that of experiment 1e was performed under identical experimental conditions at 52 oC with 72% hexane and 28% water mixture. The microstructure of the product was determined using 1H NMR spectroscopy (CDCl3) and the results are provided in table 1.

Experiment 1g
A similar experiment as that of experiment 1e was performed under identical experimental conditions at 52 o C with 67% hexane and 33% water mixture. The microstructure of the product was determined using 1H NMR spectroscopy (CDCl3) and the results are provided in table 1.
Table 1: Effect of presence or absence of water on formation of Bromobutyl rubber endo & exo microstructure content.
Expt
No. Solvent system Reaction temp
oC Reaction time
min Endo % Exo %
1a Hexane (100%) 60 oC 5 min 76 % 24 %
1b Hexane (100%) 55 oC 4 min 75 % 25 %
1c Hexane (100%) 58 oC 3 min 84 % 16 %
1d Hexane (100%) 52 oC 4 min 87 % 13 %
1e 90% Hexane + 10 % water 55 oC 5 min 70 % 30 %
1f 72% Hexane + 28 % water 52 oC 5 min 38 % 62 %
1g 67% Hexane + 33 % water 52 oC 5 min 20 % 80 %

From the results summarized in Table 1, it is observed that the amount of water present in the reaction media affects the bromobutyl microstructure. Higher amount of water produces maximum/quantitatively more, content of exo isomer. The quantification has been arrived at, using 1H NMR spectra of bromobutyl rubber ionomer products.
Further, the effect of rotation speed and the temperature in the formation of endo & exo microstructure content of bromobutyl rubber were also studied by varying the rotation speed and the temperature.
Table 2: Effect of rotational speed and temperature in the formation of Bromobutyl rubber endo & exo microstructure content.
S. No Sample Amount of bromobutyl rubber
Temp
0C Br2
wt % Time
Min of agitation
Rotor
RPM Mooney
Viscosity
1 BIIR (100 % Hexane) 50 g 58 4 5 500 30
2 BIIR ( 67 % Hexane + 33 % water) 50 g 52 4 5 500 40
3 BIIR (62 % Hexane + 38 % water) 50 g 52 4 5 500 44
4 BIIR (100 % Hexane) 250 g 55 4 5 250 14
5 BIIR (100 % Hexane) 300 g 55 4 5 250 10
6 BIIR (100 % Hexane) 10 kg 54 4 6 100 12
7 BIIR (100 % Hexane) 12 kg 54 4 6 100 14

It is observed from table 2 that the agitation /rotational speed (Rotor RPM) and temperature of the reaction mixture control the Mooney viscosity of the bromobutyl ionomer.
Experiment 2: Process for preparation of brominated butyl rubber ionomer in accordance with the present disclosure
Experiment 2a
Endo bromobutyl rubber obtained in experiment 1a (20 gm) was dissolved in toluene (400 mL) to obtain a homogeneous solution. PPh3 (1 g) was added to the homogeneous solution under stirring at 95 oC for 2 hrs to obtain a reaction mixture. The reaction mixture was coagulated in acetone to obtain a brominated butyl rubber ionomer. The so obtained brominated butyl rubber ionomer was oven dried and characterized by NMR.
Experiment 2b
Endo bromobutyl rubber obtained in experiment 1b (200 gm) was dissolved in toluene (2 L) to obtain a homogeneous solution. PPh3 (12 g) was added and the reaction mixture was stirred at 108 oC for 2 hours. The reaction mixture was coagulated in acetone to obtain brominated butyl rubber ionomer. The so obtained brominated butyl rubber ionomer was oven dried and characterized by NMR.
Experiment 2c
A similar experiment as that of experiment 2a was performed using lab synthesized bromobutyl rubber along with 1 g of 2-(methylphenylamino)ethanol as nucleophile under identical experimental conditions.
From experiments 2a to 2c, it is evident that the conversion of bromobutyl rubber having endo microstructure content and exo microstructure content, to control bromobutyl ionomers in accordance with the process of the present disclosure is carried out in one step without the need of converting the exo isomer to endo isomer.
The direct synthesis of butyl rubber ionomer starting from bromobutyl rubber circumvents the isomerization step. Phosphonium butyl ionomer was found to have 0.2 mol% phosphonium moiety. The process of the present disclosure yields bromobutyl rubber with endo-allyl bromide structures, thereby eliminating the need for exo to endo conversion. Thus, the process of the present disclosure is economical, environment friendly and industrially viable.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for preparing the halogenated butyl rubber with controlled microstructure, wherein the process
- is simple and economic; and
- provides halogenated butyl rubber with desired microstructure.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions, and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.