Title of Invention

A PROCESS FOR THE PREPARATION OF NOVEL POLYSULFIDE COPOLYMERS

Abstract

A process for the preparation of novel polysulfide copolymers is provided whereby styrene dibromide is polymerized with ethylene/methylene dibromide in presence of sodium/potassium sulfide using phase transfer catalyst. The polysulfide copolymers prepared by this new process exhibit melting point in the range of 59-125 °C and are soluble in organic solvents thereby ensuring their easy processability for industrial applications.

Full Text

The present invention relates to a process for the preparation of novel polysulfide copolymers. These polymers find potential applications in footwear, leather goods and allied industries as adhesive. These may also find enormous applications in the works pertaining to construction and maintenance of concrete structures such as highways, airport runways. Moreover, they are envisaged to have several applications as sealant in aircraft industry. The polymers may also be used as insulator in electrical industry. Polysulfide copolymers refers to two different repeating units of a molecular chain incorporated with sulfur atom. As reported by Spassky et al (Handbook of Polymer Synthesis, Part B; edited by Kricheldorf, Marcel Dekker edition, New York, Chapter 16, p991, 1992), these copolymers are conventionally prepared by polymerising dithiols with dihalides or diolefins. Montaudo et al (Polymer, 28, p 477, 1987) polymerized dithiol with dihalide in the presence of sodium-ethanol and excess benzene by refluxing the polymeric mixture for 12 hrs at 80 °C, whereby the resulting polysulfide copolymer was collected by cooling and subsequent filtering of the reaction mixture. Bass et al (Journal of Polymer Science Polymer Chemistry, 25, p 2395, 1987) prepared poly (enonsulfide) by polymerizing dithiols with diolefins in presence of m-cresol at 25-40 °C for 9-36 hrs under nitrogen atmosphere. The major limitation associated with the resulting polysulfide copolymers, as prepared by the aforesaid processes, is that they are insoluble in organic solvent, thereby making them unsuitable for use as adhesive. Attempts have however been made by several researchers to use the polysulfide as adhesive by thermal melting at temperatures ranging between 220 to 260 °C. Catsiff et al (Journal of Polymer Science, Part Al, Vol.9, p 1271, 1971) have reported that processing of the polymers at such higher temperatures breaks the polymer chain resulting in decrease in molecular weight of the polymer as well as evolution of toxic gases like hydrogen sulfide, carbondisulfide. Moreover, since the molecular structure of the polymer is affected by this treatment, its adhesive property is also adversely affected. The main object of the present invention is to provide a process for the preparation of novel polysulfide copolymers, which obviates the drawbacks as detailed above. Another object of the present invention is to provide a process for the preparation of polysulfide copolymers which are soluble in organic solvents. Still another object of the present invention is to use phase transfer catalyst for the polymerization. Accordingly, the present invention provides a process for the preparation of novel polysulfide copolymers which comprises : a) polymerizing alkali metal sulfide, dissolved in 4-10% w/v of water, with a mixture of essentially styrene dibromide and alkylene dihalide in a mole ratio in the range of 1:0.11 to 1:9, the said mixture being dissolved in 5-15% w/v, of a conventional organic solvent in presence of a phase transfer catalyst such as herein described at a temperature in the range of 15-40°C for a minimum period of 8 hrs, b) subjecting the resulting mixture, as formed in step(a), to separation by conventional method followed by aqueous washing of the separated organic layer, c) treating the separated organic layer, as obtained in step (b), with known drying agent to make it free from moisture, followed by subjecting the moisture free substance to solvent removal by known method, d) treating the resulting substance with 5-20 % w/v, of conventional non-solvent and subsequent drying by known method at a temperature in the range of 15-50 °C to obtain polysulfide copolymer. In an embodiment of the present invention, the alkali sulfide used may be selected from sodium sulfide, pottasium sulfide. In another embodiment of the present invention, the dihalide used may be selected from styrenedibromide, ethylenedibromide, methylene dibromide. In yet another embodiment of the present invention, the mole ratio of the dihalide mixture to the alkali metal sulfide used may be in the range of 1:1 to 1:1.2. In still another embodiment of the present invention, the conventional organic solvent used may be selected from benzene, chloroform, toluene, tetrahydrofuran. In yet another embodiment of the present invention the phase transfer catalyst used may be selected from Tetrabutylammonium bromide, Tetrabutylammoniumhydrogen sulphate, Cetyltrimethylammonium chloride, Cetyltributylphosphonium bromide. In still another embodiment of the present invention, the amount of phase transfer catalyst used may be in the range of 0.25-2.00 % w/w of dihalide. In yet another embodiment of the present invention, the known method for separation used may be such as decanting, funnel-separation. In still another embodiment of the present invention, the drying agent used may be such as anhydrous Na2SO4, anhydrous MgSO4. In yet another embodiment of the present invention, the non-solvent used may be selected from methanol, ethanol, petroleum ether. In still another embodiment of the present invention, the method of drying used may be such as vacuum pump drying, vacuum oven drying. The process of the present invention is described below in detail. 1.0-1.20 mole of an alkali metal sulfide per mole of dihalide is dissolved in 4-10 % w/v, of water. Then more than one dihalide is mixed by conventional method to prepare a mixture, in such a way that one of the ingredients is essentially styrene dibromide, which is mixed with methylene or ethylene dibromide in a mole ratio in the range of 1:0.11 to 1:9. This mixture is dissolved in 5-15 % w/v, of a conventional organic solvent. The alkali metal sulfide solution is then added to the dihalide solution under dynamic condition and 0.25-2.00% v/v, of known phase transfer catalyst, calculated on the dihalide solution is added to the said mixture. The polymerisation reaction is allowed to continue at a temperature in the range of 15-40°C for a minimum period of 8 hrs. The resulting heterogenous mixture is subjected to separation by conventional method, whereby the organic layer is separated from the aqueous layer. The separated organic layer is washed with water and the resulting liquid is rendered free from moisture by keeping the same in contact with known drying agents. The moisture free polymeric mixture is then freed from solvent by conventional method, followed by purification by known process, whereby the same is treated with 5-20 % w/v conventional non-solvent. Finally the resulting product is subjected to conventional drying at a temperature in the range of 15-50 °C to obtain polysulfide copolymer. The polymers of the present invention have been characterized by using DSC (Differential Scanning Calorimetry) technique, TGA (Thermogravimetric Analysis) technique as well as solubility data and the results have been compared with those available for the existing polysulfide polymers. A) Characterization in respect of DSC and TGA techniques While the characterization data in respect of the existing polysulfide polymers are furnished in TABLE I, those for the developed polymers are given in TA&L&.1T. below. Table I. Characteristic data for the Existing Polymers (Table Removed) Table II. Characteristic data for the New Polymers developed by the Present invention (Table Removed) C- heat capacity; Tm-melting temperature; TGA- Thermogravimetric analysis i) Cp Value, which signifies the heat capacity of a polymer, is the alternative measure of its thermal stability during processing. While this Cp value in respect of the existing polymers lie within the range of 0.024-0.036 J/g°, it has been possible to enhance the same to a range of 0.047-0.497 J/g° in the copolymer of the present invention depending upon the reactants used, thereby enhancing the ability of these copolymers to withstand higher temperature during processing. Thus the copolymers of present invention can be used for industrial applications of much wider range. ii)Tmvalue, which signifies the melting point of a polymer, is an essential indicator of the processability of the polymer. While this Tm value in respect of the existing polymers lie within the range of 173.7-184.2 °C, signifying difficulty in processing by way of complying with the requirement of maintaining higher temperature at that range to get the polymers under processing in liquid state, it has been possible to bring down the same to a range of 59-125 °C in the copolymers of the present invention depending upon the reactants used, thereby providing a solution for easy processability of the copolymers. It has also been observed that at a particular composition, whereby Styrenedibromide and ethylenedibromide have been used in 1:1 ratio as furnished in TABLE - II, the resulting copolymer becomes totally amorphous, thereby ensuring that the heating operation can be totally avoided for the purpose of further processing towards industrial application of the polymer, iii) TGA value which signifies the temperature at which a polymer starts decomposing during its processing, is a very useful indicator for its processability. While the initial decomposition temperature measured using thermogravimetric analysis in respect of the existing polymers lie within the range of 189.4-218 °C, it has been possible to enhance the same to a range of 225-248.2 °C in the copolymer of the present invention depending upon the reactants used thereby implying the enhanced ability of these copolymers to withstand higher temperature during heating. Thus the copolymers of the present invention ensure better processability by way of ensuring their capabilities of withstanding much higher temperature during industrial applications. B) Characterization in respect of Solubility data The polymers of the present invention have been tested for the solubility and the results have been compared with those for the existing polysulfide polymers. While the test data in respect of the existing polysulfide polymers are furnished in TABLE III, those for the new polymers, prepared by the process of the present invention are given in TABE IV below. TABLE III. Characteristic data for the Existing Polymers (Table Removed) (-) Insoluble TABLE IV. Characteristic data for the New Polymers developed by the Present invention (Table Removed) (Partially Soluble), +(Soluble) CHCls-Chloroform, DMF-N, N Dimethyl formamide, DMAc-Dimethyl acetamide, THF-Tetrahydrofuran, NMP-N methyl pyrrolidone, While the insolubility of the existing polysulfide polymers in the above mentioned solvents implies their limitation for industrial applications involving the said solvents, the present invention provides the new polysulfide copolymers exhibiting different degree of solubility in the said solvents depending on their composition, thereby ensuring their wide ranging usages for different industrial applications. The novelty and non-obviousness of the present invention lies in the use of phase transfer catalyst for the copolymerisation whereby the resulting copolymer, unlike the conventional polysulfide copolymer exhibiting alternate molecular structure leading to their insolubility in organic solvents, exhibits random molecular structure leading to its solubility in organic solvents as well as easy processability. The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention. EXAMPLE-1 2.6397g of styrene dibromide was mixed with 0.2065g of ethylene dibromide taken in a round bottom flask and 20 ml of CHC13 solution was added to it. 0.8662g of Na2S was dissolved separately in 20 ml of water and the resulting solution was added to the round bottom flask with continuous stirring. 0.0070 g of Tetrabutylammoniurn bromide was then added to the flask while continuing the stirring at 30 °C for a period of 16 hrs, when two distinct layers were formed inside the flask, CHCl2 layer was separated from the aqueous layer using separating funnel and was washed three times with 10 ml of water. This was then dried over 1g of anhydrous sodium sulphate for 1 hr. The moisture free liquid, obtained thereby, was subjected to distillation to remove CHC13 and 20ml of methanol was poured on the resulting viscous liquid with stirring. The precipitate, formed thereby as a solid mass, was collected by decanting the liquid and was vacuum oven dried at 30°C to get the polysulfide copolymer, which was stored in a plastic container. EXAMPLE-2 0.2639g of styrene dibromide was mixed with 1.6909g of ethylene dibromide taken in a round bottom flask and 20 ml of benzene solution was added to it. 1.2126g of K2S was dissolved separately in 15 ml of water and the resulting solution was added to the round bottom flask with continuous stirring. 0.0098g of Tetrabutylammoniumhydrogen sulphate was then added to the flask while continuing the stirring at 15 °C for a period of 8 hrs, when two distinct layers were formed inside the flask, benzene layer was separated from the aqueous layer using separating funnel and was washed three times with 10 ml of water. This was then dried over Ig of anhydrous magnesium sulphate for 1 hr. The moisture free liquid, obtained thereby, was subjected to distillation to remove benzene and 20 ml of petroleum ether was poured on the resulting viscous liquid with stirring. The precipitate, formed thereby as a solid mass, was collected by funnel-separation and was vacuum pump dried at 30 °C to get the polysulfide copolymer, which was stored in a plastic container. EXAMPLE-3 1.319g of styrene dibromide was mixed with 0.8692g of methylene dibromide taken in a round bottom flask and 15 ml of toluene solution was added to it. 0.9365g of NaS was dissolved separately in 10 ml of water and the resulting solution was added to the round bottom flask with continuous stirring. 0.0219g of Cetyltrimethylarnmonium chloride was then added to the flask while continuing the stirring at 35 °C for a period of 16 hrs, when two distinct layers were formed inside the flask, toluene layer was separated from the aqueous layer using separating funnel and was washed three times with 10 ml of water. This was then dried over Ig of anhydrous sodium sulphate for 1 hr. The moisture free liquid, obtained thereby, was subjected to distillation to remove toluene and 3 ml of ethanol was poured on the resulting viscous liquid with stirring. The precipitate, formed thereby as a solid mass, was collected by decanting the liquid and was vacuum oven dried at 40°C to get the polysulfide copolymer, which was stored in a plastic container. EXAMPLE-4 0.2639g of styrene dibromide was mixed with 1.5646g of methylene dibromide taken in a round bottom flask and 20 ml of tetrahydrofuran solution was added to it. 1.1020g of K2S was dissolved separately in 10 ml of water and the resulting solution was added to the round bottom flask with continuous stirring. 0.036g of Cetyltributylphosphonium bromide was then added to the flask while continuing the stirring at 40 °C for a period of 16 hrs, when two distinct layers were formed inside the flask, benzene layer was separated from the aqueous layer using separating funnel and was washed three times with 10 ml of water. This was then dried over Ig of anhydrous magnesium sulphate for 1 hr. The moisture free liquid, obtained thereby, was subjected to distillation to remove tetrahydrofuran and 2.5 ml of petroleum ether was poured on the resulting viscous liquid with stirring. The precipitate, formed thereby as a solid mass, was collected by funnel separation and was vacuum pump dried at 50 °C to get the polysulfide copolymer, which was stored in a plastic container. The main advantages of the present invention are the following. 1. The process of the present invention is simple and economical. 2. The process does not require special equipments for temperature control. 3. The polysulfide copolymer, prepared by the present process of invention exhibits melting point in the range of 59-125 °C, thereby ensuring its easy processability for different industrial applications. We claim : 1. A process for the preparation of novel polysulfide copolymers which comprises: a) polymerizing alkali metal sulfide, dissolved in 4-10% w/v of water, with a mixture of essentially styrene dibromide and alkylene dihalide in a mole ratio in the range of 1:0.11 to 1:9, the said mixture being dissolved in 5-15% w/v, of a conventional organic solvent in presence of a phase transfer catalyst such as herein described at a temperature in the range of 15-40°C for a minimum period of 8 hrs, b) subjecting the resulting mixture, as formed in step(a), to separation by conventional method followed by aqueous washing of the separated organic layer, c) treating the separated organic layer, as obtained I step (b), with known drying agent to make it free from moisture, followed y subjecting the moisture free substance to solvent removal by known method, d) treating the resulting substance with 5-20% w/v, of conventional non-solvent and subsequent drying by known method at a temperature in the range of 15-50°C to obtain polysulfide copolymer. 2. A process, as claimed in claim 1 wherein the alkali sulfide used is selected from sodium sulfide, potassium sulfide. 3. A process as claimed in claims 1-2 wherein the dihalides used are selected from styrenedibromide, ethylenedibromide, methylene dibromide. 4. A process as claimed in claims 1-3 wherein the mole ratio of the dihalide mixture to the alkali metal sulfide used is I the range of 1:1 to 1:1.2. 5. A process as claimed in claims 1-4 wherein the conventional organic solvent used is 'selected from benzene, chloroform, toluene, tetrahydrofuran. 6. A process as claimed in claims 1-5 wherein the phase transfer catalyst used is selected from Tetrabutylammonium bromide, Tetrabutylammoniumhydrogen sulphate, Cetyltrimethylammonium chloride, Cetyltributylphosphonium bromide. 7. A process as claimed in claims 1-6 wherein the amount of phase transfer catalyst used is in the range of 0.25-2.00% w/v of dihalide. 8. A process as claimed in claims 1-7 wherein the non-solvent used is selected from methanol, ethanol, petroleum ether. 9. A process for the preparation of novel polysulfide copolymers substantially as herein described with reference to the examples.

Documents:

1010-del-2001-abstract.pdf

1010-del-2001-claims.pdf

1010-del-2001-correspondence-others.pdf

1010-del-2001-correspondence-po.pdf

1010-del-2001-description (complete).pdf

1010-del-2001-form-1.pdf

1010-del-2001-form-18.pdf

1010-del-2001-form-2.pdf

1010-del-2001-form-3.pdf