Claims:1. A method of producing a sulfur-elastomer polysulfide material, comprising acts of:
a. contacting elemental sulfur and elastomer, and optionally mixing, to obtain a mixture; and
b. subjecting the mixture to temperature ranging from about 165°C to about 185°C to obtain the polysulfide material.

2. A solid-state method of producing a sulfur-elastomer polysulfide film, comprising acts of:
a. contacting elemental sulfur and elastomer, and optionally mixing, to obtain a mixture; and
b. subjecting the mixture to compression molding at temperature ranging from about 165°C to about 185°C to obtain the polysulfide film.

3. The method as claimed in claim 1 or 2, wherein the elastomer comprises one or more olefinic bonds; wherein the elemental sulfur is at an amount ranging from about 10 to 70 wt% and the elastomer is at an amount ranging from about 30 to 90 wt%; and/or wherein the elastomer is selected from a group comprising polybutadiene rubber (PBR), ethylene propylene diene terpolymer (EPDM), natural rubber, synthetic rubber, butyl rubber, styrene butadiene rubber or any combination thereof.

4. The method as claimed in claim 1 or 2, wherein the mixing is carried out in a Brabender mixer at temperature ranging from about 25°C to about 60°C for time period of about 2 to about 10 minutes.

5. The method as claimed in claim 1, wherein in step b) the mixture is subjected to compression molding at temperature ranging from about 165°C to about 185°C, preferably about 175°C, and pressure ranging from about 0.2 to about 2.6 ton per square inch and 25- 45 minutes, preferably about 2 ton per square inch /30 minutes.

6. The method as claimed in claim 1, wherein the method is a solid-state method; wherein the method is carried out in a horizontal arm reaction system, preferably for time period ranging from about 40 to about 90 minutes; and/or wherein the method does not employ a solvent or catalyst.

7. The method as claimed in claim 2, wherein the compression molding is at pressure ranging from about 0.2 to about 2.6 ton per square inch for about 25- 45 minutes, preferably about 2 ton per square inch /30 minutes; and/or wherein the method does not employ a solvent or catalyst.

8. A sulfur-elastomer polysulfide material comprising elemental sulfur and elastomer optionally along with oxygen.

9. The polysulfide material as claimed in claim 8, wherein the sulfur is present at an amount ranging from about 20 to 50 w/w%, preferably about 21 to 49.6% w/w; wherein the elastomer is present at an amount ranging from about 50 w/w% to about 80 w/w%; wherein oxygen is present at an amount ranging from 0 w/w% to about 4 w/w%; wherein the polysulfide material has thickness ranging from about 50 µm to about 650 µm; and/or wherein the polysulfide material has higher transmittance in the infrared range and lower transmittance in the UV and visible range.

10. The method or the polysulfide material of any of the preceding claims, wherein the polysulfide material is in a form selected from a group comprising film, sheet, block, tape, fibre, tube, solid lump and rod or any combination thereof.

11. A system for producing a sulfur-elastomer polysulfide material, the system comprising:
a. a reaction vessel (4) at least partially dipped in oil bath (5) and configured to rotate freely in the oil bath (5); and
b. an actuator (1) coupled to the reaction vessel (4), wherein the actuator (1) is configured to rotate the reaction vessel (4) in the oil bath;
wherein the reaction vessel (4) comprises elemental sulfur and elastomer; and wherein the oil bath (5) is maintained at temperature ranging from about 165°C to about 185°C.

12. The system as claimed in claim 11, wherein reaction is carried out for time period ranging from about 40 to about 90 minutes; wherein the reaction vessel (4) is adapted to receive elemental sulfur and elastomer or a homogenous mixture of the elemental sulfur and elastomer; and/or wherein the homogenous mixture is obtained by mixing the elemental sulfur and the elastomer at temperature ranging from about 25°C to about 60°C for time period of about 2 to about 10 minutes in a mixer.

13. The system as claimed in claim 11, wherein the reaction vessel (4) is obliquely oriented in the oil bath (5); wherein the oil bath (5) is positioned on a heat source (6); and/or wherein the oil bath is a silicon oil bath.

14. The system as claimed in claim 13, comprising:
a temperature controller (7) interfaced with the heat source (6), wherein the temperature controller (7) is configured to maintain the temperature of the oil bath in the range of about 165°C to about 185°C.

15. The system as claimed in claim 11, wherein the system comprises rod (2) coupling the actuator (1) with the reaction vessel (4).

16. The system as claimed in claim 15, wherein the rod (2) is oriented obliquely between the actuator (1) and the reaction vessel (4); wherein the rod is a glass tube; and/or the rod (2) is coupled to the reaction vessel through a teflon stopper.

17. An article comprising the sulfur-elastomer polysulfide material as claimed in any of claims 8-10.

18. A method of manufacturing an article comprising sulfur-elastomer polysulfide material, said method comprising acts of:
a. contacting elemental sulfur and elastomer and optionally mixing to obtain a mixture; and
b. subjecting the mixture to temperature ranging from about 165°C to about 185°C and optionally molding to obtain the article of desired shape.

19. The article or the method as claimed in claim 17 or 18, wherein the article has thickness ranging from about 50 µm to about 650 µm; and/or wherein the article has higher transmittance in the infrared range and lower transmittance in the UV and visible range.

20. The article or the method as claimed in any of claims 17-19, wherein the article is selected from a group comprising optic material, infrared transmitting material, sensing material, imaging material, packaging material and filtering material, sheet, lenses and clothes or any combination thereof.

21. The polysulfide material, the article or the methods as claimed in any of the preceding claims, wherein the polysulfide material or article transmits in the infrared range of about 0.175 µm to about 22.2 µm, and wherein the polysulfide material or the article has characteristics selected from a group comprising physical stability, mechanical stability, thermal stability, self-standing, flexibility, resistance to solvents or resistance to chemicals, or any combination thereof. , Description:TECHNICAL FIELD
The present disclosure generally relates to the field of polymer engineering, advanced materials and applied industrial technology. Particularly, the present disclosure relates to a polysulfide material made of elemental sulfur and elastomer having higher transmittance in the infrared region and lower transmittance in the UV-Vis range. The present disclosure also relates to a corresponding method for preparation of the sulfur-elastomer polysulfide material and system thereof. The present disclosure also provides articles comprising the sulfur-elastomer polysulfide material and corresponding methods for preparing said article. The unique transparency feature of transmitting lower ultraviolet (UV) and visible light and higher infrared light, renders the sulfur-elastomer polysulfide material and articles thereof useful for example in infrared device applications for imaging and filtering purposes.

BACKGROUND & PRIOR ART
A huge quantity (>60 MTA) of elemental sulfur is being produced as a by-product in petroleum refinery industries. The value addition of such abundantly available cheap feedstock to novel useful materials is desired. However, utilization of elemental sulfur (S8) in large volume is restricted owing to its poor solubility in organic solvents. Hence, a greener approach is needed to address both the solubility issue and the enviro-economic concerns.

Optical transparent materials obtained from materials employed in the art are not flexible, brittle, expensive and/or require sophisticated synthetic and purification processes, involving complicated machinery and expensive purification processes, to modify the reactants into useful materials.

Commercially available dienes such as diisopropenylbenzene (DIB), dicyclopentadiene (DCPD), limonene etc. have been used for producing polymer with elemental sulfur. However, the commercially employed dienes are expensive and not readily available. Further, polymers known in the art prepared from such monomeric diene require additional processing conditions such as PDMS mould/other matrix to form a free-standing flexible film, or expensive components such as DVB (commercial cross-linking agent monomers), and organically modified chalcogenides (ORMOCHALC). Accordingly, use of expensive monomeric dienes is not economic for large scale production of polymer with elemental sulfur.
Furthermore, methods of the art employ solvent for solubilizing the source of diene monomers, additional reagent/catalyst, metals, additives such as stearic acid/zinc oxide, toxic agents, or multiple steps making the process expensive, environmentally hazardous and difficult to expand at an industrial level.

Thus, there is a need for providing alternate means and methods for overcoming the constraints of the prior art, and providing simple, efficient, non-toxic, economic and environmentally friendly methods, system and products for obtaining stable infrared transparent co-polymer by employing elemental sulfur.

SUMMARY OF THE DISCLOSURE
The present disclosure provides for a method of producing a sulfur-elastomer polysulfide material, comprising acts of:
a. contacting elemental sulfur and elastomer, and optionally mixing, to obtain a mixture; and
b. subjecting the mixture to temperatures ranging from about 165°C to about 185°C to obtain the polysulfide material.

In an embodiment, the present disclosure provides for a solid-state method of producing a sulfur-elastomer polysulfide film, comprising acts of:
a. contacting elemental sulfur and elastomer, and optionally mixing, to obtain a mixture; and
b. subjecting the mixture to compression molding at temperature ranging from about 165°C to about 185°C to obtain the polysulfide film.

The present disclosure provides for a sulfur-elastomer polysulfide material comprising elemental sulfur and elastomer optionally comprising oxygen.

The present disclosure further provides for a system for producing a sulfur-elastomer polysulfide material, the system comprising:
a. a reaction vessel (4) at least partially dipped in oil bath (5) and configured to rotate freely in the oil bath (5); and
b. an actuator (1) coupled to the reaction vessel (4), wherein the actuator (1) is configured to rotate the reaction vessel (4) in the oil bath;
wherein the reaction vessel (4) comprises elemental sulfur and elastomer; and wherein the oil bath (5) is maintained at a temperature ranging from about 165°C to about 185°C.

The present disclosure also provides an article manufactured using the sulfur-elastomer polysulfide material of the present disclosure.

The present disclosure further provides a method of manufacturing an article comprising the sulfur-elastomer polysulfide material of the present disclosure, said method comprising acts of:
a. contacting elemental sulfur and elastomer and optionally mixing to obtain a mixture; and
b. subjecting the mixture to temperature ranging from about 165°C to about 185°C and optionally molding to obtain the article of desired shape.

BRIEF DESCRIPTION OF ACCOMPANYING FIGURES
In order that the disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present disclosure where:
Figure 1 depicts formation of sulfur diradical at high temperature.
Figure 2 depicts predicted molecular structures of sulfur- polybutadiene rubber (PBR) polysulfide material products, wherein ‘E’ corresponds to trans double bond and ‘Z’ correspond to cis double bond.
Figure 3 depicts infrared (IR) transmittance of sulfur-PBR polysulfide material films having a) 50 - 80 µm thickness, b) 110 - 130 µm thickness, c) 160 µm thickness,d) 230 µm thickness, and e) 660 µm thickness.
Figure 4 depicts a) FT-IR of PBR; b) FT-IR of sulfur-PBR polysulfide material film prepared.
Figure 5 depicts TGA thermogram (in air) of the sulfur-PBR polysulfide material film prepared.
Figure 6 depicts photographs of sulfur-PBR polysulfide material (a) red rubbery and (b) hard black solid, prepared in RB flask; and (c) TGA comparison of red rubbery solid and hard black solid with PBR starting material (pristine PBR).
Figure 7 depicts the horizontal arm reaction set up / system.
Figure 8 depicts a) NIR (0.83 - 2.5 µm) and b) Mid-IR Transmittance (2.5 – 22.2 µm) spectra of PBR-S compression molded films measured from FT-IR Spectrophotometer.
Figure 9 depicts a) IR camera and b-e) thermography experiments (thermal and visible images) using IR camera.

DETAILED DESCRIPTION
In view of the drawbacks associated and to remedy the need created by the art, the present disclosure aims to provide stable polysulfide material made of elemental sulfur and elastomer having higher transmittance in the infrared region and lower transmittance in the UV-Vis range. More particularly, the present disclosure provides sulfur-elastomer polysulfide material which is selective towards infrared transmittance and simple methods for preparing the same. The disclosure also provides articles comprising the sulfur-elastomer polysulfide material and corresponding methods for preparing said article.

However, before describing the elastomer based material and process of the present disclosure in greater detail, it is important to take note of the common terms and phrases that are employed throughout the instant disclosure for better understanding of the technology provided herein.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. 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 disclosure to achieve one or more of the desired objects or results. Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising” or “containing” or “has” or “having” wherever used, 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.

As used herein, the term "method" and “process” are employed interchangeably.

As used herein, the term "about" means to be nearly the same as a referenced number or value. As used herein, the term "about" should be generally understood to encompass ± 10% of a specified amount or value.

As used herein, the expression “sulfur-elastomer polysulfide material” refers to a polysulfide material obtained on subjecting a homogenous mixture of elemental sulfur and elastomer such as but not limiting to polybutadiene rubber (PBR), ethylene propylene diene terpolymer (EPDM), natural rubber, synthetic butadiene rubber, butyl rubber, styrene butadiene rubber etc., to temperature ranging from about 165°C to about 185°C.

As used herein, the expression ‘elemental sulfur’ refers to S8 octamer stable allotrope monomer molecule existing in nature. The present disclosure allows use of elemental sulfur from solid waste material obtained from the petrochemical industry, derived after the desulfurisation process in the industry.

As used herein, the expression ‘elastomer’ refers to a polymer having sufficient double bonds for inverse vulcanisation reaction with sulfur.

As used herein, the expression ‘infrared transparent material’ refers to materials which transmit infrared radiations of different wavelength through it.

As used herein, the expression ‘infrared transmittance’ is employed for property quantification of the infrared transmitting material.

As used herein, the term “horizontal” refers to position or direction parallel to the plane of the horizon or at a slight deviation from angle in the horizontal plane and includes a sloping or oblique position/direction.
In an embodiment, the present disclosure provides a simple method for making thermally stable, physically and chemically stable, flexible, non-toxic infrared transparent optical materials in large quantities using elastomers such as rubber polymers and elemental sulfur.

In an embodiment, the present disclosure provides for a method of producing a sulfur-elastomer polysulfide material, comprising contacting and optionally mixing elemental sulfur and elastomer to obtain a mixture; and subjecting the mixture to temperature ranging from about 165°C to about 185°C, preferably about 175°C to obtain the polysulfide material.

The present disclosure also provides for sulfur-elastomer polysulfide material comprising elemental sulfur and elastomer. The elastomer based polysulfide films of the present disclosure are stable and self-standing.

In an embodiment, the present disclosure provides for high volume sulfur loaded material such as films without hampering the stability, flexibility, texture, refractive index, and homogeneity of the material which in turn may affect the IR transparency property.

Elemental sulfur at about 175°C forms a linear polymeric sulfur (polysulfide) diradical which can be trapped by reacting with olefinic moiety and thereby restricts sulfur from getting back into cyclic form. The present invention works basically on the principle of inverse vulcanisation of sulfur which happens above 165°C where diradical of sulfur starts propagating to form linear polymeric structures which are ready to be cross-linked with unsaturated bonds. This process does not require any catalyst since linear polymeric sulfur radical formation above 165°C is self-propagating in nature.

In embodiments of the present disclosure, elemental sulfur is known to form di-radical above 165°C. The activation of elemental sulfur at 175°C for certain amount of time leads to the formation of linear polymeric diradical chains (Figure 1). These diradicals react with the double bonds (cis, trans, vinyl) present in the PBR to form internally cross-linked products (process is called inverse vulcanization). PBR contained 92 mol % cis-1,4 microstructure and rest is divided into 1,4-trans and 1,2-vinyl microstructures. All these microstructures are susceptible for reaction with polysulfide diradical to form various possible structures as shown in Figure 2. The sulfur-rubber polysulfide material was produced by creating more C-S and S-S bonds while reducing some of the C=C bonds. It is known that S-S bonds are dynamic and absorbs very less IR radiations, co-polymers produced by S-S bonds are good for obtaining IR transparent polymers.

In embodiments of the present disclosure, due to difficulty in solubility of elastomer such as rubber and elemental sulfur at room temperature, the present disclosure employs a solvent less mixing (such as a solid-state mixing, and preferably via Brabender) to create a homogeneous mixture of the elastomer and sulfur, which allows for higher sulfur loading on the films and yields films of superior quality.

In an embodiment, the method of the present disclosure provides for sulfur-elastomer polysulfide material which is selective towards infra-red transmittance. The developed methodology is also a green synthesis, as no solvent is used.

Thus, the methods of the present disclosure do not employ a catalyst or a solvent.

The methods of the present disclosure for producing the sulfur-elastomer polysulfide material, such as but not limiting to films, employ a solid-state reaction wherein the polysufide materials are obtained from a mixture of solid starting materials.

Usually, elastomers do not form a stable film because it wrinkles and will not hold the shape. However, the present disclosure provides for solid-state methods which results in physically stable and self-standing elastomer-based polysulfide film.

In embodiments of the present disclosure, the method of producing a sulfur-elastomer polysulfide material comprises acts of:
a. contacting elemental sulfur and elastomer, and optionally mixing, to obtain a mixture; and
b. subjecting the mixture to temperature ranging from about 165°C to about 185°C, preferably about 175°C, optionally followed by cooling, to obtain the polysulfide material.

In an embodiment of the present disclosure, the elastomer comprises one or more olefinic bonds.

In another embodiment of the present disclosure, the elastomer is selected from a group comprising but not limiting to PBR, ethylene propylene diene terpolymer (EPDM), synthetic rubber and natural rubber, butyl rubber, styrene butadiene rubber or any combination thereof.

In yet another embodiment of the present disclosure, the elemental sulfur employed in the method of producing the sulfur-elastomer polysulfide material is at an amount ranging from about 10 to 70 wt% and the elastomer is at an amount ranging from about 30 to 90 wt%.

In still another embodiment of the present disclosure, the mixing is carried out in a mixer (such as but not limited to Brabender).

In an exemplary embodiment, the mixing is carried out using a Brabender at about 20 to 50 rpm.

In still another embodiment of the present disclosure, the mixture of step a) is subjected to compression molding at temperature ranging from about 165°C to about 185°C, preferably 175°C, and pressure ranging from about 0.2 to about 2.6 ton per square inch and about 25 minutes to about 2 hours, preferably about 2 ton per square inch /30 minutes. The pressure applied during compression molding may be varied as desired, such as between 0.2 to about 2.6 ton per square inch, preferably about 1 to about 2 ton per square inch or more preferably about 1.4 to about 2 ton per square inch or about 1.8 to about 2 ton per square inch. In an exemplary and non-limiting embodiment, for large scale preparations, the pressure may be varied in the range of about 0.2 to 2.6 ton per square inchdepending on the pressing conditions in a suitable press, such as but not limiting to an automated carver press.

In embodiments of the present disclosure, the cooling may be carried out by any means known in the art. In an exemplary and non-limiting embodiment, the cooling step is carried out as fast cooling by rapidly keeping in open air or by purging air/water within the compression molding instrument while maintaining the pressure.
In an embodiment, the present disclosure provides for process of making self-standing and stable elastomer-based polysulfide film by compression molding.

In embodiments of the present disclosure, the method of producing a sulfur-elastomer polysulfide material such as films comprises acts of:
a. contacting elemental sulfur and elastomer, and mixing preferably in a Brabender, to obtain a mixture; and
b. subjecting the mixture to compression molding at temperature ranging from about 165°C to about 185°C, preferably about 175°C to obtain the polysulfide material as thin films.

In an embodiment, the solid-state method of producing a sulfur-elastomer polysulfide film, comprises acts of:
a. contacting elemental sulfur and elastomer, and optionally mixing, to obtain a mixture; and
b. subjecting the mixture to compression molding at temperature ranging from about 165°C to about 185°C to obtain the polysulfide film.

In embodiments of the present disclosure, the PBR-Sulfur premix from Brabender is subjected to compression molding at about 165°C to about 185 °C preferably about 170°C to about 175°C, more preferably at about 175°C to get films having selective IR transmittance and very less visible transparency or opaque to visible / UV lights.

In an embodiment, the present disclosure provides for use of double bond rich polybutadiene rubber to react with elemental sulfur for converting into an IR transparent stable co-polymer without the usage of any solvent through a single step process. The diverse double bond (cis, trans and vinyl) rich unsaturated polymers such as PBR etc. offer tremendous opportunity for range of co-polymer products with sulfur which can be tuned simply by altering the temperature and the reaction time.

In embodiments of the present disclosure, elastomers having varied vinyl content (such as but not limiting to PBR) is used to produce stable infrared transparent films from elemental sulfur.
In embodiments of the present disclosure, the polysulfide material is prepared by reacting elemental sulfur and elastomer such as PBR in various ratio (preferably at Sulfur: PBR ratio of about 2:1 wt. %). The formation of C-S and S-S bonds at 696 and 795 cm-1 and also the reduction of intensity of double bonds of PBR as observed by FT-IR analysis confirmed the reaction between sulfur and PBR chain. Sulfur-rubber polysulfide material films prepared by compression molding (at temperature ranging from about 165-185°C), were found to be mechanically and thermally stable, smooth, flexible and also chemically inert. Additionally, these films showed infrared transmitting properties for a wider range of 0.2 µm to 22.2 µm, more particularly in the range of 0.75 µm to 22.2 µm. These films have potential applications in the areas such as night vision camera, thermal imaging, infrared photography, optical lenses, infrared filters and infrared sensors for gas imaging etc.

In an exemplary embodiment, the present disclosure provides for a single step process for the production of stable infrared (IR) transparent material such as but not limiting to films from elemental sulfur (industrial by-products) and elastomers such as but not limiting to PBR. Elastomers containing many olefinic moiety namely cis, trans and vinyl is used to prepare polysulfide having high sulfur content in the range of about 21-50%. In another exemplary embodiment, elemental sulfur and PBR are directly mixed at a ratio of about 2:1 in the absence of any catalyst or solvent. This mix is subjected to compression molding at about 175°C to make optical thin films. It is also possible to tune the IR transmittance behavior by changing the ratio of PBR and sulfur. Higher transmittance of the product film is observed in the IR region ranging from about 0.75µm to 22.2 µm. The present disclosure also maximizes the cost reduction of optical materials. The films obtained are mechanically stable, flexible and can be molded into any desired shapes.

In embodiments of the present disclosure, elemental sulfur and elastomer such as polybutadiene rubber, natural rubber, EPDM etc. are directly mixed in a mixer such as but not limiting to Brabender internal mixer at a ratio of about 1:9 to about 7:3, preferably about 2:1, without the addition of any catalyst or solvent or reagent. This pre-mix was subjected to compression molding at temperature ranging from about 165-185°C, and pressure ranging from about 0.2 to about 2.6 ton per square inch for about 25-45 minutes to make thin films.

In embodiments of the present disclosure, the unique transparency feature of sulfur-PBR polysulfide film is that it can transmit very less amount of UV and visible light and more amount of infrared light. This contrasting behavior in light transmittance is ideally useful for infrared device applications for imaging and filtering purposes. For instance, applications include making lens/filters of thermal imaging night vision cameras or any FLIR systems.

In embodiments of the present disclosure, the polysulfide material has higher transmittance in the infrared range, i.e. at least about 70% or more transmittance in the infrared range and lower transmittance in the UV and visible range, i.e. about 20% or less transmittance in the UV and visible range.

In embodiments of the present disclosure, the polysulfide material has at least about 70% or more transmittance in the infrared range and more particularly in near infrared range and/or mid-infrared range, and lower transmittance in the UV and visible range, i.e. about 20% or less transmittance in the UV range and about 15% or less transmittance in the visible range.

As used herein, the expression “higher transmittance in the infrared range” implies that the polysulfide material of the present disclosure or the article thereof has at least about 70% (i.e. 70-100%) transmittance in the infrared range. In an exemplary embodiment, the polysulfide material or the article has at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95%, at least about 99% or 100% transmittance in the infrared range of about 0.75 to about 22.22 µm (750 – 22222 nm) comprising NIR and Mid-IR.

As used herein, the expression “lower transmittance in the UV range and visible range” implies that the polysulfide material of the present disclosure or the article thereof has less than or equal to about 20% transmittance in the UV range and/or visible range. In an exemplary embodiment, the polysulfide material or the article has less than about 19%, less than about 15%, less than about 10%, less than about 5%, less than about 1% or 0% transmittance in the UV and visible range.

In embodiments of the present disclosure, the polysulfide material or the article thereof has about 60 to about 85%, preferably about 65% to about 75% transmittance in the near infrared range.

In embodiments of the present disclosure, the polysulfide material or the article thereof has about 60 to about 85%, preferably about 65% to about 75% transmittance in the mid-infrared range.

The percentage transmittance provided herein is the average transmittance in the particular region specified (i.e. NIR/Mid-IR/VIS/UV). For instance, 75% transmittance in NIR range implies that the average transmittance in the NIR region (i.e. of 750 nm to 2600 nm) is a value of about 75%. The indicated percentage is not a particular wavelength transmittance but it is an average transmittance corresponding to that specific region, where the transmittance values coming in the particular range is averaged out.

In embodiments of the present disclosure, the infrared (IR) transparency of the film is measured using UV-Vis-NIR spectrophotometer for a wide range of about 0.175 µm to about 2.6 µm of which higher transmittance is observed specifically in the near infrared (NIR) region (about 0.75 µm to about 2.6 µm).

In embodiments of the present disclosure, the IR transparency of the film is measured using FT-IR spectrometer is to verify the IR transparency of the material in both mid-IR and NIR range.

In embodiments of the present disclosure, the FT-IR analysis of the film has shown the presence of S-S and C-S bond at stretching frequencies of 795 and 696 cm-1. In addition to that, the frequencies corresponding to cis, trans and vinyl in PBR also undergoes dramatic changes during the inverse vulcanization reaction with sulfur.

In embodiments of the present disclosure, Thermogravimetric analysis of the film (in air) confirmed its thermal stability where it decomposes step-wisely like 200-300°C (31.37% weight loss), 300-500°C (35.21%) and 500-700°C (33.4%). In TGA, sulfur alone decomposes at 200-300°C range whereas PBR decomposition range is starting from 400-500°C. The third transition in the TGA of sulfur-PBR polysulfide material film is attributed to the oxidation of the residual carbon left during heating in air.

In embodiments of the present disclosure, elemental analysis of the sulfur-PBR polysulfide material films confirmed the presence of sulfur and it is found in the range from 21 – 49.6%.

In embodiments of the present disclosure, films were resistant to chlorinated solvents, hydrocarbon solvents, DMSO, DMF, CS2, diglyme etc. even under boiling conditions.

In embodiments of the present disclosure, the films also exhibited thermal resistance up to 220°C as evident from the TGA analysis.

In embodiments of the present disclosure, sulfur and PBR or vinyl rich PBR are employed at a ratio of 2:1 and subjected to Brabender mixing at about 20 to about 50 rpm, preferably about 25 rpm at temperature of about 25°C to about 60°C, preferably about 50°C for time period ranging from about 2 to about 10 minutes, preferably about 5 minutes. The homogenized PBR+sulfur mixture obtained from Brabender mixing appeared as light yellow in color. This premix is used for next step compression molding to make PBR-S polysulfide thin IR transparent films.

In embodiments of the present disclosure, changing the ratio of elastomer and sulfur during mixing, allows tuning both the infrared transmittance and visible transmittance behavior of the material obtained.

In embodiments of the present disclosure, the homogenized Brabender mixed PBR+sulfur reactants appeared yellowish color with rubbery nature are subjected to compression molding at a temperature of 175°C for 40 minutes while maintaining a pressure of about 2.2 ton per square inch in order to obtain sulfur-PBR polysulfide material film. By varying the mold used in compression molding, it is possible to approach thickness of the film from 50 µm to 650 µm. In embodiments of the present disclosure, the thin and thick films thus obtained exhibited infrared transmittance behavior depending upon their thickness.

Conventional reaction set up using RB flask over a mechanical stirrer in laboratory for generating polysulfides lacked homogeneity due to improper mixing of solid reactants. Hence, the present disclosure also provides for a system and method thereof for obtaining polysulfides via homogeneous mixture of elastomer and elemental sulfur. The system of the present disclosure provides for producing solid-state sulfur-elastomer polysulfide material avoiding sulfur sublimation during reaction.

In embodiments of the present disclosure, to conduct the method of producing a sulfur-elastomer polysulfide material in a homogeneous way (via uniform heating and obtaining a homogenized mixture), ‘horizontal arm reaction set up/system’ is employed. In an exemplary embodiment, the horizontal arm reaction set up / system of the present disclosure is depicted in Figure 7.

In embodiments of the present disclosure, the horizontal arm reaction set up / the system of the present disclosure comprises a horizontally mount mechanical stirrer / rod (2) connected to a reaction vessel such as but not limiting to round bottom (RB) flask (4). The rod (2) is arranged horizontally/obliquely via an actuator such as but not limiting to a rotating head (1) and is connected to the reaction vessel (4) via a fluid flow passage (3), such as but not limiting to a Teflon stopper with hole where the rod is attached. The reaction vessel (4) is in turn at least partially dipped in oil bath (5), such as but not limiting to a silicon oil bath, in a substantially horizontal/oblique orientation. In an embodiment, the term substantially horizontal orientation refers to orientation of the rod in line with which is horizontal plane of the oil bath, with some deviation in angle with respect to the horizontal plane of the oil bath. The oil bath is placed on a heat source such as heating plate (6), and the temperature of which is maintained by a temperature controller (7). Once the rotation in the actuator/ rotating head (1) is switched on, the reaction vessel (4) rotates freely over the oil bath. The horizontal rotating reaction vessel (4) ensures maximum participation of sulfur for reaction with PBR without undergoing sulfur sublimation. This leads to uniform heating, which leads to highly homogenized reaction product.

In another embodiment, the system of the present disclosure allows controlling the time of polymerization reaction to harvest red rubbery solid material before being transformed into hard black solid material through appropriate optimization. In an embodiment, the average reaction time for making red rubbery solid at temperature ranging from about 165°C to about 185°C, preferably about 165°C for about 40 to 50 minutes, preferably about 45 minutes, whereas production of the hard black highly cross-linked solid material takes about 60 to 80 minutes, preferably about 70 minutes. In an embodiment, both the hard black solid and red rubbery material exhibited distinct thermogram when compared with pristine PBR.

In embodiments of the present disclosure, the system for producing sulfur-elastomer polysulfide material comprises:
a. a reaction vessel (4) at least partially dipped in oil bath (5) and configured to rotate freely in the oil bath (5); and
b. an actuator (1) coupled to the reaction vessel (4), wherein the actuator (1) is configured to rotate the reaction vessel (4) in the oil bath;
wherein the reaction vessel (4) comprises elemental sulfur and elastomer; and wherein the oil bath (5) is at a temperature ranging from about 165°C to about 185°C.

In an embodiment of the present disclosure, reaction in the system is carried out for a time period ranging from about 40 to about 90 minutes.
In another embodiment of the present disclosure, the reaction vessel (4) is adapted to receive elemental sulfur and elastomer or a homogenous mixture of the elemental sulfur and elastomer. In an exemplary embodiment, the said homogenous mixture is obtained by mixing the elemental sulfur and the elastomer at a temperature ranging from about 25°C to about 60°C for a time period of about 2 to about 10 minutes in a mixer. The homogenous mixture may be obtained by employing any suitable mixer such as but not limiting to Brabender, etc.

In yet another embodiment of the present disclosure, the reaction vessel (4) of the system is obliquely oriented in the oil bath (5).

In still another embodiment of the present disclosure, the oil bath (5) is positioned on a heat source (6).

In still another embodiment of the present disclosure, the oil bath is a silicon oil bath.

In still another embodiment of the present disclosure, the system further comprises rod (2) coupling the actuator (1) with the reaction vessel (4).

In still another embodiment of the present disclosure, the rod (2) is oriented obliquely between the actuator (1) and the reaction vessel (4).

In still another embodiment of the present disclosure, the rod (2) is a glass rod.

In still another embodiment of the present disclosure, the rod (2) is coupled to the reaction vessel through a teflon stopper.

In another embodiment of the present disclosure, the system further comprises:
a temperature controller (7) interfaced with the heat source (6), wherein the temperature controller (7) is configured to maintain the temperature of the oil bath in the range of about 165°C to about 185°C.

The present disclosure also relates to a sulfur-elastomer polysulfide material obtained by the afore-described methods.

The present disclosure also relates to a sulfur-elastomer polysulfide material comprising elemental sulfur and elastomer.

In an embodiment, the polysulfide material of the present disclosure comprises sulfur at an amount ranging from about 20 to 50 w/w%, preferably about 21 to 49.6% w/w.

In another embodiment, the polysulfide material comprises elastomer at an amount ranging from about 50 w/w% to about 80 w/w%.

In embodiments of the present disclosure, since the process of its preparation is carried out in the presence of oxygen, the polysulfide material may further comprise oxygen. In an exemplary embodiment, the polysulfide material comprises about 0 to 4 w/w% of oxygen.

In embodiments of the present disclosure, the polysulfide material is infrared transparent.
In another embodiment, the polysulfide material of the present disclosure transmits in the range of about 0.175 µm to about 22.2 µm (comprising UV range of about 0.2 µm to about 0.4 µm, VIS range of about 0.4 µm to about 0.8 µm, NIR range of about 0.75 µm to about 2.6 µm and mid-IR range of about 2.6 µm to about 22.2 µm), preferably higher transmittance in the NIR and mid-IR range of about 0.75 µm to about 22.2 µm.

In yet another embodiment of the present disclosure, the polysulfide material is mechanically stable, flexible and resistant to organic solvent, chemicals and/or temperature of up to about 220°C.

The polysulfide material of the present disclosure can be processed into any desired shape, such as but not limiting to by moulding for ease of processability.

In an exemplary embodiment of the present disclosure, the polysulfide material is in a form selected from a group comprising but not limiting to films, sheets, blocks, rods, fibres, tubes, solid lump, and tapes or any combination thereof. In non-limiting embodiments of the present disclosure, the said films include thin films, thick films, thin/thick multi-layered films, etc. In non-limiting embodiments of the present disclosure, the said films include thin sheets, thick sheets, thin/thick multi-layered sheets, etc.

In an embodiment, the polysulfide material of the present disclosure has thickness ranging from about 50 µm to about 650 µm.

The present disclosure also provides an article comprising or manufactured using the sulfur-elastomer polysulfide material of the present disclosure.

The present disclosure also relates a method of manufacturing an article comprising the sulfur-elastomer polysulfide material of the present disclosure, said method comprising acts of:
a. contacting elemental sulfur and elastomer and optionally mixing to obtain a mixture; and
b. subjecting the mixture to temperature ranging from about 165°C to about 185°C and optionally conforming/molding to obtain article of desired shape.
In a non-limiting embodiment of the present disclosure, the article can be in the shape of a film if the method is carried out by compression molding. However, it is possible to make any desired shape by using a shaped metallic mould to get the desired form / shape / article.

In another embodiment of the present disclosure, if the reaction between PBR and sulfur are performed in a reaction vessel in the horizontal reaction set up, the product/article can be a solid red rubbery solid or hard black solid.

In a non-limiting and exemplary embodiment of the present disclosure, the thickness of the article is ranging from about 50µm to about 650 µm.

In another embodiment of the present disclosure, the article is selected from a group comprising optic material, IR/NIR/mid-IR transmitting material, sensing material, imaging material, packaging material and filtering material, sheet, lenses and clothes or any combination thereof.

In an exemplary and non-limiting embodiment of the present disclosure, the article is selected from a group comprising IR/NIR/mid-IR Filters, UV cut off filter, Visible light cut off filter, Longpass filters, Night vision filters (surveillance/automotive night vision), Infrared thermal imaging camera filter, Optical gas sensing/imaging filters, IR/NIR/mid-IR lenses, Visible opaque IR transparent clothes with thermal management, Light protecting packaging materials, Convection suppression wind screen for radiative cooling technology etc.

In yet another embodiment, the article of the present disclosure transmits in the range of about 0. 175 µm to about 22.2 µm (comprising UV, VIS,NIR and Mid-IR range), however has higher transmittance in the NIR and Mid-IR range of about 0.75 µm to about 22.2 µm.

In still another embodiment, the total transmittance of the polysulfide material or article of the present disclosure is ranging from 0.175 µm to 22.2 µm comprising UV, Visible and IR ranges.

In still another embodiment, the specific transmittance of the polysulfide material or article of the present disclosure is ranging from 0.75 to 22.2 µm.

In still another embodiment, the article of the present disclosure is resistant to solvent, chemicals and/or high temperature of up to about 220°C.

In an embodiment, the present disclosure provides for a cheap optical material using a simple reaction method which involves neither solvent nor very high temperature. The commercially available infrared transmitting materials are synthesized in a sophisticated way involving complicated machineries and expensive purification processes. In lieu of that, the present disclosure offers a cheaper method for making infrared transparent materials in a simplest manner and in large volume. The present disclosure leverages the cost reduction of optical materials as it utilizes industrial by-products as feed stocks (PBR and S).

In an exemplary embodiment, advantages of the present disclosure include but are not limited to:
• One of the key advantages of the sulfur-elastomer polysulfide material such as films etc., or articles thereof is that it can transmit more IR radiations through the material/article than visible and UV lights. Particularly, it provides for broad/wide range of NIR & Mid-IR transmittance, capable of blocking UV and Visible lights. This contrast in behavior is highly useful when it comes to use in day light control applications, night vision, thermal imaging and other infrared devices.
• The present disclosure provides for broad and high IR transmitting material (i.e. having wide transparency range covering both NIR to mid-IR ranges) and is free from anti-reflective coating and which is photochemically stable.
• The sulfur-elastomer compression molded polymer film of the present disclosure is an optic material which transmits uniquely in the whole region of both NIR and Mid-IR from 0.75 µm – 22.2 µm while ensuring opacity to visible (< about 10%) and UV lights (< about 20%). This provides for UV & Daylight controlling/blocking/filtering, and photochemically stable self-standing film. Polymer films of the present disclosure block visible and UV lights to a considerable level while allowing the passage of infrared and other radiations through it.
• The material of the present disclosure is purely organic and does not involve the use of toxic metals like Germanium, Zinc, and Cadmium etc.
• The polysulfide material or articles thereof of the present disclosure is thermally stable.
• It also not sensitive towards moisture(hydrophobic) and insoluble in water.
• The polysulfide material or articles thereof of the present disclosure is also chemically inert as it is not soluble or does not swell in organic solvents such as DCM, CHCl3, toluene, DMSO, DMF and diglyme etc. even at boiling conditions of the respective solvents. The polysulfide material or articles thereof of the present disclosure is also resistant to chemicals such as but not limiting to thiols, diamines, concentrated acids such as HCl, alkalis such as NaOH etc.
• The polysulfide material of the present disclosure has mechanical stability and flexibility which offers tremendous opportunities to mold it into any desired shape. While most commercially available optic materials are brittle (mechanically unstable), not flexible and involve difficult synthetic conditions and sophisticated purification processes, the material of the present disclosure overcomes these limitations.
• The elastomer based polysulfide films or articles thereof of the present disclosure are stable and self-standing which can transmit over wide range from 0.175 µm to 22.222 µm having wide IR transparency range 750 µm – 22.22 µm comprising NIR and Mid-IR, and less UV and Visible transparency.
• The material of the present disclosure can be prepared in a single step through a greener approach (no solvent, low temperature, less carbon footprint as it does not employ high power energy source); does not need any high-end purification processes, sophisticated machineries, or a polymer matrix for making a stable film; and employs waste (sulfur, PBR) generated from the petrochemical industry. Thus, the method of the present disclosure is simple, cost effective, environment friendly and is an excellent example of waste into value generation.
• Usually, elastomers do not form a stable film because it wrinkles and will not hold the shape. However, the present disclosure provides for solid-state methods which results in physically stable and self-standing elastomer-based polysulfide film.
• The present disclosure provides for a controlled mechanism of performing solid-state reactions (so as to produce red rubbery and hard solids distinctively) between elastomer and sulfur called ‘rotating arm set up’ which decreases the evaporation loss of sulfur and increases the homogeneity of the reaction product while performing the reaction.

Additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based on the description provided herein. The embodiments herein provide various features and advantageous details thereof in the description. Descriptions of well-known/conventional methods and techniques are omitted so as to not unnecessarily obscure the embodiments herein.

Any possible combination of two or more of the embodiments described herein is comprised within the scope of the present disclosure.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments in this disclosure have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Any discussion of documents, acts, materials, devices, articles and the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

Further, while the instant disclosure is susceptible to various modifications and alternative forms, specific aspects thereof has been shown by way of examples and drawings and are described in detail below. However, it should be understood that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and the scope of the invention.

EXAMPLES:
The following illustrations in form of examples are described to bring more clarity of the invention and should not be considered as limitation or drawback of the invention.

Example 1:
Example 1(a): Preparation of homogenous mixture of PBR and elemental sulfur
A homogeneous reactant mixture of PBR and sulfur was prepared by Brabender mixing. About 20 g of sulfur and about 10 g of PBR or vinyl rich PBR were subjected to Brabender mixing employing Plasti-Corder PL 2000 Brabender at 25 rpm at 50°C for 5 minutes. About 29 g of homogenized PBR+sulfur mixture was thus obtained which appeared as light yellow in color.

Example 1(b): Preparation of Infrared transparent films
The Brabender mixed PBR+sulfur homogenous mixture is sandwiched between two transparent sheets, which in turn is pressed (by compression molding) between two hot circular blocks of diameter 10 cm. The two circular blocks are heated up to 175°C. Once the temperature is reached, pressure is applied (2.2 ton per square inch) using a Carver press manually and maintained at the said condition for up to 30-40 minutes which resulted in the formation of a homogeneous defect free sulfur-PBR polysulfide material film. Films having varying thickness ranging from about 50 µm to about 660 µm were formed. Films having thickness of 160 µm (with transparent sheet mold, 0.5 g sample), 110 µm (with aluminum foil as mold, 0.25 g sample) and 50 µm (without using any mold, 0.125 g) were obtained by using the above method.

Additionally, films having thickness of 660 µm (with 0.5 mm mold, 5.1 g sample), 230 µm thickness (employing thin transparent sheet as mold, 1.5 g sample), 130 µm (employing thin transparent sheet as mold, 0.4 g sample), 80 µm (without using any mold, 0.15 g sample) and 70 µm (without using any mold, 0.15 g sample) were also obtained by using the above method.
Thin films (having thickness <260 µm) appeared as dark red homogeneous, flexible and visibly less transparent material however thicker films (having thickness equal to >260 µm) appeared as black homogeneous visibly opaque. Both the thin and thick films exhibited infrared transmittance behavior depending upon their thickness.

Example 1(c): Near Infrared transparency of films
IR transparency of the films having thickness ranging from 50µm to 660 µm is measured using UV-Vis-NIR spectrophotometer for a wide range of 0.175 µm to 2.6 µm (Figure 3) of which higher transmittance observed specifically in the NIR region (0.75 µm to 2.6 µm). The results are depicted in Figures 3 (a)-(e).

Films having thickness of about 50 to about 80 µm are thinner films having nearly the same transmittance [spectrum of Figure 3 (a)]. Similarly, transmittance spectrum for films having about 110 to about 130 µm is found to be similar [spectrum of Figure 3 (b)]. The thinner films are very slightly visibly transparent and highly IR transparent. On the other hand, the thicker films are visually completely opaque and IR transmittance is less when compared to thin films.

Example 1(d): Near and Mid-Infrared transparency of films
Near and Mid-Infrared transparency of three thin films is tested. The films are prepared by compression molding (film sample dimension taken = 1.5 cm x 3 cm). Film 1 has a thickness of 170 µm, Film 2 has thickness of 110 µm and Film 3 has thickness of 160 µm. The IR transparency of the films is measured using FT-IR spectrophotometer in the transmission mode for a range of a) 0.83 µm to 2.6 µm (NIR) and b) 2.6 µm to 22.2 µm (Mid-IR), and the transmittance spectra obtained are depicted in Figures 8 (a) and (b) respectively.

Figure 8 depicts that the compression molded PBR-sulfur films of the present disclosure have a broad range of IR transmittance i.e. in the range of about 0.8 – 22.22 µm which comprises NIR and Mid-IR.

Example 1(e): Thermography
IR transmittance of the material is further proved by using thermal/IR imaging camera (Fluke’s Thermal Imager) depicted in Figure 9(a). Thermal imaging camera also known as infrared imaging camera, works on the principle of thermal radiations emitted from a body which covers mostly mid-IR and NIR. The thickness of the PBR-S compression molded film of the present disclosure tested herein is about 160 µm. The thermal and visible images obtained using the camera are depicted in Figures 9 (b)-(e).

Figures 9(b) and 9(d) show the infrared thermal images of a human hand when it is covered with the PBR-S compression molded film. Figures 9(c) and 9(e) correspond to their respective visual images. As the compression molded film is opaque to visible light, the visual images did not show the fingers of the human hand when it is covered with the film. However, in the infrared thermal imaging mode, the fingers of the hand are clearly visible when the hand is covered with the PBR-S compression molded film. This demonstrates the IR transmitting capacity of the PBR-S compression molded film of the present disclosure.

Example 2:
Elemental analysis of the sulfur-PBR polysulfide material films was carried out using CHNS instrument which calculates the percentages of elemental concentrations based on the principle of "Dumas method," using flash combustion of the sample to cause an instantaneous oxidization into simple compounds which are then detected with thermal conductivity detection or infrared spectroscopy. About 10-20 mg of sample was used for the analysis.

Instrument Details: Elementor, model number vario macro cube Sl no. 20135072
Analysis protocol followed as per the details furnished by the vendor.

Elemental analysis of the sulfur-PBR polysulfide material films confirmed the presence of sulfur in the films in the range from 21 – 49.6 w/w% as mentioned in the table (Table 1). The sample codes 1, 2 and 5 comprise about 1.96?%, 1.17% and 2.49% respectively of oxygen.

Table 1: CHNS data and thickness of the sulfur-PBR polysulfide material films prepared.
Sample Code N (%) C
(%) H
(%) S
(%) Mold used and thickness of film
1 0.00 49.94 6.09 42.01 Thin transparent sheet used as mold, thickness 130 µm
2 0.00 43.80 5.43 49.60 0.5 mm mold, thickness 660 µm
3 0.00 60.42 8.07 32.25 Thin transparent sheet used as mold, thickness 230 µm
4 0.00 61.67. 7.79 30.70 No mold, thickness 50 µm
5 0.00 62.23 7.04 28.24 Thin transparent sheet used as mold, thickness 160 µm
6 0.00 66.95 8.29 25.51 Aluminium sheet used as mold, thickness 110 µm

Example 3:
Fourier Transform Infrared Spectroscopy (FT-IR Analysis) of the film having thickness of 50µm is carried out in transmission mode in Mid-IR range to characterize the unsaturated polymer film to understand the different type of double bonds present in its structure. The results of the FT-IR analysis of PBR and the sulfur-PBR polysulfide film are depicted in Figure 4(a) and Figure 4(b) respectively. Figure 4(b) shows the presence of S-S and C-S bond at stretching frequencies of 795 and 696 cm-1, respectively. In addition to that, it is observed that the frequencies corresponding to cis, trans and vinyl in PBR also undergoes dramatic changes during the inverse vulcanization reaction with sulfur. FT-IR thus confirmed the reaction of cis, trans and vinyl rich double bonds in the PBR with sulfur in order to form a polysulfide with C-S and S-S bonds.

Example 4:
Thermogravimetric analysis of the film (in air) having thickness of 50µm is performed up to 700°C with about 10-20 mg of sample in presence of air and a rate of heating of about 20°C per minute, in order to understand the pattern of decomposition. The instrument used is TA instruments TGA Q500. TGA thermogram of the sulfur-PBR polysulfide material film is depicted in Figure 5. TGA of the film confirmed its thermal stability where it decomposes step-wisely like 200-300°C (31.37% weight loss), 300-500°C (35.21%) and 500-700°C (33.4%). In TGA, sulfur alone decomposes at 200-300°C range whereas PBR decomposition range starts from 400-500°C. The third transition in the TGA of sulfur-PBR polysulfide material film is attributed to the oxidation of the residual carbon left during heating in air. The TGA confirmed the incorporation of bonded sulfur in the PBR matrix to form polysulfide which showed distinct thermogram than the parent PBR matrix.

Example 5:
Solvent resistance of the film prepared as per example 1 was tested for different solvents above their boiling points. A small piece of the film having thickness of about 160µm is independently dipped in different solvents, viz.: DCM (boiling condition at 50°C), CHCl3 (boiling condition, 70°C), DMSO (at 165°C), DMF (Boiling condition at 160°C), CS2 (boiling condition at 50°C) and diglyme (Boiling condition at 163°C) for 40 minutes. The solvents remained colorless after boiling with the film and the film also remained intact. No dissolution or leaching of the film was observed in any of the solvents establishing that the film is insoluble in the said solvents even at boiling temperature.

Example 6:
In order to conduct the reaction via homogeneous heating, a horizontal arm reaction was set up, wherein a horizontally mount rod is connected to the round bottom flask which in turn is partially dipped in oil bath in a slanting fashion. Once the rotation is switched on, the RB flask rotates freely over the oil bath. This decreased the sublimation of sulfur through evaporation loss, and lead to uniform heating at a temperature of about 165°C and a highly homogenized product. The polymerization reaction is carried out for about 45 minutes to harvest red rubbery solid material [Figure 6(a)] which transformed into hard black solid material post about 70 minutes [Figure 6(b)]. Both the hard black solid and red rubbery material exhibited distinct thermogram when compared with pristine PBR [Figure 6(c)] indicating formation of polysulfide materials where sulfur is bonded with the PBR matrix.

REFERENCE NUMERAL TABLE:
Reference No. Description
1 Actuator.
2 Rod.
3 Teflon stopper with hole where rod is attached.
4 Reaction vessel freely rotating on silicon oil surface of the oil bath.
5 Silicon oil bath.
6 Heat source.
7 Temperature controller.