DESC:FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENT RULES, 2003
COMPLETE SPECIFICATION
[See Section 10 and rule 13]

PROCESS FOR PREPARING STYRENE-ACRYLONITRILE ENCAPSULATED POLYTETRAFLUOROETHYLENE

GUJARAT FLUOROCHEMICALS LIMITED an Indian company of INOX Towers, Plot No. 17, Sector 16-A, Noida, Uttar Pradesh-201301, India

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE INVENTION:
The invention relates to a process for preparing styrene-acrylonitrile encapsulated polytetrafluoroethylene. Particularly, the invention relates to a process for preparing styrene-acrylonitrile encapsulated polytetrafluoroethylene by providing reagent, monomers and redox initiator system in the initial feed.

BACKGROUND OF THE INVENTION:

The encapsulation of polytetrafluoroethylene polymer (PTFE) within Styrene-acrylonitrile polymer matrix (SAN) results in formation of Styrene-acrylonitrile encapsulated polytetrafluoroethylene composite polymer (TSAN). Styrene-acrylonitrile encapsulated polytetrafluoroethylene composite polymer, is used in the manufacture of flame retardant thermoplastics has several advantages.

The currently available processes generally do not produce stable TSAN. Also, the existing processes produce substantially large quantities of SAN particles and PTFE particles instead of producing TSAN particles. A dispersion containing PTFE particles and SAN particles needs continuous agitation to reduce premature coagulation. Despite such continuous agitation, premature coagulation cannot be completely avoided and hence, surfactant or soap is added after polymerization of the dispersion. The addition of surfactant or soap after polymerization however is not preferred for various reasons, including commercial losses.

In a commonly used process for preparation of TSAN, an initial feed of reagents can comprise PTFE dispersion, water, monomers, and tallow fatty acid (TFA) soap heated to an appropriate temperature and allowed to pre-condition for a duration of time prior. Thereafter, a continuous feed of reagents can comprise remaining monomers and initiator as the temperature is increased to provide the TSAN latex. It is believed that by adding an initial feed of reagents containing monomers, pre-conditioning the monomers, and subsequently adding a remaining quantity of the monomers and redox initiator system, the quantity of surfactant or soap required to be added after polymerization process to stabilize the TSAN latex can be reduced and the latex so produced will have slower rate of separation and higher mechanical stability. However, when such a process is followed, the amount of monomer conversion is adversely affected and the quantity of residual unreacted monomers in the final latex is very high. Also, the encapsulation of the PTFE by the SAN is not uniform and hence, dispersion of PTFE in polymer matrix is in consistent. This poor conversion rate leads to decreased efficiency of the process, wastage of raw materials, increases the overall cost of production of TSAN, and increases the cost of final product. The high residual content of unreacted monomers and the non-uniform distribution of PTFE in the TSAN latex results in low powder flowability of the TSAN particles, in particular, less than 500 g/min and decreased viscosity of the TSAN latex whereby the anti-dripping properties of the TSAN are adversely affected. Since TSAN is primarily used as an anti-dripping additive for electrical & electronic applications lack of flowability and decreased viscosity significantly reduces the applicability of the TSAN.

Thus, there exists a need to provide a process for preparing styrene-acrylonitrile encapsulated polytetrafluoroethylene with high conversion rate, reduced residual content, enhanced flowability and excellent anti-dripping properties, that addresses one or more of the aforesaid problems.

SUMMARY OF THE INVENTION:

This summary is provided to introduce a selection of concepts in a simplified format that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention, and nor is it intended for determining the scope of the invention.

The present invention provides, in an aspect, a process for preparation of styrene-acrylonitrile encapsulated polytetrafluoroethylene comprising providing an initial feed of reagents comprising a first quantity of reagent, monomers and redox initiator system and providing a subsequent feed comprising a remaining quantity of the monomers and redox initiator system.

In an embodiment, the present invention provides a process for preparation of styrene-acrylonitrile encapsulated polytetrafluoroethylene comprising additionally providing air purging after charging the reaction vessel with subsequent feed.

In another embodiment, the present invention provides a process for preparation of styrene-acrylonitrile encapsulated polytetrafluoroethylene comprising providing an initial feed of reagents wherein the reagents comprise polytetrafluoroethylene and soap solution. The soap solution comprises fatty acid or derivative thereof along with a base.

To further clarify advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES:

In order that the invention may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying drawings. The figures together with a 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 invention.

Figure 1 shows a flow chart of a process for making styrene-acrylonitrile encapsulated polytetrafluoroethylene in accordance with an embodiment of the present invention.

Figure 2 shows a Polarized Microscopic image of Styrene-acrylonitrile encapsulated Polytetrafluoroethylene and its observed uniform formation of the encapsulated material.

It may be noted that to the extent possible, like reference numerals have been used to represent like steps in the drawings. Further, skilled artisans will appreciate that the steps are illustrated for simplicity in the form of blocks, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

Detailed Description of the Invention:

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated evice, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the invention and are not intended to be restrictive thereof.

As used in the description herein and throughout the claims that follow, the meaning of “a,”“an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover anon-exclusive inclusion, such that a process that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such processor method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises... a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

As used herein, and unless the context dictates otherwise, the terms "coupled to", “connected to”, “operably connected to”, “operatively connected to” are intended to include both direct connection / coupling (in which two elements that are coupled / connected to each other contact each other) and indirect coupling / connection (in which at least one additional element is located between the two elements). Therefore, the terms "coupled to" and "coupled with" are used synonymously. Similarly, the terms “connected to” and “connected with” are used synonymously.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The methods, devices, and examples provided herein are illustrative only and not intended to be limiting.

The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims. Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

The present invention provides, in an aspect, a process for preparation of styrene-acrylonitrile encapsulated polytetrafluoroethylene comprising providing an initial feed of reagents comprising a first quantity of reagent, monomers and redox initiator system and providing a subsequent feed comprising a remaining quantity of the monomers and redox initiator system.

In an embodiment, the present invention provides a process for preparation of styrene-acrylonitrile encapsulated polytetrafluoroethylene comprising additionally providing air purging after charging the reaction vessel with subsequent feed.

In another embodiment, the present invention provides a process for preparation of styrene-acrylonitrile encapsulated polytetrafluoroethylene comprising providing an initial feed of reagents wherein the reagents comprise polytetrafluoroethylene and solution comprising fatty acid or derivative thereof along with a base solution.

In yet another embodiment, the present invention provides a process for preparation of styrene-acrylonitrile encapsulated polytetrafluoroethylene comprising adding initial feed comprising reagent, monomer, and redox initiator system to the reaction vessel, wherein the reagent is heated to appropriate temperature before adding monomer and redox initiator system.

In yet another embodiment, the present invention provides a process for preparation of styrene-acrylonitrile encapsulated polytetrafluoroethylene comprising charging the reaction vessel with subsequent feed comprising remaining predetermined amount of monomers, redox initiator system at maintained temperature.

In another embodiment of the invention, the subsequent feed is introduced in the reaction vessel by slow charging to the initial feed which is maintained at an appropriate temperature to yield styrene-acrylonitrile encapsulated polytetrafluoroethylene latex dispersion.

In yet another embodiment of the invention, the appropriate temperature maintained during charging of subsequent feed is same as the final temperature of the initial feed.

In yet another embodiment of the invention, the appropriate temperature is between 65.0°C and 74.0°C.

In yet another embodiment of the invention, the process for preparation of styrene-acrylonitrile encapsulated polytetrafluoroethylene comprising (a) providing an initial feed comprising reagents, styrene monomer, acrylonitrile monomer, and redox initiator system and (b) providing a subsequent feed comprising a styrene monomer, acrylonitrile monomer and redox initiator system.

In an embodiment of the invention, the initial feed comprises 30 to 70 parts by weight of polytetrafluoroethylene, particularly 50 to 60 parts by weight of polytetrafluoroethylene.

In another embodiment of the invention, the initial feed comprises 1 to 10 parts by weight of thestyrene monomer and acrylonitrile monomer, particularly 3 to 8 parts by weight and more particularly 3.5 to 7 parts by weight of the styrene monomer and acrylonitrile monomer.

In another embodiment of the invention, the initial feed comprises soap solution which comprises fatty acid or derivative thereof along with base in the quantity which is less than 0.8 parts by weight.

In an embodiment of the invention, the initial feed comprises 0.1 to 2.0 0.3 parts by weight of the redox initiator system, particularly 0.15 to 0.3parts by weight of the redox initiator system.

In yet another embodiment of the invention, the initial feed comprises polytetrafluoroethylene in the form of an aqueous dispersion of polytetrafluoroethylene.

In an embodiment of the invention, the aqueous dispersion of polytetrafluoroethylene comprises polytetrafluoroethylene in a water-soap solution. In an embodiment of the invention, the water-soap solution comprises less than 0.8 parts by weight of fatty acid or derivative thereof along with base, particularly 0.1 to 0.7 parts by weight and more particularly 0.15 to 0.65 parts by weight of fatty acid or derivative thereof along with base.

In an embodiment of the invention, the fatty acid derivative is selected from a group comprising saturated &unsaturated fatty acids. In an embodiment of the invention, the base is selected from a group comprising alkali metal hydroxides such as KOH & NaOH.

In an embodiment of the invention, the soap comprises oleic acid and KOH (potassium hydroxide).

In an embodiment of the invention, the initial feed further comprises 0.01 to 1.0 parts by weight, particularly 0.02 to 0.03 parts by weight of an additional reducing agent. In another embodiment of the invention, the additional reducing agent is selected from a group comprising sodium hydroxymethanesulfinate dihydrate, sodium borohydride, sodium hydroxymethylsulfinate and sodium citrate.

In an embodiment of the invention, the initial feed further comprises 0.001 to 0.15 parts by weight, particularly 0.001 to 0.015, more particularly 0.0015 to 0.0023 parts by weight of a chelating agent. In another embodiment of the invention, the chelating agent is selected from a group comprising ethylenediamine tetraacetic acid (EDTA), Porphine and Dimercaprol (2,3-dimercapto-1-propanol).

In an embodiment of the invention, the initial feed further comprises 0.01 to 0.5 parts by weight of monomer quantity by weight, particularly 0.01 to 0.02 parts by weight of a chain transfer agent. In an embodiment of the invention, the chain transfer agent includes (C9-C13) alkyl mercaptan compounds. In a preferred aspect of the invention, the chain transfer agent includes tertiary-dodecyl mercaptan (TDDM) or nonyl mercaptan.

In another embodiment of the invention, the redox initiator system comprises oxidizing agent, reducing agent, additional reducing agent, chelating agent.

In another embodiment of the invention, the redox initiator system comprises oxidizing agent, reducing agent, additional reducing agent, chelating agent, and chain transfer agent.

In another embodiment of the invention, the redox initiator system comprises cumene hydroperoxideas oxidizing agent, ferrous sulfate (FeSO4) as reducing agent, sodium hydroxymethanesulfinate dihydrateas additional reducing agent, ethylenediamine tetraacetic acid (EDTA) as chelating agent.

In another embodiment of the invention, the redox initiator system comprises cumene hydroperoxide as oxidizing agent, ferrous sulfate (FeSO4) as reducing agent, sodium hydroxymethanesulfinate dihydrateas additional reducing agent, ethylenediamine tetraacetic acid (EDTA) as chelating agent, and tertiary-dodecyl mercaptan(TDDM) as chain transfer agent.

In an embodiment of the invention, the temperature of the initial feed is maintained at a value in the range of 65oC to 74oC.

In an embodiment of the invention, the subsequent feed comprises 20 to 30 parts by weight of styrene monomer. In an embodiment of the invention, the subsequent feed comprises 5 to 15 parts by weight of acrylonitrile monomer.

In an embodiment of the invention, the subsequent feed comprises 1 to3 parts by weight of the redox initiator system.

In another embodiment of the invention, the redox initiator system comprises a combination of cumene hydroperoxide, and ferrous sulphate (FeSO4).

In an embodiment of the invention, the subsequent feed further comprises 0.1 to 1 parts by weight of an additional reducing agent.

In another embodiment of the invention, the additional reducing agent is selected from a group comprising sodium hydroxymethanesulfinatedihydrate, sodium borohydride, sodium hydroxymethylsulfinate and sodium citrate.

In an embodiment of the invention, the subsequent feed comprises 0.5 to 1.5 parts by weight of a chelating agent. In another embodiment of the invention, the chelating agent is selected from a group comprising ethylenediamine tetraacetic acid (EDTA), Porphine and Dimercaprol (2,3-dimercapto-1-propanol).

In an embodiment of the invention, the subsequent feed further comprises 0.01 to 0.1 parts by weight of a chain transfer agent. In an embodiment of the invention, the chain transfer agent includes (C9-C13) alkyl mercaptan compounds. In a preferred aspect of the invention, the chain transfer agent includes tertiary-dodecyl mercaptan (TDDM) or nonyl mercaptan.

In an embodiment of the invention, providing the subsequent feed comprises introducing the subsequent feed into the initial feed over a time period of 1 to 2 hours. In an embodiment of the invention, a temperature of a reaction mixture comprising the initial feed and the subsequent feed is maintained at a value in the range of 65 to 74oC.In an embodiment of the invention, a reaction mixture comprising the initial feed and the subsequent feed is air purged.

In an embodiment of the invention, the process further comprises adding an aqueous coagulant salt solution in cold condition to the reaction mixture to produce a slurry comprising styrene-acrylonitrile encapsulated polytetrafluoroethylene.

In an embodiment of the invention, the aqueous coagulant salt solution comprises a mixture of water and ammonium chloride. In another embodiment of the invention, the process involves removing the styrene-acrylonitrile encapsulated polytetrafluoroethylene from the slurry, followed by washing and drying the styrene-acrylonitrile encapsulated polytetrafluoroethylene.

In manufacturing process, as per the present invention monomers are added along with initiator in the initial phase and product having following advantages:
1. Very high conversion of monomers and residual content in product is <20 ppm;
2. Very high powder Flowability >500 g/min; and
3. Uniform encapsulation of polytetrafluoroethylene particles by the styrene-acrylonitrile polymer matrix providing very good dispersion of product in polymer matrix, resulting in very good anti-drip properties, as shown in figure 2.
4. Excellent anti-dripping properties with increased apparent viscosity of Styrene-acrylonitrile encapsulated Polytetrafluoroethylene.

EXAMPLES

Now referring to Figure 1, the process for preparation of styrene-acrylonitrile encapsulated polytetrafluoroethylene comprises introducing an aqueous dispersion of polytetrafluoroethylene into a vessel alongwith soap solution. The soap solution comprises fatty acid along with a base, particularly oleic acid and KOH solution. The aqueous dispersion of polytetrafluoroethylene is then heated to between 65°C to 74°C. The process further comprises adding predetermined amount of styrene and acrylonitrile monomers along with redox initiator system while maintaining the temperature between 65°C to 74°C. The aforesaid steps complete the step of providing the initial feed.

After this, the remaining predetermined amount of monomers and redox initiator system is added to the reactor vessel while maintaining the temperature between 65°C to 74°Cin a duration of 1 to 2 hours with air purging. This completes the step of providing a subsequent feed comprising a styrene monomer, acrylonitrile monomer and redox initiator system.

The details of the compositions of the present invention prepared by the process of the present invention are as follows:

Examples 1 2
Initial Charge pbw pbw
PTFE 50 60
Styrene 4.2 4
Acrylonitrile 2.3 1.6
Initial Soap Feed (Oleic Acid + KOH) 0.65 0.25
Redox Initiator System:-
Chelating agent (EDTA) 0.0021 0.0015
Reducing agent(SFS) 0.02 0.029
Oxidizing agent (Cumenehydro peroxide) 0.18 0.15
(Chain-transfer agent) (TDDM) 0.018 0.012
FeSO4 solution 0.000025 0.000021

Subsequent feed
Styrene 28 22
Acrylonitrile 7.8 11.3
Redox Initiator System:-
Chelating agent (EDTA) 1.2 1.1
Reducing agent(SFS) 0.7 0.3
Oxidizing agent (Cumenehydro peroxide) 0.12 0.18
(Chain-transfer agent) TDDM 0.07 0.03
FeSO4 solution 0.0004 0.0006
Residual content (ppm) <20 <20
Flowability (g/min) 571 628
Bulk Density (lbs/ft3) 28 28
*pbw- parts by weight

The above exemplified compositions of the present invention prepared by the process of the invention were assessed for their viscosity to infer their anti-dripping property when used as an anti-drip additive for electrical & electronic applications.

Rheology data
PE + 1.5% Anti-dripping agent PE PE + Example 1 PE + Example 2
Apparent Viscosity (poise) 4583 5637.09 6141.22

*Anti-dripping agent = Styrene-acrylonitrile encapsulated Polytetrafluoroethylene
*PE = Polyethylene
According to the results in above table, apparent viscosity increases after the addition of an anti-dripping agent synthesized with different examples. The formation of PTFE fibrils increases the apparent viscosity, indicating and assuming that drips decrease. This is a proven mechanism for increasing apparent viscosity and decreasing drip properties.

A comparator composition was prepared as per the commonly used process wherein initial feed including a PTFE dispersion, water, tertiary-dodecyl mercaptan (TDDM), and tallow-fatty acid soap were heated to 54.4°C before the addition of monomer (styrene). The mixture was pre-conditioned for at least 15 minutes before adding the continuous feed comprising the remaining amount of acrylonitrile and styrene monomers and the redox initiator system [0.3 parts cumene hydroperoxide CHP, 0.003 parts ferrous sulfate, 0.03 parts tetrasodium pyrophosphate TSPP, and 0.375 parts reducing sugar fructose] were added via a continuous feed as the temperature was raised to 65.6°C at the midpoint for 1.5 hours. The TSAN resin was obtained by coagulating the latex in hot water and sulfuric acid H2S04 as a coagulant at about 93.3° C. The resultant slurry was then centrifuged to separate water and the resulting wet resin was dried to less than 0.5 wt. % moisture content. The properties of the resulting resin were assessed for residual content, flowability, and bulk density.

The properties of the compositions of present invention and the comparator example were assessed and compared for residual content, flowability, and bulk density. The results were as follows:
Properties Examples comparison with Comparative Example
1 2 Comparative Example
Residual content (ppm) <20 <20 Max 240
Flowability (g/min) 571 628 528
Bulk Density lbs/ft3 28 28 24.3

Above table illustrates that Example 1& Example 2 have better flowability compared with comparative example. The residual content in Examples 1 and 2 is also significantly lower than in comparative example.

While certain present preferred embodiments of the invention have been illustrated and described herein, it is to be understood that the invention is not limited thereto. Clearly, the invention may be otherwise variously embodied, and practiced.
,CLAIMS:We claim:

1. A process for preparation of styrene-acrylonitrile encapsulated polytetrafluoroethylene comprising providing an initial feed comprising reagent, monomers and redox initiator system; and a subsequent feed comprising a remaining quantity of the monomers and redox initiator system.

2. The process as claimed in claim 1, wherein the process comprises additionally providing air purging after charging the reaction vessel with subsequent feed.

3. The process as claimed in claim 1, wherein the reagent comprises polytetrafluoroethylene and soap solution comprising fatty acid or derivative thereof along with a base solution.

4. The process as claimed in claim 1, wherein the process comprises adding initial feed comprising reagent, monomer, and redox initiator system to the reaction vessel, wherein the reagent is heated to appropriate temperature before adding monomers and redox initiator system.

5. The process as claimed in claim 1, wherein the process comprises charging the reaction vessel with subsequent feed comprising remaining predetermined amount of monomers, redox initiator system while appropriate temperature is maintained.

6. The process as claimed in claim 4 and 5, wherein the appropriate temperature maintained during charging of subsequent feed is same as the final appropriate temperature of the initial feed.

7. The process as claimed in claims4 to 6, wherein the appropriate temperature is between 65.0°C and 74.0°C.

8. The process as claimed in claim 1, wherein the process comprises (a) providing an initial feed comprising reagents, styrene monomer, acrylonitrile monomer, and redox initiator system and (b) providing a subsequent feed comprising a styrene monomer, acrylonitrile monomer and redox initiator system.

9. The process as claimed in claim 1, wherein the initial feed comprises 30 to 70 parts by weight of polytetrafluoroethylene, comprises 1 to 10 parts by weight of the styrene monomer and acrylonitrile monomer, 0.1 to 2.0 parts by weight of the redox initiator system, soap solution in less than 0.8 parts by weight, 0.01 to 1.0 parts by weight of additional reducing agent, 0.001 to 0.15 parts by weight of a chelating agent, and optionally 0.01 to 0.5 parts by weight of a chain transfer agent.

10. The process as claimed in claim 9, wherein the initial feed comprises 50 to 60 parts by weight of polytetrafluoroethylene, 3 to 8 parts by weight of the styrene monomer and acrylonitrile monomer, 0.15 to 0.3parts by weight of the redox initiator system, soap solution in 0.1 to 0.7 parts by weight, 0.02 to 0.03 parts by weight of additional reducing agent, 0.0015 to 0.023 parts by weight of a chelating agent, and optionally 0.01 to 0.02 parts by weight of a chain transfer agent.

11. The process as claimed in claim 9, wherein the soap solution comprises of fatty acid or derivative thereof and base, wherein the fatty acid or derivative thereof is selected from a group comprising saturated and unsaturated fatty acids and the base is selected from a group comprising KOH & NaOH.

12. The process as claimed in claim 11, wherein the soap solution comprises oleic acid and KOH (potassium hydroxide).

13. The process as claimed in claim 1, wherein the redox initiator system comprises oxidizing agent, reducing agent, additional reducing agent, chelating agent, and optionally chain transfer agent.

14. The process as claimed in claim 1, wherein the subsequent feed comprises 20 to 30 parts by weight of styrene monomer and 5 to 15 parts by weight of acrylonitrile monomer, 1 to 3 parts by weight of the redox initiator system, 0.1 to 1 parts by weight of an additional reducing agent, 0.5 to 1.5 parts by weight of a chelating agent, 0.01 to 0.1 parts by weight of a chain transfer agent.

15. The process as claimed in claim 9 and 14, wherein the additional reducing agent is selected from a group comprising sodium hydroxymethanesulfinatedihydrate, sodium borohydride, sodium hydroxymethylsulfinate and sodium citrate.

16. The process as claimed in claim 9 and 14, wherein the chelating agent is selected from a group comprising ethylenediamine tetra acetic acid (EDTA), Porphine and Dimercaprol (2,3-dimercapto-1-propanol).

17. The process as claimed in claim 9 and 14, wherein the chain transfer agent is selected from C9-C13 alkyl mercaptan compounds, particularly tertiary-dodecyl mercaptan (TDDM) or nonyl mercaptan.

18. The process as claimed in claim 1, wherein the process comprises introducing the subsequent feed into the initial feed over a time period of 1 to 2 hours.

19. The process as claimed in claim 1, wherein the process further comprises adding an aqueous coagulant salt solution in cold condition to the reaction mixture to produce a slurry comprising styrene-acrylonitrile encapsulated polytetrafluoroethylene.

20. The process as claimed in claim 20, wherein the aqueous coagulant salt solution comprises a mixture of water and ammonium chloride.

21. The process as claimed in claim 1, wherein the process comprises removing the styrene-acrylonitrile encapsulated polytetrafluoroethylene from the slurry, followed by washing and drying the styrene-acrylonitrile encapsulated polytetrafluoroethylene.