A process for preparation of an acrylonitrile-butadiene-styrene graft copolymer and preparation of a molding composition thereof

Abstract

The present invention relates to a process for preparation of an ABS graft copolymer. The process comprises (i) grafting a butadiene latex with a gel content in a range from 75% to 90% with a first portion of acrylonitrile and styrene monomers in a percentage ratio in a range from 1.4 to 1.6, in presence of an initiator- 1 and a molecular weight regulator, carrying out the polymerization for 0.5 hours to 1.5 hours, (ii) adding a second portion of acrylonitrile and styrene, additional initiator- 1 and molecular weight regulator to step (i), and continuing polymerization for 3 hours to 5 hours, and (iii) additionally adding the initiator- 1 or an initiator-2 to step (ii), and continuing polymerization for 1 hour to 2 hours. The feeding pattern of monomers in the process provides a high polymerization rate and thereby reduces residual monomer content.

Description

[0001] A PROCESS FOR PREPARATION OF AN ACRYLONITRILE- BUTADIENE-STYRENE GRAFT COPOLYMER AND PREPARATION OF A MOLDING COMPOSITION THEREOF

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to a process for the preparation of acrylonitrile - butadiene-styrene (ABS) graft copolymer. The present invention further provides a process for preparation of a thermoplastic molding composition comprising the ABS graft copolymer.

[0004] BACKGROUND OF THE INVENTION

[0005] ABS is a versatile polymer that is widely accepted by automotive and white goods industries. ABS is a preferred thermoplastic for many applications due to its superior mechanical properties like impact strength combined with good surface finish and dimensional stability of the molded articles. However, the performance requirements for diverse applications can be extensively different. While designing recipes of compositions, a high level of understanding is required of the performance and processing requirements of the intermediate and end use customers.

[0006] The graft rubber is the component of ABS which gives superior impact strength to the resin. Most of the manufacturers worldwide follow emulsion polymerization technique to produce graft rubber powder.

[0007] Reference is herein made to below patent publications that describe a process for preparation of ABS polymers.

[0008] WO2018 / 084436 describes a process using dimer acid salts as emulsifiers in place of fatty acids.

[0009] EP3626754 describes a process that involves two grafting steps.

[0010] US 2003036586 describes a process using a mix of three different particle sizes of latex. KR102157627B1 describes aprocess where grafting is carried out in absence of an emulsifier for high rate polymerization.

[0011] KR101401098 describes a process of grafting where a cross linking agent is added to achieve a better graft ratio.

[0012] WO 2022 / 074101 describes a process for preparation of latex having high gel content and a process for preparation of ABS graft rubber copolymer using the high gel content latex.

[0013] WO 1998 / 020057 describes aprocess of grafting using rubber latex having high gel content (90% to 100%) and containing a mixture of two or more rubber lattices having different particle sizes.

[0014] The abovementioned references do not describe a process for preparation of ABS graft copolymer that provides an ABS graft copolymer having reduced residual monomer content. Hence, there remains a need to provide a process that provides ABS graft copolymer with reduced residual monomer content. The reduced residual monomer content will not only ensure high polymerization rate and improved conversion but also reduce the complications of waste water treatment.

[0015] SUMMARY OF THE INVENTION

[0016] In an aspect, the present invention provides a process for preparation of an ABS graft copolymer, the process comprises:

[0017] (i) grafting a butadiene latex with a gel content in a range from 75% to 90% with a first portion of acrylonitrile and styrene monomers in a percentage ratio in a range from 1.4 to 1.6, in presence of an initiator- 1 and a molecular weight regulator, carrying out the polymerization for 0.5 hours to 1.5 hours, (ii) adding a second portion of acrylonitrile and styrene, additional initiator- 1, and molecular weight regulator to step (i), and continuing polymerization for 3 hours to 5 hours, and

[0018] (iii) additionally adding the initiator- 1 or an initiator-2 to step (ii), and continuing polymerization for 1 hour to 2 hours.

[0019] DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention provides a process for preparation of acrylonitrile-butadiene- styrene (ABS) graft copolymer, the process comprises: i. grafting a butadiene latex with a gel content in a range from 75% to 90% with a first portion of acrylonitrile and styrene monomers in a percentage ratio in a range from 1.4 to 1.6, in presence of an initiator- 1 and a molecular weight regulator, carrying out the polymerization for 0.5 hours to 1.5 hours, ii . adding a second portion of acrylonitrile and styrene, additional initiator- 1 , and molecular weight regulator to step (i), and continuing polymerization for 3 hours to 5 hours, and iii. additionally adding the initiator- 1 or an initiator-2 to step (ii), and continuing polymerization for 1 hour to 2 hours.

[0021] The monomers, styrene and acrylonitrile, are present in the process in a weight ratio in a range from 95:5 to 50:50. Preferably, styrene and acrylonitrile monomers are present in a weight ratio in a range from 80:20 to 70:30.

[0022] The process comprises acrylonitrile monomer in a range from 9.12 parts by weight to 11.4 parts by weight and the styrene monomer in a range from 26.6 parts by weight to 28.9 parts by weight.

[0023] Alternatively, styrene and / or acrylonitrile monomers may be replaced wholly or partially with copolymerizable monomers such as alpha-methyl styrene, methyl methacrylate, maleic anhydride, or N-phenyl maleimide. The initiator-1 employed in the process comprises 0.07 parts by weight to 0.25 parts by weight of one or more of hydrogen peroxide, di-tert-butyl hydroperoxide, cumene hydroperoxide, dicyclohexyl percarbonate, tert-butyl peroxide, p-methane hydroperoxide, 0.08 parts by weight to 0.39 parts by weight of dextrose, 0.0025 parts by weight to 0.007 parts by weight of ferrous sulfate or ferrous sulphide, 0.08 parts by weight to 0.28 parts by weight of tetrasodium pyrophosphate, or a mixture thereof.

[0024] The molecular weight regulator comprises less than 0.3 parts by weight of an alkyl mercaptan selected from n-dodecyl mercaptan or tert-dodecyl mercaptan, dimeric alpha-methyl-styrene, terpinols, or a mixture thereof. Preferably, the molecular weight regulator is tert-dodecyl mercaptan. Preferably, the molecular weight regulator is present in the process in a range from 0.15 parts by weight to 0.26 parts by weight.

[0025] Step (i) of the process is termed as ‘slug feeding’. The butadiene latex in step (i) is present in a range from 20 parts by weight to 80 parts by weight. Preferably, the butadiene latex in step (i) is present in a range from 40 parts by weight to 70 parts by weight. Preferably, the butadiene latex is an agglomerated butadiene latex having a particle size Dwin a range from 250 nm to 750 nm. More preferably, the process in step (i) comprises the agglomerated butadiene latex having unimodal particle size distribution.

[0026] The process in step (i) has a higher percentage of acrylonitrile monomer than styrene monomer in the first portion. Preferably, the first portion comprises acrylonitrile monomer in a range from 40% to 50% and styrene monomer in a range from 25% to 35% based on the total respective monomer content.

[0027] The higher amount of acrylonitrile monomer in step (i) results in a high polymerization rate and an improved conversion of the monomer in the polymerization system and thereby reduces the residual monomers present in the system after completion of the polymerization and thus, provides the graft copolymer with low volatile matter. Further, the higher polymerization rate optimizes the copolymer formation thereby, creating a graft shell with higher acrylonitrile (AN) content and uniform characteristics and thus, leads to improved mechanical properties of the thermoplastic molding composition.

[0028] The initiator-1 included in step (i) comprises 0.01 parts by weight to 0.06 parts by weight of one or more of hydrogen peroxide, di -tert-butyl hydroperoxide, cumene hydroperoxide, dicyclohexyl percarbonate, tert-butyl peroxide, p-methane hydroperoxide, 0.05 parts by weight to 0.3 parts by weight of dextrose, 0.002 parts by weight to 0.004 parts by weight of ferrous sulfate or ferrous sulphide, and 0.05 parts by weight to 0.2 parts by weight of tetrasodium pyrophosphate. The content of initiator- 1 added in step (i) is 20% to 45% by weight based on the total initiator- 1 used in the process.

[0029] Preferably, the initiator- 1 included in step (i) is a redox initiator system comprising 0.03 parts by weight to 0.05 parts by weight of cumene hydroperoxide, 0.1 parts by weight to 0.2 parts by weight of dextrose, 0.0025 parts by weight to 0.0037 parts by weight of ferrous sulfate or ferrous sulphide, and 0.1 parts by weight to 0.15 parts by weight of tetrasodium pyrophosphate.

[0030] The process in step (i) comprises less than 0.1 parts by weight of the molecular weight regulator. Preferably, step (i) of the process has the molecular weight regulator in a range from 0.03 parts by weight to 0.08 parts by weight.

[0031] The inclusion of the molecular weight regulator in this range provides an increased molecular weight of the grafted styrene-acrylonitrile (SAN) shell on the butadiene core. The increased molecular weight of graft shell induces an improved compatibility of impact modifier and the matrix polymer which will in turn cause better load transfer in the system leading to enhanced mechanical properties. Additionally, step (i) comprises one or more emulsifiers selected from alkyl sulphates, alkyl sulfonates, aralkyl sulfonates, soaps of saturated or unsaturated fatty acids, resin acid-based emulsifiers, tall resin based emulsifiers, or a mixture thereof. Preferably, the emulsifiers are resin acid-based emulsifiers or tall resinbased emulsifiers.

[0032] Post feeding, polymerization in step (i) is carried out for 0.5 hours to 1.5 hours and the polymerization system is kept under stirring. Preferably, the polymerization is carried out for 1 hour.

[0033] After polymerization in step (i), the process in step (ii) comprises addition of the second portion of acrylonitrile and styrene monomers, i.e., remaining amount based on the total respective monomer content, to the mixture in step (i). The second portion comprises acrylonitrile monomer in a range from 50% to 60% and styrene monomer in a range from 65% to 75% based on the total respective monomer content.

[0034] Step (ii) of the process is termed ‘incremental feeding’ where the second portion of acrylonitrile and styrene monomers is fed continuously to step (i). In step (ii), an additional amount of the initiator- 1 and molecular weight regulator is also added. The polymerization is continued in step (ii). Step (ii) of the process is completed within 5 hours.

[0035] The initiator-1 in step (ii) comprises 0.05 parts by weight to 0.12 parts by weight of one or more of hydrogen peroxide, di-tert-butyl hydroperoxide, cumene hydroperoxide, dicyclohexyl percarbonate, tert-butyl peroxide, p-methane hydroperoxide. Preferably, the initiator- 1 in step (ii) comprises 0.06 parts by weight to 0. 10 parts by weight of cumene hydroperoxide. The process in step (ii) comprises less than 0.2 parts by weight of the molecular weight regulator as defined in preceding paragraphs. Preferably, step (ii) of the process comprises 0.12 parts by weight to 0.18 parts by weight of the molecular weight regulator.

[0036] After step (ii), the process in step (iii) comprises further addition of the initiator- 1 or an initiator-2 to step (ii) and continuing polymerization for 1 to 2 hours, preferably for 1.5 hours.

[0037] Step (iii) of the process is termed as ‘boost feeding’. This step ensures that all available monomers take part in polymerisation reaction and thus, helps to achieve a maximum conversion.

[0038] The initiator- 1 in step (iii) comprises 0.01 parts by weight to 0.07 parts by weight of one or more of hydrogen peroxide, di-tert-butyl hydroperoxide, cumene hydroperoxide, dicyclohexyl percarbonate, tert-butyl peroxide, p-methane hydroperoxide, 0.03 parts by weight to 0.09 parts by weight of dextrose, 0.0005 parts by weight to 0.003 parts by weight of ferrous sulfate or ferrous sulphide and 0.03 parts by weight to 0.08 parts by weight of tetrasodium pyrophosphate.

[0039] Preferably, the initiator- 1 used in step (iii) is a redox initiator system comprising 0.01 parts by weight to 0.05 parts by weight of cumene hydroperoxide, 0.04 parts by weight to 0.08 parts by weight of dextrose, 0.001 parts by weight to 0.0025 parts by weight of ferrous sulfate or ferrous sulphide and 0.04 parts by weight to 0.07 parts by weight of tetrasodium pyrophosphate.

[0040] The initiator-2 in step (iii) is a water-soluble inorganic compound, particularly an inorganic per-salt, more particularly an alkali persulfate such as potassium persulphate (KPS). The initiator-2 is added in a range from 0.01 parts by weight to 1 part by weight. Preferably, the initiator-2 is added in a range from 0.025 parts by weight to 0.075 parts by weight. The advantage of employing initiator-2 is that its reactivity and decomposition rate are higher than initiator- 1, such as cumene hydroperoxide, which improves the conversion and further reduces the residual monomer content. Additionally, the initiator-2 in the boost feeding step does not impact cross-linking related mechanical property reduction.

[0041] The process of the present invention is an emulsion polymerization process carried out at a temperature in a range from 60°C to 75°C. Preferably, the emulsion polymerization process is carried out at a temperature of 68°C.

[0042] The process further comprises recovering the graft copolymer from the polymerization system. The recovery is carried out by commonly known procedures such as coagulation with salts, e.g., Epsom salt and / or acids, washing, drying or spray drying to obtain an ABS graft copolymer powder.

[0043] Further, the present invention provides a process for preparation of a thermoplastic molding composition. The process comprises preparing a premix comprising 15% to 50% by weight of the ABS graft copolymer, 50% to 85% by weight of a copolymer of styrene and acrylonitrile with an acrylonitrile content in a range from 20% to 35%, and 2% to 3% by weight of an additive selected from one or more of a lubricant, an antioxidant, a co-stabilizer, a processing aid and an acid scavenger; and melt extruding the premix at a temperature in a range from 190°C to 220°C.

[0044] The copolymer of styrene and acrylonitrile has molecular weight in a range from 90,000 to 2,50,000 g / mol and a melt flow index (MFI) in range from 5 to 75 g / lOmin at 220°C / 10kg.

[0045] The lubricants / glidants are employed as mould release agents and are preferably selected from amide waxes such as ethylene bis-stearamide and salt of fatty acids such as magnesium stearate. Alternative for ethylene bis-stearamide comprises long-chain fatty acids containing 12 to 30 carbon atoms selected from stearic acid, and their corresponding fatty acid mixtures, derivatives such as stearic esters, fatty alcohol selected from stearyl alcohol and polyolefin waxes.

[0046] Alternatively, magnesium stearate may be replaced with long-chain fatty acids such as stearic acid or behenic acid, their salts such as calcium or zinc, or their esters such as stearyl stearate or pentaerythrityl tetra stearate.

[0047] The antioxidants include antioxidants-based heat stabilizer and are selected from halides of the metals from group I of the periodic table, such as sodium, potassium and / or lithium halides, sterically hindered phenols selected from but not limited to Pentaerythritol tetrakis (3 -(3 , 5 -di-tert-butyl-4-hydroxyphenyl)propionate) ,

[0048] Octadecyl 3 -(3 ,5 -di-tert-butyl-4-hydroxyphenyl)propionate, 1 ,3 ,5 -Tris(3 ,5 -di-tert- butyl-4-hydroxybenzyl)-l, 3, 5-triazinane-2, 4, 6-trione, Octyl-3,5-di-tert-butyl-4- hydroxy-hydrocinnamate, Triethylene glycol bis(3-tert-butyl-4-hydroxy-5- methylphenyl)propionate, 2,2'-Methylenebis(4-methyl-6-tert-butylphenol) etc., substituted hydroquinone such as tert-butyl hydroxyquinone (TBHQ), or a mixture thereof. In addition to the phenolic antioxidants, co-stabilizers, in particular phosphorus- or sulfur-containing co-stabilizers can be employed. Preferably the antioxidant is distearyl pentaerythritol diphosphite.

[0049] The processing aid is selected from silicon oil, mineral oil, or a combination thereof. Preferably, the processing aid is silicon oil.

[0050] The acid scavengers are selected from magnesium oxide, metal stearate, zinc oxide (ZnO), or a combination thereof. Preferably, the acid scavenger is magnesium oxide.

[0051] Additionally, the thermoplastic molding composition may comprise other additives selected from UV stabilizers, fillers, dyes, and pigments. Examples

[0052] Example 1: Preparation of butadiene latex with gel content of 78.8%

[0053] Butadiene latex was prepared by the process described in W02022074101 wherein, the butadiene is polymerized with 10% wt. styrene (vinyl aromatic monomers) by emulsion polymerisation to obtain butadiene latex.

[0054] The latex thus obtained was agglomerated with an acid anhydride as per process described in WO 2012 / 022710 and WO 2014 / 170406 to obtain an agglomerated butadiene latex.

[0055] The particle size of the agglomerated butadiene latex was in a range from 250 nm to 750 nm.

[0056] Example 2: Preparation of butadiene latex with gel content of 81%

[0057] The procedure used for preparing the butadiene latex was the same as described in Example 1.

[0058] Comparative Example A: Butadiene latex with gel content of 91%

[0059] The procedure used for preparing the butadiene latex was the same as described in Example 1.

[0060] Example 3: Preparation of ABS graft copolymer

[0061] ABS graft copolymer was prepared as per the graft recipe described in Table 1. Table 1

[0062] *Butadiene latex prepared in Example 1 was used in Control, Samples 1 and 2; Butadiene latex prepared in Example 2 was used in Comparative Examples B and C; Butadiene latex prepared in Comparative Example A was used in Comparative Example D.

[0063] The monomers described in Table 1 were added in three steps (slug feeding, incremental feeding, and boost feeding) to the polymerization system as shown in Table 2, for preparation of the ABS graft copolymer. Table 2

[0064] Samples 1 and 2 were prepared as per the process of the present invention, acrylonitrile and styrene in the slug feeding step were present in a percentage ratio of 1.5. The process for preparation of Samples 1 and 2 was different in the boost feeding. Sample 1 contained the initiator- 1, a redox initiator system, whereas Sample 2 contained the initiator-2, potassium persulphate.

[0065] The Control and Comparative Example D contained acrylonitrile and styrene in slug feeding step in a percentage ratio of 1 : 1.

[0066] The Comparative Example B contained acrylonitrile and styrene in slug feeding step in a percentage ratio of 1.37.

[0067] The Comparative Example C contained acrylonitrile and styrene in slug feeding step in a percentage ratio of 1.62.

[0068] Procedure for preparation: In step (i) (slug feeding), the reactor system comprising 62 parts by weight of the agglomerated butadiene latex was flooded with a first portion of acrylonitrile and styrene monomers. Further, the initiator- 1, molecular weight regulators and emulsifiers were added to the reactor system. The polymerization was continued for 1 hour at a temperature of 68°C, and the polymerization system was kept under stirring.

[0069] In step (ii) (incremental feeding), a second portion comprising acrylonitrile monomer and styrene monomer was fed continuously to the polymerization system following step (i). Further, an additional amount of the initiator- 1 and molecular weight regulator was added in step (ii), and polymerization was continued for a minimum of 3 hours at a temperature of 68°C.

[0070] In step (iii) (boost feeding), initiator- 1 or initiator-2 was added to the polymerization system following step (ii), and polymerization was further continued for 1.5 hours at a temperature of 68°C. The polymerization process achieved a conversion of 97% to 99%, which was confirmed by checking the total solid content (TSC).

[0071] After the polymerization, the graft copolymer was coagulated with salts, e .g . Epsom salt and / or acids, washed, and dried or spray dried to obtain a uniform powder of the said copolymer.

[0072] Example 4: Analysis of residual monomer content of ABS graft copolymer

[0073] ABS graft polymer prepared in Example 3 was analysed for the residual monomer using a gas chromatograph with flame ionization detector (FID) of Perkin Elmer, USA., by a method similar to ASTM D5508. Table 3 demonstrates the residual monomer content of the Control, Samples 1 and 2, and Comparative Examples B to D.

[0074] Table 3

[0075] Table 3 shows that the residual monomer content for Samples 1 and 2 prepared by the process as per the present invention was significantly lower than the Control and Comparative Examples B to D. This shows that the process of the present invention, by using butadiene latex with a gel content in range from 75% to 90% along with acrylonitrile and styrene monomers in a percentage ratio in a range from 1.4 to 1.6 in step (i) provided higher conversion of all available monomers in the polymerisation process thus, resulting in reduced residual monomer content. Example 5: Synthesis of thermoplastic molding compositions

[0076] Thermoplastic molding compositions were prepared as per the recipe shown in Table 4 and Table 5

[0077] Table 4- Compound Set- 1

[0078] Table 5- Compound Set-2 ABS graft powder (Ingredient A) prepared in Example 3 was used in the compound sets that was prepared with a weight average particle size Dwof the agglomerated butadiene rubber latex (A) in a range from 250 nm to 750 nm. The variants Al to A6 correspond to Control, Sample 1, Sample 2, Comparative Example B, Comparative Example C, and Comparative Example D, respectively.

[0079] Ingredient Bl (compound set 1, Table 4) was a copolymer of styrene and acrylonitrile. It had MFI of 65 g / 10 min at 220°C / 10kg and ‘AN’ content of 27%. The weight average molar mass Mwof copolymer (B) generally was 112,000 g / mol.

[0080] Ingredient B2 (compound set 2, Table 5) was a copolymer of styrene and acrylonitrile. It had MFI of 30 g / 10 min at 220°C / 10kg and AN content of 30%. The weight average molar mass Mwof copolymer (B) generally is 125,000 g / mol.

[0081] C-l - Primary lubricant for ABS (Ethylene bis-stearamide with trade name ‘Palmowax’ obtained from PALMAMIDE SDN BHD),

[0082] C-2 - SPEP (Distearyl pentaerythritol diphosphite, a phosphorous-based primary antioxidant, procured from Addivant),

[0083] C-3 - Silicon oil as a process aid, obtained from KK Chempro India Pvt Ltd, C-4 - Magnesium Stearate as a secondary lubricant, from Sunshine organics, C-5 - Metal oxide as an acid scavenger, received from Kyowa Chemicals.

[0084] Compounding of the ABS powder obtained in Example 3 with SAN along with other additives was carried out in twin screw extruders. SAN in the form of granules, ABS powder and other additives were measured and mixed in the highspeed mixture for 2 minutes to attain good dispersion and create uniform premix for compounding. Then it was extruded through twin screw extruder. The premix was melt blended at a screw speed of 80 rpm using an incremental temperature profile from 190°C to 220°C for the different barrel zones. The extruded strands were water cooled, air-dried, and pelletized. The batch size for all the compounding and extrusion trials was 6 kg. This was followed by injection moulding of this blend to mould the standard test specimens. The temperature profile of injection moulding machine barrel was an incremental temperature profile from 190°C to 240°C. Injection moulding was done, and test specimens were prepared for mechanical testing.

[0085] Example 6: Evaluation of specimen made from thermoplastic molding composition prepared in Example 5.

[0086] The specimen made from thermoplastic molding composition prepared in Example 5 was investigated fortheir mechanical properties as below.

[0087] Melt Flow Index

[0088] Melt Flow Index test was performed for ABS pellets (ASTM D 1238) using an MFI machine of CEAST, Italy.

[0089] Impact test

[0090] Izod impact tests were performed on molded and notched specimens (ASTM D 256) using a CEAST Italy instrument.

[0091] Tensile test

[0092] Tensile test (ASTM D 638) was carried out at room temperature using Instron, UK UTM.

[0093] Flexural test

[0094] The Flexural test was carried (ASTM D 790) at room temperature using the Lloyd, UK UTM.

[0095] Gloss

[0096] Gloss (ASTM D 523) was measured using BYK Gardner, Germany.

[0097] The results are tabulated in Tables 6 and 7. Table 6: Properties of ABS moulding compound set-1. Table 7: Properties of ABS molding compound set- 2 Table 6 show that the specimens made from thermoplastic composition of Samples 3 and 4 of the present invention had higher impact strength than Control and Comparative Examples E to G. Similarly, Table 7 show that the specimens made from thermoplastic composition of Samples 5 and 6 of the present invention had higher impact strength than Control and Comparative Examples H to J. Thus, the process of the present invention provided a thermoplastic composition having reduced residual monomer content while also achieving better mechanical properties.

[0098] The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to a person skilled in the art, the invention should be construed to include everything within the scope of the disclosure.

Claims

AMENDED CLAIMS received by the International Bureau on 13 April 2026 (13.04.2026)Claims :

1. A process for preparation of an acrylonitrile-butadiene-styrene (AB S) graft copolymer, the process comprising: i. grafting a butadiene latex with a gel content in a range from 75% to 90% with a first portion of acrylonitrile and styrene monomers comprising acrylonitrile monomer in a range from 40% to 50% based on the total content of acrylonitrile monomer and percentage ratio of acrylonitrile to styrene monomers is in a range from 1.4 to 1.6, in presence of an initiator- 1 and a molecular weight regulator, carrying out the polymerization for 0.5 hours to 1.5 hours, ii. adding a second portion of acrylonitrile and styrene, additional initiator- 1, and molecular weight regulator, to step (i), and continuing polymerization for 3 hours to 5 hours, and iii. additionally adding the initiator- 1 or an initiator-2 to step (ii), and continuing polymerization for 1 hour to 2 hours.

2. The process as claimed in claim 1, wherein the process comprises the acrylonitrile monomer in a range from 9.12 parts by weight to 11.4 parts by weight, the styrene monomer in a range from 26.6 parts by weight to 28.9 parts by weight, the initiator-1 comprises 0.07 parts by weight to 0.25 parts by weight of one or more of hydrogen peroxide, di-tert-butyl hydroperoxide, cumene hydroperoxide, dicyclohexyl percarbonate, tert-butyl peroxide, p-methane hydroperoxide, 0.08 parts by weight to 0.39 parts by weight of dextrose, 0.0025 parts by weight to 0.007 parts by weight of ferrous sulfate or ferrous sulphide and 0.08 parts by weight to 0.28 parts by weight of tetrasodium pyrophosphate, or a mixture thereof, and the molecular weight regulator comprises less than 0.3 parts by weight of an alkyl mercaptan selected from n-dodecyl mercaptan or tert-dodecyl mercaptan, dimeric alpha-methyl-styrene, terpinols, or a mixture thereof.

273. The process as claimed in claim 1 or 2, wherein step (i) comprises the butadiene latex in a range from 20 parts by weight to 80 parts by weight, and the butadiene latex is an agglomerated butadiene latex having a particle size in a range from 250 nm to 750 nm, the first portion of acrylonitrile and styrene monomer comprises styrene monomer in a range from 25% to 35% based on the total styrene monomer content, the initiator-1 comprises 0.01 parts by weight to 0.06 parts by weight of one or more of hydrogen peroxide, di-tert-butyl hydroperoxide, cumene hydroperoxide, dicyclohexyl percarbonate, tert-butyl peroxide, p-methane hydroperoxide, 0.05 parts by weight to 0.3 parts by weight of dextrose, 0.002 parts by weight to 0.004 parts by weight of ferrous sulfate or ferrous sulphide, and 0.05 parts by weight to 0.2 parts by weight of tetrasodium pyrophosphate, and the molecular weight regulator is present in an amount of less than 0.1 parts by weight.

4. The process as claimed in claim 1 or 2, wherein step (ii) comprises the second portion of acrylonitrile and styrene monomer with acrylonitrile monomer in a range from 50% to 60% and styrene monomer in a range from 65% to 75% based on the total respective monomer content, the initiator-1 comprises 0.05 parts by weight to 0.12 parts by weight of one or more of hydrogen peroxide, di-tert-butyl hydroperoxide, cumene hydroperoxide, dicyclohexyl percarbonate, tert-butyl peroxide, p-methane hydroperoxide, and the molecular weight regulator is present in an amount of less than 0.2 parts by weight.

5. The process as claimed in claim 1, wherein in step (ii) comprises continuously feeding the second portion of acrylonitrile and styrene monomers to step (i).

6. The process as claimed in claim 1, wherein the monomers styrene and acrylonitrile are present in a weight ratio in a range from 95:5 to 50:50 based on total respective monomer content.

7. The process as claimed in claim 1 or 3, wherein the initiator-1 in step (iii) comprises 0.01 parts by weight to 0.07 parts by weight of one or more of hydrogen peroxide, di-tert-butyl hydroperoxide, cumene hydroperoxide, dicyclohexyl percarbonate, tert-butyl peroxide, p-methane hydroperoxide, 0.03 parts by weight to 0.09 parts by weight of dextrose, 0.0005 parts by weight to 0.003 parts by weight of ferrous sulfate or ferrous sulphide and 0.03 parts by weight to 0.08 parts by weight of tetrasodium pyrophosphate.

8. The process as claimed in claim 1, wherein the initiator-2 in step (iii) is present in a range from 0.01 parts by weight to 1 part by weight, and is a water -soluble inorganic compound, an alkali persulfate.

9. The process as claimed in claim 1, wherein the process is an emulsion polymerization process and step (i) comprises an emulsifier selected from alkyl sulphates, alkyl sulfonates, aralkyl sulfonates, soaps of saturated or unsaturated fatty acids, resin acid-based emulsifiers, tall resin-based emulsifiers, or a mixture thereof.

10. The process as claimed in claim 1, wherein the process is carried out at a temperature of 60°C to 75°C.

11. The process as claimed in claim 1, for preparation of a thermoplastic molding composition, the process comprising: preparing a premix comprising 15% to 50% by weight of the ABS graft copolymer, 50% to 85% by weight of a copolymer of styrene and acrylonitrile with an acrylonitrile content in a range from 20% to 35%, and 2% to 3% by weightof an additive selected from one or more of a lubricant, an antioxidant, a processing aid and an acid scavenger; and melt extruding the premix at a temperature in a range from 190°C to 220°C.

12. The process as claimed in claim 11, wherein, the copolymer of styrene and acrylonitrile has a molecular weight in a range from 90,000 to 2,50,000 g / mol, the lubricant is selected from one or more of long-chain fatty acids containing 12 to 30 carbon atoms selected from stearic acid or behenic acid, and their corresponding fatty acid mixtures, their ester derivatives selected from steric esters, stearyl stearate or pentaerythrityl tetra stearate, their salts selected from calcium, magnesium or zinc stearate, fatty alcohols selected from stearyl alcohol, bisstearylamide based amide waxes -ethylene bisstearamide, polyolefin waxes, or a mixture thereof, the antioxidant is selected from halides of the metals from group I of the periodic table selected from sodium, potassium and / or lithium halides, sterically hindered phenols selected from Pentaerythritol tetrakis(3-(3,5-di- tert-butyl-4-hydroxyphenyl)propionate), Octadecyl 3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate, l,3,5-Tris(3,5-di-tert-butyl-4-hydroxybenzyl)- 1, 3, 5-triazinane-2, 4, 6-trione, Octyl-3,5-di-tert-butyl-4-hydroxy- hydrocinnamate, Triethylene glycol bis(3-tert-butyl-4-hydroxy-5- methylphenyl)propionate, 2,2'-Methylenebis(4-methyl-6-tert-butylphenol), substituted hydroquinone-tert-butyl hydroxy quinone, di stearyl pentaerythritol diphosphate, or a mixture thereof, the processing aid is selected from silicon oil, mineral oil, or a combination thereof, and the acid scavenger is selected from magnesium oxide, metal stearate, zinc oxide (ZnO), or a combination thereof.