EP4634247A1

EP4634247A1 - A process for preparing a high impact vinyl aromatic polymer

Info

Publication number: EP4634247A1
Application number: EP23817132.6A
Authority: EP
Inventors: Basavaraju KOTTAGALU CHIKKALINGAIAH; Mahesh VIRUPASANDRA SHIVARAMU; Bander Fahad M ALFARHOOD; Naif Mohammed AL-AJMI
Original assignee: SABIC Global Technologies BV
Current assignee: SABIC Global Technologies BV
Priority date: 2022-12-15
Filing date: 2023-12-01
Publication date: 2025-10-22
Also published as: CN120530149A; WO2024126090A1

Abstract

The invention relates to a process for preparing polymer such as a styrenic polymer. The process comprises the steps of: (a) obtaining a reaction mixture, comprising at least one vinyl aromatic monomer and at least one elastomeric compound; (b) heating the reaction and adding at least one initiator compound to the reaction mixture to obtain a pre-polymerization mixture; and (c) heating the pre-polymerization mixture and obtaining the polymer. The invention further relates to a polymer such as a styrenic polymer obtainable by the process of the present invention and to the use of a peroxyester in the process of the present invention for improving the Notched Izod Impact strength of the polymer.

Description

A Process for Preparing a High Impact Vinyl Aromatic Polymer

[0001] The invention relates to a process for preparing a polymer and in particular a process for preparing a high impact vinyl aromatic or styrenic polymer. The invention further relates to a polymer such as a styrenic polymer, obtainable by the process of the present invention and to the use of a peroxyester, in the process of the present invention, for improving the impact strength of a polymer.

[0002] It is well known that rubber-reinforced polymers derived from vinyl aromatic compounds, such as styrene, alpha-methyl-styrene and ring-substituted sytrenes are suitable as monomers for a variety of industrial application. For example, polybutadiene rubber-reinforced polystyrene can be used in a variety of applications including refrigerator linings, packaging applications, furniture, household appliances and toys. The conventional term for such rubber-reinforced polymers is "high impact polystyrene" or "HIPS". The physical characteristics and mechanical properties of HIPS are often dependent upon many factors such as the amount of impurities, which may be present in the starting vinyl aromatic monomer.

[0003] Styrene, for example, is often produced by the dehydrogenation of ethylbenzene (EB) and during such production, phenyl acetylene (PA) is an undesirable by-product that is formed.

Bi-products

[0004] As a result the styrene so produced, may be contaminated with phenyl acetylene (PA) and toluene as impurities. Toluene may be removed by distillation but the presence of phenyl acetylene (PA) beyond a certain limit is a concern, as phenyl acetylene (PA) can affect styrene polymerization and impede molecular weight build-up and reduce product yield. In particular, when it comes to the production of high impact polystyrene (HIPS) the presence of phenyl acetylene (PA) affects the grafting of rubber particles on polystyrene resulting in a HIPS product having low impact property. Further, when it comes to the production of HIPS, phenyl acetylene may affect the extent to which rubber particles graft onto polystyrene resulting in a HIPS product having low impact strength. In addition to impact properties, it is often desired that the polymer obtained has a suitable flow property and thermal resistivity for using such polymers in injection moulding, extrusion & thermoforming applications and often attempts to enhance impact properties of a polymer has come at the cost of sacrificing other polymer properties.

[0005] In the past, industry practitioners have relied on catalytic hydrogenation treatment of the styrene monomer, for the removal of phenyl acetylene. The treatment involves injection of hydrogen gas into the styrene monomer in presence of palladium/aluminium catalyst to convert at least a part of the phenyl acetylene to styrene. However, in the presence of hydrogen, such a process can lead to the conversion of styrene back to ethyl benzene thereby lowering the overall styrene product yield. Further, such any such process involving the purification of the vinyl aromatic monomers is a capital intensive step and results in increasing the cost of production of the final polymeric product.

[0006] Therefore, it is an object of the present invention to provide a process for the production of a polymer at high production yield, derived from a vinyl aromatic monomer without the need of removing phenyl acetylene while ensuring that the polymer so obtained has a desired impact strength, flow and thermal property. Another, objective of the present invention is to provide a polymer having sufficiently high impact, flow and thermal properties obtained from a vinyl aromatic monomer without the need of removing phenyl acetylene from such a monomer.

DESCRIPTION

[0007] Accordingly, the one or more objectives of the present invention is achieved by a process for preparing a polymer, comprising the steps of:

(a) obtaining a reaction mixture, comprising: i. at least one vinyl aromatic monomer present in an amount from > 85.0 wt.% and < 98.0 wt.% based on the total weight of the reaction mixture; and ii. at least one elastomeric compound present in an amount from > 2.0 wt.% and < 15.0 wt.% based on the total weight of the reaction mixture; (b) heating the reaction mixture to a temperature of > 50°C and adding at least one initiator compound to the reaction mixture to obtain a pre-polymerization mixture; and

(c) heating the pre-polymerization mixture at a temperature of > 100°C and < 200°C for time period of > 2.0 hours and < 10.0 hours and obtaining the polymer;

• preferably wherein the initiator compound has an active oxygen content of > 1.0 wt.% and < 8.0 wt.% based on the total weight of the initiator compound; and

• wherein if the active oxygen content of the initiator compound is > 1.0 wt.% and < 4.0 wt.% based on the total weight of the initiator compound, the amount of initiator compound added to the reaction mixture in step (b) is > 300 and < 610 parts per million by weight based on the total weight of the reaction mixture; and

• wherein if the active oxygen content of the initiator compound is > 4.0 wt.% and < 8.0 wt.% based on the total weight of the initiator compound, the amount of initiator compound added to the reaction mixture in step (b) is > 20 and < 200 parts per million by weight based on the total weight of the reaction mixture; and wherein the active oxygen content of the initiator compound is determined in accordance with ASTM D 2180- 89(2008).

[0008] Preferably the vinyl aromatic monomer has a phenyl acetylene content of > 10 and < 150, preferably > 80 and < 110, parts per million by weight based on the total weight of the vinyl aromatic monomer.

[0009] Preferably the process for preparing the polymer, comprises the steps of:

(a) obtaining the reaction mixture, comprising: i. at least one vinyl aromatic monomer present in an amount from > 85.0 wt.% and < 98.0 wt.% based on the total weight of the reaction mixture; and ii. at least one elastomeric compound present in an amount from > 2.0 wt.% and < 15.0 wt.% based on the total weight of the reaction mixture;

(b) heating the reaction mixture to a temperature of > 50°C and adding at least one initiator compound to the reaction mixture to obtain the pre-polymerization mixture; and

• wherein the initiator compound has an active oxygen content of > 1.0 wt.% and < 8.0 wt.% based on the total weight of the initiator compound; and • wherein if the active oxygen content of the initiator compound is > 1.0 wt.% and < 4.0 wt.% based on the total weight of the initiator compound, the amount of initiator compound added to the reaction mixture in step (b) is > 300 and < 610 parts per million by weight based on the total weight of the reaction mixture; and

[0010] Preferably, wherein the polymer is a styrenic polymer, preferably wherein the polymer is polystyrene. More preferably the polymer is a high impact polystyrene (HIPS).

[0011] The inventors found that when the process of the present invention is used for the production of a polymer, the resultant polymer obtained has a desired impact property even without purifying the starting vinyl aromatic monomer. In other words, the process of the present invention enables a skilled person to use commercially available vinyl aromatic monomer, (e.g. commercial grade styrene) having relatively high concentration of phenyl acetylene, for the production of polymers such as polystyrene or high impact polystyrene without having to purify the commercial grade monomer. Advantageously, the process of the present invention helps in optimizing operating costs and renders the process of making polymers derived from vinyl aromatic compounds more efficient.

[0012] The vinyl aromatic monomer may have a phenyl acetylene content of < 150, preferably < 120, preferably < 100 parts per million (ppm) by weight, based on the total weight of the vinyl aromatic monomer. The phenyl acetylene content may be determined using gas chromatography. Accordingly, even when the vinyl aromatic monomer has a phenyl acetylene content as high as 150 ppm by weight, the process of the present invention results in a polymer having the desired Notched Impact strength property.

[0013] Preferably, the vinyl aromatic monomer ranges has a phenyl acetylene content of > 10 ppm by weight and < 150 ppm by weight, preferably > 50 ppm by weight and < 120 ppm by weight, preferably > 50 ppm by weight and < 100 ppm by weight, based on the total weight of the vinyl aromatic monomer.

Reaction mixture

[0014] The reaction mixture may be obtained by the dissolution under agitation, at least one elastomeric compound in at least one vinyl aromatic monomer along with optional amounts of a processing aid, a mineral oil compound and one or more additives, to obtain the reaction mixture. The agitation may be carried out at stages at a rotation per minute (RPM) of > 40 and < 310, preferably > 50 and < 250.

[0015] The reaction mixture comprises:

(i) at least one vinyl aromatic monomer present in an amount from > 85.0 wt.% and < 98.0 wt.%, preferably > 87.0 wt.% and < 98.0 wt.%, preferably > 90.0 wt.% and < 95.0 wt.%, based on the total weight of the reaction mixture; and

(ii) at least one elastomeric compound present in an amount from > 2.0 wt.% and < 15.0 wt.%, preferably > 2.0 wt.% and < 13.0 wt.%, preferably > 5.0 wt.% and < 10.0 wt.%, based on the total weight of the reaction mixture.

[0016] The vinyl aromatic monomer may be selected from the group consisting of styrene, a-methyl styrene, dibromostyrene, vinyltoluene, vinylxylene, butylstyrene, p- hydroxystyrene, methoxystyrene, and any combinations thereof. Preferably the vinyl aromatic monomer is selected from styrene, a-methyl styrene, and any combinations thereof. More preferably the vinyl aromatic monomer is styrene.

[0017] The elastomeric compound may be a polymeric rubber selected from polybutadiene, an elastomeric copolymer comprising polymeric units derived from 1 ,3 butadiene and styrene, an elastomeric copolymer comprising polymeric units derived from butadiene and acrylonitrile, and an elastomeric terpolymer comprising polymeric units derived from styrene, butadiene and acrylonitrile.

[0018] Preferably the polymeric rubber is selected from polybutadiene, an elastomeric copolymer comprising polymeric units derived from 1 ,3 butadiene and styrene, an elastomeric copolymer comprising polymeric units derived from butadiene and acrylonitrile. More preferably the polymeric rubber is polybutadiene.

[0019] The reaction mixture may further comprise of at least one processing aid compound present in an amount of < 5.0 wt.%, preferably < 4.0 wt.%, based on the total weight of the reaction mixture.

[0020] Preferably, the reaction mixture comprises at least one processing aid compound present in an amount of > 0.0 and < 5.0 wt.%, preferably > 0.0 and < 4.0 wt.%, preferably > 1.0 and < 4.0 wt.%, based on the total weight of the reaction mixture. Preferably the processing aid compound is ethyl benzene. The processing aid such as ethyl benzene, functions as a diluent and helps to maintain the viscosity of the reaction mixture during the course of agitation.

[0021] The reaction mixture may further comprise at least one mineral oil compound present in an amount of < 3.0 wt.%, preferably < 2.0 wt.%, based on the total weight of the reaction mixture. Preferably, the reaction mixture comprises at least one mineral oil compound present in an amount of > 0.0 and < 3.0 wt.%, preferably > 0.0 and < 2.0 wt.%, preferably > 1.0 and < 2.0 wt.%, based on the total weight of the reaction mixture.

[0022] The mineral oil compound may be selected from paraffin oil, naphtha based hydrocarbon solvent, and petroleum based solvent. Preferably, the mineral oil compound is paraffin oil. Preferably, the mineral oil compound is petroleum based solvent. The mineral oil compound may aid in maintaining the viscosity of the reaction mixture and in addition function as an internal mold release agent during processing of the reaction mixture.

[0023] The reaction mixture may further comprise one or more additives present in an amount of < 1.0 wt.%, preferably < 0.8 wt.%, preferably < 0.1 wt.%, preferably < 0.08 wt.% based on the total weight of the reaction mixture.

[0024] Preferably, the reaction mixture comprises one or more additives present in an amount of > 0.0 and < 1.0 wt.%, preferably > 0.0 and < 0.8 wt.%, preferably > 0.01 and < 0.1 wt.%, preferably > 0.01 and < 0.08 wt.%, based on the total weight of the reaction mixture. Preferably the one or more additives are selected from anti-oxidants, UV stabilizers, color stabilizers and combinations thereof. Preferably the additive is an anti-oxidant. The anti-oxidant may aid in preventing undesirable oxidation of the elastomeric compound during the step of polymerization.

[0025] Preferably, wherein the reaction mixture comprises:

(a) at least one vinyl aromatic monomer present in an amount from > 87.0 wt.% and < 98.0 wt.%, based on the total weight of the reaction mixture;

(b) at least one elastomeric compound present in an amount from preferably > 2.0 wt.% and < 13.0 wt.%, based on the total weight of the reaction mixture;

(c) at least one processing aid compound present in an amount of preferably > 0.0 and < 4.0 wt.%, based on the total weight of the reaction mixture;

(d) at least one mineral oil compound present in an amount of > 0.0 and < 2.0 wt.% based on the total weight of the reaction mixture; and

(e) one or more additives present in an amount of > 0.0 and < 0.8 wt.%, based on the total weight of the reaction mixture.

[0026] Preferably, wherein the reaction mixture comprises:

(a) at least one vinyl aromatic monomer present in an amount of > 90.0 wt.% and < 95.0 wt.%, based on the total weight of the reaction mixture;

(b) at least one elastomeric compound present in an amount of > 2.0 wt.% and < 10.0 wt.%, based on the total weight of the reaction mixture;

(c) at least one processing aid compound present in an amount of > 1.0 and < 4.0 wt.%, based on the total weight of the reaction mixture;

(d) at least one mineral oil compound present in an amount of > 1.0 and < 2.0 wt.%, based on the total weight of the reaction mixture; and

(e) one or more additives present in an amount of > 0.01 and < 0.1 wt.%, based on the total weight of the reaction mixture.

[0027] The reaction mixture obtained after the dissolution of the elastomeric compound may be in the form of a clear solution. Thereafter, the process involves the step of, heating the reaction mixture to a temperature of > 50°C, preferably > 60°C. Preferably the process involves the step of heating the reaction mixture to any temperature of > 50°C and < 80°C, preferably to a temperature of > 50°C and < 70°C.

[0028] Subsequently, the process involves the step of adding at least one initiator compound to the reaction mixture to obtain a pre-polymerization mixture. The initiator compound is added to the reaction mixture when the temperature of the reaction mixture is > 50°C and < 80°C, preferably > 50°C and < 70°C.

Initiator Compound

[0029] The term “active oxygen content” as used throughout this disclosure means the weight percentage of active or peroxide oxygen present in the initiator compound. The active oxygen content of the initiator compound is determined in accordance with ASTM D 2180-89(2008). It is preferred that the initiator compound has an active oxygen content of > 1.0 wt.% and < 8.0 wt.% based on the total weight of the initiator compound.

[0030] The present inventors found that, depending on the active oxygen content of the initiator compound, the initiator compound may be added to the reaction mixture at a certain concentration in order to counter the effect of phenyl acetylene present in the vinyl aromatic monomer during the polymerization of the vinyl aromatic monomer.

[0031] For example, if the active oxygen content of the initiator compound is > 1.0 wt.% and < 4.0 wt.% based on the total weight of the initiator compound, the amount of initiator compound added to the reaction mixture is > 300 and < 610 parts per million (ppm) by weight, preferably > 320 and < 600 parts per million (ppm) by weight, preferably > 350 and < 550 parts per million (ppm) by weight, preferably > 380 and < 450 parts per million (ppm) by weight, preferably > 390 and < 450 parts per million (ppm) by weight, based on the total weight of the reaction mixture.

[0032] Preferably, the active oxygen content of the initiator compound is > 2.5 wt.% and < 3.9 wt.% based on the total weight of the initiator compound and the amount of initiator compound added to the reaction mixture is > 310 and < 500 parts per million (ppm) by weight, preferably > 390 and < 450 parts per million (ppm) by weight, based on the total weight of the reaction mixture. [0033] Preferably, the active oxygen content of the initiator compound is > 2.8 wt.% and

< 3.9 wt.% based on the total weight of the initiator compound and the amount of initiator compound added to the reaction mixture is > 310 and < 500 parts per million (ppm) by weight, preferably > 390 and < 450 parts per million (ppm) by weight, based on the total weight of the reaction mixture.

[0034] Preferably, the active oxygen content of the initiator compound is > 3.0 wt.% and

< 3.9 wt.% based on the total weight of the initiator compound and the amount of initiator compound added to the reaction mixture is > 380 and < 450 parts per million (ppm) by weight, preferably > 390 and < 410 parts per million (ppm) by weight, based on the total weight of the reaction mixture.

[0035] Alternatively, if the active oxygen content of the initiator compound is > 4.0 wt.% and < 8.0 wt.% based on the total weight of the initiator compound, the amount of initiator compound added to the reaction mixture may be > 20 and < 200 parts per million (ppm) by weight, preferably > 50 and < 150 parts per million (ppm) by weight, preferably > 60 and < 100 parts per million (ppm) by weight, preferably > 60 and < 80 parts per million (ppm) by weight based on the total weight of the reaction mixture.

[0036] Preferably, the active oxygen content of the initiator compound is > 5.0 wt.% and

< 6.5 wt.% based on the total weight of the initiator compound and the amount of initiator compound added to the reaction mixture is > 50 and < 80 parts per million (ppm) by weight, preferably > 60 and < 80 parts per million (ppm) by weight, based on the total weight of the reaction mixture.

[0037] The initiator compound may be added to the reaction mixture in the form a solution having 40.0 to 60.0 wt.%, preferably 50.0 wt.% of the initiator compound. The solvent used may be any suitable inert hydrocarbon solvent such as paraffin oil, petroleum based oil, and naphtha based hydrocarbon solvent.

[0038] The inventors found that when the initiator compound is added to the reaction mixture in the range prescribed in accordance with the invention, the resultant polymer is produced at a suitable yield and at high monomer conversion with suitable molecular weight build up. Further, the resultant polymer has the desired impact property and a desired molecular weight as may be expected for a high impact polymer such as HIPS.

[0039] For example, if the amount of initiator compound is below the limit prescribed, the desired impact property and monomer conversion is not achieved. On the other hand, if the amount of the initiator compound is above the range prescribed, the desired molecular weight, thermal resistivity property and flow property of the polymer is not achieved along with reduced monomer conversion as evidenced from the examples shown in this disclosure. In particular, the polymer obtained has high flow rate and is often not suitable for injection molding application. Further, the resultant polymer has lower thermal resistive property indicated by the lower Vicat Softening Temperature.

[0040] The amount of initiator compound that is added is calibrated with the amount of active oxygen content that is present. For example, with high active oxygen content, for example > 4.0 wt.% and < 8.0 wt.%, the amount of initiator compound that may be added is > 20 and < 200 parts per million by weight based on the total weight of the reaction mixture. Above this amount thermal resistivity (indicated by Vicat softening temperature) and flow property may be affected while below this level the desired conversion and molecular weight build-up may not take places as desired. On the other hand, if the high active oxygen content, for example, > 1.0 wt.% and < 4.0 wt.% based on the total weight of the initiator compound, the amount of initiator compound added to the reaction mixture may be > 300 and < 610 parts per million by weight based on the total weight of the reaction mixture in order to obtain the desired properties of impact strength, molecular weight build up, flow property for processing and thermal resistivity.

[0041] The initiator compound may be selected from the group consisting of peroxyester, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 3-di-t-butylperoxide, t-dicumylperoxide, 2,5- dimethyl-2,5-di(t-butylperoxy)hexyne, dicumylperoxide, a,a'-bis(t- butylperoxyisopropyl)benzene, n-butyl-4,4-bis(t-butylperoxy)butane, 2,2-di(tert- butylperoxy)butane, 1 ,1-bis(t-butylperoxy)cyclohexane, tertiarybutylperoxy-2-ethylhexyl carbonate, 1 ,6-di(t-butylperoxycarbonyloxy)hexane, and combinations thereof.

[0042] Preferably the initiator compound is a peroxyester. [0043] Preferably, the peroxyester is selected from i) t-butyl peroctoate, ii) t-butylperoxy 2-ethylhexanoate, iii) ethyl 3,3-di(tert-butylperoxy)butyrate, iv) hexaneperoxoic acid, 2- ethyl-, 1 ,1 -dimethylethyl ester, v) t-butylperoxybenzoate, and combinations thereof. Preferably the peroxyester is selected from i) ethyl 3, 3-d i (tert- butyl peroxy) butyrate, or ii) hexaneperoxoic acid, 2-ethyl-, 1 ,1 -dimethylethyl ester. More preferably the peroxyester is hexaneperoxoic acid, 2-ethyl-, 1 ,1 -dimethylethyl ester.

[0044] It is particularly preferred that for the process of the present invention, the vinyl aromatic monomer is styrene; the elastomeric compound is polybutadiene; and the initiator compound is hexaneperoxoic acid, 2-ethyl-, 1 ,1 -dimethylethyl ester.

[0045] Preferably, the process for preparing the polymer of the present invention, comprises the steps of:

(a) obtaining the reaction mixture, comprising:

(i) at least one vinyl aromatic monomer present in an amount from > 85.0 wt.% and < 98.0 wt.% based on the total weight of the reaction mixture, wherein the vinyl aromatic monomer is styrene; and

(ii) at least one elastomeric compound present in an amount from > 2.0 wt.% and < 15.0 wt.% based on the total weight of the reaction mixture, wherein the elastomeric compound is a polymeric rubber and wherein the polymeric rubber is polybutadiene;

(b) heating the reaction mixture to a temperature of > 50°C and adding at least one initiator compound to the reaction mixture to obtain a pre-polymerization mixture; and

• wherein the initiator compound has an active oxygen content of > 1 .0 wt.% and < 8.0 wt.% based on the total weight of the initiator compound; and

• wherein if the active oxygen content of the initiator compound is > 1.0 wt.% and < 4.0, wt.% based on the total weight of the initiator compound, preferably > 2.5 wt.% and < 3.9 wt.% based on the total weight of the initiator compound, and the amount of initiator compound added to the reaction mixture in step (b) is > 300 and < 610 parts per million by weight based on the total weight of the reaction mixture, preferably > 310 and < 500 parts per million (ppm) by weight based on the total weight of the reaction mixture; and

• wherein if the active oxygen content of the initiator compound is > 4.0 wt.% and < 8.0 wt.% based on the total weight of the initiator compound, the amount of initiator compound added to the reaction mixture in step (b) is > 20 and < 200 parts per million by weight based on the total weight of the reaction mixture; and wherein the active oxygen content of the initiator compound is determined in accordance with ASTM D 2180-89(2008); and wherein the initiator compound is a peroxyester, preferably wherein the the peroxyester is selected from i) t-butyl peroctoate, ii) t- butylperoxy 2-ethylhexanoate, iii) ethyl 3,3-di(tert-butylperoxy)butyrate, iv) hexaneperoxoic acid, 2-ethyl-, 1 ,1 -dimethylethyl ester, v) t-butylperoxybenzoate, and combinations thereof. Preferably the peroxyester is selected from i) ethyl 3,3-di(tert-butylperoxy)butyrate, or ii) hexaneperoxoic acid, 2-ethyl-, 1,1 -dimethylethyl ester, more preferably the peroxyester is hexaneperoxoic acid, 2-ethyl-, 1 ,1 -dimethylethyl ester.

[0046] Preferably, the process for preparing the polymer of the present invention, comprises the steps of:

(a) obtaining the reaction mixture, comprising:

• wherein the initiator compound has an active oxygen content of > 1.0 wt.% and < 8.0 wt.% based on the total weight of the initiator compound; and

• wherein if the active oxygen content of the initiator compound is > 2.5 wt.% and < 3.9 wt.% based on the total weight of the initiator compound, and the amount of initiator compound added to the reaction mixture in step (b) is > 310 and < 500 parts per million (ppm) by weight based on the total weight of the reaction mixture; and wherein the active oxygen content of the initiator compound is determined in accordance with ASTM D 2180-89(2008); and wherein the initiator compound is a peroxyester, preferably the peroxyester is hexaneperoxoic acid, 2-ethyl-, 1 ,1 -dimethylethyl ester.

Use of peroxyester as the Initiator compound

[0047] In an aspect of the invention, the invention is directed to the use of a peroxyester selected from i) t-butyl peroctoate, ii) t-butylperoxy 2-ethylhexanoate, iii) ethyl 3,3-di(tert- butylperoxy)butyrate, iv) hexaneperoxoic acid, 2-ethyl-, 1 ,1 -dimethylethyl ester, v) t- butylperoxybenzoate, and combinations thereof, preferably from i) ethyl 3,3-di(tert- butylperoxy)butyrate, or ii) hexaneperoxoic acid, 2-ethyl-, 1 ,1 -dimethylethyl ester, more preferably the peroxyester is hexaneperoxoic acid, 2-ethyl-, 1 ,1 -dimethylethyl ester, for improving the Notched Izod Impact strength of a polymer. The polymer, for example, is obtained by the process of the present invention.

Pre-polymerization mixture

[0048] Once the pre-polymerization mixture is obtained by the addition of the initiator compound to the reaction mixture, the process involves the step of heating the pre- polymerization mixture at a temperature of > 110°C and < 200°C, preferably > 112°C and < 170°C, preferably > 115°C and < 170°C for time period of > 2.0 hours and < 10.0 hours, preferably > 4.0 hours and < 8.0 hours and obtaining the polymer.

[0049] Preferably, the process involves the step of heating the pre-polymerization mixture at a temperature of > 115°C and < 170°C for time period of > 4.0 hours and < 7.0 hours and obtaining the polymer.

[0050] Once the initiator compound is added the reaction mixture to obtain the pre- polymerization mixture, the resultant pre-polymerization mixture may be heated to a temperature of > 115°C and < 120°C for a time period of about 2.5 hours to 3.0 hours. Thereafter, the heating of the pre-polymerization mixture may take place over four different stages. [0051] In the first stage (R1), the pre-polymerization mixture may be heated at a temperature of > 140°C and < 150°C for about 40-55 minutes and at an agitator speed of > 140 rpm and < 155 rpm.

[0052] Thereafter, the pre-polymerization mixture may be subjected to a second stage (R2) of heating, at a temperature of > 140°C and < 150°C for about 40-55 minutes and at an agitator speed of > 40 rpm and < 50 rpm. Thereafter, the pre-polymerization mixture may be subjected to a third stage (R3) of heating, at a temperature of > 150°C and < 160°C for about 40-55 minutes and at an agitator speed of > 20 rpm and < 30 rpm.

[0053] In the fourth stage (R4), the pre-polymerization mixture may be subjected to a fourth stage (R4) of heating, at a temperature of > 160°C and < 170°C for about 40-55 minutes and at an agitator speed of > 20 rpm and < 30 rpm to obtain the polymer. The heating of the pre-polymerization mixture over the four stages of heating results in the polymerization of the vinyl aromatic monomer allowing steady molecular weight build up.

Polymer obtainable by the process of the invention

[0054] In an aspect of the invention, the invention relates to a polymer obtained by or obtainable by the process of the present invention. Preferably, wherein the polymer is a styrenic polymer, preferably wherein the polymer is polystyrene. More preferably the polymer is a high impact polystyrene (HIPS).

[0055] The polymer may be derived from a vinyl aromatic monomer having a phenyl acetylene content of > 10 and < 150 parts, preferably > 80 and < 110 parts, per million by weight based on the total weight of the vinyl aromatic monomer; wherein the polymer is derived from a vinyl aromatic monomer having a phenyl acetylene content of > 10 and < 150 parts per million by weight based on the total weight of the vinyl aromatic monomer; and

(a) wherein an article prepared from the polymer has or selected to have a Notched Izod Impact strength of > 6.0 kJ/m², preferably > 6.0 kJ/m² and < 13.0 kJ/m² preferably > 7.5 kJ/m² and < 13.0 kJ/m², preferably > 6.0 kJ/m² and < 12.0 kJ/m² determined in accordance with ASTM D256; and/or (b) wherein the polymer has a melt volume flow rate (MVR) of > 2.5 cm³/10 min and

< 5.5 cm³/10 min, preferably > 2.5 cm³/10 min and < 4.5 cm³/10 min, when determined at 190°C at 2.16 kg, in accordance with ISO 1133:(2005); and/or

(c) wherein the polymer has weight average molecular weight from > 220,000 g/mol and < 260,000 g/mol, preferably > 220,000 g/mol and < 250,000 g/mol, preferably 230,000 g/mol to 260,000 g/mol determined with gel permeation chromatography using polystyrene standard in accordance with ASTM D5296-11.

[0056] Preferably, the polymer may be derived from the vinyl aromatic monomer having the phenyl acetylene content of > 10 and < 150, preferably > 80 and < 110, parts per million by weight based on the total weight of the vinyl aromatic monomer; and

(a) wherein an article prepared from the polymer has or selected to have a Notched Izod Impact strength of > 6.0 kJ/m², preferably > 6.0 kJ/m² and < 13.0 kJ/m² preferably > 7.5 kJ/m² and < 13.0 kJ/m², preferably > 6.0 kJ/m² and < 12.0 kJ/m² determined in accordance with ASTM D256; and

(b) wherein the polymer has a melt volume flow rate (MVR) of > 2.5 cm³/10 min and

< 5.5 cm³/10 min, preferably > 2.5 cm³/10 min and < 4.5 cm³/10 min, when determined at 190°C at 2.16 kg, in accordance with ISO 1133:(2005); and

(c) wherein the polymer has weight average molecular weight from > 220,000 g/mol and < 260,000 g/mol, preferably > 220,000 g/mol and < 250,000 g/mol, preferably 230,000 g/mol to 260,000 g/mol determined with gel permeation chromatography using polystyrene standard in accordance with ASTM D5296-11 , preferably the vinyl aromatic monomer is styrene and the polymer is derived with a peroxyester initiator compound having an active oxygen content of > 1.0 wt.% and < 8.0 wt.% based on the total weight of the initiator compound.

[0057] The polymer obtained at the end of stage (R4) stage may be pulverized to form polymeric powder (3-4 mm) to facilitate smooth feeding in an extruder. Thereafter, the pulverized polymer, which may contain 2-3 wt.% of residual vinyl aromatic monomer, may be passed through an extruder with high vacuum (100-200 mbar) at 200-220 °C so as to remove the unreacted monomer. The final extruded polymer pellets may contain 500- 1000 ppm of residual vinyl aromatic monomer. [0058] The present invention will now be further elucidated based on the following nonlimiting examples.

EXAMPLES

[0059] Purpose: Demonstrate the effect of adding the initiator compound in a process for preparing high impact polystyrene starting from styrene monomer having 100 parts per million (ppm) by weight of phenyl acetylene and polybutadiene rubber.

[0060] Material: For the purposes of this example the following materials were used:

Table 1

[0061] Process for preparing High Impact Polystyrene (HIPS): 800 g batch size of high impact polystyrene was prepared.

Preparing the reaction mixture

[0062] Around 48 g (6.0 wt. %) of polybutadiene rubber (PBR) was dissolved in 740 g (92.5 wt %) of styrene monomer in a jacketed glass reactor with continuous agitation (200-300 rpm) at room temperature. 12 g (1.5 wt.%) of mineral oil, 0.48 g (600 ppm or 0.06 wt.%) of Irgonox 1076 (antioxidant), and 24 g (3 wt.%,) of ethylbenzene as processing aid were also added during dissolution of rubber. Ethylbenzene as a processing aid was used as diluent in the process to maintain viscosity during agitation. Antioxidant helped in avoiding undesirable oxidation of rubber during the process, while mineral oil functioned as a processing aid as well as internal mold releasing agent.

Rubber dissolution took around 4-5 hours and the reaction mixture was obtained.

Preparing the pre-polymerization mixture and subsequent heating

[0063] After complete dissolution of PBR, the reaction mixture obtained was a clear solution. Subsequently, the reaction mixture was agitated at 300 rpm, and heated at a temperature of 60-70 °C. Once after internal reaction temperature reached 60 °C, the initiator compound was added to obtain the pre-polymerization mixture. The addition of the initiator compound was done in the form of a solution containing 50.0 wt.% of the initiator compound. The amount of initiator compound added is shown in the samples below in Table 1 and Table 2.

[0064] The pre-polymerization mixture was then heated to a temperature of 115 °C and the temperature was maintained under agitation for -174 minutes.

[0065] Thereafter, the pre-polymerization mixture was subjected to heating at four different stages. First stage (R1): Then mixture was heated at a temperature of 140 °C and the agitation speed was reduced to 150 rpm and maintained for -48 minutes.

[0066] Second stage (R2): The mixture was then heated at a temperature of 145 °C and the agitation speed was maintained at 50 rpm for 48 minutes.

[0067] Third stage (R3): The mixture was heated at a temperature of 155 °C, and the agitation speed was maintained at 25 rpm for -48 min.

[0068] Fourth stage (R4): The mixture was heated at a temperature of 165 °C, with an agitation of 25 rpm and maintained for -48 min to obtain the high impact polystyrene polymer (HIPS). Then HIPS obtained was subjected to vacuum (-200 mbar) for 10 minutes to take out the un-reacted styrene and diluent ethylbenzene. After breaking the vacuum, HIPS polymer was removed as lumps in hot condition and chopped into small pieces (1-2 cm). The HIPS polymer obtained was pulverized to powder (3-4 mm) to facilitate smooth feeding into an extruder. [0069] The pulverized HIPS contained 2-3 % of residual styrene monomer, to remove this unreacted styrene, the powder was passed through an extruder with high vacuum (100-200 mbar) at 200-220 °C. A 10 barrel, twin screw extruder setup with vacuum port was used and the temperature range was maintained at 150-220 °C. The extruded HIPS pellets obtained contained 500-1000 ppm of residual styrene, which was further tested.

[0070] Results and Conclusion: T able 1 provides the data for the deterioration of impact properties of the high impact polystyrene obtained by varying the amount of phenyl acetylene present in the starting styrene monomer. The amount of initiator compound added during the process was 300 ppm.

Table 1

[0071] As is evident from the data provided under Table 1 , with the increase in the content of phenyl acetylene present in the starting styrene monomer, the resultant polymer or articles prepared from the resultant polymer has significantly lowered impact property. For example, compared to sample CE1 that is free of phenyl acetylene, the sample CE5 having 150 ppm of phenyl acetylene, has -67% lower impact property than that of the sample CE1. Accordingly, the amount of phenyl acetylene present in the starting monomer had a direct influence in the impact property.

[0072] Table 2 provides the properties of high impact polystyrene obtained by varying the amount of initiator compound that is added during polymer production while keeping the amount of phenyl acetylene present in the starting styrene monomer constant at 100 ppm by weight.

Table 2

[0073] From Table 2, it is evident that at identical levels of phenyl acetylene content present in the starting monomer, with the increase in the amount of initiator compound added during the process of polymerization, the impact property surprisingly increases. For example, the sample IE1 and CE7 have identical content of phenyl acetylene present in the starting styrene monomer. However, sample IE1 has nearly 3.5 times higher impact property than that of sample CE7. In particular, the impact strength of the polymer obtained (IE1 , IE2) using the process of the present invention starting from styrene having 100 ppm of phenyl acetylene, is higher compared to the polymer (CE6) obtained from styrene, which was purified to lower the content of phenyl acetylene.

[0074] However, it is observed from Table 2, that the increase in the amount of initiator compound that is added during the process, has a beneficial effect in improving the polymer properties only to a certain extent. It may be observed that although sample CE8 has excellent impact property, the increase in the impact property of the polymer comes at a cost of lower polymer conversion, evidenced from the high content of styrene residue present in the polystyrene product, and lower thermal resistivity determined by the Vicat Softening Temperature. Further, the sample CE8 has high melt flow (Melt Volume Flow Rate), rendering it less suitable for certain injection molding application.

Claims

1. A process for preparing polymer, comprising the steps of:

(a) obtaining a reaction mixture, comprising: i. at least one vinyl aromatic monomer present in an amount from > 85.0 wt.% and < 98.0 wt.% based on the total weight of the reaction mixture; ii. at least one elastomeric compound present in an amount from > 2.0 wt.% and < 15.0 wt.% based on the total weight of the reaction mixture; and

• wherein if the active oxygen content of the initiator compound is > 4.0 wt.% and < 8.0 wt.% based on the total weight of the initiator compound, the amount of initiator compound added to the reaction mixture in step (b) is > 20 and < 200 parts per million by weight based on the total weight of the reaction mixture; and wherein the active oxygen content of the initiator compound is determined in accordance with ASTM D 2180-89(2008).

2. The process of claim 1 , wherein the active oxygen content of the initiator compound is > 2.5 wt.% and < 3.9 wt.% based on the total weight of the initiator compound and the amount of initiator compound added to the reaction mixture in step (b) of claim 1 is > 310 and < 500 parts per million (ppm) by weight based on the total weight of the reaction mixture. The process of claim 1 , wherein the active oxygen content of the initiator compound is > 5.0 wt.% and < 6.5 wt.% based on the total weight of the initiator compound and the amount of initiator compound added to the reaction mixture in step (b) of claim 1 is > 50 and < 80 parts per million (ppm) by weight based on the total weight of the reaction mixture. The process according to any one of claims 1-3, wherein the vinyl aromatic monomer has a phenyl acetylene content of < 150, preferably < 120, more preferably < 100 parts per million by weight (ppm), based on the total weight of the vinyl aromatic monomer. The process according to any one of claims 1-4, wherein the reaction mixture further comprises at least one processing aid compound present in an amount of < 5.0 wt.% based on the total weight of the reaction mixture, preferably wherein the processing aid compound is ethyl benzene. The process according to any one of claims 1-5, wherein the reaction mixture further comprises at least one mineral oil compound present in an amount < 3.0 wt.% based on the total weight of the reaction mixture, preferably wherein the mineral oil compound is a paraffin oil. The process according to any one of claims 1-6, wherein the reaction mixture further comprises one or more additives in an amount of < 1.0 wt.% based on the total weight of the reaction mixture, preferably wherein the one or more additives are selected from anti-oxidants, UV stabilizers, color stabilizers and combinations thereof. The process according to any one of claims 1-7, wherein the vinyl aromatic monomer is selected from the group consisting of styrene, a-methyl styrene, dibromostyrene, vinyltoluene, vinylxylene, butylstyrene, p-hydroxystyrene, methoxystyrene, and any combinations thereof, preferably the vinyl aromatic monomer is selected from styrene, a- methyl styrene, and any combinations thereof, more preferably the vinyl aromatic monomer is styrene. The process according to any one of claims 1-8, wherein the initiator compound is selected from the group consisting of peroxyester, 2 ,5-dimethyl-2, 5-di(t- butylperoxy)hexane, 3-di-t-butylperoxide, t-dicumylperoxide, 2,5-dimethyl-2,5-di(t- butylperoxy)hexyne, dicumylperoxide, a,a'-bis(t-butylperoxyisopropyl)benzene, n-butyl- 4,4-bis(t-butylperoxy)butane, 2,2-di(tert-butylperoxy)butane, 1 , 1 -bis(t- butylperoxy)cyclohexane, tertiarybutylperoxy-2-ethylhexyl carbonate, 1 ,6-di(t- butylperoxycarbonyloxy)hexane, and combinations thereof, preferably wherein the initiator compound is a peroxyester. The process according to claim 9, wherein the peroxyester is selected from i) t-butyl peroctoate, ii) t-butylperoxy 2-ethylhexanoate, iii) ethyl 3,3-di(tert-butylperoxy)butyrate, iv) hexaneperoxoic acid, 2-ethyl-, 1 ,1 -dimethylethyl ester, v) t-butylperoxybenzoate, and combinations thereof, preferably wherein the peroxyester is selected from i) ethyl 3,3- di(tert-butylperoxy)butyrate, or ii) hexaneperoxoic acid, 2-ethyl-, 1 ,1 -dimethylethyl ester, more preferably the peroxyester is hexaneperoxoic acid, 2-ethyl-, 1,1 -dimethylethyl ester. The process according to any one of claims 1-10, wherein the elastomeric compound is a polymeric rubber selected from polybutadiene, an elastomeric copolymer comprising polymeric units derived from 1,3 butadiene and styrene, an elastomeric copolymer comprising polymeric units derived from butadiene and acrylonitrile, and an elastomeric terpolymer comprising polymeric units derived from styrene, butadiene and acrylonitrile, preferably the polymeric rubber is selected from polybutadiene, an elastomeric copolymer comprising polymeric units derived from 1 ,3 butadiene and styrene, an elastomeric copolymer comprising polymeric units derived from butadiene and acrylonitrile, more preferably the polymeric rubber is polybutadiene. The process according to any one of claims 1-11, wherein

(a) the vinyl aromatic monomer is styrene;

(b) the elastomeric compound is polybutadiene; and

(c) the initiator compound is hexaneperoxoic acid, 2-ethyl-, 1 ,1 -dimethylethyl ester. A polymer obtained by or obtainable by the process of claims 1-12, preferably wherein the polymer is a styrenic polymer, preferably wherein the polymer is polystyrene, more preferably the polymer is a high impact polystyrene (HIPS). The polymer of claim 13, wherein the polymer is derived from the vinyl aromatic monomer having a phenyl acetylene content of > 10 and < 150 parts per million by weight based on the total weight of the vinyl aromatic monomer; and

(a) wherein an article prepared from the polymer has or selected to have a Notched Izod Impact strength of > 6.0 kJ/m², preferably > 6.0 kJ/m² and < 13.0 kJ/m² preferably > 7.5 kJ/m² and < 13.0 kJ/m², preferably > 6.0 kJ/m² and < 12.0 kJ/m² determined in accordance with ASTM D256; and/or

(c) wherein the polymer has weight average molecular weight from > 220,000 g/mol and < 260,000 g/mol, preferably > 220,000 g/mol and < 250,000 g/mol, preferably 230,000 g/mol to 260,000 g/mol determined with gel permeation chromatography using polystyrene standard in accordance with ASTM D5296-11. Use of a peroxyester selected from i) t-butyl peroctoate, ii) t-butylperoxy 2-ethylhexanoate, iii) ethyl 3,3-di(tert-butylperoxy)butyrate, iv) hexaneperoxoic acid, 2-ethyl-, 1 ,1- dimethylethyl ester, v) t-butylperoxybenzoate, and combinations thereof, preferably from i) ethyl 3,3-di(tert-butylperoxy)butyrate, or ii) hexaneperoxoic acid, 2-ethyl-, 1 ,1- dimethylethyl ester, more preferably the peroxyester is hexaneperoxoic acid, 2-ethyl-, 1 ,1- dimethylethyl ester, for improving the Notched Izod Impact strength of a polymer.