WO2017118544A1

WO2017118544A1 - Method for preparing ethylene copolymer

Info

Publication number: WO2017118544A1
Application number: PCT/EP2016/080862
Authority: WO
Inventors: Carolina De Los Angeles TOLOZA PORRAS; Jan Nicolaas Eddy DUCHATEAU; Peter Neuteboom; Diego Mauricio CASTANEDA ZUNIGA; Franciscus Petrus Hermanus SCHREURS; Markus Busch; Maria Ingrid STIMEIER
Original assignee: Sabic Global Technologies B.V.; Technische Universität Darmstadt
Priority date: 2016-01-05
Filing date: 2016-12-14
Publication date: 2017-07-13

Abstract

The invention provides a process for preparing an ethylene copolymer by copolymerizing ethylene and at least one comonomer at pressures in the range of from 150 MPa to 350 MPa and temperatures in the range of from 50°C to 350°C by: (i) a process in the presence of a system initially consisting of an initiator having a radically transferable atom and a catalyst of a transition metal complex or (ii) a process in the presence of a system initially consisting of an initiator having a radically transferable atom, a catalyst of a transition metal complex and a reducing agent, wherein the amount of the at least one comonomer in the ethylene copolymer is 0.05- 65 mol%.

Description

Method for preparing ethylene copolymer

The invention relates to a process for preparing an ethylene copolymer. The invention further relates to such ethylene copolymer obtainable by the process.

Known processes for making polyethylene and its copolymers include random polymerization. US4177340A discloses a high pressure free radical polymerization of ethylene with oxygen as initiator and 0.01 -0.5% weight of an alkyl ester or

alkenemonocarboxilic acid ester, in this case butyl acrylate. Final polymer contains about 0.2% by weight of n-butyl acrylate incorporated.

US2012035323 (A1 ) mentions commercially available unfunctionalized acrylate copolymers, which are made by high pressure random polymerization. These copolymers generally comprise a major portion by weight of an olefin monomer, usually ethylene, and a minor portion, typically up to about 30% by weight, of an acrylic monomer, usually methyl acrylate or butyl acrylate.

Ethylene vinyl acetate copolymers made by high pressure random polymerization are also known. Examples of commercially available EVA copolymers generally comprise 9-42 wt% of vinyl acetate.

Macromol. Chem. Phys. 2001 , 202, No 7, Buback et. al., High-Pressure Free Radical Copolymerization of ethene and methyl methacrylate, refers to free radical high pressure Copolymerization of ethylene and butyl methacrylate with incorporation up to 45%mol BMA.

Atom transfer radical polymerization (ATRP) is well-known and described in detail in many publications. For example, US201 1/0082230 gives a detailed description of the ATRP technique and some of its improved techniques, such as ICAR (Initiators for Continuous Activator Regeneration) ATRP and ARGET (Activator ReGenerated by Electron Transfer) ATRP.

ATRP has been applied in the homopolymerization of acrylates at high pressure as well as in the copolymerization of (meth)acrylates and small percentages of oolefins under normal reaction conditions. For example, EP1 171496 discloses the (co)polymerization of (meth)acrylates using ATRP. EP1 171496 discloses preparation of methyl methacrylate grafted polyethylene by ATRP (Example 37e). In this process, the location of the methyl methacrylate block is limited to the side branches and the amount of methyl methacrylate incorporated in the polyethylene backbone is limited.

Macromolecular rapid communications, 2013, 34, 604-609, Wang et. al describes high pressure Atom Transfer Radical Polymerization (ATRP) of n-butyl acrylate.

Known processes for preparing an ethylene copolymer have the disadvantage that a limited amount of comonomers is incorporated in the final ethylene copolymer.

It is an object of the invention to provide a process for preparing an ethylene copolymer in which above-described and/or other problems are solved. Accordingly, the invention provides a process for preparing an ethylene copolymer by copolymerizing ethylene and at least one comonomer at pressures in the range of from 150 MPa to 350 MPa and temperatures in the range of from 50°C to 350°C by:

(i) a process in the presence of a system initially consisting of an initiator having a radically transferable atom and a catalyst of a transition metal complex or

(ii) a process in the presence of a system initially consisting of an initiator having a radically transferable atom, a catalyst of a transition metal complex and

a reducing agent,

wherein the amount of the at least one comonomer in the ethylene copolymer is 0.05- 65 mol%.

Advantageously, the process according to the invention allows the incorporation of a high amount of the comonomer in the polyethylene backbone. At similar comonomer concentrations in the feed, the process according to the invention results in ethylene copolymers with a higher amount of incorporated comonomer compared to known processes.

Further advantages of the process according to the invention may include that the process according to the invention results in an ethylene copolymer with a narrow molecular weight distribution (lower polydispersity index (PDI).)

The term "ethylene copolymer" is herein understood as a copolymer in which at least 35 mol% of the copolymer is ethylene. Accordingly, the invention is a process for preparing an ethylene copolymer by copolymerizing ethylene and at least one comonomer at pressures in the range of from 150 MPa to 350 MPa and temperatures in the range of from 50°C to 350°C by:

a reducing agent,

wherein the amount of the at least one comonomer in the ethylene copolymer is 0.05- 65 mol% and the amount of ethylene in the ethylene copolymer is35-99.95 mol%.

The process (i) is generally known as ATRP process. The process (ii) is generally known as an ICAR ATRP process or an ARGET ATRP process, depending on the type of the reducing agent. All of these processes are well known.

For the description of ATRP, ICAR ATRP and ARGET ATRP, US201 1/0082230 is referred and incorporated herein by reference. ATRP, ICAR ATRP and ARGET ATRP are described below based on US201 1/0082230 as follows.

The term "ATRP" is herein understood to mean the 'classical' ATRP process described generally by scheme 1. p_n— X + M VLigand M ^+'Viigand

Scheme 1. General mechanism of ATRP

A typical ATRP process comprises the use of a transition metal complex in its lower oxidation state that acts as a catalyst for the controlled polymerization of radically (co)polymerizable monomers and an initiator possessing one or more transferable atoms which are typically halogen (ATRP initiator).

Suitable ATRP initiators are substituted alkyl halides attached to a low molecular weight molecule with an additional non-initiating functionality, a low molecular weight initiator or macroinitiator with two or more transferable atoms.

The ATRP initiator (P_nX, n=0 in scheme 1 ) or dormant polymer (n>1 , in that case called macroinitiator) and the lower oxidation state transition metal catalyst take part in a redox reaction continuously in which the lower oxidation state transition metal catalyst (M_t7Ligand in scheme 1 ) induces the homolytic cleavage of the Pn-X bond of the ATRP initiator or dormant polymer chain removing therefore a transferable atom (X= typically halogen) to form an active radical (P_n ) at a rate of reaction k_a. The reverse reaction (kda), in which the higher oxidation state transition metal catalyst (X-

M_t ⁿ⁺¹/Ligand) deactivates these radicals by donating back a transferable atom proceeds at a faster rate so that the radical concentration is lowered and these active species have only short time to propagate (k_p) / terminate (k_t) before they are trapped into the dormant state (P_nX).

Importantly, the catalyst is not bound to the polymer chains, as in coordination polymerization, and can therefore be used in a controlled/living polymerization process at sub-stoichiometric amounts relative to the initiator. Modifications of the ATRP technique in terms of amount of catalyst used are for instance ARGET ATRP and ICAR ATRP, generally described by scheme 2, using Cu as transition metal.

The amounts of the catalyst used for the ARGET ATRP and the ICAR ATRP can be reduced from for example 10,000 ppm with respect to the monomers to 1 -100 ppm with respect to the monomers by addition of a reducing agent that acts throughout the polymerization continuously regenerating the lower oxidation state transition metal catalyst (IWVLigand) from accumulating higher oxidation state transition metal catalyst (X-M_t ⁿ⁺¹/Ligand).

In Scheme 2, when the regeneration is conducted by addition of a reducing agent which does not take part in radical reactions, the technique is called activators regenerated by electron transfer (ARGET ATRP). In case that such reducing agent is a free radical initiator which additionally participates in the polymerization as an extra source of radicals, the process is called Initiators for Continuous Activator

Regeneration Atom Transfer Radical Polymerization (ICAR ATRP). process (i): ATRP

The copolymerization in the process according to the invention may be performed by process (i) (ATRP). The process (i) is performed in the presence of a system initially consisting of an initiator having a radically transferable atom and a catalyst of a transition metal complex. The radically transferable atom is typically a halogen.

Suitable examples of the initiators having a radically transferable atom include compounds represented by formulas

R¹R²R³C-X, R¹-(CO)-X, R¹R²R³Si-X or R¹R²N-X or R¹NX₂

wherein

X is selected from the group consisting of CI, Br and I;

R¹, R² and R³ are each independently selected from the group consisting of

H, halogen, C1-C20 linear or branched alkyl, C₂-C₈ cycloalkyl, COCI, COBr, OH, CN, C₂- C20 alkenyl or alkynyl, oxiranyl, glycidyl, C2-C6 alkylene or alkenylene substituted with oxiranyl or glycidyl, aryl, heterocyclyl, aralkyl, aralkenyl and COO-R⁴

wherein R⁴ is selected from the group consisting of

C1-C20 linear or branched alkyl, C2-C6 alkenyl, C2-C6 alkynyl, N-hydroxysuccinimide, poly(ethylene glycol) methyl ether, C1-C20 alkyl substituted with e.g. an azide, methacrylate, alcohol, phthalimido or 2,2-dimethyl-1 ,3-dioxolan-4-yl. Particularly preferred examples of the initiators include methyl-2- bromopropionate (R¹R²R³C-X wherein X=Br, R¹=H, R²=CH₃, R³=COOR⁴ wherein R⁴=CH₃). Further suitable initiators include multifunctional initiators such as bis[2-(2'- bromoisobutyryloxy)ethyl]disulfide, bis[2-(2-bromoisobutyryloxy)undecyl] disulfide, 2- bromoisobutyric anhydride, dipentaerythritol hexakis(2-bromoisobutyrate), ethylene bis(2-bromoisobutyrate), pentaerythritol tetrakis(2-bromoisobutyrate), poly(ethylene glycol) bis(2-bromoisobutyrate), 1 ,1 ,1 -tris(2-bromoisobutyryloxymethyl)ethane.

The transition metal complex comprises a transition metal salt and a ligand.

Suitable examples of the transition metal salt include compounds represented by formula Μ^ηΎ_η

wherein

Mⁿ⁺ is selected from the group consisting of Cu¹⁺, Cu²⁺, Co⁺, Co²⁺,Fe²⁺, Fe³⁺, Mo°, Mo⁺, Mo²⁺, Mo³⁺, Mo⁵⁺, Ni°, ΝΓ, Ni²⁺, Ru²⁺, Ru³⁺, Ru⁴⁺, Ru⁵⁺, Ru⁶⁺, Ti³⁺, Ti⁴⁺, Ag⁺, Ag²⁺, Pd°, Pd⁺, Pd²⁺, Pt°, Pt⁺, Pt²⁺, Pt³⁺, Pt⁴⁺, Zn⁺ and Zn²⁺,

Y is selected from the group consisting of halogen, OH, (0)i/2, CN, NC, SCN, CNS, OCN, CNO, N3 and R5CO2 where R5 is selected from H, linear or branched alkyl or aryl which may optionally be substituted with one or more halogens and

n is the formal charge on the metal. Particularly preferred examples of the transition metal complex include CuBr.

Suitable examples of the ligands which can be used in combination with above mentioned transition metal salts include

pyridines such as N-butyl-2-pyridylmethanimine, N-dodecyl-N-(2- pyridylmethylene)amine, N-octadecyl-N-(2-pyridylmethylene)amine and N-octyl-2- pyridylmethanimine,

bipyridines such as 2,2'-bipyridyl, 4,4'-di-tert-butyl-2,2'-dipyridyl, 4,4'-dimethyl-2,2'- dipyridyl and 4,4'-inonyl-2,2'-dipyridyl,

bipyrrole and derivatives thereof,

acetonitrile,

1 ,10-phenanthroline,

porphyrin and derivatives thereof,

porphycene and derivatives thereof,

crown ethers such as 18-crown-6,

cyclopentadienyl and derivatives thereof,

benzene and derivatives thereof, amines such as ethylenediamine, propylenediamine, 1 ,1 ,4,7,10,10- hexamethyltriethylenetetramine, N,N,N',N",N"-pentamethyldiethylenetriamine, 1 ,4,8,1 1- tetraazacyclotetradecane, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine, 1 ,4,8,1 1- tetramethyl-1 ,4,8,1 1 -tetraazacyclotetradecane, tris[2-(dimethylamino)ethyl]amine, tris(2-pyridylmethyl)amine,

aminoethanol and aminoproponal (both optionally substituted one to three times on the oxygen and/or nitrogen atom with a C1-C4 alkyl group),

ethylene glycol and propylene glycol (both optionally substituted one to two times on the oxygen atoms with a C1-C4 alkyl group) and

carbon monoxide.

Particularly preferred examples of the ligand include tris(2-pyridylmethyl)amine..

Preferably, the amount of the initiator may be 10-1000 molppm with respect to the total of the ethylene and the at least one comonomer to be copolymerized.

Preferably, the amount of the transition metal salt is 5000-10000 molppm with respect to the total of the ethylene and the at least one comonomer to be copolymerized. Preferably, the amount of the ligand is used in excess respect to the transition metal salt in order to ensure the formation of transition metal complex. process (ii): ICAR and ARGET ATRP

Preferably, the copolymerization in the process according to the invention is performed by process (ii) (ICAR ATRP or ARGET ATRP). The process (ii) is performed in the presence of a system initially consisting of an initiator having a radically transferable atom, a catalyst of a transition metal complex and a reducing agent.

Suitable examples of the initiator, transition metal salt and ligand suitable for process (ii) include the initiator, transition metal salt and ligand described with respect to process (i). The transition metal complex is in its high oxidation state.

When the reducing agent is a free radical initiator which additionally participates in the polymerization as an extra source of radicals, the process is ICAR ATRP. The free radical initiator may be any molecule that may be induced to form free radicals, such as a molecule that forms radicals by thermal, photoiniated or other decomposition processes. Free radical initiators include peroxides, azo compounds, disulfides, and tetrazines. More specifically, free radical initiators include acyl peroxides, benzoyl peroxides, alkyl peroxides, cumyl peroxides, tributyl peroxides, hydroperoxides, cumyl hydroperoxide, tert-butyl hydroperoxide, peresters, tert-butyl perbenzoate, alkyl sulfonyl peroxides, dialkyl peroxydicarbonates, diperoxyketals, ketone peroxides, 2,2'- azobisisobutyronitrile ("AIBN"), 2,2'-azobis(2,4-dimethyl pertanenitrile), and 1 ,1 '-azobis (cyclohexane-carbonitrile).

When the reducing agent does not act as an extra source of radicals, the process is ARGET ATRP. Such reducing agent may be an organic compound selected from the group consisting of alkylthiols, mercaptoethanol, enolizable carbonyl compounds, ascorbic acid, acetyl acetonate, camphorsulfonic acid, hydroxy acetone, reducing sugars, monosaccharides, glucose, hydrazine, aldehydes, and derivates of any thereof. Other examples of such reducing agent are Cu° and tin(ll) 2-ethylhexanoate.

The amounts of the initiator having a radically transferable atom or group, the transition metal salt and the ligand may be easily selected by the skilled person depending on the desired product properties. For example, the amount of the initiator having a radically transferable atom or group is 10-300 molppm with respect to the total of the ethylene and the at least one comonomer to be copolymerized.

Preferably, the amount of the initiator having a radically transferable atom may be 10- 1000 molppm with respect to the total of the ethylene and the at least one comonomer to be copolymerized.

Preferably, the amount of the transition metal salt is 10-200 molppm with respect to the total of the ethylene and the at least one comonomer to be copolymerized.

Preferably, the amount of the ligand is in excess respect to the transition metal salt to ensure the formation of the transition metal complex.

In the cases where the reducing agent is a free radical initiator, the molar ratio of the reducing agent which is the free radical initiator with respect to the initiator having a radically transferable atom is preferably 0.01-0.5, more preferably 0.01-0.1.

In the cases where the reducing agent does not act as an extra source of radicals, the amount of the reducing agent is preferably 10-1000 molppm with respect to the total of the ethylene and the at least one comonomer to be copolymerized. high pressure polymerisation process

The high pressure polymerisation process of ethylene is disclosed e.g. by Andrew

Peacock (Handbook of Polyethylene. Marcel Dekker, Inc. ISBN: 0-8247-9546-6; 2000), in particular, at pages 43-66. Peacock describes the free radical chemical processes, the high pressure production facilities and the high pressure reaction conditions. The high pressure reactors for the ethylene copolymer can take one of two forms being either an autoclave, with a height-to-diameter ratio in the region of 2-20, or a tubular reactor, with a length-to-diameter ratio from a few hundred up to tens of thousands. These two divergent reactor geometries pose uniquely different chemical engineering problems requiring disparate control conditions. Tubular and autoclave reactors with their disparate profiles require different methods of temperature control.

The autoclave process and the tubular process result in different chain architecture (Tackx and Tacx, Polymer Volume 39, number 14, pp 3109-31 13, 1998) and different molecular weight distribution of the polymer (Kaltenbacher et al, Vol 50, No 1 , January 1967, TAPPI).

The process of the invention is carried out at pressures of from 150 MPa to 350 MPa. The pressures may preferably be 160 MPa to 300 MPa or more preferably 160 MPa to 280 MPa. The temperatures are in the range from 50°C to 350°C, preferably from 60°C to 300°C, for example 65 °C to 250 °C, for example 70 °C to 200 °C, for example 75 °C to 150 °C, for example 80 °C to 100 °C.

It is important that the compounds present in the copolymerization process do not undergo degradation during the copolymerization. The temperature and pressure should be chosen to ensure that degradation does not occur. High pressure Differential Thermal Analysis (DTA) may be carried out on the compounds present in the copolymerization process for determining its thermal stability to choose the

temperature and pressure for the copolymerization. For example, the temperature is preferably below 220 °C when the initiator having a radically transferable atom is methyl-2-bromopropionate. Examples of suitable comonomers for use in the process of the present invention include α,β-unsaturated Cs-Cs-carboxylic acids, in particular maleic acid, fumaric acid, itaconic acid, acrylic acid, methacrylic acid and crotonic acid;

derivatives of α,β-unsaturated Cs-Cs-carboxylic acids, e.g. unsaturated C3-C15- carboxylic esters, in particular esters of Ci-C6-alkanols, in particular methyl

methacrylate, ethyl methacrylate, n-butyl methacrylate or tert-butyl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, tert-butyl acrylate, or anhydrides, in particular methacrylic anhydride, maleic anhydride or itaconic anhydride;

1 -olefins such as propene, 1 -butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1- nonene or 1 -decene;

cyclic olefins such as cyclobutene, cyclopentene, cyclohexene, cycloheptene and cyclooctene, cyclooctadiene, cyclononene, cyclodecene, 1-methyl-1 -cyclohexene, 3- methyl cyclohexene, alpha-pinene or norbornene.

Vinyl monomers such as vinyl carboxylates, particularly preferably vinyl acetate, or styrene can be used as comonomers.

Preferably, the at least one comonomer is selected from the group consisting of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate and tert-butyl acrylate.

Suitable comonomers for use in the process of the present invention further include bifunctional comonomers. Examples of suitable bifunctional comonomers for use in the process of the present invention are 1 ,4-butanediol dimethacrylate, hexanediol dimethacrylate, ethylene glycol dimethacrylate, 1 ,3-butylene glycol dimethacrylate, dodecanediol dimethacrylate, glycerol dimethacrylate, 1 ,4-butanediol diacrylate, hexanediol diacrylate, ethylene glycol diacrylate, 1 ,3-butylene glycol diacrylate, dodecanediol diacrylate, glycerol diacrylate, poly(ethylene glycol) dimethacrylate, poly(propylene glycol) dimethacrylate, poly(ethylenepropyleneglycol) dimethacrylate, 1 ,4-butanediol divinyl ether, poly(ethylene glycol) divinyl ether, di(ethyleneglycol) divinyl ether, 1 ,5-hexadiene, 1 ,7-octadiene, 1 ,9-decadiene and 1 ,13-tetradecadiene.

The amount of the at least one comonomer in the ethylene copolymer is 0.05-65 mol%, for example at least 1 mol%, at least 5 mol%, at least 10 mol%, at least 15 mol%, and/or at most 60 mol%, at most 50 mol%, at most 40 mol% or at most 30 mol%. Preferably, the amount of the at least one comonomer with respect to the total of the ethylene and the at least one comonomer to be copolymerized is 0.001 -10 mol%, for example at least 0.1 mol%, at least 1 mol% or at least 2 mol% and/or at most 7.5 mol% or at most 5 mol%.

Preferably, the ethylene copolymer according to the present invention has a density of 900 to 1 100 kg/m³ for example 905 to 1000 kg/m³, 910 to 990 kg/m³, 915 to 970 kg/m³ or 918 to 960 kg/m³, 920 to 950 kg/m³, according to IS01 183. Preferably, the ethylene copolymer according to the present invention has a melt flow rate of 0.10 g/10 min to 150 g/10 min according to ASTMD1238 measured at 190 °C and 2.16 kg. Preferably, the ethylene copolymer according to the present invention has a melt flow rate of 10 to 900 g/10min according to ASTMD1238 measured at 125°C and 0.325kg.

The process of the present invention can be carried out with all types of tubular reactors suitable for high-pressure polymerization.

Preferably the comonomer is first mixed with ethylene before it is brought into contact with the system comprising the initiator. It is possible to feed such a mixture of ethylene and the comonomer only to the inlet of the tubular reactor. It is also possible to feed more than one stream of ethylene and the comonomer and feed accordingly one or more of these streams as side stream to the tubular reactor. The process of the present invention can also be carried out with all types of autoclave reactor. Such reactors generally have height to diameter ratios from 1 up to 20.

Residence time may generally be between 8 up to 120 s.

The process of the present invention can be carried out in a single tubular reactor or a single autoclave reactor. The process of the present invention can also be carried out in 2 or more tubular reactors connected in series, 2 or more autoclave reactors connected in series or an autoclave reactor and a tubular reactor connected in series. Such a process for producing polymers or copolymers of ethylene using an autoclave reactor and a tubular reactor connected in series is known e.g. from US4496698.

The invention further relates to an ethylene copolymer obtainable by the process of the invention.

Preferably, the ethylene copolymer according to the invention has M_w of at least 10 kg/mol, for example at least 20 kg/mol, at least 30 kg/mol or at least 40 kg/mol. .

Typically, the ethylene copolymer has M_w of at most 500 kg/mol, for example at most 450 kg/mol, according to gel permeation chromatography. M_n and M_w may be determined by gel permeation chromatography, e.g. by the methods described in the experimental section. Preferably, the ethylene copolymer according to the invention has a polydispersity index (PDI=Mw/Mn) of at most 4, more preferably at most 3.5, more preferably at most 3, more preferably at most 2.5.

In some embodiments wherein the comonomer is butyl methacrylate, the ethylene copolymer according to the invention has Mw of 40-100 kg/mol according to gel permeation chromatography and/or a polydispersity index of at most 3.5, more preferably at most 3, more preferably at most 2.5.

In some embodiments wherein the comonomer is butyl acrylate, the ethylene copolymer according to the invention has Mw of 40-400 kg/mol, according to gel permeation chromatography and/or a polydispersity index of at most 4, more preferably at most 3.5, more preferably at most 3.

The invention further relates to articles comprising the ethylene copolymer according to the invention. The articles may be a film, e.g. upholstery wrap, a disposable glove or a film made by encapsulation; a molded article; an extruded article; an article made by 3D printing; an article made by compounding; a foam; a profile; an adhesive, a bitumen modifier; a sealant or a polymer alloy. It is noted that the invention relates to all possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It will therefore be appreciated that all combinations of features relating to the composition according to the invention; all combinations of features relating to the process according to the invention and all combinations of features relating to the composition according to the invention and features relating to the process according to the invention are described herein. It is further noted that the term 'comprising' does not exclude the presence of other elements. However, it is also to be understood that a description on a

product/composition comprising certain components also discloses a

product/composition consisting of these components. The product/composition consisting of these components may be advantageous in that it offers a simpler, more economical process for the preparation of the product/composition. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps. The process consisting of these steps may be advantageous in that it offers a simpler, more economical process.

The invention is now elucidated by way of the following examples, without however being limited thereto. Examples

The reagents used in the experiments described below are listed in table 1 :

Table 1 : Used reagents for the high pressure copolymerizations.

Chemical purity / class

Monomers Ethylene 3.0,

catalytically purified

n-butyl acrylate >99 %^*

n-butyl methacrylate 99 %^**

ATRP initiator Methyl-2- bromopropionate 98 %

(MBrP)

ATRP catalyst Copper bromide (II) - CuBr2 99 %, purified

Tris- 98%

(2-pyridylmethyl)amine

(TPMA)

Reducing Agents ascorbic acid reagent grade

α, a^'- >98 %

Azobisisobutyronitrile (AIBN)

Others Acetonitrile 99.6 %

n-heptane 99+%,

distilled under

nitrogen

Nitrogen 5.0 ^* Contains 10-60 ppm monomethylether hydroquinone which is removed by basic alumina column

^** Contains 10 ppm monomethylether hydroquinone which is removed by basic alumina column

The high pressure copolymerizations were performed in a high pressure reactor with inner volume of 100 mL used in batch mode and operated at 2000 bar and 90°C.

Stirring was operated by a double blade stirring rotor. Heating of the reactor was implemented by two removable heating sleeves from WEMA providing 1200 W each. Temperature was measured by a type-K thermocouple which is attached to the reactor. The regulating mechanism was performed by a eurotherm regulating unit. Furthermore, a type-K thermocouple was applied inside the reactor to monitor the reaction mixtures temperature. Pressure was measured above the reactor by a Burster pressure transducer.

For all examples listed in table 2, reagents (except ethylene) were fed in the reactor by a separate injection system. It contains a pipe system with a variable injection volume. The solutions to be injected are comonomer and initiator (MBrP), catalyst

(CuBr2+TPMA) in acetonitrile and reducing agent (AIBN or ascorbic acid) in acetonitrile or water. They were prepared in a flask with septum by degassing it with nitrogen for 20 minutes. The solutions were added to the reaction mixture by using certain high pressure injection pipe. After the targeted pressure of 2000 bar was reached the ethylene feed was stopped. The solution of the comonomer and ATRP initiator (MBrP) was injected first, the catalyst solution (CuBr2+TPMA) was injected second and the solution of the reducing agent/free radical initiator was subsequently injected. For the comparative experiments (1 and 5: free radical copolymerization), only comonomer and AIBN were injected. After a reaction time of 2h, the reaction solution was depressurized and the obtained polymer was collected. The reactor was flushed with 1500 bar ethylene for ten minutes to collect the remaining polymer.

The conversion was calculated according to the amount of comonomers in the feed and the amount of polymer obtained. The obtained polymers were characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR).

A high temperature GPC (PolymerChar) equipped with 4 detectors, namely two infrared (IR) detectors, one viscosity detector with four capillaries (H502) and dilution chamber and one multi angle light scattering (MALS) detector manufactured by Wyatt with 18 possible angles of incidence (Wyatt DAWN Heleos II) was employed to characterize the molecular weight distribution of the polymers. For injecting the samples, an autosampler Agilent 1200 was used. The GPC has five columns, four are high temperature separating columns. The first column is a Shodex-UT-G protecting column with a particle size of 30 μηη. Three of the four high temperature columns are Shodex UT 806M columns with a maximum particle size of 30 μηη and a maximum pore size of 10,000 A. The last high temperature column is a Shodex UT 307 column with a maximum particle size of 30 μηη and a maximum pore size of 20,000 A.

For a GPC measurement 10-20 mg of polymer were dissolved in 1 ,2,4- trichlorobenzene (TCB). This yields a concentration of 1 -2 mg/mL. The autosampler added 8 mL of TCB and heated the solution up to 160 °C in a heated zone for 60-90 mins. It injected 190 μΙ_ into the systems and the flow rate of the mobile phase (TCB) constituted 1.0 mL/min which resulted in an analyzing period of 60 mins. The temperatures of the columns and detectors were adjusted to 150 °C. The entire CH- signal from IR-detector (IR5) was used as concentration detector. Analysis was performed using calibrating standards of polystyrene/polyethylene with analysis software PSS WinGPC Unity 7.4.0.

NMR was performed at high temperature in a 100/400 MHz (13C/1 H) spectrometer with tempering package with a range from 100 °C to +200 °C. It takes 8000 scans at 100 °C with a pulse relaxation delay of 10s. The spectra are decoupled by inverse gating to make it possible to integrate them. For a NMR measurement 3-4 wt.% polymer were dissolved in 1 ,1 ,2,2-Tetrachloroethane-d2 (C2D2CI4). To dissolve the polymer the NMR tube was put in a 100 °C heating block for 2 hours and the solution was mixed and heated again. Comonomer content in the final polymer (mol %) was measured by integration of characteristic peaks of a given comonomer. Table 2. Initial conditions for the polymerization experiments. Pressure 2000bar. Temperature 90°C

^*: experiment at a temperature of 130°C Table 3. Results

In all experiments, ethylene copolymer was successfully prepared. It can be understood that ethylene copolymers obtained by the process according to the invention (Ex 2-4 and 6-8) has a higher comonomer incorporation than the ethylene copolymers obtained by free radical copolymerization at similar conditions (Ex 1 and 5). The use of similar concentrations of comonomer resulted in ethylene copolymers with a higher amount of incorporated comonomer in the ethylene copolymer, according to the invention. Further, the process according to the invention resulted in a copolymer with a lower PDI than that obtained by free radical polymerization.

Claims

A process for preparing an ethylene copolymer by copolymerizing ethylene and at least one comonomer at pressures in the range of from 150 MPa to 350 MPa and temperatures in the range of from 50°C to 350°C by:

(i) a process in the presence of a system initially consisting of

an initiator having a radically transferable atom and a catalyst of a transition metal complex or

(ii) a process in the presence of a system initially consisting of

an initiator having a radically transferable atom, a catalyst of a transition metal complex and a reducing agent,

wherein the amount of the at least one comonomer in the ethylene copolymer is 0.05-65 mol%.

The process according to claim 1 , wherein the copolymerization is performed by process (ii).

The process according to claim 2, wherein the reducing agent is a free radical initiator.

The process according to claim 3, wherein the free radical initiator selected from the group consisting of acyl peroxides, benzoyl peroxides, alkyl peroxides, cumyl peroxides, tributyl peroxides, hydroperoxides, cumyl hydroperoxide, tert- butyl hydroperoxide, peresters, tert-butyl perbenzoate, alkyl sulfonyl peroxides, dialkyl peroxydicarbonates, diperoxyketals, ketone peroxides, 2,2'- azobisisobutyronitrile ("AIBN"), 2,2'-azobis(2,4-dimethyl pertanenitrile), and 1 ,1 '- azobis (cyclohexane-carbonitrile).

The process according to claim 2, wherein the reducing agent does not participate as an extra source of radicals in the polymerization process.

The process according to claim 5, wherein the reducing agent is an organic compound selected from the group consisting of alkylthiols, mercaptoethanol, enolizable carbonyl compounds, ascorbic acid, acetyl acetonate,

camphorsulfonic acid, hydroxy acetone, reducing sugars, monosaccharides, glucose, hydrazine, aldehydes, and derivates of any thereof; or Cu° or tin(ll) 2- ethylhexanoate.

The process according to any one of claims 2-6, wherein the amount of the transition metal salt is 10-200 molppm with respect to the total of the ethylene and the at least one comonomer to be copolymerized.

The process according to any one of the preceding claims, wherein the at least one comonomer is selected from the group consisting of

α,β-unsaturated Cs-Cs-carboxylic acids, in particular maleic acid, fumaric acid, itaconic acid, acrylic acid, methacrylic acid and crotonic acid;

derivatives of α,β-unsaturated Cs-Cs-carboxylic acids, e.g. unsaturated C3-C15- carboxylic esters, in particular esters of Ci-C6-alkanols, in particular methyl methacrylate, ethyl methacrylate, n-butyl methacrylate or tert-butyl

methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, tert-butyl acrylate, or anhydrides, in particular methacrylic anhydride, maleic anhydride or itaconic anhydride;

1 -olefins such as propene, 1 -butene, 1-pentene, 1-hexene, 1-heptene, 1- octene, 1 -nonene or 1 -decene;

cyclic olefins such as cyclobutene, cyclopentene, cyclohexene, cycloheptene, cyclooctene, cyclooctadiene, cyclononene, cyclodecene, 1-methyl-1 - cyclohexene, 3-methyl cyclohexene, alpha-pinene or norbornene;

vinyl monomers such as vinyl carboxylates, particularly preferably vinyl acetate, or styrene; and

1 ,4-butanediol dimethacrylate, hexanediol dimethacrylate, ethylene glycol dimethacrylate, 1 ,3-butylene glycol dimethacrylate, dodecanediol

dimethacrylate, glycerol dimethacrylate, 1 ,4-butanediol diacrylate, hexanediol diacrylate, ethylene glycol diacrylate, 1 ,3-butylene glycol diacrylate,

dodecanediol diacrylate, glycerol diacrylate, poly(ethylene glycol)

dimethacrylate, poly(propylene glycol) dimethacrylate,

poly(ethylenepropyleneglycol) dimethacrylate, 1 ,4-butanediol divinyl ether, poly(ethylene glycol) divinyl ether, di(ethyleneglycol) divinyl ether, 1 ,4- hexadiene, 1 ,7-octadiene, 1 ,9-decadiene and 1 ,13-tetradecadiene.

9. The process according to any one of the preceding claims, wherein the at least one comonomer is selected from the group consisting of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate and tert-butyl acrylate.

10. The process according to any one of the preceding claims, wherein the amount of the at least one comonomer with respect to the total of the ethylene and the at least one comonomer to be copolymerized is 0.001 -10 mol%.

1 1 . The process according to any one of claims 1-10, wherein the comonomer is butyl methacrylate, and the ethylene copolymer has Mw of 40-100 kg/mol according to gel permeation chromatography and/or a polydispersity index of at most 3.5, more preferably at most 3, more preferably at most 2.5.

12. The process according to any one of claims 1-10, wherein the comonomer is butyl acrylate, and the ethylene copolymer has Mw of 40-400 kg/mol according to gel permeation chromatography and/or a polydispersity index of at most 4, more preferably at most 3.5, more preferably at most 3.

13. The process according to any one of the preceding claims, wherein the

ethylene copolymer has a density of 900 to 1 100 kg/m³, for example 905 to 1000 kg/m³, 910 to 990 kg/m³, 915 to 970 kg/m³, 918 to 960 kg/m³ or 920 to 950 kg/m³, according to IS01 183.

4. The ethylene copolymer obtained by or obtainable by the process according to any one of the preceding claims.

5. An article comprising the ethylene copolymer according to claim 14, wherein preferably the article is a film, e.g. upholstery wrap, a disposable glove or a film made by encapsulation; a molded article; an extruded article; an article made by 3D printing; an article made by compounding; a foam; a profile; an adhesive, a bitumen modifier; a sealant or a polymer alloy.