Method of preparing ethylene polymers by controlled high pressure polymerization

Abstract

The present invention relates to a method for the radical polymerization or copolymerization of ethylene at high pressures using a hydroxylamine ester as radical initiator. The hydroxylamine esters according to the invention are suitable initiators for the high pressure polymerization of ethylene leading to high molecular weight polyethylenes with narrow molecular weight distributions (Poyldispersity Index PD=1, 2-4.5).

Claims

1. A method for the polymerization or copolymerization of ethylene, which method comprises: polymerizing or copolymerizing ethylene at an operating pressure of from 1000 to 3000 bar, at a polymerization temperature between 140° C. and 205° C. in a high pressure reactor, operating continuously or batch wise and in the presence of a radical polymerization initiator, wherein the polydispersity, PD, of the resulting polyethylene is between 1.2 and 4.5, as measured by gel permeation chromatography, and the weight average molecular weight of the resulting polyethylene is at least 284,000 to 547,000 g/mol, characterized in that the radical polymerization initiator is a hydroxylamine ester of formula (C′) used in an amount of from 5 to 200 parts per million based on the weight of the total reaction mixture, wherein solely the hydroxylamine ester of formula (C′) is used as the radical initiator, ##STR00068## wherein X is hydrogen or C.sub.1-C.sub.18 alkyl and R.sub.100 is C.sub.4-C.sub.24 alkyl.

2. The method according to claim 1, wherein the hydroxylamine ester is ##STR00069##

3. The method according to claim 1, wherein additionally a chain transfer agent is added.

4. The method according to claim 3, wherein the chain transfer agent is selected from the group consisting of ketones, aldehydes, C.sub.3-C.sub.20alkanes, C.sub.3-C.sub.20alkenes, mercaptanes and disulfides.

5. The method according to claim 1, wherein a comonomer is present which is a monomer containing a vinyl group, an allyl group, a vinylidene group, a diene group or an olefinic group and which is other than ethylene.

6. The method according to claim 5, wherein the comonomer is selected from the group consisting of methyl acrylate, ethyl acrylate, n-butyl acrylate, vinyl acetate, styrene, a-methylstyrene and methyl methacrylate.

7. The method according to claim 1, wherein the hydroxylamine ester is present in the amount of from 10 to 200 parts per million based on the weight of the total reaction mixture.

Description

(1) The instant invention provides a different solution for the preparation of polyethylenes with even narrower polydispersities by using solely the hydroxylamine esters of the instant invention as radical initiators. These compounds allow an excellent control of the polyethylene polymerization process without the need to adjust the ratio of different molecules. Furthermore the process can be carried out advantageously at comparatively low temperatures. Moreover, as the method of the present invention can be performed at low temperatures, copolymers of ethylene with e.g. styrene, vinylacetate and narrow molecular weight distribution are accessible. These copolymers are not accessible at high temperatures due to the ceiling temperature of these monomers, which results otherwise in a polymerization/depolymerization equilibrium with only low molecular weight products unsuitable for industrial applications.

(2) Hydroxylamine esters do not form any nitroxyl radicals during decomposition but selectively cleave into aminyl and carbon centered radicals, which surprisingly are able to initiate ethylene polymerization under high pressure. The result is a polyethylene with low polydispersity.

(3) One aspect of the invention is a method for the polymerization or copolymerization of ethylene at an operating pressure of from 500 to 3500 bar, at a polymerization temperature between 100° and 400° C. in a suitable high pressure reactor, operating continuously or batch wise

(4) by the use of a radical polymerization initiator,

(5) characterized in that the radical polymerization initiator is a hydroxylamine ester containing a structural element of formula (I) or (I′)

(6) ##STR00001##
wherein

(7) X is hydrogen, C.sub.1-C.sub.36alkyl, C.sub.1-C.sub.36alkyl which is substituted by halogen, C.sub.5-C.sub.12cycloalkyl, C.sub.7-C.sub.12bicyclo- or tricycloalkyl, C.sub.2-C.sub.36alkenyl, C.sub.2-C.sub.18alkynyl, C.sub.6-C.sub.10aryl, —O—C.sub.6-C.sub.10aryl, —NH—C.sub.6-C.sub.10aryl, —N(C.sub.1-C.sub.6alkyl).sub.2;

(8) X′ is a direct bond or C.sub.1-C.sub.36alkylene, C.sub.2-C.sub.36alkenylene, C.sub.2-C.sub.36alkynylene, —(C.sub.1-C.sub.6alkylene)-phenyl-(C.sub.1-C.sub.6alkylene) or a group

(9) ##STR00002##
and
* indicates the bond to which the carbonyl groups are attached.

(10) Preferably the operating pressure is of from 1000 to 3000 bar.

(11) Preferably the polymerization temperature is of from 140° to 300° C.

(12) In a preferred method the polydispersity, PD, of the resulting polyethylene is between 1.2 and 4.5, in particular between 1.2 and 3.5.

(13) The hydroxylamine ester is, for example, used in an amount of from 5 to 500 parts per million, preferably of from 5 to 300 parts per million and more preferably of from 10 to 200 parts per million based on the weight of the total reaction mixture.

(14) Suitable reactors for high pressure ethylene polymerization using peroxides are well known and for example described by H. Seidl, G. Luft, J. Macromol. Sci.-Chem. 1981, A15(1), pp. 1-33. The process is typically a continuous process using, for example, a continuous tubular reactor or a stirred autoclave reactor. A detailed flow sheet is for example given in U.S. Pat. No. 6,562,915

(15) The hydroxylamine ester is preferably a compound of formula (Ia) or (I′a)

(16) ##STR00003##
wherein

(17) X is hydrogen, C.sub.1-C.sub.36alkyl, C.sub.1-C.sub.36alkyl which is substituted by halogen, C.sub.5-C.sub.12cycloalkyl, C.sub.7-C.sub.12bicyclo- or tricycloalkyl, C.sub.2-C.sub.36alkenyl, C.sub.2-C.sub.18alkynyl, C.sub.6-C.sub.10aryl, —O—C.sub.1-C.sub.18alkyl, —O—C.sub.6-C.sub.10aryl, —NH—C.sub.1-C.sub.18alkyl, —NH—C.sub.6-C.sub.10aryl, —N(C.sub.1-C.sub.6alkyl).sub.2;

(18) X′ is a direct bond or C.sub.1-C.sub.36alkylene, C.sub.2-C.sub.36alkenylene, C.sub.2-C.sub.36alkynylene, phenylene, —(C.sub.1-C.sub.6alkylene)-phenyl-(C.sub.1-C.sub.6alkylene) or a group

(19) ##STR00004##

(20) R.sub.20, R′.sub.20, R.sub.30 and R′.sub.30 are each independently of the others unsubstituted, halo-, CN—, NO.sub.2— or —COOR.sub.40-substituted or O— or NR.sub.40-interrupted C.sub.1-C.sub.18alkyl, C.sub.2-C.sub.18alkenyl, C.sub.2-C.sub.18alkynyl;

(21) R.sub.40 is hydrogen, phenyl or C.sub.1-C.sub.18alkyl; or

(22) R.sub.20 and R.sub.30 and/or R′.sub.20 and R′.sub.30, together with the nitrogen atom to which they are bonded, form a 5- or 6-membered ring which may be interrupted by a nitrogen or oxygen atom and which may be substituted one or more times by C.sub.1-C.sub.6alkyl groups and carboxyl groups.

(23) Any substituents that are C.sub.1-C.sub.12alkyl are, for example, methyl, ethyl, n-propyl, n-butyl, sec-butyl, tert-butyl, n-hexyl, n-octyl, 2-ethyl-hexyl, n-nonyl, n-decyl, n-undecyl or n-dodecyl. C.sub.1-C.sub.18Alkyl may be, for example, the groups mentioned above and also, in addition, for example, n-tridecyl, n-tetradecyl, n-hexadecyl and n-octadecyl.

(24) C.sub.2-C.sub.36alkenyl may be, for example, 1-propenyl, allyl, methallyl, 2-butenyl, 2-pentenyl, 2-hexenyl, 2-octenyl or 4-tert-butyl-2-butenyl.

(25) C.sub.2-C.sub.36alkinyl may be, for example, propinyl, butinyl, hexinyl or dodecinyl

(26) C.sub.5-C.sub.12Cycloalkyl is, for example, cyclopentyl, cyclohexyl or cycloheptyl.

(27) Any substituents that are C.sub.2-C.sub.12alkylene are, for example, ethylene, propylene, 2,2-dimethyl-propylene, tetramethylene, hexamethylene, octamethylene, decamethylene or dodecamethylene.

(28) Any substituents that are aryl are for example phenyl or naphthyl.

(29) Any substituents that are C.sub.6-C.sub.12arylene are, for example, o-, m- or p-phenylene, 1,4-naphthylene or 4,4′-diphenylene.

(30) Halogen is F, Cl, Br and I. Alkyl substituted by halogen is for example trifluormethyl.

(31) The hydroxylamine esters are known and for example described in WO 02/092653.

(32) Preparation of hydroxylamine esters that may advantageously be used in the above-mentioned method are described, for example, in U.S. Pat. Nos. 4,590,231, 5,300,647, 4,831,134, 5,204,473, 5,004,770, 5,096,950, 5,021,478, 5,118,736, 5,021,480, 5,015,683, 5,021,481, 5,019,613, 5,021,486, 5,021,483, 5,145,893, 5,286,865, 5,359,069, 4,983,737, 5,047,489, 5,077,340, 5,021,577, 5,189,086, 5,015,682, 5,015,678, 5,051,511, 5,140,081, 5,204,422, 5,026,750, 5,185,448, 5,180,829, 5,262,538, 5,371,125, 5,216,156 and 5,300,544.

(33) Further hydroxylamine esters and the preparation thereof are described in WO 01/90113.

(34) Preferred hydroxylamine esters are of formula (Ia) wherein R.sub.20 and R.sub.30, together with the nitrogen atom to which they are bonded, form a piperidine ring which is substituted in the 2,2- and 6,6-positions by C.sub.1-C.sub.4alkyl groups and in the 4-position has an ether, amine, amide, urethane, ester or ketal group. Special preference is given to cyclic ketals.

(35) For example the hydroxylamine esters are of formula (A), (B), (C) or (O)

(36) ##STR00005##
wherein

(37) G.sub.1, G.sub.2, G.sub.3 and G.sub.4 are each independently of the others alkyl having from 1 to 4 carbon atoms;

(38) G.sub.5 and G.sub.6 are each independently of the other hydrogen or C.sub.1-C.sub.4alkyl;

(39) m is a number 1-2;

(40) R, when m is 1, is hydrogen, uninterrupted C.sub.1-C.sub.18alkyl or C.sub.2-C.sub.18alkyl interrupted by one or more oxygen atoms, or is cyanoethyl, benzoyl, glycidyl, a monovalent radical of an aliphatic carboxylic acid having from 2 to 18 carbon atoms, of a cycloaliphatic carboxylic acid having from 7 to 15 carbon atoms or of an α,β-unsaturated carboxylic acid having from 3 to 5 carbon atoms or of an aromatic carboxylic acid containing from 7 to 15 carbon atoms, it being possible for each carboxylic acid to be substituted in the aliphatic, cycloaliphatic or aromatic unit by from 1 to 3 groups —COOZ.sub.12 wherein Z.sub.12 is hydrogen, C.sub.1-C.sub.20alkyl, C.sub.3-C.sub.12alkenyl, C.sub.5-C.sub.7cycloalkyl, phenyl or benzyl; or R is a monovalent radical of a carbamic acid or phosphorus-containing acid or is a monovalent silyl radical;

(41) R, when m is 2, is C.sub.2-C.sub.12alkylene, C.sub.4-C.sub.12alkenylene, xylylene, a bivalent radical of an aliphatic dicarboxylic acid having from 2 to 36 carbon atoms or of a cycloaliphatic or aromatic dicarboxylic acid having from 8 to 14 carbon atoms or of an aliphatic, cycloaliphatic or aromatic dicarbamic acid having from 8 to 14 carbon atoms, it being possible for each dicarboxylic acid to be substituted in the aliphatic, cycloaliphatic or aromatic unit by one or two groups —COOZ.sub.12; or

(42) R is a bivalent radical of a phosphorus-containing acid or a bivalent silyl radical;

(43) p is 1,

(44) R.sub.1 is C.sub.1-C.sub.12alkyl, C.sub.5-C.sub.7cycloalkyl, C.sub.7-C.sub.8aralkyl, C.sub.2-C.sub.18alkanoyl, C.sub.3-C.sub.5alkenoyl or benzoyl;

(45) R.sub.2 is C.sub.1-C.sub.18alkyl, C.sub.5-C.sub.7cycloalkyl, C.sub.2-C.sub.8alkenyl, each unsubstituted or substituted by a cyano, carbonyl or carbamide group, or is glycidyl, a group of formula —CH.sub.2CH(OH)—Z or of formula —CO—Z or —CONH—Z, wherein Z is hydrogen, methyl or phenyl;

(46) n is a number 1 or 2;

(47) when n is 1,

(48) R.sub.3 is C.sub.2-C.sub.8alkylene or hydroxyalkylene or C.sub.4-C.sub.36acyloxyalkylene; or, when n is 2,

(49) R.sub.3 is (—CH.sub.2).sub.2C(CH.sub.2—).sub.2 and

(50) X is as defined above.

(51) A likewise preferred group consists of hydroxylamines wherein G.sub.1 and G.sub.2 are ethyl and G.sub.3 and G.sub.4 are methyl, or G.sub.1 and G.sub.3 are ethyl and G.sub.2 and G.sub.4 are methyl; and G.sub.5 and G.sub.6 are each independently of the other hydrogen or methyl.

(52) C.sub.4-C.sub.36Acyloxyalkylene is, for example, 2-ethyl-2-acetoxymethylpropylene. R.sub.3 is especially a group of the formula

(53) ##STR00006##

(54) The other substituents have the definitions, including the preferred meanings, given above.

(55) Preferably the substituent X is selected from the group consisting of C.sub.1-C.sub.36alkyl, C.sub.2-C.sub.19alkenyl and C.sub.6-C.sub.10aryl.

(56) Special preference is given to a hydroxylamine ester of formula (C′)

(57) ##STR00007##
wherein X is hydrogen or C.sub.1-C.sub.18alkyl and R.sub.100 is C.sub.4-C.sub.24alkyl

(58) Further suitable hydroxylamine esters are oligomers or polymers obtained by reacting a dicarboxylic acid with a compound of formula A1 or B1 or by reacting a diisocyanate with a compound of formula A1

(59) ##STR00008##
wherein G.sub.1, G.sub.2, G.sub.3 and G.sub.4 are each independently of the others C.sub.1-C.sub.4alkyl, or G.sub.1 and G.sub.2 together and G.sub.3 and G.sub.4 together, or G.sub.1 and G.sub.2 together or G.sub.3 and G.sub.4 together are pentamethylene;

(60) G.sub.5 and G.sub.6 are each independently of the other hydrogen or C.sub.1-C.sub.4alkyl; and

(61) R.sub.1 is C.sub.1-C.sub.12alkyl, C.sub.5-C.sub.7cycloalkyl, C.sub.7-C.sub.8aralkyl, C.sub.2-C.sub.18alkanoyl, C.sub.3-C.sub.5alkenoyl or benzoyl.

(62) The compounds of formula A1 may be reacted to form polyesters. The polyesters may be homo- or co-polyesters that are derived from aliphatic, cycloaliphatic or aromatic dicarboxylic acids and diols and a compound of formula A1.

(63) The aliphatic dicarboxylic acids may contain from 2 to 40 carbon atoms, the cycloaliphatic dicarboxylic acids from 6 to 10 carbon atoms, the aromatic dicarboxylic acids from 8 to 14 carbon atoms, the aliphatic hydroxycarboxylic acids from 2 to 12 carbon atoms and the aromatic and cycloaliphatic hydroxycarboxylic acids from 7 to 14 carbon atoms.

(64) It is also possible for the polyesters, in small amounts, for example from 0.1 to 3 mol %, based on the dicarboxylic acids present, to be branched by means of more than difunctional monomers (for example, pentaerythritol, trimellitic acid, 1,3,5-tri(hydroxyphenyl)benzene, 2,4-dihydroxybenzoic acid or 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)propane).

(65) Suitable dicarboxylic acids are linear and branched saturated aliphatic dicarboxylic acids, aromatic dicarboxylic acids and cycloaliphatic dicarboxylic acids.

(66) Suitable aliphatic dicarboxylic acids are those having from 2 to 40 carbon atoms, for example oxalic acid, malonic acid, dimethylmalonic acid, succinic acid, pimelic acid, adipic acid, trimethyladipic acid, sebacic acid, azelaic acid and dimeric acids (dimerisation products of unsaturated aliphatic carboxylic acids such as oleic acid), alkylated malonic and succinic acids such as octadecylsuccinic acid.

(67) Suitable cycloaliphatic dicarboxylic acids are: 1,3-cyclobutanedicarboxylic acid, 1,3-cyclo-pentanedicarboxylic acid, 1,3- and 1,4-cyclohexanedicarboxylic acid, 1,3- and 1,4-(dicarboxylmethyl)cyclohexane and 4,4′-dicyclohexyldicarboxylic acid.

(68) Suitable aromatic dicarboxylic acids are: especially terephthalic acid, isophthalic acid, o-phthalic acid, and 1,3-, 1,4-, 2,6- or 2,7-naphthalenedicarboxylic acid, 4,4′-diphenyl-dicarboxylic acid, 4,4′-diphenylsulfonedicarboxylic acid, 4,4′-benzophenonedicarboxylic acid, 1,1,3-trimethyl-5-carboxyl-3-(p-carboxylphenyl)-indan, 4,4′-diphenyl ether dicarboxylic acid, bis-p-(carboxylphenyl)-methane or bis-p-(carboxylphenyl)-ethane.

(69) Preference is given to the aromatic dicarboxylic acids and, amongst those, especially terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid.

(70) Further suitable dicarboxylic acids are those that contain —CO—NH— groups; they are described in DE-A 2 414 349. Dicarboxylic acids that contain N-heterocyclic rings are also suitable, for example those that are derived from carboxylalkylated, carboxylphenylated or carboxybenzylated monoamine-s-triazinedicarboxylic acids (cf. DE-A 2 121 184 and 2 533 675), mono- or bis-hydantoins, optionally halogenated benzimidazoles or parabanic acid. The carboxyalkyl groups therein may contain from 3 to 20 carbon atoms.

(71) When additional diols are used, suitable aliphatic diols are the linear and branched aliphatic glycols, especially those having from 2 to 12, more especially from 2 to 6, carbon atoms in the molecule, for example: ethylene glycol, 1,2- and 1,3-propylene glycol, 1,2-, 1,3-, 2,3- or 1,4-butanediol, pentyl glycol, neopentyl glycol, 1,6-hexanediol and 1,12-dodecanediol. A suitable cycloaliphatic diol is, for example, 1,4-dihydroxycyclohexane. Further suitable aliphatic diols are, for example, 1,4-bis(hydroxymethyl)cyclohexane, aromatic-aliphatic diols such as p-xylylene glycol or 2,5-dichloro-p-xylylene glycol, 2,2-(β-hydroxyethoxyphenyly propane and also polyoxyalkylene glycols such as diethylene glycol, triethylene glycol, polyethylene glycol and polypropylene glycol. The alkylene diols are preferably linear and contain especially from 2 to 4 carbon atoms.

(72) Polyoxyalkylene glycols having molecular weights of from 150 to 40 000 are also suitable.

(73) As aromatic diols mention is made of those wherein two hydroxy groups are bonded to one or to different aromatic hydrocarbon radical(s).

(74) Preferred diols are the alkylene diols, and 1,4-dihydroxycyclohexane and 1,4-bis(hydroxy-methyl)cyclohexane. Special preference is given to ethylene glycol, 1,4-butanediol, and also 1,2- and 1,3-propylene glycol.

(75) Further suitable aliphatic diols are the β-hydroxyalkylated, especially β-hydroxyethylated, bisphenols such as 2,2-bis[4′-(β-hydroxyethoxy)phenyl]propane. Further bisphenols are mentioned hereinafter.

(76) A further group of suitable aliphatic diols comprises the heterocyclic diols described in German Offenlegungsschriften 1 812 003, 2 342 432, 2 342 372 and 2 453 326. Examples are: N,N′-bis(β-hydroxyethyl)-5,5-dimethyl-hydantoin, N,N′-bis(β-hydroxypropyl)-5,5-dimethyl-hydantoin, methylenebis[N-(β-hydroxyethyl)-5-methyl-5-ethylhydantoin], methylenebis[N-(β3-hydroxyethyl)-5,5-dimethylhydantoin], N,N′-bis(β-hydroxyethyl)benzimidazolone, N,N′-bis(β-hydroxyethyl)-(tetrachloro)-benzimidazolone and N,N′-bis(β-hydroxyethyl)-(tetrabromo)-benzimidazolone.

(77) Suitable aromatic diols include mononuclear diphenols and, especially, binuclear diphenols carrying a hydroxyl group on each aromatic nucleus. “Aromatic” is understood to refer preferably to hydrocarbon-aromatic radicals, for example phenylene or naphthylene. Besides, for example, hydroquinone, resorcinol and 1,5-, 2,6- and 2,7-dihydroxynaphthalene, special mention should be made of bisphenols that can be represented by the following formulae:

(78) ##STR00009##

(79) The hydroxyl groups may be in the m-position, but especially in the p-position; R′ and R″ in those formulae may be alkyl having from 1 to 6 carbon atoms, halogen such as chlorine or bromine, and especially hydrogen atoms. A can denote a direct bond or —O—, —S—, —(O)S(O)—, —C(O)—, —P(O)(C.sub.1-C.sub.20alkyl)-, unsubstituted or substituted alkylidene, cycloalkylidene or alkylene.

(80) Examples of unsubstituted or substituted alkylidene are: ethylidene, 1,1- or 2,2-propylidene, 2,2-butylidene, 1,1-isobutylidene, pentylidene, hexylidene, heptylidene, octylidene, dichloro-ethylidene and trichloroethylidene.

(81) Examples of unsubstituted or substituted alkylene are methylene, ethylene, phenyl-methylene, diphenylmethylene and methylphenylmethylene. Examples of cycloalkylidene are cyclopentylidene, cyclohexylidene, cycloheptylidene and cyclooctylidene.

(82) Examples of bisphenols are: bis(p-hydroxyphenyl) ether or thioether, bis(p-hydroxyphenyl)-sulfone, bis(p-hydroxyphenyl)methane, bis(4-hydroxyphenyl)-2,2′-biphenyl, phenylhydro-quinone, 1,2-bis(p-hydroxyphenyl)ethane, 1-phenyl-bis(p-hydroxyphenyl)methane, diphenyl-bis(p-hydroxyphenyl)methane, diphenyl-bis(p-hydroxyphenyl)ethane, bis(3,5-dimethyl-4-hydroxyphenyl)sulfone, bis(3,5-dimethyl-4-hydroxyphenyl)-p-diisopropylbenzene, bis(3,5-dimethyl-4-hydroxyphenyl)-m-diisopropylbenzene, 2,2-bis(3′,5′-dimethyl-4′-hydroxyphenyl)-propane, 1,1- or 2,2-bis(p-hydroxyphenyl)butane, 2,2-bis(p-hydroxyphenyl)hexafluoro-propane, 1,1-dichloro- or 1,1,1-trichloro-2,2-bis(p-hydroxyphenyl)ethane, 1,1-bis(p-hydroxy-phenyl)cyclopentane and especially 2,2-bis(p-hydroxyphenyl)propane (bisphenol A) and 1,1-bis(p-hydroxyphenyl)cyclohexane (bisphenol C).

(83) Suitable polyesters of hydroxycarboxylic acids are, for example, polycaprolactone, polypivalolactone and the polyesters of 4-hydroxycyclohexanecarboxylic acid, 2-hydroxy-6-naphthalenecarboxylic acid or 4-hydroxybenzoic acid.

(84) Furthermore, polymers that may contain mainly ester bonds, but also other bonds, for example polyester amides and polyester imides, are also suitable.

(85) Oligomers/polymers are obtained which contain, as structural repeating unit, a group of

(86) formula A2 wherein the

(87) ##STR00010##
substituents G.sub.1-G.sub.6 are as defined hereinbefore, v is a number 2-200 and the meaning of G results from the dicarboxylic acid used. Suitable dicarboxylic acids are mentioned hereinbefore.

(88) When a compound of formula B1 is reacted with the described dicarboxylic acids and, optionally, further diols, polyester amides are obtained having the structural repeating unit (B2)

(89) ##STR00011##

(90) The definitions of the substituents are given hereinbefore.

(91) A third group of very suitable oligomers/polymers comprises polyurethanes that are obtained by reacting diisocyanates with compounds of formula A1 and, optionally, further diols.

(92) Very suitable diisocyanates are 1,6-bis[isocyanato]hexane, 5-isocyanato-3-(isocyanatomethyl)-1,1,3-trimethylcyclohexane, 1,3-bis[5-isocyanato-1,3,3-trimethyl-phenyl]-2,4-dioxo-1,3-diazetidine, 3,6-bis[9-isocyanato-nonyl]-4,5-di(1-heptenyl)cyclohexene, bis[4-isocyanato-cyclohexyl]methane, trans-1,4-bis[isocyanato]cyclohexane, 1,3-bis[isocyanatomethyl]-benzene, 1,3-bis[1-isocyanato-1-methyl-ethyl]benzene, 1,4-bis[2-isocyanato-ethyl]cyclohexane, 1,3-bis[isocyanatomethyl]cyclohexane, 1,4-bis[1-isocyanato-1-methylethyl]penzene, bis[isocyanato]isododecylbenzene, 1,4-bis[isocyanato]benzene, 2,4-bis[isocyanato]toluene, 2,6-bis[isocyanato]toluene, 2,4-/2,6-bis[isocyanato]toluene, 2-ethyl-1,2,3-tris[3-isocyanato-4-methyl-anilinocarbonyloxy]propane, N,N′-bis[3-isocyanato-4-methylphenyl]urea, 1,4-bis[3-isocyanato-4-methylphenyl]-2,4-dioxo-1,3-diazetidine, 1,3,5-tris[3-isocyanato-4-methylphenyl]-2,4,6-trioxohexahydro-1,3,5-triazine, 1,3-bis[3-isocyanato-4-methylphenyl]-2,4,5-trioxoimidazolidine, bis[2-isocyanatophenyl]methane, (2-isocyanato-phenyl)-(4-isocyanato-phenyl)-methane, bis[4-isocyanato-phenyl]methane, 2,4-bis-[4-isocyanatobenzyl]-1-isocyanatobenzene, [4-isocyanato-3-(4-isocyanato-benzyl)-phenyl]-[2-isocyanato-5-(4-isocyanato-benzyl)-phenyl]methane, tris[4-isocyanato-phenyl]methane, 1,5-bis[isocyanato]-naphthalene and 4,4′-bis[isocyanato]-3,3′-dimethyl-biphenyl.

(93) Especially preferred diisocyanates are 1,6-bis[isocyanato]hexane, 5-isocyanato-3-(isocyanatomethyl)-1,1,3-trimethylcyclohexane, 2,4-bis[isocyanato]toluene, 2,6-bis[isocyanato]-toluene, 2,4/2,6-bis[isocyanato]toluene or bis[4-isocyanato-phenyl]methane.

(94) Polyurethanes having the structural repeating unit (A3)

(95) ##STR00012##
are obtained. The substituents are defined hereinbefore. The meaning of G results from the diisocyanates used.

(96) Especially suitable individual compounds are mentioned herein below, Table 1.

(97) TABLE-US-00001 TABLE 1 Compound no. Structural formula 101 102 103 104 105 106 107 108 0 109 110 111 112 113 114 115 116 117 118 0 119 120 121 122 123 124 125 126 127 128 0 129 130 131 132 133 134 135 136 137 138 0 139 140 141 142 143 144 145 146 147 148 0 149 150 151 152 153 154

(98) In a specific embodiment of the invention an additional organic radical initiator is added.

(99) Examples of free-radical initiators will be known to the person skilled in the art and are commercially available, for example:

(100) 2,2′-azo-bis(2-methyl-butyronitrile)=AIBN, 2,2′-azo-bis(2,4-dimethylvaleronitrile), 2,2′-azo-bis(4-methoxy-2,4-dimethylvaleronitrile), 1,1′-azo-bis(1-cyclohexanecarbonitrile), 2,2′-azo-bis(isobutyramide) dihydrate, 2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile, dimethyl-2,2′-azo-bisisobutyrate, 2-(carbamoylazo)isobutyronitrile, 2,2′-azo-bis(2,4,4-tri-methylpentane), 2,2′-azo-bis(2-methylpropane), 2,2′-azo-bis(N,N′-dimethylene-isobutyro-amidine) in the free base or hydrochloride form, 2,2′-azo-bis(2-amidinopropane) in the free base or hydrochloride form, 2,2′-azo-bis{2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]propionamide} or 2,2′-azo-bis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxy-ethyl]propionamide}.

(101) Acetyl cyclohexane-sulfonyl peroxide, diisopropyl-peroxy-dicarbonate, tert-amyl perneodecanoate, tert-butyl perneodecanoate, tert-butyl perpivalate, tert-amyl perpivalate, di(2,4-dichlorobenzoyl) peroxide, diisononanoyl peroxide, didecanoyl peroxide, dioctanoyl peroxide, dilauroyl peroxide, di(4-methyl-benzoyl) peroxide, disuccinic acid peroxide, diacetyl peroxide, dibenzoyl peroxide=BPO, tert-butyl per-2-ethyl hexanoate, di(4-chloro-benzoyl) peroxide, tert-butyl perisobutyrate, tert-butyl permalei nate, 1,1-bis(tert-butylperoxy)-3,5,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, tert-butyl-peroxy-isopropyl carbonate, tert-butyl perisononaoate, 2,5-dimethylhexane-2,5-dibenzoate, tert-butyl peracetate, tert-amyl perbenzoate, tert-butyl perbenzoate, diisopropyl peroxydicarbonate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, 2,2-bis(tert-butylperoxy)butane, 2,2-bis(tert-butyl-peroxy)propane, dicumyl peroxide=DCP, 2,5-dimethyl hexane-2,5-di-tert-butyl peroxide, 3-tert-butylperoxy-3-phenyl phthalide, di-tert-amyl peroxide, 1,3-bis(tert-butylperoxy-isopropyl)benzene, 3,5-bis(tert-butylperoxy)-3,5-dimethyl-, 2-dioxolane, di-tert-butyl peroxide, 2,5-dimethyl-hexyne-2,5-di-tert-butyl peroxide, n-butyl 4,4-di(tert-butyl peroxy)valerate, ethyl 3,3-di(tert-butyl peroxy)butyrate, di(1-hydroxycyclohexyl) peroxide, dibenzyl peroxide, tert-butyl-cumyl peroxide, 3,3,6,6,9,9-hexamethyl-1,2,4,5-tetraoxa-cyclononane, p-menthane hydroperoxide, pinane hydroperoxide, diisopropylbenzene mono-hydroperoxide, cumene hydroperoxide, methyl ethyl ketone peroxide and tert-butyl hydroperoxide.

(102) There may also be mentioned commercially available ‘C free-radical-formers’, for example: 2,3-dimethyl-2,3-di phenyl butane, 3,4-dimethyl-3,4-diphenyl hexane or poly-1,4-diisopropylbenzene.

(103) Where appropriate, combinations of such free-radical-formers may also be used.

(104) Particularly preferred are the organic peroxides selected from the group consisting of isobutyryl-peroxide, isopropylperoxy-dicarbonate, di-n-butylperoxy-dicarbonate, di-sec-butyl peroxy-dicarbonate, dicyclohexyl peroxy-dicarbonate, di(2-ethyl hexyl)peroxy-dicarbonate, t-butyl-perneodecanoate, t-butyl-perpivalate, bis(3,5,5-trimethyl-hexanoyl)peroxide, didecanoyl-peroxide, dilauroyl-peroxide, t-butyl-perisobutyrate, t-butyl-per2-ethyl-hexanoate, t-butyl-peracetate, t-butyl-per-3,5,5-trimethylhexanoate, t-butyl-perbenzoate, di-t-butyl-peroxide, t-butyl-hydroperoxide and di-t-amyl peroxide.

(105) In another embodiment of the invention additionally a chain transfer agent is added.

(106) The chain transfer agent is, for example, selected from the group consisting of ketones, aldehydes, C.sub.3-C.sub.20alkanes, C.sub.3-C.sub.20alkenes, mercaptanes and disulfides.

(107) Specific examples for sulfur containing compounds are mercaptoethanol, dodecylmercaptane, dibenzylsufide, dibutylsulfide, octadecyldisulfide, distearylthiodi propionate (Irganox PS 802), dipalmityldithiodipropionate, dilaurylthiodipropionate (Irganox® PS 800).

(108) Most preferred is dodecylmercaptane.

(109) Chain transfer agents are known and for example described in “The Chemistry of Free Radical Polymerization”, Ed. G. Moad, E. Rizzardo, Pergamon 1995, pages 234-251. They are largely items of commerce.

(110) In a further embodiment of the invention the method is carried out in the presence of a comonomer, which is selected from a monomer containing a vinyl group, an allyl group, a vinylidene group, a diene group or a olefinic group other than ethylene.

(111) The term vinyl group containing monomer is understood to mean in particular (meth)acrylates, vinylaromatic monomers, vinylesters, vinyl ethers, (meth)acrylonitrile, (meth)acrylamide, mono and di(C.sub.3-C.sub.18alkyl)(meth)acrylamides and monoesters and diesters of maleic acid.

(112) Mention may be made as examples of useful (meth)acrylates of glycidyl, methyl, ethyl, 2,2,2-trifluoroethyl, n-propyl, isopropyl, n-butyl, sec-buty, tert-butyl, n-amyl, i-amyl, n-hexyl, 2-ethylhexyl, cyclohexyl, octyl, i-octyl, nonyl, decyl, lauryl, stearyl, phenyl, benzyl, β-hydroxy-ethyl, isobornyl, hydroxypropyl (meth)acrylates.

(113) The term vinylaromatic monomer is understood to mean, for example, styrene, vinyltoluene, α-methylstyrene, 4-methoxystyrene, 2-(hydroxymethyl)styrene, 4-ethylstyrene, vinylanthracene.

(114) Mention may be made as vinyl esters, of vinyl acetate, vinyl propionate, vinyl chloride and vinyl fluoride, as vinyl ethers, of vinyl methyl ether and vinyl ethyl ether.

(115) An example of a vinylidene monomer is vinylidene fluoride.

(116) The term diene group containing monomer is understood to mean a diene chosen from conjugated or nonconjugated, linear or cyclic dienes, such as, for example, butadiene, 2,3-dimethyl-butadiene, 1,5-hexadiene, 1,9-decadiene, 5-methylene-2-norbornene, 1,5 cyclooctadiene or 4,7,8,9-tetrahydroindene.

(117) Typically other olefinic monomers than ethylene are, for example, propylene, 1-butene, 4-methyl-1-pentene, octene or 1-decene.

(118) Further comonomers may be maleic acid anhydride, fumaric acid anhydride or itaconic acid anhydride and N-alkyl or N-arylmaleimide.

(119) Particulary preferred comonomers are methylacrylate, ethylacrylate, n-butylacrylate, vinylacetate, styrene, α-methylstyrene and methylmethacrylate.

(120) The proportion of comonomers for the preparation of random copolymers of ethylene may be in general from 0 to 90% by weight, preferably from 0 to 50% by weight and in particular from 0 to 10% by weight.

(121) A further aspect of the invention is the use of a hydroxylamine ester containing a structural element of formula (I) or (I′) as radical forming species for the continuous or batch wise polymerization or copolymerization of ethylene at an operating pressure of from 500 to 3500 bar, at a polymerization temperature between 100° and 400° C. in a suitable high pressure reactor.

(122) The following examples illustrate the invention.

(123) General Polymerization Procedure

(124) The ethylene polymerization experiments are carried out in a continuously operating laboratory plant. The center piece is a small stirred tank autoclave with jacket heating and 15 mL capacity. The polymerizations can be carried out at pressures up to 3000 bar and temperatures up to 300° C. The ethylene is compressed by means of a multistage diaphragm compressor. The initiator is dissolved in dry hexane and passed into the reactor through a metering device. Polymer samples can be separated from the reactor by a heated needle valve at the bottom of the autoclave. The formed polymer is separated from the unreacted ethylene by pressure release and the amount (conversion) is determined by gravimetry. The reaction parameters, mass flows and valves are computer controlled.

(125) All polymerization experiments are carried out at a pressure of 1800 bar, the mean residence time in the autoclave is 120 sec. The corresponding polymerization temperatures can be taken from Table 1. The initiator consumption (efficiency) per kg polymer can be calculated from the conversion and the amount of initiator used.

(126) Molecular weights and molecular weight distributions (PD) are determined by gel permeation chromatography in trichlorobenzene (140° C.) calibrated with polystyrene standards.

(127) The hydroxylamine ester used is compound 139, prepared according to WO 01/90113

(128) ##STR00067##

(129) TABLE-US-00002 TABLE 1 reaction conditions and analysis of LDPEs manufactured by high pressure polymerization of ethylene initiated by compound 139 Compound Reaction Conver- Initiator Number of MVR* 139/ Temp./ sion/ efficiency/ M.sub.n/ M.sub.w/ branches 190/21.6/ Specimen mol ppm 0° C. % g/kg.sub.polymer g/mol g/mol PD- CH.sub.3/1000 C. cm.sup.3/10 min Example 1 15 205 13 1.3 8.45E+04 3.67E+05 4.3 22.5 0.34 Example 2 30 170 1.5 22.3 8.11E+04 2.84E+05 3.5 17.9 ** Example 3 15 170 1.4 12.4 1.16E+05 3.89E+05 3.4 15.3 ** Example 4 30 160 2.7 25.1 2.02E+05 5.47E+05 2.7 15.6 <0.1 Lupolen 2420 F — — — — 79.9 (commercial prod.)*** Comparative — 230 28.8 0.6 2.32E+04 1.87E+05 8.1 14.1 10.9 example**** *according to ISO1133 **not determined ***producer: Basell Polyolefins ***initiated by 30 mol ppm t-butylperbenzoate

(130) The data in Table 1 show that polymerizations carried out according to the invention lead to polyethylenes having high molecular weights (small MVR values) and narrow molecular weight distributions (PDs) whereas the polymer specimen from the comparative example as well as the commercial product show very broad PDs at even lower molecular weights.