USE OF AT LEAST ONE HEMI-PEROXYACETAL, ALONE OR IN COMBINATION WITH OTHER PEROXIDES, TO PROMOTE POLYMERISATION OR COPOLYMERISATION OF ETHYLENE UNDER HIGH PRESSURE

Abstract

The present invention relates to the use of at least one peroxide selected from the group consisting of hemiperoxyacetals, alone or in combination with one or more distinct additional peroxides, for the radical polymerization or copolymerization of ethylene under high pressure.

The invention also concerns a process for preparing polyethylene, comprising a step of radical polymerization or copolymerization of ethylene under high pressure in the presence of at least one peroxide selected from the group consisting of hemiperoxyacetals, alone or in combination with one or more distinct additional peroxides.

The present invention likewise pertains to a composition comprising ethylene, at least one peroxide selected from the group consisting of hemiperoxyacetals, and optionally one or more additional peroxides distinct from hemiperoxyacetals.

Claims

1-21. (canceled)

22. An organic peroxide, for use alone or in combination with one or more distinct additional organic peroxides, selected from the group consisting of hemiperoxyacetals for the radical polymerization or copolymerization of ethylene under high pressure.

23. The organic peroxide of claim 22, which is selected from the group consisting of hemiperoxyacetals having a half-life temperature at one minute and at atmospheric pressure of from 125° C. to 160° C.

24. The organic peroxide of claim 22, which is selected from the group consisting of hemiperoxyacetals conforming to the general formula (I) below: ##STR00003## wherein in formula (I): R.sub.1 represents a linear or branched C.sub.1-C.sub.4, R.sub.2 represents a branched C.sub.4-C.sub.12, n denotes zero or an integer from 1 to 3, and R.sub.3 represents a linear or branched C.sub.1-C.sub.3 alkyl group.

25. The organic peroxide of claim 22, wherein the organic peroxide is selected from the group consisting of 1-methoxy-1-tert-amylperoxycyclohexane (TAPMC), 1-methoxy-1-t-butylperoxycyclohexane (TBPMC), 1-methoxy-1-t-amylperoxy-3,3,5-trimethylcyclohexane, 1-methoxy-1-t-butylperoxy-3,3,5-trimethylcyclohexane, 1-ethoxy-1-t-amylperoxycyclohexane, 1-ethoxy-1-t-butylperoxycyclohexane, 1-ethoxy-1-t-butyl-3,3,5-peroxycyclohexane and mixtures thereof.

26. The organic peroxide of claim 22, wherein the organic peroxide is 1-methoxy-1-tert-amylperoxycyclohexane.

27. The organic peroxide of claim 22, wherein the additional peroxide or peroxides is or are selected from the group consisting of peroxyacetals.

28. The organic peroxide of claim 22, wherein the additional peroxide or peroxides is or are selected from the group consisting of peroxyacetals capable of initiating the radical polymerization or copolymerization of ethylene under high pressure in a temperature range of from 190° C. to 250° C.

29. The organic peroxide of claim 22, wherein the additional peroxide or peroxides is or are selected from the group consisting of peroxyacetals conforming to the general formula (II) below: ##STR00004## in which formula (II) R.sub.4 to R.sub.11, which are identical or different, represent a linear or branched C.sub.1-C.sub.6 alkyl group.

30. The organic peroxide of claim 22, wherein the additional peroxide or peroxides is or are selected from the group consisting of 2,2-di(tert-amylperoxy)propane, 2,2-di(tert-amylperoxy)butane and mixtures thereof.

31. The organic peroxide of claim 22, wherein the additional peroxide or peroxides are selected from the group consisting of peroxides having a half-life temperature at one minute and at atmospheric pressure which is lower than the half-life temperature of the hemiperoxyacetal as defined in claim 22.

32. The organic peroxide of claim 31, wherein the additional peroxide or peroxides is or are selected from the group consisting of tert-amyl peroxyneodecanoate, tert-butyl peroxyneodecanoate, diethylhexyl peroxydicarbonate, tert-amyl perpivalate, tert-butyl perpivalate, di(3,5,5-trimethylhexanoyl) peroxide, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, tert-amyl peroxy-2-ethylhexanoate and mixtures thereof.

33. The organic peroxide of claim 22, wherein the additional peroxide or peroxides are selected from the group consisting of peroxides having a half-life temperature at one minute and at atmospheric pressure which is higher than the half-life temperature of the hemiperoxyacetal as defined in claim 22.

34. The organic peroxide of claim 33, wherein the additional peroxide or peroxides is or are selected from the group consisting of tert-amyl peroxy-3,5,5-trimethylehexanoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, tert-butyl peracetate, 2,2-di(tert-amylperoxy)butane, 2,2-di(tert-butylperoxy)butane, tert-amyl peroxybenzoate, tert-butyl peroxybenzoate and mixtures thereof.

35. The organic peroxide of claim 22, wherein the additional peroxide or peroxides are selected from the group consisting of peroxy esters which are capable of initiating the radical polymerization or copolymerization of ethylene under high pressure at a temperature of from 160° C. to 190° C.

36. The organic peroxide of claim 22, wherein the additional peroxide or peroxides are selected from the group consisting of peroxy esters which are capable of initiating the radical polymerization or copolymerization of ethylene under high pressure at a temperature higher than 220° C.

37. The organic peroxide of claim 22, for the radical polymerization of ethylene under high pressure.

38. A process for preparing polyethylene or an ethylene copolymer, comprising a step of radical polymerization or copolymerization of ethylene under high pressure, in the presence of at least one peroxide as defined in claim 22, alone or in combination with one or more distinct additional peroxides as defined in claim 22.

39. The process as claimed in claim 38, wherein the polymerization or copolymerization step is implemented by injecting the peroxide as defined in claim 22, alone or in combination with one or more distinct additional peroxides as defined in claim 22, at one point or at a plurality of points of a reactor.

40. The process as claimed in claim 38, wherein the ethylene copolymer is selected from the group consisting of copolymers of ethylene and acrylate(s), copolymers based on ethylene and at least one alpha- or alpha, omega-olefin copolymers, copolymers based on ethylene and carbon monoxides, and copolymers based on ethylene and unsaturated cyclic anhydride comonomers.

41. The process as claimed in claim 38, wherein the polymer for preparation is polyethylene.

42. A composition comprising: i. at least one ethylene monomer, ii. at least one peroxide selected from the group consisting of hemiperoxyacetals as defined in claim 22, and iii. optionally at least one additional peroxide, distinct from the peroxide (ii), as defined in claim 22.

Description

EXAMPLES

Example 1

[0226] Organic Peroxide Tested

[0227] In the example that follows, a radical polymerization of ethylene under high pressure was carried out, on the one hand with tert-butyl peroxy-2-ethylhexanoate (Luperox® 26), called the reference peroxide, and on the other hand with 1-methoxy-1-tert-amylperoxycyclohexane, TAPMC, called peroxide (1).

[0228] Peroxide (1) and the reference peroxide are two organic peroxides which are capable of initiating the radical reaction of ethylene under high pressure within a temperature range, referred to as medium temperature range, of from 160° C. to 190° C.

[0229] In this comparative example, the reference peroxide was replaced weight for weight by the peroxide (1).

[0230] The reference peroxide has a self-accelerating exothermic decomposition temperature (SADT) of 35° C., which means that it must be stored in a cold environment, at a temperature in the region of 5-10° C., and that particular precautions must be taken when transporting it.

[0231] Peroxide (1), for its part, has a self-accelerating exothermic deposition temperature (SADT) of 60° C., allowing it to be stored and transported at ambient temperature.

[0232] Experimental Protocol

[0233] In a 435 ml high-pressure stirred batch reactor of autoclave type, the ethylene is injected until a pressure of 1800 bar is reached, i.e. approximately 207 g. Stirring is at 1000 rpm (revolutions per minute). The initial temperature was established at the reactor wall temperature at 160° C. by means of heater rods placed in the walls of the reactor.

[0234] The peroxides (peroxide (1) and reference peroxide) are respectively diluted in heptane before being injected into the reactor.

[0235] A transfer agent, propionaldehyde, is also used in order to limit the molecular masses and the fouling of the reactor.

[0236] Thus each organic peroxide (peroxide (1) and the reference peroxide) is diluted in heptane, and the propionaldehyde upstream of the reactor and at low temperature, so as not to initiate the reaction prior to entry into the reactor. Each mixture is then injected into the reactor using a high-pressure pump. The polymerization is triggered as soon as the peroxide is injected at an initial temperature of 160° C.

[0237] During the radical polymerization reaction, the thermal evolution curve, which follows the introduction of each peroxide into the reactor and corresponds to the exotherm of polymerization of ethylene, is ascertained. The exothermic curve corresponds to the kinetics of the radical reaction.

[0238] The exothermic curve passes through a temperature maximum, referred to as the maximum temperature attained and recorded as Tmax.

[0239] Determinations are made of Tmax and also the rate at which this Tmax is attained for a given level of addition.

[0240] The reaction proceeds until the final temperature returns to the same level of value as the initial temperature.

[0241] The reactor is then depressurized and the resin is recovered for a measurement of the specific peroxide consumption.

[0242] Results

[0243] Attainment of Tmax

[0244] Under the operating conditions referred to above (initial temperature=160° C. and pressure=1800 bar), the Tmax values observed for the two peroxides, the reference peroxide tert-butyl peroxy-2-ethylhexanoate (Luperox® 26) and the 1-methoxy-1-tert-amylperoxycyclohexane (TAPMC) peroxide, and for a respective concentration in ppm by weight relative to the ethylene monomer of 46 and 45 ppm by relative weight, are attained respectively in: 8.3 s and 11.7 s.

[0245] These Tmax values are attained according to virtually superimposed kinetic curves, and the slightly slower attainment of the Tmax with the TAPMC according to the invention is due to the fact that the Tmax attained with this peroxide is higher: 243° C. as against 214° C. for the reference, in spite of virtually the same level of addition by weight.

[0246] Specific Consumption

[0247] The specific consumption of the peroxide (1) and of the reference peroxide is also measured for two radical polymerizations using the same levels of addition and enabling the attainment of the maximum temperature Tmax for each of said peroxides, namely of 230° C. and of 205° C., still with an initial temperature of 160° C.

TABLE-US-00001 TABLE 1 Specific peroxide consumption Tmax 230° C. g commercial initiator/kg LDPE Luperox ® 26 1.096 0 TAPMC 0 0.281 Specific 1.096 0.281 consumption compared Tmax 205° C. kg commercial initiator/mt LDPE Luperox ® 26 0.587 0 TAPMC 0 0.181 Specific 0.587 0.181 consumption compared

[0248] According to this example, it is found that the production of LDPE when using a single initiator allows a gain in specific consumption of the order of 70% in terms of commercial peroxide (that is, undiluted peroxide) with peroxide (1) (TAPMC) relative to the reference peroxide (Luperox® 26) which is generally considered to be preferred in the state of the art.

Example 2

[0249] Organic Peroxides Tested

[0250] In the example which follows, a radical polymerization of ethylene under high pressure was carried out, with two organic peroxide cocktails containing respectively one peroxide of the medium range of operational temperatures (peroxide (1) or reference peroxide from example 1) combined with a more reactive organic peroxide and another less reactive organic peroxide, as defined above.

[0251] The two radical polymerizations of ethylene under high pressure were therefore carried out with the following peroxidic initiator systems: [0252] ternary cocktail 1: tert-butyl peroxypivalate (Luperox® 11) (as the peroxide more reactive than the reference peroxide), the reference peroxide (tert-butyl peroxy-2-ethylhexanoate—Luperox® 26) and tert-butyl peroxy-3,5,5-trimethylhexanoate (Luperox® 270) (as the peroxide less reactive than the reference peroxide), [0253] ternary cocktail 2: tert-butyl peroxypivalate (Luperox® 11) (as the peroxide more reactive than the reference peroxide (1)), peroxide (1) (1-methoxy-1-tert-amylperoxycyclohexane—TAPMC) and tert-butyl peroxy-3,5,5-trimethylhexanoate (Luperox® 270) (as the peroxide less reactive than the reference peroxide).

[0254] In the ternary cocktail 2, the reference peroxide was replaced weight for weight by the peroxide (1).

[0255] The ratio by mass of the three peroxides (Lup11/Lup26/Lup 270 and Lup11/TAPMC/Lup270) in their commercial presentation for each of the two ternary cocktails was in all cases 2:1:1.

[0256] Only Luperox® 11 was used in a diluted commercial form for safety reasons, at 75% in the phlegmatizer isododecane, in the commercial presentation of Luperox 11M75 (Lup11M75), the other peroxides being available in undiluted form. The ratio by mass of the Lup11/Lup26/Lup270 system therefore expresses a weight ratio between undiluted peroxidic active substances of 1.5/1/1 respectively, corresponding to the 2:1:1 by weight mixture of Lup11M75/Lup26/Lup270.

[0257] The ternary cocktail 1 is called the reference cocktail.

[0258] Experimental Protocol

[0259] The two radical polymerizations were carried out in the same batch reactor as that of example 1.

[0260] However, the initial temperature of the ethylene charge at 1800 bar was established at the lower initial temperature of 145° C., by virtue of the ternary cocktail, in which the most reactive organic peroxide dictates operation at a lower initial temperature than in example 1.

[0261] As in example 1, the ternary reference cocktail containing TBO and the cocktail 2 containing peroxide (1) were tested at the same overall level of addition in terms of organic peroxides in a first phase, in order to judge the kinetics (examination of the reaction exotherm climb ramp and Tmax attained as a function of time).

[0262] Result

[0263] Attainment of Tmax

[0264] As in example 1, the kinetic curves exhibit a very similar exothermic ramp, attaining Tmax in 12.3 seconds for the ternary reference cocktail, but in 14.2 seconds for the ternary cocktail 2 employing TAPMC in place of the Luperox® 26, at substitution weight for weight.

[0265] Again, this difference in time for attainment of Tmax is due to the fact that with peroxide (1), the Tmax was 256° C. as against 249° C. for the ternary reference cocktail, in spite of a total level of addition of peroxides, expressed in pure form, of 91 ppm by weight versus 113 ppm by weight for the ternary reference.

[0266] Specific Consumption

[0267] The specific consumption of the overall amounts of peroxides involved in the two ternary cocktails was also measured, at two maximum temperatures Tmax, namely of 250° C. and of 240° C., with an initial temperature of 145° C. for each of the cocktails.

TABLE-US-00002 TABLE 2 Specific overall consumption of peroxides Cocktail of peroxides Tmax Peroxides injected Specific consumption in ° C. (total in ppm by weight) in g peroxide/kg LDPE Luperox ® 11/Luperox ® 26/Luperox ® 270 250 116 0.898 Luperox ® 11/TAPMC/Luperox ® 270 250 83 0.627 Luperox ® 11/Lup26/Luperox ® 270 240 87 0.734 Luperox ® 11/TAPMC/Luperox ® 270 240 55 0.454

[0268] According to this example, it is found that the production of LDPE profits from a gain in overall specific consumption of the order of 30% in terms of pure peroxide (that is, undiluted peroxide) with peroxide (1) (TAPMC) relative to Luperox® 26, which is generally considered to be preferred by those skilled in the art, when the ternary cocktail is a mixture with a composition including a more reactive peroxide and a less reactive peroxide than peroxide (1), which replaces Luperox® 26 according to the invention, and in spite of the presence of peroxide (1) at less than 30% by mass in the cocktail.

Example 3

[0269] In the example which follows, a radical polymerization of ethylene under high pressure was carried out, with two organic peroxide cocktails containing respectively one peroxide of the medium range of operational temperatures (peroxide (1) or reference peroxide from example 1) combined with a more reactive organic peroxide and another less reactive organic peroxide, as defined above.

[0270] The two radical polymerizations of ethylene under high pressure were therefore carried out with the following peroxidic initiator systems: [0271] ternary cocktail 3: tert-butyl peroxypivalate (Luperox® 11) (as the peroxide more reactive than the reference peroxide), the reference peroxide (tert-butyl peroxy-2-ethylhexanoate—Luperox® 26) and tert-butyl peroxy-3,5,5-trimethylhexanoate (Luperox® 270) (as the peroxide less reactive than the reference peroxide), [0272] ternary cocktail 4: tert-butyl peroxypivalate (Luperox® 11), peroxide (1) (1-methoxy-1-tert-amylperoxycyclohexane—TAPMC) and 2,2-di(tert-amylperoxy)butane (peroxide (2) belonging to the formula (II)—Luperox® 520) (as the peroxide less reactive than peroxide (1)).

[0273] In the two ternary cocktails, the reference peroxide (Luperox® 26) was replaced weight for weight by peroxide (1), and the tert-butyl peroxy-3,5,5-trimethylhexanoate (Luperox® 270) was replaced weight for weight by 2,2-di(tert-amylperoxy)butane which belongs to the formula (II) described above (called peroxide (2)). [0274] The ratio by mass of the three peroxides (Luperox® 11/Luperox® 26/Luperox® 270 and Luperox® 11/TAPMC/Luperox® 520) for each of the two cocktails in their commercial form is 2:1:1. [0275] Luperox® 11 was used in a diluted commercial form for safety reasons, at 75% in the phlegmatizer isododecane, in the commercial presentation of Luperox® 11M75. [0276] Luperox® 520 was used in a diluted form for safety reasons, at 50% in the phlegmatizer isododecane (Luperox® 520M50). [0277] The ratio by mass of pure peroxides in the ternary cocktail 3 is 1.5/1/1 respectively in the order described above, and the ratio by mass of pure peroxides in the ternary cocktail 4 is 1.5/1/0.5. [0278] The ternary cocktail 3 corresponds to a conventional peroxidic initiator system based on peroxy esters, and corresponds hereinafter to the reference cocktail.

[0279] Experimental Protocol

[0280] The two radical polymerizations were carried out in the same batch reactor as that of example 2 and under the same conditions, meaning that the initial temperature of the ethylene charge at 1800 bar was established at an initial temperature of 145° C.

[0281] As in example 1, the exothermic curve of the radical reaction, the maximum temperature attained and the specific consumption of peroxides are ascertained for each polymerization reaction. The characteristics of polymerization of ethylene are therefore compared for each ternary cocktail.

[0282] Results

[0283] The kinetic curves ascertained for each cocktail exhibit very similar exothermic ramps, attaining Tmax in 12.3 seconds for the ternary reference cocktail (ternary cocktail 3), and 11.7 seconds for the ternary cocktail 4.

[0284] However, in spite of a very much lower overall amount of peroxides engaged in the radical polymerization for the ternary cocktail 4 (48 ppm expressed as pure peroxides), relative to 113 ppm for the ternary cocktail 3, the maximum temperature (Tmax) attained with the cocktail 4 is 256° C., as against 249° C. for the reference cocktail.

[0285] This difference indicates a greater production of resin (polymer) with cocktail 4 according to the invention, with a smaller overall amount of peroxides engaged.

Example 4

[0286] In this example, the experiment described in example 3 was repeated a number of times, retaining the same initial conditions (initial temperature=145° C. and pressure of 1800 bar) with the reference cocktail (ternary cocktail 3) and cocktail 4, by varying the total concentration of peroxides, still in the ratios indicated above (weight ratio of the commercial organic peroxides 2/1/1).

[0287] Result

[0288] The maximum temperature Tmax is greater in all cases when the overall concentration of peroxides increases within the cocktails tested. However, the ternary cocktail 4, comprising the peroxide (1)/peroxide (2) pairing, results in a higher Tmax, and therefore in a greater production of polymer, relative to the reference cocktail 3. The difference observed is of the order of 20° C., when the same overall amount by weight of peroxides is used, over an overall peroxide concentration range of from 20 to 130 ppm by weight, expressed in their commercial formulation.

[0289] The overall specific consumption for the ternary cocktail 4 is lower than that of the ternary cocktail 3, by at least 35%, for the same overall concentration of peroxides engaged.

Example 5

[0290] The specific consumption of the overall amounts of peroxide involved in the two ternary cocktails described in example 3 was also measured at two maximum temperatures Tmax, namely of 240° C. and of 250° C., with an initial temperature of 145° C.

[0291] The total amounts of peroxides in the table below are expressed in ppm by weight of peroxides in their commercial dilution (at 75% in isododecane for Luperox® 11, called Lup11M75, at 50% in isododecane for Luperox® 520, then called Luperox® 520M50, Luperox® 270 and Luperox® 26 are not diluted and are therefore taken at 100% for their contribution in the ternary mixture).

TABLE-US-00003 TABLE 3 Overall specific consumption of peroxides Tmax = 240° C. Commercial Specific consumption Conversion peroxides injected in g of total of ethylene (total in ppm by commercial in total % weight) peroxides/kg LDPE by weight) /kg LDPE Luperox ® 11M75/Luperox ® 26/Luperox ® 270 86.6 0.734 10.4 Luperox ® 11 M75/TAPMC/Luperox ® 520M50 45.9 0.323 13.9 Gain 47% 56% 33.6% indicates data missing or illegible when filed

TABLE-US-00004 TABLE 4 Overall specific consumption of peroxides Tmax = 250° C. Commercial Specific consumption Conversion of peroxides injected in g of ethylene in % (total in ppm total commercial by weight) peroxides/kg LDPE Luperox ® 11M75/Luperox ® 26/Luperox ® 270 116.2 0.898 11.5 Luperox ® 11M75/TAPMC/Luperox ® 520M50 62.5 0.420 14.8 Gain 46% 53% 28.7%

[0292] According to this example, it is found that for the same maximum temperature Tmax attained in a given zone of a reactor, the ternary cocktail according to the invention demonstrates better radical initiation performance, not only in terms of a reduction in specific consumption of the order of 50% but also in terms of conversion. Indeed, the commercial amount of peroxides enabling the maximum temperatures to be attained is lower by at least 45% with the ternary cocktail according to the invention.