Process for modifying ethylene-based polymers and copolymers

Abstract

Process for functionalizing an ethylene-based (co)polymer comprising the step of contacting an ethylene-based (co)polymer at a temperature in the range 100-250 C. with an azide of formula (I) wherein Y is either (Ia) or (Ib) m is 0 or 1, n is 0 or 1, n+m=1 or 2, and X is a linear or branched, aliphatic or aromatic hydrocarbon moiety with 1-12 carbon atoms, optionally containing heteroatoms. ##STR00001##

Claims

1. Process for functionalising an ethylene-based (co)polymer comprising the step of contacting an ethylene-based (co)polymer at a temperature in the range 100-250 C. with an azide of formula (I) ##STR00008## wherein Y is either ##STR00009## m is 0 or 1, n is 0 or 1, n+m=1 or 2, and X is a linear or branched, aliphatic or aromatic hydrocarbon moiety with 1-12 carbon atoms, optionally containing heteroatoms.

2. Process according to claim 1 wherein the ethylene based (co)polymer is LDPE.

3. Process according to claim 1 wherein the ethylene-based (co)polymer is EPM.

4. Process according to claim 1 wherein the azide is selected from 4-(3-methyl-2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)benzene sulfonyl azide (also called citraconimide benzenesulfonylazide) and 2-(3-methyl-2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)ethyl carbonazidate (also called citraconimide-C2-azidoformate).

5. Process according to claim 1 wherein the ethylene-based (co)polymer and the azide are contacted at a temperature in the range 140-230 C.

6. Process according to claim 1 wherein the azide is mixed with the ethylene-based (co)polymer in an amount of 0.1-5 phr.

7. Process for modifying an ethylene-based (co)polymercomprising the steps of: preparing a functionalised ethylene-based (co)polymer according to the process of claim 1 contacting the functionalised ethylene-based (co)polymer with an organic peroxide to form a polymer/peroxide mixture, and heating said polymer/peroxide mixture at a temperature in the range 140-300 C.

8. Process according to claim 7 wherein the polymer/peroxide mixture is shaped prior to heating.

9. Process according to claim 7 wherein the polymer/peroxide mixture is shaped by extrusion.

10. Process according to claim 7 wherein the organic peroxide is a dialkyl peroxide or a trioxepane.

11. Process according to claim 7 wherein the organic peroxide is selected from the group consisting of 3,3,5,7,7-pentamethyl-1,2,4trioxepane, 2,5-dimethyl-2,5-di(tertbutylperoxy)hexyne-3, 2,5-dimethyl-2,5-di(tertbutylperoxy)hexane, di(tert-butylperoxyisopropyl)benzene, dicumyl peroxide, and tert-butyl cumyl peroxide.

12. Functionalised ethylene-based (co)polymer obtainable by the process according to claim 1.

13. Modified ethylene-based (co)polymer obtainable by the process according to claim 7.

14. A process for making power cables comprising an electrical connector surrounded by one or more layers of the functionalised ethylene-based (co)polymer of claim 1.

15. A power cable comprising one or more layers of the modified ethylene-based (co)polymer of claim 1.

Description

EXAMPLES

Example 1

Modification of LDPE

(1) LDPE (BPD2000 ex Ineos) was extruded together with 0, 1, or 2 phr citracon benzenesulfonylazide on a Thermo Scientific Haake PTW16, 40L/D lab extruder. The temperature in the extruder mixing zones ranged from 180 to 230 C., the screw speed was 150 rpm, the output was 1 kg/hr, and the residence time in the extruder was about 90 seconds. These settings were sufficient to fully decompose the azide, as confirmed by FT-IR spectrometry.

(2) After extrusion, the grafted LDPE extrudates were chopped and liquid tert-butyl cumyl peroxide (Trigonox T, ex-AkzoNobel) was added at different dosage levels to the chopped polymer beads at 60 C. to allow fast and homogeneous incorporation of the peroxide into the polymer particles. After absorption of the peroxide on the LDPE, the cure speed and crosslink density were evaluated at 180 C. using rheometry (Alfa technologies rheometer MDR 2000).

(3) In a separate experiment, the gel percentage of the crosslinked LDPE was measured by immersion of a specific amount of crosslinked LDPE in refluxing xylenes (approximately 140 C.) to determine the insolubles (=gel) content. This is an industrial method to determine the ultimate state of cure.

(4) The results are indicated in the table below. Recorded are the indication for cure speed: t5, t50 and t90, these are the times needed to reach 5, 50 or 90% of the ultimate maximal crosslink density. The delta torque (S) as measured in the rheometer is used as an indication of the crosslink density of the crosslinked LDPE.

(5) TABLE-US-00001 TABLE 1 Comp 1 2 Comp 3 4 Comp. 5 6 Comp 7 8 azide (phr) 0 1 2 0 1 2 0 1 2 0 1 2 Perox. (phr) 0.5 0.5 0.5 1 1 1 1.6 1.6 1.6 2 2 2 t5 (min) 0.9 0.5 0.5 0.8 0.5 0.5 0.5 0.5 0.5 0.8 0.5 0.4 t50 (min) 3.3 1.8 1.7 3.0 1.3 1.3 2.9 2.1 1.5 2.9 2.1 1.6 t90 (min) 10.2 7.3 7.5 8.8 6.1 6.0 8.6 7.2 6.1 8.5 7.0 6.1 S (Nm) 0.15 0.26 0.24 0.26 0.53 0.54 0.44 0.62 0.74 0.57 0.68 0.84 gel % 69 81 81 80 90 91 89 92 93 91 94 96

(6) It can be observed from the experiments that the grafting of the azide has two advantages: enhancement of the cure speed (shortening of t90) and enhancement of the level of cure (increase in S and gel %). The effect of the citraconazide content depends on the level of peroxide dosage. At low peroxide dosage levels, an increase in citraconazide level from 1 to 2 phr is not leading to a further enhancement of the properties. When increasing the peroxide level, the effect of the increase in citraconazide on the crosslink density becomes more apparent. This shows that the amount of citraconazide and the amount of peroxide can be fine-tuned to allow control over cure speed and crosslink density.

Example 2

Modification of EPM

(7) An ethylene-propylene copolymer (EPM), without unsaturations, was modified with the citraconazide used in Example 1. To achieve this, an EPM-based compound containing carbon black fillers and oil (see Table 2 for the composition) was mixed with 2 parts per hundred rubber (phr) of the citracon benzenesulfonylazide and heat treated at 150-180 C. in a Banbury type internal mixer to allow grafting of the azide onto the EPM.

(8) After modification of the EPM compound with the azide, 3 phr of Perkadox 14-40B-pd ex-AkzoNobel (=40 wt % di(tert-butylperoxyisopropyl)benzene on calcium carbonate), corresponding to 0.4 wt % pure peroxide, was mixed with the EPM using a two-roll-mill.

(9) The EPM was cured by heating at 170 C.

(10) The cure speed and crosslink density were evaluated using rheometry (Alfa technologies rheometer MDR 2000). The results are indicated in Table 2.

(11) As a comparative experiment, an unmodified EPM was mixed with peroxide and crosslinked in the same manner.

(12) TABLE-US-00002 TABLE 2 Inv. Exp. Comparative exp. EPM (Dutral CO 038) 100 100 Carbon black N771 70 70 Carbon black N550 70 70 Sunpar 550 oil 50 50 Citraconazide (phr) 2 Perkadox 14-40B-pd (phr) 3 3 Rheometer results: t5 (min) 0.4 0.5 t50 (min) 1.5 3.1 t90 (min) 6.2 11.1 M.sub.L (min) 0.3 0.3 M.sub.H (min) 1.9 1.0 S (Nm) 1.6 0.7

(13) The delta torque (S) as measured in the rheometer is an indication of the crosslink density of the crosslinked EPM. It can be observed that the grafting of the azide has two advantages: to enhance the speed of cure (shorter t90) and to enhance the level of cure (increase in S).