Process for modifying polymers

Abstract

Process for modifying a polymer in the absence of elemental sulfur amounts larger than 0.5 phr, comprising the steps of a. mixing said polymer with a maleimide-functionalized mono-azide at a temperature in the range 80-250 C. to form a functionalized polymer, and b. thermally treating the functionalized polymer at a temperature in the range 50-270 C.

Claims

1. A process for modifying a polymer in the absence of elemental sulfur amounts greater than 0.5 phr and in the absence of a peroxide, comprising (a) mixing said polymer with a maleimide-functionalized mono-azide at a temperature in the range 80-250 C. to form a polymer containing maleimide functionalities, and (b) thermally treating the polymer containing maleimide functionalities at a temperature in the range 150-270 C.

2. The process according to claim 1 wherein the polymer is an elastomer.

3. The process according to claim 2 wherein the elastomer is natural rubber (NR), styrene butadiene rubber (SBR), butadiene rubber (BR), butyl rubber (IIR), ethylene propylene copolymer elastomer (EPM), ethylene propylene diene terpolymer elastomer (EPDM), or ethylene vinylacetate copolymer (EVA).

4. The process according to claim 1 wherein the polymer is a polyolefin.

5. The process according to claim 4 wherein the polyolefin polystyrene, polyethylene, polypropylene, or a copolymers of ethylene and/or propylene.

6. The process according to claim 1 wherein the polymer is polylactic acid.

7. The process according to claim 1 wherein the maleimide-functionalized azide has the following structure: ##STR00005## wherein Y is ##STR00006## 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.

8. A process for modifying a polymer in the absence of elemental sulfur amounts greater than 0.5 phr, comprising (a) mixing said polymer with a maleimide-functionalized mono-azide in the absence of a peroxide at a temperature in the range 80-250 C. to form a polymer containing maleimide functionalities, and (b) adding an anionic polymerization catalyst, a C-C initiator, or a peroxide and thermally treating the polymer containing maleimide functionalities at a temperature in the range 150-270 C.

9. The process according to claim 8 wherein the polymer is an elastomer.

10. The process according to claim 9 wherein the elastomer is natural rubber (NR), styrene butadiene rubber (SBR), butadiene rubber (BR), butyl rubber (IIR), ethylene propylene copolymer elastomer (EPM), ethylene propylene diene terpolymer elastomer (EPDM), or ethylene vinylacetate copolymer (EVA).

11. The process according to claim 8 wherein the polymer is a polyolefin.

12. The process according to claim 11 wherein the polyolefin is polystyrene, polyethylene, polypropylene, or a copolymer of ethylene and/or propylene.

13. The process according to claim 8 wherein the polymer is polylactic acid.

14. The process according to claim 8 wherein the maleimide-functionalized azide has the following structure: ##STR00007## wherein Y is ##STR00008## 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.

Description

EXAMPLES

Example 1

(1) A natural rubber-based compound comprising the ingredients listed in Table 1 was used in this Example. This rubber compound is suitable for truck tire tread compounds.

(2) TABLE-US-00001 TABLE 1 NR base compound NR SVR-3L 100 Carbon black FEF-N550 30 Carbon black HAF-N330 20 distilled aromatic extract oil (VivaTec 500) 8 Anti-ozonant (Santoflex 6PPD) 2 Antioxidant TMQ 1

(3) 47 grams of the compound were mixed on a two roll mill with 0.93 grams of maleimide sulfonylazide (4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)benzenesulfonyl azide). This equals 3.2 phr azide. The mixture is heat treated in a Banbury type mixer with an internal volume of 50 mL at a temperature of 120 C. for 30 minutes to graft the azide onto the NR rubber.

(4) After grafting the azide onto the natural rubber, the compound was cured by heat treatment at 170 C. During this heat treatment, the maleimide functionalities react with each other and form a network, thereby crosslinking the rubber.

(5) As a comparison, the same NR rubber was mixed on a two roll mill with 2.9 phr dicumyl peroxide at a temperature above 50 C.; sufficient to melt the peroxide. The resulting compound was cured by heat treatment at a 170 C. During this heat treatment the peroxide decomposes into radicals, which react with the polymer chain thereby forming a network and crosslinking the rubber.

(6) Table 2 lists the properties of the resulting modified polymers. Listed are the scorch time (ts2; the time required to increase the torque with 0.2 Nm from the curve minimum) and the t50 and t90, i.e. the times needed to reach 50 resp. 90% of the ultimate maximal crosslink density, measured in a rheometer. The delta torque (S) as measured in the rheometer is used as an indication of the crosslink density. The results show that the crosslinking behaviour of a natural rubber compound modified with 3.2 phr azide is similar to that modified with 2.9 phr dicumyl peroxide.

(7) TABLE-US-00002 TABLE 2 3.2 phr azide 2.9 phr dicumyl peroxide Rheometer at 170 C. ts2 (min) 1.0 1.1 t50 (min) 0.3 0.4 t90 (min) 8.1 7.1 S (Nm) 0.62 0.79 M.sub.L (Nm) 0.19 0.05 M.sub.H (Nm) 0.81 0.84 Tensile properties after cure at 170 C. for 15 minutes Tensile strength (N/mm2) 19 18 Elongation at break 444 416

(8) The ultimate crosslink level, as expressed by M.sub.H, is comparable for both cure systems. Also the mechanical properties, as expressed by the tensile strength and elongation at break, are similar for both cure systems.

(9) These results indicate that the process according to the present invention results in satisfactory crosslinking behaviour without production of volatiles other than nitrogen.

Example 2

(10) A polypropylene homopolymer (Moplen HP500N) was mixed in a Banbury mixer, with maleimide sulfonylazide at a temperature of 170 C. and reacted at this temperature for 20 minutes. During this reaction, the azide was grafted onto the polypropylene. After raising the temperature to 200 C. and mixing at 200 C. for 2-3 minutes, the maleimide groups on the polymer started to react and create branches and crosslinks as is apparent from the decreased melt flow index (MFI) in Table 3.

(11) This table shows the effect of the amount of azide added (in phr). The more azide used, the lower the MFI and the higher the crosslinking level.

(12) Irganox 1010 was added as a stabilizer for the polypropylene and to prevent polymerization of the maleimide groups at 170 C. Irganox 1010 influences the crosslinking reaction between the maleimide groups, which can be observed from the penultimate entry in Table 3, where an increase in the Irganox 1010 level led to an increase in MFI, which was most probably due to interference with the maleimide crosslinking by radical scavenging.

(13) Crosslinking was observed by measuring torque increase at 200 C. on samples which had been mixed at 170 C. These samples showed no crosslinking at 170 C.; only after exposing to 200 C. in the rheometer they started to crosslink. The torque increase is listed in Table 3.

(14) TABLE-US-00003 TABLE 3 maleimide Irganox MFI (230 C. 2016 Rheometer torque sulfonylazide (phr) 1010 (phr) kg) increase (dNm) 0 0.1 12.5 0 0.25 0.1 5.5 0.375 0.1 1.5 0.5 0.1 <0.5 0.3 0.5 0.5 8 1 0.1 No measurable MFI 0.5

Example 3

(15) An SBR-based compound comprising the ingredients listed in Table 4 was used in this Example. This rubber compound is suitable for truck tire tread compounds.

(16) 47 grams of the compound were mixed on a two roll mill with 0.93 grams of maleimide sulfonylazide (4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)benzenesulfonyl azide). This equals to 3.2 phr azide. The mixture was heat treated in a Banbury type mixer with an internal volume of 50 mL at a temperature of 120 C. for 20 minutes to graft the azide onto the SBR rubber.

(17) After grafting the azide onto the SBR rubber, the compound was cured by heat treatment at either 170 C. or 180 C.

(18) The experiments show that SBR can be thermally crosslinked after modification with maleimide sulfonylazide. Table 4 shows that after increasing the temperature from 170 C. to 180 C., the crosslink speed increased while the crosslink density (M.sub.H) has also improved.

(19) TABLE-US-00004 TABLE 4 1 2 Buna SB 1500 100 100 FEF-N550 30 30 HAF-N330 20 20 VivaTec 500 8 8 Santoflex 6PPD 2 2 Antioxidant TMQ 1 1 TBHQ 0.3 0.3 maleimide sulfonylazide 3.2 3.2 Temperature 170 C. 180 C. ts2 (min) 5 2 t50 (min) 7 4 t90 (min) 23 17 M.sub.L (Nm) 0.29 0.27 M.sub.H (Nm) 0.77 0.92 S (Nm) 0.48 0.65