METHOD FOR PREPARING A GRAFTED UNSATURATED SYNTHETIC RUBBER

Abstract

A method for preparing a synthetic rubber, including a step of graft-polymerizing a main polymer with a methyl-methacrylate monomer in the presence of a peroxide initiator of formula (I): R.sub.1—O—O—R.sub.2, wherein each of R.sub.1 and R.sub.2 is independently an alkyl group or an alkanoyl group including from 1 to 30 carbon atoms.

Claims

1. A method for preparing a synthetic rubber, comprising a step of graft-polymerizing a main polymer with a methyl-methacrylate monomer in the presence of a peroxide initiator of formula (I):
R.sub.1—O—O—R.sub.2,  (I) wherein each of R.sub.1 and R.sub.2 is independently an alkyl group or an alkanoyl group comprising from 1 to 30 carbon atoms.

2. The method of claim 1, wherein at least one of R.sub.1 and R.sub.2 is an alkanoyl group.

3. The method of claim 1, wherein at least one of R.sub.1 and R.sub.2 is a t-butyl group.

4. The method of claim 1, wherein each of R.sub.1 and R.sub.2 comprises from 3 to 20 carbon atoms.

5. The method of claim 1, wherein the peroxide initiator is selected from lauroyl peroxide, didecanoyl peroxide, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)-hexane, t-butyl peroxypivalate and t-butyl peroxy-2-ethylhexanoate and combinations thereof.

6. The method of claim 1, wherein the main polymer is selected from polychloroprene, SBS copolymer and combinations thereof.

7. The method of claim 1, comprising: dissolving the main polymer in a solvent to provide a reaction mixture; increasing the temperature of the reaction mixture and adding the methyl-methacrylate monomer and the peroxide initiator to the reaction mixture, in order to perform the graft-polymerization.

8. The method of claim 7, wherein the solvent is selected from dimethyl carbonate, ethyl acetate, cyclohexane, methylcyclohexane, acetone, toluene and combinations thereof.

9. The method of claim 1, wherein the graft-polymerization is performed at a temperature from 60 to 120° C.

10. The method of claim 1, wherein the weight ratio of methyl methacrylate monomer to main polymer is from 1:10 to 1:1.

11. The method of claim 1, wherein the weight ratio of peroxide initiator to methyl methacrylate monomer is from 1:1000 to 1:10.

12. The rubber obtainable by the method of claim 1.

Description

DESCRIPTION OF EMBODIMENTS

[0029] The invention will now be described in more detail without limitation in the following description. Unless specified otherwise, all concentrations and ratios are expressed by weight.

[0030] The invention is directed to the preparation of a synthetic rubber, in particular a thermoplastic rubber or thermoplastic elastomer, i.e. a copolymer having both thermoplastic and elastomeric properties.

[0031] This rubber comprises a main polymer (which can itself be a copolymer) grafted with methyl methacrylate.

[0032] The method of the invention generally comprises dissolving the main polymer in a solvent to provide a reaction mixture. Thereafter, the temperature of the reaction mixture is increased and the methyl-methacrylate monomer and the peroxide initiator are added to the reaction mixture, so as to perform the graft-polymerization of methyl methacrylate on the main polymer.

[0033] If the main polymer is provided in the form of a solid, it is usually cut into pieces before being dissolved.

[0034] The main polymer used in the context of the invention is primarily polychloroprene (also known as chloroprene rubber). However, other polymers may be used, such as styrene block copolymers and in particular poly(styrene-butadiene-styrene) or SBS rubber.

[0035] The preferred example of solvent used in the context of the invention is toluene. Other useful solvents notably include dimethyl carbonate, ethyl acetate, cyclohexane, methylcyclohexane and acetone.

[0036] The dissolution of the main polymer into the solvent can be performed for instance at a temperature of from 20 to 60° C., preferably from 30 to 50° C. and more preferably at approximately 40° C.

[0037] Thereafter, the temperature of the reaction mixture can be increased and the methyl methacrylate monomer and the initiator can be added. The temperature increase and the addition of methyl methacrylate and initiator can be performed simultaneously or sequentially in any order.

[0038] The (increased) temperature of the reaction mixture for the purpose of the graft-polymerization reaction is typically from 60 to 120° C., preferably from 70 to 100° C., and more preferably is approximately 80° C.

[0039] The initiator used in accordance with the invention is a peroxide initiator of formula (I):

R.sub.1—O—O—R.sub.2,  (I)

[0040] wherein each of R.sub.1 and R.sub.2 is independently an alkyl group or an alkanoyl group comprising a total number of carbon atoms from 1 to 30.

[0041] Each of R.sub.1 and R.sub.2 can be linear or branched, and the carbon atoms can be substituted or non-substituted. Substituents may notably include alkanoyl substituents or peroxy substituents. Preferably, the initiator consists of carbon, hydrogen and oxygen atoms.

[0042] According to one embodiment, each of R.sub.1 and R.sub.2 is a non-substituted, linear or branched alkyl or alkanoyl group.

[0043] No aryl group is present in the initiator of the invention.

[0044] The preferred total number of carbon atoms in each of R.sub.1 and R.sub.2 is 3 to 20, preferably 4 to 20.

[0045] For each initiator, a 1-hour half-life temperature in the relevant solvent (for instance toluene) can be defined: this is the temperature at which the half-life of the initiator in the solvent (i.e. the time after which half of the initiator in a dilute solution has decomposed) is 1 hour.

[0046] It has been found that it is desirable to use an initiator having a 1-hour half-life temperature close to the temperature of the graft-polymerization step.

[0047] For instance, the initiator is selected so that its 1-hour half-life temperature is from T.sub.R−ΔT to T.sub.R+ΔT, where T.sub.R is the temperature of the graft-polymerization step, and where ΔT is 20° C.; or 15° C., or 10° C.; or 5° C.

[0048] According to some embodiments, the initiator is selected so that its 1-hour half-life temperature is from 70 to 100° C., more preferably from 75 to 95° C.

[0049] Preferred examples of initiators to be used in connection with the present invention are: [0050] (A) lauroyl peroxide (for example marketed by Arkema under the name Luperox® LP), of formula:

##STR00001## [0051] (1-hour half-life temperature of 81° C.); [0052] (B) didecanoyl peroxide (for example marketed by Arkema under the name Luperox® DEC), of formula:

##STR00002## [0053] (1-hour half-life temperature of 83° C.); [0054] (C) 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)-hexane (for example marketed by Arkema under the name Luperox® 256), of formula:

##STR00003## [0055] (1-hour half-life temperature of 91° C.); [0056] (D) t-butyl peroxypivalate (for example marketed by Arkema under the name Luperox® 11M75), of formula:

##STR00004## [0057] (1-hour half-life temperature of 76° C.); [0058] (E) t-butyl peroxy-2-ethylhexanoate (for example marketed by Arkema under the name Luperox® 26), of formula:

##STR00005## [0059] (1-hour half-life temperature of 94° C.).

[0060] Instead of a single peroxide initiator, use may be made of combinations of peroxide initiators as described above.

[0061] The duration of the graft-polymerization reaction step can typically be from 30 minutes to 24 hours, preferably from 1 hour to 10 hours, more preferably from 2 hours to 6 hours. The duration can be for instance of approximately 4 hours. The reaction is stopped by stopping heating and decreasing the temperature to e.g. 30 to 50° C. Thereafter, inhibitors may be used, such as butylhydroxytoluene.

[0062] The weight ratio of methyl methacrylate to main polymer in the reaction mixture can be from 1:10 to 1:9; or from 1:9 to 1:8; or from 1:8 to 1:7; or from 1:7 to 1:6; or from 1:6 to 1:5; or from 1:5 to 1:4; or from 1:4 to 1:3; or from 1:3 to 1:2; or from 1:2 to 2:3; or from 2:3 to 3:4; or from 3:4 to 1:1.

[0063] The weight ratio of initiator to methyl methacrylate monomer in the reaction mixture can be from 1:1000 to 1:500; or from 1:500 to 1:300; or from 1:300 to 1:200; or from 1:200 to 1:150; or from 1:150 to 1:100; or from 1:100 to 1:50; or from 1:50 to 1:10.

[0064] At the end of the reaction, the reaction mixture can also comprise various additives. Use may in particular be made of inhibitors such as butylhydroxytoluene or hydroquinone to terminate all the left unreacted free radicals.

[0065] The grafted rubber obtained according to the method of the invention has improved properties. According to some embodiments, it is notably characterized by a graft ratio of at least 30% and a peeling strength of at least 2000 N/m.

[0066] The grafted rubber of the invention can be used in particular as an adhesive, notably for bonding leather substrates, synthetic leather substrates, polyvinyl chloride substrates, polyurethane substrates, ethylene vinyl acetate substrates, etc.

EXAMPLES

[0067] The following examples illustrate the invention without limiting it.

[0068] Chloroprene rubber (CR) (DENKA A90) was cut into small pieces and dissolved in toluene at 40° C. Then the temperature was increased to 80° C. and methyl methacrylate (MMA) monomer was added together with an initiator. Two initiators were tested: [0069] Luperox® A75 (by Arkema), i.e. benzoyl peroxide (abbreviated below as LupA75). [0070] Luperox® 26 (by Arkema), i.e. t-butyl peroxy-2-ethylhexanoate (abbreviated below as Lup26).

[0071] Different weight ratios were tested. The grafted polymers thus obtained were tested in terms of: [0072] Conversion rate: use is made of a precision balance to weigh the final adhesive solution W.sub.1 (in grams). Then the sample is put in a vacuum oven at 120° C. to remove all solvent for 8 hours. Then the weight after solvent removal W.sub.2 is measured (in grams). The conversion rate is defined as [W.sub.2−W.sub.1/W.sub.0×G]/[W.sub.1×A/W.sub.0], where W.sub.0 is the total weight of raw materials (in g), G is the weight of CR (in g) and A is the weight of monomer (in g). [0073] Graft ratio: this parameter is determined by determining the accurate weight W.sub.2 of the sample after vacuum for 8 hours, cutting the sample to small pieces and putting it in a Soxhlet extractor. Acetone is used as solvent to wash the sample for more than 24 hours. After extraction, the sample is transferred to a vacuum oven at 120° C. for more than 4 hours and the final weight W.sub.3 is measured. The graft ratio (in %) is defined as (W.sub.3−W.sub.4)/(W.sub.2−W.sub.4)×100, where W.sub.4 is the weight of CR in the sample. [0074] Viscosity: use is made of a Brookfield viscometer, at a temperature of 25° C. [0075] Peeling strength: this parameter is measured according to test method ISO 36:2005.

[0076] The results are summarized in the table below (tests No. 1-5 are comparative examples, while tests No. 6-8 are according to the invention):

TABLE-US-00001 Test No. 1 2 3 4 5 6 7 8 Toluene 166 166 166 166 166 166 166 169.2 amount (g) CR 24 24 24 24 24 24 24 24 amount (g) MMA 10 10 10 10 10 10 10 6.8 amount (g) Initiator LupA75 LupA75 LupA75 LupA75 LupA75 Lup26 Lup26 Lup26 type Initiator 0.04 0.07 0.1 0.13 0.2 0.05 0.1 0.068 amount (g) Conversion 35.8 52.7 49.9 54.55 58.8 42.5 76.2 73.15 rate (%) Graft ratio 5.09 17.27 17.85 21.69 33.25 34.32 35.09 30.5 (%) Viscosity 600 ND 1100 3800 500 980 3065 2300 (cps) Peeling ND ND 1599 2714 ND ND 4566 2166 strength (N/m)