BIOMIMETIC SYNTHETIC RUBBER

Abstract

The present invention relates to a composition comprising (i) a crosslinkable synthetic cis-1,4-polydiene having a cis content of at least 95% and a functional group in the terminal position, and (ii) an amphiphilic compound.

Claims

1. A composition, comprising a crosslinkable synthetic cis-1,4-polydiene having a cis content of at least 95% and a functional group in the terminal position, an amphiphilic compound.

2. The composition as claimed in claim 1, wherein the cis-1,4-polydiene is a cis-1,4-polyisoprene or a cis-1,4-polybutadiene or a mixture of these two polymers; and/or wherein the synthetic cis-1,4-polydiene is obtainable via a polymerization in the presence of a coordination catalyst that comprises a transition metal or a rare earth metal.

3. The composition as claimed in claim 1 or 2, wherein the terminal functional group is a carboxyl or carboxylate group, a hydroxyl group, an amine or ammonium group, an ester group or a cyano group.

4. The composition as claimed in any of the preceding claims, wherein the amphiphilic compound is a polar lipid; a protein; a fatty acid or a salt of a fatty acid; a fatty acid derivative; a surfactant or a mixture of at least two of these compounds.

5. The composition as claimed in any of the preceding claims, wherein the amphiphilic compound is present in the composition in an amount of not more than 30% by weight.

6. The composition as claimed in any of the preceding claims, wherein the amphiphilic compound is not covalently bonded to the cis-1,4-polydiene.

7. The composition as claimed in any of the preceding claims, additionally comprising a crosslinker, in particular sulfur or a peroxide.

8. A process for producing the composition as claimed in any of claims 1-7, comprising following process steps: producing a cis-1,4-polydiene having a cis content of at least 95% by a polymerization in the presence of a coordination catalyst, attaching a functional group in the terminal position of the cis-1,4-polydiene, mixing the cis-1,4-polydiene with the amphiphilic compound.

9. The process as claimed in claim 8, wherein the cis-1,4-polydiene is reacted with a modifier compound, with the result that a functional group is introduced in the terminal position of the cis-1,4-polydiene.

10. An elastomeric composition obtainable by crosslinking of the cis-1,4-polydiene in the composition as claimed in any of claims 1-7.

11. A shaped body comprising the elastomeric composition as claimed in claim 10.

12. The shaped body as claimed in claim 11, wherein the shaped body is a tire, a medical device or an industrial rubber product.

13. The use of the composition as claimed in any of claims 1-7 for the production of a shaped body, preferably a tire or a hose.

Description

EXAMPLES

Comparative Example 1

[0084] A cis-1,4-polyisoprene having a cis content of 98% was produced via a coordination polymerization in the presence of a neodymium-containing catalyst as follows:

[0085] Destabilized isoprene was initially charged in dried cyclohexane (10% by weight), the system was temperature-controlled at 50° C., and an Nd-containing catalyst (marketed by Comar Chemicals) dissolved in n-hexane (1.0% by volume based on monomer) was added, isothermal reaction time 3 h. The resulting polymer solution was stopped with isopropanol, stabilized with butylated hydroxytoluene and freed of solvent by coagulation/stripping.

[0086] The cis-1,4-polyisoprene produced was dissolved in chloroform (10% by weight). To the solution was additionally added 1% by weight of dicumyl peroxide (crosslinker) based on the polymer.

[0087] After stirring sufficiently vigorously, the solvent was evaporated. A film having a thickness of 1 mm was thermally treated at 160° C. to initiate crosslinking of the polyisoprene.

[0088] The strain crystallization was then determined for the crosslinked composition as follows:

[0089] Based on uniaxially stretched rubber strips, relative crystallinities were determined within a static stretch range of 0% to 650%. The method employed is based on the analysis of one-dimensional X-ray scattering data detected perpendicular to the direction of stretching. After quantifying the intensity (area evaluation) of the contributions of amorphous (halo) and crystalline scatter ((200) and (120) reflections), a relative degree of crystallization D.sub.c,rel=(I.sub.200+I.sub.120)/(I.sub.halo+I.sub.200+I.sub.120)=I.sub.cryst/I.sub.total is determined as a function of static stretch ε.sub.stat. The values for the relative degree of crystallization were calculated for 10-15 static stretches and presented as a graphical plot. Linear extrapolation of the graphical plot was used to determine the stretch value ε.sub.onset at which strain-induced crystallization commences.

[0090] At static stretch of 600%, a relative degree of crystallization D.sub.c,600% of about 28% was observed. The onset of crystallization was detected at stretch values ε.sub.onset of approx. 350%.

Comparative Example 2

[0091] A cis-1,4-polyisoprene was produced under the same polymerization conditions as in Comparative Example 1. The cis-1,4-polyisoprene had a cis content of 98%. After performance of the polymerization, but before it had been stopped, CO.sub.2 was further passed into the reaction solution as a modifier compound for end-group functionalization of the polyisoprene. This afforded a cis-1,4-polyisoprene having terminal carboxyl groups. The polymer solution obtained was stopped with isopropanol, stabilized with butylated hydroxytoluene, and freed of solvent in the conventional manner by coagulation/stripping.

[0092] The cis-1,4-polyisoprene produced was dissolved in chloroform (10% by weight). To the solution was then added 1% by weight of dicumyl peroxide (crosslinker) based on the polymer. After stirring sufficiently vigorously, the solvent was evaporated. A film having a thickness of 1 mm was thermally treated at 160° C. to initiate crosslinking of the polyisoprene.

[0093] The strain crystallization for the crosslinked composition is then determined according to the method described in Comparative Example 1.

[0094] At static stretch of 600%, a relative degree of crystallization D.sub.c,600% of about 32.9% was observed. The onset of crystallization was detected at stretch values ε.sub.onset of approx. 350%.

Inventive Example 1

[0095] A cis-1,4-polyisoprene was first produced under the same polymerization conditions as in Comparative Example 1. After performance of the polymerization, but before it had been stopped, CO.sub.2 was further passed into the reaction solution as a modifier compound for end-group functionalization of the polyisoprene. This afforded a cis-1,4-polyisoprene having terminal carboxyl groups. The cis-1,4-polyisoprene had a cis content of 98%. The polymer solution obtained was stabilized with butylated hydroxytoluene and freed of solvent by coagulation/stripping.

[0096] The cis-1,4-polyisoprene produced was dissolved in chloroform (10% by weight). To the solution was additionally added 0.4% by weight of L-alpha-lecithin (a phospholipid that functions as an amphiphilic compound) and 1% by weight of dicumyl peroxide (crosslinker), based on the polymer.

[0097] After stirring sufficiently vigorously, the solvent was evaporated. A film having a thickness of 1 mm was thermally treated at 160° C. to initiate crosslinking of the polyisoprene.

[0098] The strain crystallization for the crosslinked composition was then determined according to the method described in Comparative Example 1.

[0099] At static stretch of 600%, a relative degree of crystallization D.sub.c,600% of 46.9% was observed. The onset of crystallization was detected at stretch values ε.sub.onset of approx. 300%.

Comparative Example 3

[0100] For comparison purposes, the strain crystallization was also determined on an identically vulcanized sample of natural rubber.

[0101] At static stretch of 600%, a relative degree of crystallization D.sub.c,600% of 42.4% was observed. The onset of crystallization was detected at stretch values ε.sub.onset of approx. 200%.

[0102] With the composition according to the invention, which comprises the end-group-functionalized cis-1,4-polydiene and the amphiphilic compound, strain crystallization after crosslinking corresponding to almost that of natural rubber can be achieved.

[0103] The relative crystallinities at 600% stretch S.sub.c,600% exceed that of the natural rubber sample (SRV) with identical crosslinking investigated as reference.