GB1586861A - Polymers - Google Patents

Description

(54) MODIFICATION OF POLYMERS (71) We, IMPERIAL CHEMICAL INDUSTRIES LIMITED, Imperial Chemical House, Millbank, London SWIP 3JF, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to the modification of polymeric materials particularly polymeric materials containing carbon-carbon unsaturation.

In the context of this specificaion the term modification is used to denote the chemical attachment of atoms or groups of atoms to the polymeric material and the term includes the processes of cross-linking, chain extension and the bonding of additive groups to the polymer molecules.

According to the present invention a process for the modification of a polymeric material having carbon-carbon unsaturation recurrent in its molecular structure, comprises contacting the polymeric material with an organic compound which is a source of adjacent nitroso groups on a six-membered aromatic ring, the contact being under conditions whereby at least two of the nitroso groups are made available for reaction with the polymeric material.

The organic compound may be a compound containing at least one furoxan ring fused to a six membered quinonoid ring ring. In this compound the quinonoid ring may contain hetero atoms for example nitrogen, but it will in general be a six carbon ring. Alternatively the organic compound may be of a complex of a furoxan compound as described above with an aromatic hydrocarbon. Both of these types of organic compound act as a source of adjacent nitroso groups by reason of the fact that the furoxan ring is thermally labile and will open to produce the desired adjacent nitroso groups and in so doing the quinonoid ring changes to an aromatic form. For example

The six-membered ring may be fused to other rings as in for example the naphthalene, anthracene, and quinoline nucleii and more than one furoxan group may be present fused either to the same or to a different six membered quinonoid ring.

If there is more than one furoxan ring fused to the same quinonoid ring for example as in benzo difuroxan (II wherein Rl=R2=H) and benzo trifuroxan (I) it will be appreciated that more than two adjacent nitroso groups can result from the thermolysis of the furoxan rings. For example from the compounds named above tetranitrosobenzene and hexanitroso benzene would ultimately result and in these compounds there are a greater number of possibilities for reaction of nitroso groups with the polymer. Without prejudice to the generality of our invention it is believed that nitroso groups in the 1,4 positions on a six-membered aromatic ring are even more favourably disposed for the process of the invention to occur than those which are adjacent. Therefore for greater reactivity with polymeric materials we prefer to use in this invention a source of at least two pairs of adjacent nitroso groups for example a difuroxan or a trifuroxan having two or three furoxan rings fused to one or more six-membered quinonoid rings or the hydrocarbon adducts thereof.

The furoxans hereinbefore described are the so called "aromatic furoxans" but from the foregoing explanation it will be realised that this name is not, by certain nomenclature, strictly correct because the six-membered ring fused to the furoxan is more correctly a quinonoid ring and it may be converted to the aromatic form only when the furoxan ring is opened.

Groups other than furoxan may be also attached to the six-membered quinonoid ring provided they do not interfere with the use of the furoxan in the modification process. Suitable groups include hydrocarbon groups for example alkyl and aryl groups and substituted hydrocarbon groups the substituents being for example halogen, nitro, alkoxy, aryloxy, alkyl sulphonyl and aryl sulphonyl groups (see for example groups R1-R6 in formulae below).

For example included within the scope of the invention is the use of furoxan compounds of the following general formulae

X is a linking group and for example X may be (CH2)rn, -O, SO2- phenylene or

n is one less than the valency of the group X and m is an integer from 1 to 12.

wherein the groups R, which may be of the same or different are as described above.

The above formulae are generalisations and we intend to include other possible N-oxide isomers. For example in (II) where Rl*R2 the two isomers as shown below are also implied:

As will be readily appreciated compounds such as (I) and (II), and (111) if suitably substituted, will, because of the electron deficiency of the central C6 ring, form acceptor-donor complexes with a wide range of aromatic hydrocarbons. The furoxan being the acceptor and the aromatic hydrocarbon the donor. It may be convenient to use the complexed furoxan in the process of the invention rather than the furoxan itself; for example, it may improve handleability and facilitate dispersion in the polymer. The preparation of such complexes is well described in the literature (see for example: A S Bailey and J R Case, Proc. CSoc., (1957)176; Tetrahedron (1958)3 113).

Hydrocarbons suitable for the formation of complexes of the above type include: naphthalene, I-phenyl naphthalene, 2-phenyl naphthalene, hexamethylbenzene, biphenyl, tetrahydronaphthalene, trimethyl benzene and xylenes. The choice of complexing hydrocarbon will be governed by the strength of the complex formed with a particular furoxan.

The methods for preparation of furoxans used in the present invention are also adequently described in the literature. They may be obtained for example b.y thermal decomposition of the corresponding ortho nitroazides:

(Ref J V R Kaufman and J P Picard, Chem. Reviews, 59429 (1959), and references therein) or by oxidation of ortho-nitroanilines.

(Ref: V G Pesin et al, Z Obsch. Khim, 28 2094 (1958)) Polymeric materials which may be modified and, especially, cross-linked by the process of the present invention are mainly those incorporating copolymerised diene monomers and they include: polybutadiene styrene-butadiene copolymers acrylonitrile-butadiene copolymers butyl rubber natural rubber styrene-butadiene-acrylonitrile copolymers ethylene-propylene-diene terpolymers (the so-called EPDM rubbers) polychloroprene polyisoprene, polysiloxanes containing unsaturated groups and polyesters incorporating unsaturated acid units e.g. from maleic or fumaric acids or from maleic or itaconic anhydrides.

The polymeric materials may be mixtures or blends of two or more such unsaturated polymers and also include latices and other dispersions of such polymers. When used for cross-linking polymeric materials, the present invention is conveniently carried out by mixing the furoxan intimately with the polymeric material and subsequently heating the mixture to effect the cross-link. Mixing the furoxan or its hydrocarbon complex with the polymer is readily achieved using conventional rubber mixing techniques or other conventional plastics or paints technology.

The amount of furoxan or its complex which is mixed with the polymer depends mainly upon the degree of cross-linking desired but generally from 0.010/, to 30 /" by weight of furoxan or its complex is employed (calculated with reference to the weight of the polymer). Preferably at least 0.2 /" of furoxan or its complex is used.

Once the polymer and the furoxan or its complex have been thoroughly mixed the mixture may be heated to effect the modification, e.g. cross-linking, of the polymer. Temperatures usually employed are in the range 700C to 2000 C; but temperatures over a wider range may be used, provided the temperature is sufficient to cause the cross-linking, etc., but not so great as to cause undue degradation of the polymeric materials.

Additional ingredients may be mixed into the polymer before reacting it with the furoxan, if desired. Examples of such ingredients include common rubber additives, such as extenders, fillers, pigments, plasticisers and stabilisers.

The polymeric materials when cross-linked by the process of the present invention will be of much higher molecular weight and possess superior physical properties compared with the uncross-linked material. The cross-linked polymers may be used in a wide range of applications such as decorative or protective coatings for a variety of substrates, e.g. wood, metal, concrete, paper and plastics, and as ingredients for vehicle tyres, hoses, belting and other rubber articles. The ability to obtain quick cures at relatively low temperatures with many of the furoxans used in the present invention gives added scope to fabrication processes.

For example the compound obtained when a carbon-black filled styrene-butadiene rubber is mixed with benzodifuroxan is easily extruded but will cure quickly at the temperature of boiling water. Thus, for example, hose may be produced which is subsequently cured by passing hot water through it.

Although our invention has been mainly described with reference to crosslinking, as previously mentioned, it may also be used to bond additives to polymeric materials. Examples of such additives include dyestuffs, antistatic agents, antioxidants, anti-ozonants, and reinforcing agents. Examples of reinforcing agents are polyester, nylon, glass and carbon fibres or particulate fillers such as carbon black or fumed silica, the surfaces of which contain, either as a result of their method of preparation, or as a result of subsequent treatment, groups reactive towards the furoxans under the conditions of the invention.

The chemistry involved in the preparation of the furoxans of the present invention and the chemistry of the furoxans themselves makes it particularly easy to produce functionalised furoxans, for example furoxans containing chromophoric groups, for use as polymer additives in order to obtain for example dyestuffs chemically bonded to polymeric material or water repellent groups attached to the surface of a polymeric material.

The invention will be illustrated by the following Examples, in which all parts are by weight.

General Procedure for Cross-linking Rubbers In the preparation of solid rubber compositions, all components other than the furoxan were first milled together on conventional rubber mixing equipment and then mixed with the furoxan, also on the rubber mill Cure times (where given) were determined using a Wallace Shawbury cure-meter, taking the time required for the curing process as measured on the cure-meter trace to be at least 95% complete.

Example I Curing an EPDM Rubber with Benzofuroxan (EPDM=ethylene/propylene/diene Mixtures) Benzofuroxan prepared by the method of V G Pesin et al (Z Obsch. Khint 28 2094 (1958)) (4 parts) was mixed with an EPDM rubber (100 parts) plus carbon black (50 parts). The termonomer i.n the rubber was ethylidene norbornene ca. 77 / weight. The rubber mix was cured in about 50 minutes at 1500C and in about 10 minutes at 1750C. A sample of the rubber compound cured in a press at 1600C for 20 minutes had tensile strength 1000 psi and elongation at break of 250%.

Example 2 Curing a Styrene-butadiene Rubber (SBR) with Benzofuroxan Benzofuroxan (8 parts) was mixed with a styrene-butadiene rubber (100 parts) plus carbon black (50 parts). The rubber mixture could be cured in less than 25 minutes at 1700C. A sample of the rubber compound which was cured under pressure for 20 minutes at 1600C had tensile strength 1650 psi and elongation at break of 280%.

Example 3 Curing an EPDM rubber with

(5-chlorobenzofuroxan) The EPDM rubber of Example 1(100 parts), carbon black (50 parts) and the chlorobenzofuroxan (4 parts) prepared by the method of Boulton et al, (J Chem.

Soc. (1965) 5958) were mixed together. This rubber compound could be cured to a tough product in less than 15 minutes at 1740C.

Example 4 Curing an EPDM rubber with

(5-chloro-4-nitro benzofuroxan) Example 3 was repeated except that 5 - chloro - 4 - nitrobenzofuroxan (4 parts) (prepared by the method of Boulton et al, J Chem. Soc. (1965) 5958) was used as the cross-linking agent; the rubber compound could be cured in less than 10 minutes at 1800C. A sample which was cured under pressure for 30 minutes at 1500C had tensile strength of 1270 psi and elongation at break of 345%.

Example 5 Curing a Styrene-butadiene Rubber (SBR) with Benzodifuroxan Benzodifuroxan (furoxanobenzofuroxan) was prepared by the method of A J Boulten et al (J Chem Soc. (1965) 5958). The furoxan (4 parts) was milled into a styrene-butadiene co-polymer (100 parts) to which had been added carbon black (50 parts). The rubber mix was shown to cure completely in about 5 minutes at 120"C. A sample of the rubber, cured in a press at 900C for 15 minutes had a tensile strength of 1910 psi, elongation at break 230, 100% modulus 493 psi.

Another sample of the rubber was easily extruded as a flat ribbon which was subsequently cured to a tough rubber by immersion in boiling water.

Example 6 Example 5 was repeated except that the rubber mixture contained only 2 parts of benzodifuroxan. A sample of this compound was placed in a press pre-heated to 100"C which was subsequently allowed to cool to 750C (during approximately 30 minutes). On removal from the press and cooling to room temperature the cured rubber was found to have a tensile strength of 2180 psi and elongation at break of 270.

Example 7 Curing Natural Rubber (NR) with Benzodifuroxan The procedure of Example 5 was repeated using natural rubber instead of styrene butadiene rubber. The rubber mix was shown from the curemeter to be completely cured in less than 5 minutes at 120 C. A sample press-cured at 900C for 15 minutes had tensile strength of 2240 psi, elongation at break of 2550/,, and 100% modulus of 431 psi.

Another sample was tested in the curemeter at 1900C for 2.5 hours, after having been initially cured at 100"C; no signs of reversion could be detected.

Example 8 Curing an EPDM rubber with benzodifuroxan The procedure of Example 1 was repeated using benzodifuroxan in place of benzofuroxan. The rubber mixture was shown to cure in approximately 15 minutes at 120"C.

Example 9 Curing a styrene-butadiene rubber with the hexamethylbenzene complex of benzodifuroxan 1. Preparation of the complex: benzodifuroxan (5.7 parts) dissolved in warm ethanol:acetic acid (4:1) (20 parts) was added to a solution of hexamethylbenzene (5.1 parts) in warm ethanol:acetic acid (4:1) (50 parts). On cooling, the mixed solutions afforded the adduct as a crystalline solid, mp 1830C.

2. Cross-linking the rubber: The procedure of Example 5 was repeated but using 8 parts of the complex in place of 4 parts of the furoxan. Cure-meter experiments showed that curing was complete in about 15 minutes at 1000C.

Example 10 Curing an SBR with benzotrifuroxan Benzotrifuroxan was prepared by the method of A S Bailey and J R Case (Tetrahedron 3 (1958)113).

The procedure of Example 5 was repeated using benzotrifuroxan in place of benzodifuroxan. The resulting rubber mixture could be cured in less than a minute at 150"C. A sample which was press cured for 15 minutes at 1100C had tensile strength of 1900 psi and elongation at break of 290%.

Example 11 Curing NR with benzotrifuroxan Natural rubber (100 parts) and carbon black (50 parts) were compounded with the trifuroxan (3 parts). The mixture was cured in a heated press for 15 minutes at 110"C to give a product which had tensile strength of 766 psi and elongation at break of 440%.

Example 12 Curing an EPDM rubber with benzotrifuroxan The procedure of Example I was repeated except that benzotrifuroxan was used in place of benzofuroxan. The resulting rubber compound could be cured in less than 5 minutes at 1200C. A sample which had been cured under pressure at 1200C for 15 minutes had tensile strength of 1000 psi and elongation at break at 210%.

Example 13 Curing SBR with the tetrahydronaphthalene complex of benzotrifuroxan Benzotrifuroxan (0.96 part) was dissolved in ethanol-acetic acid (4:1, 8 parts) by warming to 600 C. The resultant solution was filtered onto tetrahydronaphthalene (0.94 part) and pale yellow plates separated.

Recrystallisation from ethanol-acetic acid gave the required complex (0.56 part) mp 153154 (A S Bailey and J R Case Tetrahedron 1958 3 113 mp 151 152"). Evaporation of the filtrates gave a further yield of the crude complex.

A rubber compound of the following composition was prepared complex 0.56 part SBR 14 parts carbon black 7 parts Curometer experiments showed that cross-linking takes place above 140"C.

Example 14 Cross-linking SBR with the l-phenylnaphthalene complex of benzotrifuroxan Benzotrifuran (0.536 part) was dissolved in ethanol:acetic acid (4: 1, 5 parts) by warming to 500. I-Phenylnaphthalene was then added (0.51 parts). Crystals of the complex were separated from the cooled solution.

Yield (0.883 part) 91 /n on benzofuroxan mp 148160 .

A rubber compound of the following formulation was then milled Complex 0.85 part SBR 14 parts Carbon Black 7 parts Curemeter experiments showed a very rapid cure at 1600C (-1 min) and a slightly slower cure at 1000C (-5 min).

The rubber compound was then pressed at 1 500C for 5 minutes to give a crosslinked rubber with the following properties tensile strength 2030 psi elongation at break 385% Example 15 Curing an EPDM rubber with the azine of bis(m-nitrobenzoyl) furoxan

The azine was prepared by the method of H R Snyder and N E Boyer (J Am Chem Soc. 77 4233 (1955)) from bis-(m-nitrobenzoyl) furoxan and hydrazine.

The azine (15 parts) and carbon black (50 parts) were mixed with the EPDM rubber of Example 1 (100 parts). The resulting rubber compound was cured in approximately 10 minutes at 2000 C.

WHAT WE CLAIM IS:- 1. A process for the modification of a polymeric material having carboncarbon unsaturation recurrent in its molecular structure comprising contacting the polymeric material with an organic compound which is a source of adjacent nitroso groups on a six-membered aromatic ring, the contact being under conditions whereby at least two of the nitroso groups are made available for reaction with the polymeric material.

2. A process as claimed in claim 1 wherein the organic compound is a source of at least two pairs of adjacent nitroso groups on a six-membered aromatic ring.

3. A process for the modification of a polymeric material having carboncarbon unsaturation recurrent in its structure comprising contact of the polymeric material with an organic compound having at least one furoxan ring fused to a sixmembered quinonoid ring and thermolysis of the furoxan ring to form two adjacent nitroso groups on the six-membered ring.

4. A process as claimed in claim 3 wherein the six-membered quinonoid ring contains at least one nitrogen atom.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (15)

**WARNING** start of CLMS field may overlap end of DESC **. Recrystallisation from ethanol-acetic acid gave the required complex (0.56 part) mp 153154 (A S Bailey and J R Case Tetrahedron 1958 3 113 mp 151 152"). Evaporation of the filtrates gave a further yield of the crude complex. A rubber compound of the following composition was prepared complex 0.56 part SBR 14 parts carbon black 7 parts Curometer experiments showed that cross-linking takes place above 140"C. Example 14 Cross-linking SBR with the l-phenylnaphthalene complex of benzotrifuroxan Benzotrifuran (0.536 part) was dissolved in ethanol:acetic acid (4: 1, 5 parts) by warming to 500. I-Phenylnaphthalene was then added (0.51 parts). Crystals of the complex were separated from the cooled solution. Yield (0.883 part) 91 /n on benzofuroxan mp 148160 . A rubber compound of the following formulation was then milled Complex 0.85 part SBR 14 parts Carbon Black 7 parts Curemeter experiments showed a very rapid cure at 1600C (-1 min) and a slightly slower cure at 1000C (-5 min). The rubber compound was then pressed at 1 500C for 5 minutes to give a crosslinked rubber with the following properties tensile strength 2030 psi elongation at break 385% Example 15 Curing an EPDM rubber with the azine of bis(m-nitrobenzoyl) furoxan The azine was prepared by the method of H R Snyder and N E Boyer (J Am Chem Soc. 77 4233 (1955)) from bis-(m-nitrobenzoyl) furoxan and hydrazine. The azine (15 parts) and carbon black (50 parts) were mixed with the EPDM rubber of Example 1 (100 parts). The resulting rubber compound was cured in approximately 10 minutes at 2000 C. WHAT WE CLAIM IS:-

1. A process for the modification of a polymeric material having carboncarbon unsaturation recurrent in its molecular structure comprising contacting the polymeric material with an organic compound which is a source of adjacent nitroso groups on a six-membered aromatic ring, the contact being under conditions whereby at least two of the nitroso groups are made available for reaction with the polymeric material.

2. A process as claimed in claim 1 wherein the organic compound is a source of at least two pairs of adjacent nitroso groups on a six-membered aromatic ring.

3. A process for the modification of a polymeric material having carboncarbon unsaturation recurrent in its structure comprising contact of the polymeric material with an organic compound having at least one furoxan ring fused to a sixmembered quinonoid ring and thermolysis of the furoxan ring to form two adjacent nitroso groups on the six-membered ring.

4. A process as claimed in claim 3 wherein the six-membered quinonoid ring contains at least one nitrogen atom.

5. A process as claimed in claim 3.wherein the six-membered quinonoid ring

contains only carbon atoms.

6. A process as claimed in claim 3 wherein the organic compound is a benzo furoxan of formula

wherein R3 R4 R5 and R6 which may be the same or different are hydrogen or halogen atoms or are nitro or alkoxy groups.

7. A process as claimed in claim 3 wherein the organic compound is benzo trifuroxan.

8. A process as claimed in claim 3 wherein the organic compound is an unsubstituted or substituted benzo difuroxan.

9. A process as claimed in claim 3 wherein the organic compound is a complex of the furoxan and an aromatic hydrocarbon.

10. A process as claimed in any one of the preceding claims wherein the organic compound which is a source of adjacent nitroso. groups is used at a concentration of from 0 0.01 to 30%, preferably at least 0.20/,, by weight of the polymeric material.

I 1. A process as claimed in any one of the preceding claims wherein the temperature used is in the range 700 to 200"C.

12. A process as claimed in claims 1 or 3 and substantially as described herein with reference to or as shown in any one of the foregoing examples.

13. A cross-linked polymeric material produced by a process as claimed in any one of the preceding claims.

14. A cross-linked polymeric material as claimed in claim 13 the polymeric material being formed from a diene monomer.

15. A composition comprising the components of an uncured rubber compound and an organic compound having at least one furoxan ring fused to a six-membered quinonoid ring.