WO2004074362A1

WO2004074362A1 - Elastomeric compositions

Info

Publication number: WO2004074362A1
Application number: PCT/GB2004/000645
Authority: WO
Inventors: William Stephen Fulton
Original assignee: OMG UK Ltd
Current assignee: OMG UK Ltd
Priority date: 2003-02-20
Filing date: 2004-02-19
Publication date: 2004-09-02
Anticipated expiration: 2005-08-20
Also published as: GB0517918D0; GB2414240A; GB0303957D0

Abstract

An elastomeric composition is described comprising an unvulcanised polymer, silica, a silane coupling agent and a condensate obtainable by condensing an alkoxide or aryloxide of a trivalent cation with an acyloxide of a divalent cation, or a compound obtainable by reacting a divalent metal oxide with a polyoxoaluminium acylate.

Description

ELASTOMERIC COMPOSITIONS

This invention relates to elastomeric compositions having improved processibility and improved vulcanisate properties. In the art of processing elastomeric compounds it is desirable to use process additives to improve processibility and subsequent vulcanisate properties. Such process additives include substances like fatty acids, fatty acid esters, metal soaps and different hydrocarbons and these are effective in different elastomers, formulations and process operations. The mixing of elastomeric compounds is an energy intensive process and typically a process additive is included to reduce the viscosity of the resulting compound. A reduction of compound viscosity will result in a concomitant reduction of power consumption, the rate of throughput in processing equipment is increased and maximum compound temperature can be reduced. Avoidance of high temperatures can improve the scorch safety of the compound and subsequent processing operations, such as calendering, extrusion or injection moulding of rubber compounds.

Current process aids, such as rubber-compatible hydrocarbon oils, improve the processibility of uncured rubber compounds but may impart undesirable physical properties to the rubber compound. Therefore there is a requirement for additives that can be mixed with the rubber to improve processibility without adversely affecting other physical properties, such as the mechanical properties of the vulcanisates. Ideally, the process additive should realise a synergism of properties from compounds before and after vulcanisation.

In the ait it is also desirable to produce elastomeric compounds exhibiting improved dynamic mechanical properties, such as reduced hysteresis or tanδ at temperatures greater than ambient temperature. Such elastomers, when compounded, fabricated and vulcanised into articles such as tyres will manifest properties of increased resilience and decreased rolling resistance and decreased heat-build up when subjected to the normal stresses associated with service. In the context of this invention, the dynamic properties of the vulcanised elastomeric composition at low temperature are particularly significant. At 0°C an increased tanδ indicates improved wet traction for the tread compound and good ice traction is predicted by high values of tanδ at -20°C. It is well known in the art, that it is important to obtain a good balance of dynamic mechanical properties at all working temperatures, especially with regard to rolling resistance, wet skid and ice skid. Consequently, tread compounds with a relatively high tanδ at 0°C and -20°C indicates good wet traction and good ice traction, respectively.

It has been known for many years to incorporate a reinforcing filler into elastomeric compositions containing an unvulcanised polymer rubber used for many years for the manufacture of rubber tyres for vehicles. Unfortunately the use of silica results in rubber compositions having inferior properties tσ those contaimng carbon black in respect of dynamic properties such as heat build-up and rolling resistance and physical properties such as abrasion resistance, modulus, flex resistance and compression set. Various ways have been attempted to overcome these deficiencies but it is generally recognised that properties comparable to those obtained with carbon black compositions can be obtained if a silica-containing rubber compositions also contains a silane coupling agent.

It has now surprisingly been found according to the present invention that the properties of such compositions can be improved, in particular their dynamic mechanical properties but also improved processibility and resistance to storage hardemng, by incorporating into them a mixed metal carboxylate. Accordingly, the present invention provides an elastomeric composition which comprises an unvulcanised polymer rubber, silica, a silane coupling agent and a mixed metal carboxylate (hereinafter referred to as MMC) obtainable by condensing an alkoxide or aryloxide of a trivalent cation with an acyloxide of a divalent cation, or a compound obtainable by reacting a divalent metal oxide with a polyoxoaluminium acylate.

The trivalent cations are typically elements such as aluminium or boron although it is also possible to use a mono-substituted tetravalent radical such as silicon. Typical divalent elements which can be used include magnesium, calcium, barium, zinc, nickel and cobalt. Preferred trivalent cations include aluminium while zinc is a preferred divalent cation, the preferred mixed metal carboxylates being derived from zinc and aluminium. The precise nature of the alkoxide or aryloxide is not particularly important. Typically the alkoxide is a lower alkoxide, typically of 1 to 6, generally 1 to 4 carbon atoms such as isopropanol or 2-butanol while the aryloxide is typically a phenoxide.

The acyloxide is typically derived from a carboxylic acid or a sulphonic acid, including aliphatic carboxylic acids, for example lower alkylcarboxylates wherein the alkyl group has 1 to 6 carbon atoms such as acetic acid, propionic acid and methacrylic acid as well as longer chain aliphatic acids, typically having 7 or 8 to 24 carbon atoms such as tall oil fatty acids, sebacic acid and azelaic acid as well as alicyclic acids such as a naphthenic acid (hexahydrobenzoic acid). Dimeric acids such as maleic acid and dimerised fatty acids may also be employed. The condensates can be used as free acids or as salts. It is believed that the condensates have the general formula:

COOH

R²

or a salt thereof

where M is a trivalent cation, M^π is a divalent cation, each of R¹, R² and R³ is independently a divalent aliphatic group or a single bond, y = 1 or more, typically 2 to 6 and especially 2, and x = 1 or more, typically 2 to 6 and especially 2.

It is to be understood that x and y refer merely to the number of the specified units present. It is not intended that when x is 2, for example, the two groups are necessarily connected to each other as a block. Rather the groups can be present randomly in the molecule.

R¹, R² and R³ are either independently a single bond or a divalent unsaturated or saturated aliphatic radical, typically of 1 to 22 or 24 carbon atoms. Suitable aliphatic radicals include straight-chain or branched alkylene or alkenylene radicals, especially with at least 4 carbon atoms, for example 4 to 18 carbon atoms, such as butylene, pentylene, hexylene, heptylene, octylene, octenylene, nonylene, decylene, dodecylene, tefradecylene, hexadecylene and octadecylene, these being straight-chain or branched as well as vinylene and methyl vinylene, together with alicyclic radicals such as cyclohexylene. The aliphatic groups can be substituted, typically by one or more, generally one or two, groups, especially hydroxy and alkoxy groups as well as carboxyl or alkylcarbonyl groups i.e. the radical is derived from a di- or poly-meric acid. The alkoxy groups generally have 1 to 4 carbon atoms as in methoxy and ethoxy. A typical example is carboxyvinylene. R^],R² and R³ are, more particularly, derived from stearic acid, oleic acid or linoleic acid; these acids can be present as a tall oil fatty acid.

Of course if the condensates are derived from an acyl oxide which is not a carboxylate then the corresponding acid groups will be present in the formula in place of the COOH groups.

Thus a particular preferred condensate for use in the present invention is believed to have the structure:-

X X χ_^Zπ-__{0^ A1}__{0^ AI}__{0^ Zn^ χ}

where X represents an alkyl carboxyl group, especially a tall oil fatty acid carboxylate, e.g. one derived from about 3% stearic acid, 59% oleic acid and 38% linoleic acid.

Since the condensates have hydrophilic moieties (oxygen-linked metal cations) and hydrophobic groups (e.g. alkyl or alkenyl), the hydrophilic groups may be adsorbed onto the surface of the reinforcing agent and the hydrophobic groups may be dissolved in the rubber. Accordingly, interaction between the reinforcing agent is modified which has the effect of improving the processibility of the composition and the reinforcing agent is well dispersed to improve the visco-elastic properties.

The present invention also provides a method of improving the processibility of a rubber composition which comprises silica and a silane coupling agent which comprises incorporating therein the above specified mixed metal carboxylate.

A particular feature of the composition of the present invention is that the product obtained on vulcanisation provides an increased tanδ at 0°C indicating improved wet traction for the tread compound and good ice traction as predicted by high values at tanδ at -20 °C. This indicates that the compounds of the present invention are particularly useful in the preparation of "winter" or "all weather" or "snow" tyres. The compositions used for such tyres differ from ordinary formulations in that they contain natural rubber as well as a synthetic rubber. Accordingly, compounds of the present invention which comprise natural rubber are particularly preferred. In general, such compositions contain at least 30%, typically 40%) to 60%, natural rubber based on the weight of the rubber in the composition. Typically, in such foπnulations a blend of natural rubber and polybutadiene is used, for example in approximately equal proportions (by weight).

Accordingly, the present invention also provides a rubber tyre and, more generally, a vulcanisate obtainable from a composition of the present invention and, in particular, an "all weather" tyre obtainable from a composition of the present invention comprising natural rubber. Such compositions will, of course, comprise a vulcanising agent, especially sulphur.

The present invention also provides a process for preparing a vehicle tyre which comprises placing a composition of the present invention comprising a vulcanising agent in a tyre mould, vulcanising e.g. heating -to a vulcanisation temperature, the composition and then removing the resulting tyre. Vulcanisation can be carried out using conventional procedures.

The amount of condensate needed is typically 0.5 to 20 parts by weight per

100 parts by weight of the vulcanisable rubber. If the amount of MMC is less than 0.5 part by weight, an improvement in the processibility and visco-elastic properties is generally not observed and if the amount exceeds 20 parts by weight, the physical properties of the vulcanised rubber compound tend to be affected adversely. An amount ranging from 1 to 10 parts by weight is particularly preferred.

The vulcanisable rubber used in the present invention is not specifically restricted and, for example, natural rubber, styrene-butadiene copolymerised rubber, butadiene and isoprene rubber can all be used alone or in combination. The reinforcing silica is typically used in an amount from 20 to 120 parts, especially 40 to

100, by weight per 100 parts of vulcanisable rubber.

Conventional amorphous precipitated silica can be used in the compositions although it is preferred to use the highly dispersible silicas which have been developed more recently. For example, the micropearl technology developed by

Rhodia Silica Systems creates a specific silica morphology at the precipitation stage that is retained to give high dispersibility. It is the use of such silica in combination with a coupling agent and rubber that can significantly reduce rolling resistance of a tyre by at least 20%> with equivalent or better wear resistance and improved snow and wet traction. The silane coupling agent is typically used in an amount that is related to the loading and surface area of the silica, but more normally from 5% to 15%> of the weight of silica. The silane coupling agent used in the invention may be defined as an at least bi-functional silane molecule. All the usual silane coupling agents, generally polyfunctional organosilanes, can be used. The use of bis[(3-triethyl oxysilyl)propyl] tetrasulfide (TESP) having the structure:

C₂H₅0 OC₂H₅

C₂H₆0 Si (CH₂)₃-S-S-S-S-(CH 1₂)H. -Si- OC -,H¹ '5

C₂H₅0 OC₂H_g

is preferred. In the coupling reaction, it is believed that the silanol groups on the silica surface react with, say, alkoxy groups of the coupling agent eliminating alkanol. Further coupling with dienic polymers can be achieved through the oligosulphane group. Generally, the silica-silane reaction is achieved during mixing and the final coupling reaction of the silane to the polymer during vulcanization Further, the rubber composition of the present invention can, if desired, contain the usual compounding agents and additives such as sulphur and vulcanisation accelerators, the amounts used typically being the same as in conventional rubber compositions.

Additives which may be used include, for example, zinc oxide which may be used in an amount, for instance, from 2 to 10 parts by weight per 100 parts of rubber; stearic acid at a concentration, for instance, from 0.5 to 5 parts by weight per 100 parts by weight of rubber. It has been found that in the presence of the mixed metal carboxylates the amount of stearic acid can be significantly reduced or eliminated completely. Other additives include antioxidants or antidegradants, for example N- (l,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, typically used at a concentration from 0.5 to 5 parts by weight per 100 parts by weight of rubber; and accelerators, for example, N-cyclohexyl-2-benzothiazolesulfenamide and N,N'-diplιenylguanidine. In the compositions of the invention, these are typically used individually in amounts from 0.1 to 3 parts by weight per 100 parts by weight of rubber depending on the nature of the rubber, the amount of sulphur and the properties required in the cured rubber. If sulphur is used as the vulcanising agent, the amount is typically in the range from 0.3 to 6 parts by weight per 100 parts by weight of rubber. The following Example further illustrates the present invention. EXAMPLE

Tyre tread formulations were investigated as shown in Table 1 in which 4 parts by weight of MMC per 100 parts by weight of rubber were added to the composition. The properties evinced by this addition were, compared to a control compound derived from a generic tread composition. As well as the control compound, comparisons were also made between MMC and two commercially available process aids, designated as PAl and PA2. PAl is a two-part system added in the first and second stages of the mix cycle, containing a mixture of fatty acid esters and a zinc soap of an unsaturated fatty acid and PA2 is a mix of zinc soaps, fatty acid ester and filler.

Table 1

COMPOUND FORMULATION

Ingredient Control PA1 PA2 WIWIC

S-VSBR¹ 103 103 103 103

BR² 25 25 25 25

Silica³ 80 80 80 80

Stearic acid 2 2 2 2

Si69⁴ 6.4 6.4 6.4 6.4

N220 Black 2 2 2 2

Zinc oxide 2.5 2.5 2.5 2.5

Antioxidant⁵ 2 2 2 2

PA1 (1^st Stage) 2

PA1 (2^nd Stage) 3

PA2 4

MMC - - - 4

DPG⁶ 2.0 2.0 2.0 2.0

CBS⁷ 1.7 1.7 1.7 1.7

Sulphur 1.4 1.4 1.4 1.4

1 - Buna VSL 5025-1, HM (37% oil extended) 2 - Taktene 1220 3 - Zeosil ll65MP

4 - Bis [(3-triethoxysilyl) propyl] tetrasulfi.de

5 - N-(l,3-Dimetiιylburyl)-N'-phenyl-p-phenylenediamine 6 - N,N'-Diphenylguanidine

7 - N-Cyclohexyl-2-benzothiazolesulfenamide 6 and 7 constitute an accelerator package for silica systems.

For mixing, a laboratory scale internal mixer with tangential rotors was used. Ingredients were incorporated in accordance with the following schedule at intervals determined by the integral value of power consumption and the temperature of the mix as shown in Tables 2a - 2c.

Table 2a Mix Schedule 1^st Stage

Power (kWh) Operation

0 Add rubbers 0.045 Add 2/3 silica, silane and carbon black.

0.150 Add 1/3 silica, stearic acid and process aid when required.

When temperature reached 150°C, the rotor speed was slowed to 50rpm to maintain constant temperature

0.430 Dump (Temperature 145°C - 148"C).

Table 2b Mix Schedule 2^nd Stage

Power (kWh) Operation

0 Add masterbatch.

0.019 Add zinc oxide, antioxidant and process aid when required. When temperature reached 150°C, the rotor speed was slowed to 50rpm to maintain constant temperature.

0.650 Dump (Temperature 149°C - 153°C). The mixing schedules shown in Tables 2a and 2b illustrate a special mixing procedure adopted whereby once the desired mixing temperature has been reached the motor speed was reduced so as to keep the temperature substantially constant. This improves the degree of silane coupling that can be achieved.

The mixing procedure, for the final mixes of all the compounds is shown in Table 2c.

Table 2c ;

Mix Schedule 3rd Stage

Power (kWh) Operation

0 Add masterbatch, curatives. 0.190 Dump (Temperature 90°C - 95°C).

The unvulcanised stock compound was characterised as to Mooney viscosity and cure characteristics. The Mooney viscosity measurement was performed using both a small and large rotor at 100°C with a pre-heat of 5 minutes, after which the torque was recorded after the rotor had rotated for 4 minutes.

For measurement of Mooney-scorch, the sample was pre-heated at 130°C for 1 minute before the rotor was started and the scorch behaviour was measured as the time required for the viscosity to increase by 5 Mooney units, the so-called T₅ time. This time is used as an indicator to predict how quickly the compound viscosity will increase during processing, for example during extrusion. Times T₂ and T₉₅ are the times taken for a torque increase of 2% and 95% respectively of the total torque increase during characterisation of the cure at 170°C. Such values are useful to predict the viscosity increase and rate of cure during the vulcanisation process. The results of testing the unvulcanised stock are shown in Table 3. The results show that with the addition of the MMC process aid, the Mooney viscosity of the compound is significantly reduced to that of the control. A reduced Mooney viscosity will be beneficial because it provides better processability and handling, particularly during the extrusion process. The peak Mooney viscosity and the ratio of peak viscosity to final viscosity is reduced by the addition of the MMC process aid which is an indication that the MMC has reduced the rubber-filler interaction and the tendency for the filler to re-agglomerate. Also note that the ratio of the height of the Mooney peak of the MMC modified compound to that of the control has been defined as a processability index (PI) and as given in Table 3 the lower the value, the better the compound processability.

The peak Mooney value is significantly greater for the control and indicates poorer processability, for example, the roughness of the profile after extrusion.

When compared to the control compound, the longer scorch time (T₅) and T₂ values in the MMC containing compound allow for adequate time to flow and better fill the mould. Additionally, the slighter faster cure rate (T₉₅) may also be beneficial.

Table 3 COMPOUND PROPERTIES (UMCURED)

Property Control PA1 PA2 MMC

MS. 5+4).100°C

1^st Stage 87 84 84 85

2^nd Stage 86 68 67 58

3^rd Stage 57 47 43 40

ML.(5+4).100°C

Peak 120 99 95 87

Final 92 79 75 70

P.I. - 0.825 0.792 0.725

Scorch @ 130°C 13.26 16.81 21.38 28.51

(min)

T₉₅ @ 170°C (min) 19.88 21.38 21.33 18.81

T_s? @ 170°C (min) 1.55 1.88 1.95 2.31

In order to determine the effect of the MMC process aid on the mechanical and dynamic properties, each compound was compression moulded in a 2mm thick mould at 170°C for a period equal to T₉₅ plus, where appropriate, additional time to account for mould lag. For tensile testing, dumbbell shape specimens were cut from 2mm thick sheet obtained after curing and tested in accordance with ISO37 at room temperature at a crosshead speed of 500mm/min. Tensile strength, elongation at break, stress at 100% strain (M100), stress at 300%> strain were measured. The ratio M300/M100 was calculated as an assessment of the filler-rubber coupling efficiency.

Other physical properties, such as hardness, tear and DIN abrasion properties were measured according to standard procedures described in ISO 48, ISO 34 and ISO 4649, respectively.

Table 4 illustrates the effect that addition of the MMC process aid had upon certain physical properties. The 100% and 300% moduli decreased without any deleterious effect on the efficiency of the silane coupling. The MMC compound was softer but the ultimate tensile strength was unaffected and the elongation at break increased. Abrasion resistance and tear strength (aged at 70°C) was improved by addition of the process aid.

Table 4

COMPOUND PHYSICAL PROPERTIES

Property Control PA1 PA2 MMC

M100 (MPa) 3.3 2.9 2.6 2.2

M300 (MPa) 16.7 14.5 13.1 11.2

M300/M100 5.05 4.99 5.15 5.02

Tensile strength (MPa) 20.0 18.8 19.7 20.5

Elongation @ Break % 340 360 400 460

Aαed 70°C. 7d

M100 (MPa) 4.9 4.5 4.1 3.5

M300 (MPa) - 20.3 8.8 16.5

Tensile Strength 19.1 20.4 19.2 20.1

(MPa)

Elongation @ Break % 260 300 300 350

Crescent Tear

Strenαth

Unaged (kN/m) 46.5 41.8 41.9 46.0

Aged 70°C, 7d (kN/m) 31.7 34.6 36.3 53.8

Hardness (IRHD) 69 66 65 62

DIN Abrasion loss 243 221 225 216

(mg)

Compound dynamic properties displayed in Table 5 were obtained by dynamic tests performed in a shear configuration. Double shear test-pieces comprising of two discs of rubber, nominally 6mm thick and 25.4mm diameter bonded between three metal cylinders to make a double sandwich. Each test-piece was moulded for 23 minutes at 170°C at 30 tons pressure. Testing consisted of a temperature sweep (70°C, 22°C, 0°C and -20°C) on duplicate test-pieces at a frequency of 10Hz and a shear strain of 1% for each of the compounds. Test were performed on a VH7 Schenck Servohydrauhc test machine with a load cell of 7kN with multiple ranges and a Solartron 1250 Frequency Response Analyser was used to control the actuator of the Schenck, analyse the data and was programmed to report dynamic stiffness and phase angle of the test-piece at each condition tested.

The influence that MMC has upon the Payne effect is illustrated when the shear modulus over shear strain in the range of 1%> - 40% for the MMC compound was compared to that of the control and other process aids. The difference in dynamic modulus at high and low strains (ΔG) has been attributed to the breakdown of filler aggregate structure at low amplitude, in conjunction with rupture of rubber- filler interactions at greater strain amplitude. The ΔG value for the control was calculated to be 7.74MPa, whereas that for the MMC compound gave a value of 3.97MPa. Such results indicate the effect that MMC has upon the filler-filler network, impeding the re-agglomeration of filler particles and the subsequent Payne effect with a simultaneous improvement of the dispersion of filler within the rubber matrix. The properties of the compounds listed in Table 5 also illustrate the effect that the MCC process aid has upon the dynamic viscoelasticity at different temperatures (70°C, 22°C, 0°C and -20°C). It is crucial to note that tanδ of the MMC compound is 25% higher than the Control compound at 0°C and some 50% higher at -20°C. The improvement in these values was totally unpredicted and will result in much improved wet traction and ice skid resistance. Table 5 COMPOUND DYNAMIC PROPERTIES

Property Control PA1 PA2 MMC

10Hz. 1% Shear strain

G' @ -20°C (MPa) 46.63 44.10 45.81 33.60

G' @ 0°C (MPa) 15.81 14.33 14.90 8.92

G' @ 22°C (MPa) 9.25 8.38 8.76 5.24

G' @ 70°C (MPa) 5.30 4.82 5.00 2.99 tanδ @ -20°C 0.443 0.496 0.483 0.647 tanδ @ 0°C 0.306 0.342 0.300 0.378 tanδ @ 22°C 0.187 0.194 0.189 0.185 tanδ @ 70°C 0.131 0.119 0.144 0.141

10Hz. 22°C.

G' @ 1 % Strain 9.10 8.6 8.8 5.23

(MPa)

G' @ 2% Strain 7.68 7.23 7.44 4.41

(MPa)

G' @ 4% Strain 5.98 5.71 5.84 3.58

(MPa)

G' @ 10% Strain 3.73 3.51 2.53

(MPa)

G' @ 20% Strain 2.39 2.25 2.38 1.81

(MPa)

G' @ 40% Strain 1.56 1.43 1.42 1.26

(MPa)

Claims

1. An elastomeric composition comprising an unvulcanised polymer, silica, a silane coupling agent and a condensate obtainable by condensing an alkoxide or aryloxide of a trivalent cation with an acyloxide of a divalent cation, or a compound obtainable by reacting a divalent metal oxide with a polyoxoaluminium acylate.

2. A composition according to claim 1 wherein the condensate is present in an amount from 1 to 10 parts per 100 parts by weight of rubber.

3. A composition according to claim 1 or 2 wherein the condensate has the formula:

COOH R²

where M^m is a trivalent cation, M^π is a divalent cation, each of R¹, R² and R³ is independently a divalent aliphatic group or a single bond, y = 1 or more and x = 1 or more, or a salt thereof.

4. A composition according to any one of the preceding claims wherein the trivalent cation is aluminium or boron.

5. A composition according to claim 4 wherein the trivalent cation is aluminium.

6. A composition according to claim 6 wherein the divalent cation is magnesium, calcium, barium, zinc, nickel or cobalt.

7. A composition according to any one of the preceding claims wherein the divalent cation is zinc.

8. A composition according to any one of the preceding claims wherein the rubber polymer comprises cis-polyisoprene, styrene-butadiene, nitrile rubber or a blend of any such rubber with polybutadiene. .

9. A composition according to any one of the preceding claims wherein part of the rubber polymer is natural rubber.

10. A composition according to claim 9 wherein the rubber polymer comprises at least 30% by weight of natural rubber.

11. A composition according to any one of the preceding claims wherein the silane coupling agent is bis[(3-triethyloxysilyl)propyl] tetrasulfi.de.

12. A composition according to any one of the preceding claims which contains a vulcanising agent.

13. A composition according to claim 1 substantially as hereinbefore described.

14. A method for improving the processibility of rubber which comprises incorporating into the rubber with silica, a silane coupling agent and a condensate as defined in any one of claims 1 and 3 to 7.

15. A vehicle tyre obtainable from an elastomeric composition as claimed in claim 12 or obtained by a method as claimed in claim 14.

16. A rubber tyre according to claim 15 obtainable from a composition as claimed in claim 9 or 10.

17. A process for preparing a vehicle tyre which comprises placing a composition as claimed in any one of claims 1 to 13 or obtained by a method as claimed in claim 14 in a tyre mould, vulcanising the composition and removing the resulting tyre.

18. A vulcanisate obtainable by heating to a vulcanisation temperature a composition as claimed in claim 12.

19. A method of improving the low temperature dynamic properties of a vulcanised rubber stock which comprises incorporating into the rubber prior to vulcanisation a condensate as defined in any one of claims 1 and 3 to 7.