Crosslinked siloxanyl polymer compositions

Abstract

A polymeric composition comprising at least one covalently cross-linked siloxanyl polymer cluster which is further cross-linked by a boron compound, wherein the concentration of boron is in the range 0.005-0.160 wt. %.

Claims

1. A composite material comprising: at least 2 vol. % of a polymeric composition comprising at least one covalently cross-linked siloxanyl polymer cluster which is further cross-linked by a boron compound; and at least 1 vol. % of a particulate or granular material; wherein said composite material does not return to its original shape when deformed; and wherein the composite material has a boron concentration in the range 0.005-0.160 wt. %.

2. The composite material as claimed in claim 1 wherein said cluster, prior to further cross-linking with boron, comprises on average more than one hydroxyl moiety per cluster.

3. The composite material as claimed in claim 1 wherein the average molecular weight between branching points within said cluster ranges from 4-80 kD.

4. The composite material as claimed in claim 1 wherein said cluster, prior to further cross-linking with boron, comprises hydroxyl moieties at a concentration equivalent to 1-100 ?mol [OH] per g of the cluster.

5. The composite material as claimed in claim 1 wherein said cluster, prior to further cross-linking with boron, comprises hydroxyl moieties at an average concentration corresponding to 10-1000 kD of polymer cluster per hydroxyl moiety.

6. The composite material as claimed in claim 1 wherein said cluster comprises at least one linear or branched siloxanyl polymer, wherein prior to cross-linking to form said cluster, said polymer comprises on average more than one hydroxyl moiety per molecule.

7. The composite material as claimed in claim 1 wherein said cluster comprises at least one siloxanyl polymer, wherein prior to cross-linking to form said cluster, said polymer comprises hydroxyl moieties at a concentration equivalent to 20-2000 ?mol [OH] per g of the polymer and/or comprises hydroxyl moieties at an average concentration corresponding to 0.5-50 kD of polymer per hydroxyl moiety.

8. The composite material as claimed in claim 1 wherein said cluster comprises at least one siloxanyl polymer covalently cross-linked with at least one siloxy-containing compound.

9. The composite material as claimed in claim 6 wherein prior to covalent cross-linking said siloxanyl polymer has the structure:
(R.sup.1)(R.sup.2)(R.sup.3)Si[OSi(R.sup.4)(R.sup.5)].sub.nOSi(R.sup.6)(R.sup.7)(R.sup.8) wherein n is an integer; and wherein each of R.sup.1-R.sup.8 may be the same or different and is independently selected from the group consisting of hydrogen, methyl, ethyl, propyl, butyl, phenyl, vinyl and hydroxyl; and wherein at least one of R.sup.1-R.sup.8 is hydroxyl.

10. The composite material as claimed in claim 9 wherein at least one of R.sup.1, R.sup.2, R.sup.3, R.sup.6, R.sup.7 and R.sup.8 is hydroxyl.

11. The composite material as claimed in claim 6 wherein said siloxanyl polymer is selected from the group consisting of polydiphenylsiloxane, polydibutylsiloxane, polydipropylsiloxane, polydiethylsiloxane, polydimethylsiloxane, and hydroxy-functionalised compounds thereof.

12. The composite material as claimed in claim 8 wherein said siloxy-containing compound is selected from the group consisting of acetoxysilanes, oximosilanes, alkoxysilanes, isopropenoxysilanes, amidosilanes, aminosilanes and aminoxysilanes.

13. The composite material as claimed in claim 8 wherein said siloxy-containing compound is selected from the group consisting of tetraacetoxysilane, triacetoxy methylsilane, triacetoxy ethylsilane, tetraethyl silicate, acetoxy-functionalised polydimethylsiloxane and alkoxy-functionalised polydimethylsiloxane.

14. The composite material as claimed in claim 1 wherein said boron compound is selected from triethyl borate, diboron trioxide, tetraboron disodium heptaoxide, disodium tetraborate and boric acid.

15. The composite material as claimed in claim 1 wherein the polymeric composition has a boron concentration ranging from 0.005 wt. % to less than 0.12 wt. %.

16. The composite material as claimed in claim 1 wherein said cluster comprises at least two siloxanyl polymers each of which is covalently cross-linked with at least one siloxy-containing compound.

17. The composite material as claimed in claim 16 wherein said siloxy-containing compounds are independently selected for each siloxanyl polymer and may be the same or different.

18. The composite material as claimed in claim 1, wherein the polymeric composition has a Shore 00 hardness in the range of 20 to 80.

19. The composite material as claimed in claim 1, wherein the polymeric composition, when formed into a 0.4 g ball, bounces to a height of at least 20 cm when dropped from a height of 2m onto a flat glass surface.

20. The composite material as claimed in claim 1 comprising 1-75 vol. % of said particulate or granular material.

21. The composite material as claimed in claim 1 wherein said particulate or granular material has an average particle size in the range of 0.02-0.5 mm.

22. The composite material as claimed in claim 1 wherein said particulate or granular material is selected from the group consisting of borosilicate glass beads, sand, ground marble, polymer grains or balls, cenospheres, microspheres of plastic, ceramics or glass, and mixtures of these materials.

23. The composite material as claimed in claim 8 wherein said siloxy-containing compound is a siloxanyl polymer functionalized with at least one group selected from the group consisting of acetoxysilanes, oximosilanes, alkoxysilanes, isopropenoxysilanes, amidosilanes, aminosilanes and aminoxysilanes.

Description

(1) The invention is further demonstrated and described in the following non-limiting examples and the attached Figures, in which:

(2) FIG. 1 shows the viscosity of a silly putty at varying shear rates at 23 C.

(3) FIG. 2 shows the the elastic modulus (G) and the viscous modulus (G) of a silly putty at varying shear rates

(4) FIG. 3 shows the viscosity of a polymer cluster (prior to addition of boron) at varying shear rates.

(5) FIG. 4 shows the the elastic modulus (G) and the viscous modulus (G) of a polymer cluster (prior to addition of boron) at varying shear rates

EXAMPLES

Example 1

(6) Reduction of the amount of boron containing compound results in loss of desired properties well before the content of boron containing substance is below the levels stipulated by the European Union. A series of bouncing putties in which the boric acid content was varied was prepared in the following way: A saturated aqueous solution of boric acid was prepared, which at 25? C. has a concentration corresponding to 5.4% wt. The saturated boric acid solution was mixed with a hydroxyl-terminated polydimethylsiloxane; WACKER? POLYMER CDS 100 (molecular weight of about 4000 Dalton and viscosity ca. 100 cP, as given by the manufacturer Wacker Chemie AG). Water was evaporated during continuous stirring of the mixture and the properties of the final mixture were evaluated. The bouncing property was evaluated by dropping a ball (0.4 g) from a height of 2 m onto a flat glass surface. Table 1 shows that loss of properties was observed below a molar ratio of 1:1 (boric acid:PDMS) corresponding to 1.6 wt %. It is clear that desired properties are lost well before content of the boric acid is sufficiently low.

(7) TABLE-US-00001 TABLE 1 Molar ratio WACKER? Saturated boric Boric Bounce POLYMER Binder Filler Voids boric acid acid:CDS acid Boron from 2 m CDS 100 (g) (% vol) (% vol) (% vol) solution (g) 100 (% wt) (% wt) Observation (cm) 1 100 0 0 0.15 0.5:1 0.80 0.14 Thin solution, no None noticeable increase in viscosity 1 100 0 0 0.22 0.75:1 1.2 0.21 Slight viscosity increase - None viscosity like syrup 1 100 0 0 0.29 1:1 1.6 0.28 Strongly increased 78 viscosity as compared to previous sample, but flows under gravity 1 100 0 0 0.44 1.5:1 2.3 0.40 Somewhat increased 80 viscosity as compared to previous sample, but flows under gravity

Example 2

(8) An increase in molecular weight of the polydimethylsiloxane (PDMS) chain used as starting material results in a loss of the desired properties before the content of boron containing substance is sufficiently low. A series of bouncing putties, prepared as described in Example 1, with WACKER? POLYMER C 2 T (molecular weight of about 25000 Dalton and viscosity ca. 2000 cP, as given by the manufacturer Wacker Chemie AG) shows that essential properties are lost already at a molecular weight at and above 25000 since none of the samples in Table 2 has desired properties. Yet the concentration of boric acid is above the levels stipulated by the European Union.

(9) TABLE-US-00002 TABLE 2 Molar ratio WACKER? Saturated boric Boric Bounce POLYMER C 2 Binder Filler Voids boric acid acid:C acid Boron from 2 m T (g) (% vol) (% vol) (% vol) solution (g) 2 T (% wt) (% wt) Observation (cm) 1 100 0 0 0.023 0.5:1 0.12 0.021 No noticeable increase None in viscosity 1 100 0 0 0.034 0.75:1 0.18 0.031 Minor viscosity None increase - soft texture, but still too liquid 1 100 0 0 0.046 1:1 0.25 0.044 Somewhat thicker as None compared to previous sample, but still too liquid 1 100 0 0 0.069 1.5:1 0.37 0.065 Thicker as compared to None previous sample, but still too liquid 1 100 0 0 0.0923 2:1 0.49 0.086 No notable difference None as compared to previous sample

Example 3

(10) Addition of inactive filler material results in loss of the desired properties before the content of boron containing substance is sufficiently low. A series of bouncing putties with increased filler content shows a loss of properties at filler contents above 40% wt. All samples were based on WACKER? POLYMER CDS 100 with a molar ratio of 1:1 (boric acid: CDS 100), and as filler was used hydrophilic amorphous pyrogenic silica; WACKER? HDK? N20. The putties were prepared as described in Example 1, and filler was added by kneading. Sometimes a small amount of ethanol was used as processing liquid, which was evaporated in the late stages. By preparing samples both with, as well as without ethanol it was verified that properties of the putty was not affected by the use of the processing solvent. Table 3 shows loss of properties well before content of the boric acid is sufficiently low.

(11) TABLE-US-00003 TABLE 3 Boric Bounce Bouncing WACKER? Binder Filler acid Boron from 2 m putty (g) HDK? N20 (g) (% wt) (% wt) (% wt) (% wt) Observation (cm) 100 0 1.6 0.28 Stretchable, elastic and flows under 78 gravity. 3.5 0.5 87.5 12.5 1.4 0.24 Resembling previous sample, but has 102 less flow under gravity. 1.75 0.46 79.2 20.8 1.32 0.23 Does not appear to flow under gravity. 100 0.348 0.154 69.3 30.7 1.22 0.21 Hard and difficult to reshape. Does 66 not flow under gravity. 0.322 0.178 64.4 35.6 1.18 0.21 Hard and difficult to reshape. Does 50 not flow under gravity. 1.19 0.81 59.4 40.6 1.14 0.20 Crumbly and too low cohesion. It is not possible to obtain a homogeneous mixture.

Example 4

(12) A steeply increasing viscosity during the final stages of cross-linking hydroxyterminated PDMS with WACKER? CROSS-LINKER ES 23 is an indication of a desired cross-linking density for further processing. For WACKER? POLYMER C 2 T this is obtained at an amount of about 0.9% wt ES 23. A lower amount of ES 23 gives a net-work with a (too) high concentration of hydroxyl groups which consumes a too high amount of boric acid to obtain a product with the desired properties, while a higher amount of ES 23 gives a (too) stiff and less flexible matrix to be useful, see Table 4. In the same way appropriate amounts of ES 23 to WACKER? POLYMER CDS100, WACKER? POLYMER CDS750, and WACKER? POLYMER C 1 T corresponds to 3.9% wt, 1.5% wt, and 1.1% wt.

(13) TABLE-US-00004 TABLE 4 Molar WACKER? ratio Observed properties about 15 h after mixing. Samples were WACKER? CROSSLINKER ES 23 ES 23 ES 23:C kept at room temperature during mixing and during the POLYMER C 2 T (g) (g) (% wt) 2 T reaction period. 20 0.10 0.50 0.53:1 Viscosity somewhat increased. 20 0.15 0.74 0.80:1 Viscosity increased as compared to previous sample. Threads appear when separating fingers between which sample has been applied. 20 0.20 0.99 1.07:1 Higher viscosity and harder. More threads appear as compared to previous sample. 20 0.25 1.23 1.34:1 Sample too stiff to be practically useful. 20 0.30 1.48 1.60:1 Hard and not useable. 20 0.18 0.90 0.96:1 The best sample in the series.

Example 5

(14) Dynamic cross-links and a final product with properties desired from a bouncing putty can be obtained without adding boric acid, but instead by using a filler of microspheres from borosilicate glass (3M? Glass Bubbles K37) to form the dynamic cross-links. In a first stage the binder is conveniently mixed with the filler in a low viscous solution, after which the pH is lowered by adding hydrochloric acid. Addition of HCl activates dynamic cross-linking, viscosity of the binder/material increases strongly and the final properties of the bouncing putty are achieved. From the three samples with 0.38 g K37 per gram CDS 100 it can be seen that at a certain amount acid added there is no further gain in properties, and ca. 8% wt of HCl (30%) based on weight of K37 was used as a standard addition. From the table can be concluded that K37 can replace addition of boric acid, and furthermore gives a convenient route for processing.

(15) TABLE-US-00005 TABLE 5 3M? Apparent Apparent WACKER? Glass content content HCl Bounce POLYMER Bubbles boric acid boron Binder Filler Voids (30%) from 2 m CDS 100 (g) K37 (g) (% wt)*.sup.) (% wt)*.sup.) (% vol).sup.#) (% vol).sup.#) (% vol).sup.#) (g) Observation (cm) 1.0 0.26 0.64 (0.80) 0.11 (0.14) 58.7 41.3 0 0.02 Thin solution, minor None viscosity increase. 1.0 0.38 0.85 (1.2) 0.15 (0.21) 49.3 50.7 0 0.005 Thin solution, minor None viscosity increase. 1.0 0.38 0.85 (1.2) 0.15 (0.21) 49.3 50.7 0 0.03 Strongly increased 90 viscosity as compared to previous sample, but flows under gravity. 1.0 0.38 0.85 (1.2) 0.15 (0.21) 49.3 50.7 0 0.06 Similar to previous 78 sample and flows under gravity. 1.0 0.51 1.0 (1.6) 0.17 (0.28) 42.0 58.0 0 0.04 Increased viscosity as 110 compared to previous sample, flows slowly under gravity. 1.0 0.77 1.3 (2.3) 0.23 (0.40) 32.5 67.5 0 0.06 Increased viscosity as 104 compared to previous sample, appears not to flow under gravity. 1.0 1.00 1.5 (3.0) 0.26 (0.52) 27.0 73.0 0 0.08 Hard and does not flow 88 under gravity. 1.0 1.42 1.8 (4.2) 0.31 (0.73) 19.3 74.0 6.7 0.11 Similar to previous 65 sample. Hard and does not flow under gravity. 1.0 4.0 2.5 (11) 0.44 (1.92) 6.8 74.0 19.2 0.32 Too hard and crumbly, 30 but adding 0.1 g stearic acid as softener gives a material with dough- like properties. *.sup.)By observing that the sample containing 0.51 g K37 and 1 g CDS 100 has properties similar to the sample in Table 1 with a molar ratio 1:1 (boric acid:CDS 100), 1 g of K37 appears to replace 0.5 mmol boric acid. Number within bracket relates to boric acid concentration with the calculation based on weight of binder and omitting the weight of filler. .sup.#)Estimated by in the calculation using a density of K37 of 0.37 g/mL, and assuming that space filled by K37 has a volume fraction of 0.74 in close packing.

Example 6

(16) To obtain a final product with properties expected from a bouncing putty, and with a boric acid content that is below the levels stipulated by the European Chemicals Agency (ECHA) candidate list a certain amount of WACKER? POLYMER CDS 100, and fillers were added to the formula. First five different partly covalently cross-linked networks were prepared using the method outlined above, Table 6. These were then used to prepare the putties in Table 7.

(17) In Table 8 is given preparations with very high volume content particles. This is to show that the silicone-based binder can be disposed in a thin layer as a coating on the particles, or the grains, which is the majority component (by volume). The preparation has dough-like properties.

(18) TABLE-US-00006 TABLE 6 WACKER? WACKER? Molar ratio Mix POLYMER (g) CROSSLINKER ES 23 (g) ES 23:POLYMER Comments A C 2 T: 397 3.5 0.94:1 Prepared during mixing at 130? C. B CDS100: 384.5 15.4 0.68:1 Made in two steps during mixing at 130? C. First CDS100 was C 2 T: 192.3 1.71 0.95:1 reacted with ES23, followed by adding C 2 T and reacting with ES23. C CDS100: 384.5 15.4 0.68:1 Prepared during mixing at 130? C. D CDS750: 197 3.0 0.97:1 Prepared during mixing at 130? C. E C 1 T: 197.8 2.2 0.95:1 Prepared during mixing at 130? C.

(19) TABLE-US-00007 TABLE 7 Filler Solid glass spheres (53-106 Saturated Apparent Binder microns), boric content Apparent Bounce WACKER? 3M? Boud acid Softener boric content from Mix POLYMER K37 minerals solution Binder Filler Voids Stearic acid boron 2 m (g) (g) (g) Ltd (g) (g) (% vol).sup.#) (% vol).sup.#) (% vol).sup.#) acid (g) (% wt)*.sup.) (% wt)*.sup.) Observation (cm) A; 9 CDS100; 0.5 4.5 75.9 24.1 0 0.10 0.10 0.017 Tacky and None 0.7 too liquid. B; 9 CDS100; 0.5 4.5 75.9 24.1 0 0.10 0.10 0.017 Short and 29 0.7 rubbery when worked with. A; CDS100; 0.5 4.5 75.9 24.1 0 0.10 0.10 0.017 Slightly too 22 4.5 0.7 tacky and B; yet short in 4.5 character. C; 9 CDS100; 0.5 4.5 75.9 24.1 0 0.10 0.10 0.017 Stretchable, 42 0.7 elastic and flows under gravity, but somewhat sticky C; 9 CDS100; 0.75 4.5 72.1 27.9 0 0.10 0.15 0.026 Stretchable, 52 0.7 elastic, less sticky C; 9 C 2 T; 1.5 0.5 4.5 77.3 22.7 0 0.10 0.10 0.017 Ok 35 properties, but lower bounce. C; 9 CDS100; 0.5 4.5 76.6 23.4 0 0.10 0.10 0.017 Ok 54 0.35 properties, C 2 T; 0.75 and better bounce. A; 6 CDS100; 0.5 4.5 76.6 23.4 0 0.10 0.10 0.017 Ok 35 C; 3 0.35 properties, C 2 T; 0.75 but lower bounce. D; 4 0.14 91.4 8.6 0 0.03 0.10 0.017 Ok 70 properties E; 4 0.14 91.4 8.6 0 0.03 0.10 0.017 Ok 60 properties D; 4 0.075 100 0 0 0.03 0.10 0.017 Ok 50 (true) (true) properties E; 4 0.075 100 0 0 0.03 0.10 0.017 Ok 50 (true) (true) properties *.sup.)By observing that the sample containing 0.51 g K37 and 1 g CDS 100 has properties similar to the sample in Table 1 with a molar ratio 1:1 (boric acid:CDS 100), 1 g of K37 appears to replace 0.5 mmol boric acid. In the last two examples boric acid has been added via an aqueous solution saturated in boric acid (5.4% wt), and is therefore denoted true value. .sup.#)Estimated by in the calculation using a density of K37 of 0.37 g/mL, a density of 2.6 g/mL for glass spheres, and assuming that space filled by filler has a volume fraction of 0.74 in close packing.

(20) TABLE-US-00008 TABLE 8 Binder Filler Softener Apparent Apparent WACKER? 3M? Sibelco Stearic Sasol Danisco content content Mix POLYMER K37 quartz acid Isofol Soft-n- Binder Filler Voids boric acid boron (g) (g) (g) sand (g) (g) 20 (g) Safe (g) (% vol).sup.#) (% vol).sup.#) (% vol).sup.#) (% wt)*.sup.) (% wt)*.sup.) Observation A; CDS100; 0.64 GA39 0.10 0.005 11.9 74 14.1 0.20 0.034 Dough-like 0.24 0.56 (D.sub.50 = 91 properties microns); 8.4 A; CDS100; 0.12 M32 (D.sub.50 = 0.03 0.01 0.02 4.1 74 21.9 0.04 0.006 Cohesive 0.02 0.20 260 sand-like microns); material 9.6 .sup.#)Estimated by in the calculation using a density of K37 of 0.37 g/mL, a density of 2.6 g/mL for quartz sand, and assuming that space filled by filler has a volume fraction of 0.74 in close packing.

Example 7

(21) The alcohol ethoxylate C12-13 Pareth-12 supplied by Croda under the trade name BRIJ? LT12-SO(RB) was added in an amount corresponding to 1, 2, or 4 parts to 100 parts organosiloxane. Polyglycol can improve properties after extended kneading and use. Intermediate amounts gave a putty somewhat less tacky, yet retaining the bounce, as compared to a putty without polyglycol.

(22) TABLE-US-00009 TABLE 9 Filler Solid glass spheres (53-106 Binder microns), Saturated Apparent Apparent WACKER? 3M? Boud Softener boric acid content content C12-13 Bounce Mix POLYMER K37 minerals Ltd Stearic solution boric acid boron Pareth- from 2 m (g) (g) (g) (g) acid (g) (g) (% wt)*.sup.) (% wt)*.sup.) 12 Observation (cm) A; 6 CDS100; 0.5 4.5 0.1 0 0.10 0.017 0 Ok properties. 35 C; 3 0.35 C 2 T; 0.75 A; 6 CDS100; 0.5 4.5 0.1 0 0.10 0.017 0.10 No major 30 C; 3 0.35 difference. C 2 T; 0.75 Somewhat less tacky when kneaded A; 6 CDS100; 0.5 4.5 0.1 0 0.10 0.017 0.20 As above 30 C; 3 0.35 C 2 T; 0.75 A; 6 CDS100; 0.5 4.5 0.1 0 0.10 0.017 0.40 Somewhat 20 C; 3 0.35 lower bounce C 2 T; 0.75 A; 6 CDS100; 0 4.5 0.1 0.27 0.10 0.017 0 Ok properties. 60 C; 3 0.35 C 2 T; 0.75 A; 6 CDS100; 0 4.5 0.1 0.27 0.10 0.017 0.10 No major 60 C; 3 0.35 difference. C 2 T; 0.75 Somewhat less tacky when kneaded A; 6 CDS100; 0 4.5 0.1 0.27 0.10 0.017 0.20 Somewhat 45 C; 3 0.35 lower bounce C 2 T; 0.75 A; 6 CDS100; 0 4.5 0.1 0.27 0.10 0.017 0.40 As above 45 C; 3 0.35 C 2 T; 0.75 *.sup.)By observing that the sample containing 0.51 g K37 and 1 g CDS 100 has properties similar to the sample in Table 1 with a molar ratio 1:1 (boric acid:CDS 100), 1 g of K37 appears to replace 0.5 mmol boric acid.

Example 8

(23) 11.1 g Wacker CDS100 was mixed with 0.104 g Wacker Crosslinker V24 (SiH oligo-siloxane) and 0.020 g Wacker Catalyzt OL (Pt-catalyst in PDMS). At heating hydrogen gas was released and the solution became thick like syrup. By adding boric acid via a saturated solution corresponding to a final concentration of 0.21 wt. % boron a cohesive and SillyPutty like material was obtained. Although being above the limits given by the new European legislation this is in contrast to the result obtained by adding the same amount boric acid to CDS100 by itself (compare Table 1 in Example 1) which gives a syrup-like texture. The observation was repeated by using another SiH oligo-siloxane crosslinker (Wacker V88) and mixing 9.8 g CDS100 with 0.14 g V88 and 0.030 g Catalyzt OL.

Example 9

(24) The rheological properties of a commercial sample of a Silly Putty (Intelligente Knete or Thinking Putty from Crazy Aaron's putty world) was investigated with a Bohlin CVO 100 Digital controlled-stress rheometer equipped with a 20 mm parallel plate. The gap was held constant at 250 micrometers. The results are shown in FIG. 1 and FIG. 2. The properties of this putty are representative of puttys of the invention.

(25) In the continuous shear mode the investigated shear stress ranged up to above 44 kPa resulting in a shear rate of 2 s.sup.?1. In this shear rate range (0.015 s.sup.?1 to 2 s.sup.?1) the sample behaved virtually Newtonian with a viscosity of about 1*10.sup.4 Pas to 1*10.sup.5 Pas. The data clearly shows that the sample flows with viscous properties dominating the elastic at these time scales. In the hands of a user this viscous property manifests it self by that the sample can be moulded and reformed to new shapes without returning to its original shape.

(26) The viscosity behaviour at higher shear rates was obtained via the empirical Cox-Mertz rule and data of complex viscosity as a function of angular frequency is included in the figure. These data were obtained with the rheometer in the oscillatory shear mode and the frequency was swept from 0.05 Hz to 100 Hz. The viscosity decreases at higher angular frequencies with a cross over from Newtonian behaviour located in the range 1 s.sup.?1 to 100 s.sup.?1. The deviation from a Newtonian behaviour indicates that at shorter time scales (higher angular frequencies) the sample does not have time to relax to an equilibrium position.

Example 10

(27) The rheological properties of the sample in table 4 which was judged to have the most appropriate crosslinking density, with a molar ratio 0.96:1 of crosslinker ES 23 to polymer C 2 T, was investigated with a Bohlin CVO 100 Digital controlled-stress rheometer equipped with a 20 mm parallel plate. The gap was held constant at 250 micrometer. In an oscillatory shear experiment the viscous property is dominating and G (the viscous modulus) exceeds G (the elastic modulus) in virtually the whole frequency domain accessible with the present rheometer. The results are shown in FIG. 3.

(28) With the rheometer in the continuous shear mode the viscosity at the Newtonian plateau is about 100 Pas. The results are shown in FIG. 4. This is much lower than in a final Silly Putty sample (see example 9) and demonstrates the influence of further (dynamic) cross-linking with a boron compound.