GB1577222A - Thermoplastic polyurethane elastomers - Google Patents

Description

(54) THERMOPLASTIC POLYURETHANE ELASTOMERS (71) We, IMPERIAL CHEMICAL INDUSTRIES LIMITED, Imperial Chemical House, Millbank, London SW1P 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 thermoplastic polyurethane elastomers and is more particularly concerned with thermoplastic polyurethane elastomers having improved processing characteristics.

It is well known that elastomeric polyurethanes made from entirely di-functional starting materials and ratios of reactants having a NCO:OH ratio of 0.9:1 to 1.1:1 are thermoplastic and can be formed into shaped articles by conventional injection moulding techniques.

Typical products are obtained, e.g. by reacting polyethylene adipate of M.W. about 2000 with 4-7 moles of 4,4'-diphenylmethane diisocyanate and further reacting the prepolymer so obtained with a slight excess or deficiency of 1,4-butane diol.

Thermoplastic polyurethanes are soluble in some organic solvents and have been used for coating textiles, leather, paper and similar substrates by application of a film of solution followed by removal of the solvent. Thermoplastic polyurethanes which can be processed as solvent-free compounds on calenders or laminating rollers have an advantage over those which must be applied in a solvent since they do not pollute the atmosphere with solvent vapours. Thermoplastic polyurethane elastomers have nevertheless been used to only a limited extent for coating by non-solution methods because commercially available products require very critical temperature control to avoid undue viscosity variations of the molten mass.

The present invention provides a thermoplastic polyurethane elastomer which is the reaction product of an organic diisocyanate, a diol of molecular weight greater than 800 and a mixture of aliphatic diols of molecular weight below 250 and having 2 to 10 carbon atoms which mixture contains a major proportion by weight of one diol and a minor proportion by weight of one or more different diols, which minor proportion is within the range 1% to 20% by weight of the total diols of molecular weight below 250 in the case of a single different diol or individually in the range 1% to 10% by weight of the total diols of molecular weight below 250 in the case of more than one different diols, the overall NCO:OH ratio of the reactants being within the range 0.90:1 to 1.10:1.

As diols of molecular weight greater than 800, there may be mentioned polyetherthioethers, polyacetals, hydroxyl-ended polyolefines, and more especially polyethers, polyesters or mixed polyether-polyesters.

As examples of polyetherthioethers suitable for use there may be mentioned the products of the self-condensation of thioglycols, e.g. thiodiglycol, or of the condensation of thioglycols with glycols.

As examples of polyacetals suitable for use there may be mentioned the reaction products of aldehydes, e.g. formaldehyde. acetaldehyde and butyraldehyde and dihydric alcohols, e.g. propylene glycol. butylene glycols and diethylene glycol.

As examples of hydroxyl-terminated polyolefines suitable for use there may be mentioned the products obtained by oxidative degradation of polyolefins of higher molecular weight. Typically, polymers of butadiene or of its copolymers with other monomers, e.g. styrene or acrylonitrile, may be oxidised to produce a lower molecular weight product having terminal isocyanate-reactive hydroxyl groups. Residual ethylenic unsaturation may be removed by hydrogenation. Alternatively, the olefin monomer may be polymerised or copolymerised by (i) a free radical mechanism of by (ii) an anionic mechanism. Typically in the case of (i) the olefinic monomer is polymerised in the presence of initiators and optionally chain transfer agents both of which bear two isocyanate-reactive hydroxyl groups or groups which are readily converted into isocyanate-reactive hydroxy groups. In the case of (ii), typically the monomer is polymerised using as initiator a compound which provides a difunctional polymer, the terminal functionalities of which are readily convertible into isocyanate-reactive hydroxyl groups by methods well known in the art.

As examples of hyroxyl-terminated polyesters suitable for use there may be mentioned those obtained by known methods from carboxylic acids and glycols, more especially from aliphatic a, -dicarboxylic acids, e.g. succinic, glutaric, adipic, pimelic, suberic, azelaic and sebacic acids and mixtures of these, and straight chain or branchea aiipnatic atoms, e.g.

ethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol, 2,3-butyleneglycol, diethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol and 2,2-dimethyl-trimethylene glycol and mixtures of these. Small proportions. up to 20 molar % of the total acid, of aromatic dicarboxylic acids, e.g.

phthalic, isophthalic or terephthalic acids may be used if desired. The acid value of the polyester used should generally be less than 6 mg KOH/g. and preferably less than 3 mg KOH/g.

The preferred polyesters have a melting point below 60"C and are derived from glycols having 2 to 8 carbon atoms and aliphatic dicarboxylic acids having from 4 to 10 carbon atoms. Especially suitable are polyesters of molecular weight between 1000 and 2500 derived from these aliphatic dicarboxylic acids, especially adipic acid, and a glycol or mixture of two glycols in the ratio of 50:50 to 70:30 by weight.

Polystel-s obtained by polymerisation of a- o-hydroxy-alkylcarboxylic acids or lactones derived therefrom. or mixtures of these, e.g. E-caprolactone and its alkyl substituted derivatives are also suitable.

As examples of hyroxyl-terminated polyethers which may be used, there may be mentioned polymers and copolymers of cyclic oxides, for example 1,2-alkylene oxides e.g.

ethylene oxide. epichlorohydrin, 1,2-propylene oxide and 1,2-butylene oxide, 2,3-butylene oxide, oxycyclobutane and substituted oxycyclobutanes and tetrahydrofuran. There may also be mentioned polyethers obtained by the polymerisation of an alklene oxide in the presence of a basic catalvst and water. glycol or a primary monoamine. Mixtures of such polyethers may be used. The preferred polyethers are polyethylene glycols, polypropylene glycols and polytetramethylene glycols of MW 1000-2500.

As examples of polyether-polyesters which may be used, there may be mentioned the condensation products of dicarboxylic acids, such as described above, with hydroxyl terminated polvethers of the kind just described; or alternatively the products obtained by reacting hyroxyl-ended polyesters with alkylene oxides whereby polyether radicals are introduced.

As examples of organic diisocyanates which may be used there may be mentioned aliphatic diisocvanates such as hexamethvlene diisocyanate, tetramethylene diisocyanate, 2,2.4- 4- and 2*4 4 '4-trimethyl hexamethvlene diisocyanates, aromatic diisocyanates such as tolylene-2 .4-diisocyanate. tolylene-2 .6-diisocyanate, diphenylmethane-4.4'-diisocyanate , 3-methyldiphenylmethane-4 .4'-diisocyanate. m- and p-phenylene diisocyanate, chlor ophenylene-2 ,4-diisocyanate. xylene diisocyanate. naphthalene- 1 .5-diisocyanate, diphenyl 4,4 -diisocyanate. 4.4'-diisocyanato-3 ,3-dimethyldiphenyl and diphenyl ether diisocyanate and cycloaliphatic diisocyanates such as dicyclohexylmethane diisocyanates. methylcyclohexvlene diisocyanates and 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate.

The preferred diisocyanate is diphenyl-methane-4,4'-diisocyanate.

As aliphatic diols of molecular weight below 250 having 2 to 10 carbon atoms which may be used. there may be mentioned straight chain or branched diols, e.g. ethylene glycol, 1.2-propylene glycol, 2,3-butylene glycol. 1,3-butylene glycol, trimethylene glycol, tetramethylene glycol. pentamethylene glycol. hexamethylene glycol. decamethylene glycol, 2.2-dimethyltrimethylene glycol, diethylene glycol and triethylene glycol. In accordance with the present invention, a mixture of these diols is used, with one diol constituting a major proportion of the mixture. The preferred diol for this purpose is tetramethylene glycol.

Where a mixture of only two diols is used, the minor constituent is from 1% to 20% by weight of the mixture and is more especially from 5% to 20% by weight of the mixture.

Where a mixture of three or more diols is used, each minor constituent is from 1% to 10% by weight of the mixture and more especially from 3% to 10% by weight of the mixture.

The polyurethanes can be made from the above constituents by conventional methods, e.g. by the one shot or more preferably by the prepolymer method.

In the latter case, the diisocyanate should be reacted first with the diol of molecular weight greater than 800 to form an isocyanate-ended prepolymer which is then reacted with the mixture of aliphatic diols. The first condensation is preferably carried out in the presence of a small amount of an acid or acid-liberating substance, e.g. adipic acid or benzoyl chloride, which appears to assist in reducing side-reactions leading to the formation of branched polymers. The amount of acid present for this purpose should be that equivalent at most to an amount of hydrogen chloride corresponding up to 0.2% by weight of the diisocyanate. This reaction is preferably carried out at a temperature of 60-100 C more especially at from 75-850C; it is advisable to dehydrate the diol by heating it to about 100"C under reduced pressure for a period of time immediately prior to the reaction to avoid the deleterious effects of small amounts of water. It is also preferred at this stage to avoid the presence of metal salts which behave as catalysts for the polyurethane-forming reaction.

The isocyanate-ended prepolymer is then preferably reacted with the mixture of diols at a temperature high enough to keep the mixture molten; final temperatures of 1500C upwards are usually employed. Alternatively the reaction can be carried out at a lower temperature, e.g. 60-120"C, in which case, a solid or semi-solid reaction mixture ensues.

Preferably, reaction of the isocyanate ended prepolymer and the mixture of diols is effected in a continuous manner, e.g. by feeding the reactants independently at the desired temperature to a heated chamber containing a device for mixing the reactants, and so constructed that the liquid mixture issues on to or into a further heated receptacle, e.g. a moving belt which passes over a platen heated to the desired temperature. In contrast to formation of the prepolymer, a conventional catalyst for the polyurethane forming reaction e.g. tertiary bases, metal salts or organometallic compounds, can be added with the mixtue of diols to accelerate the rate of formation of the polyurethane.

It is particularly advantageous to carry out the reaction in double screw extruders and then to pelletise the material discharged from the extruder.

Other conventional additives for thermoplastic polyurethanes may be added in a similar manner, e.g. pigments, UV stabilisers, antiblocking compounds, UV absorbers and antioxidants. In such cases it may be desirable to use a carrier for the additives, ethylene-vinyl acetate copolymers being especially useful for this purpose.

The new polyurethanes are suitable for a wide range of uses associated with moulded thermoplastic polyurethane products. Compared with polyurethanes obtained by use of a signal glycol as reactant in their formation, their endothermic peaks measured by Differential Scanning Calorimetry occur over a wider range of temperatures, but they are similar to such polyurethanes in their other physical properties, e.g. their hardness, tensile strength, extensibility, permanent set, low temperature resilience. They can be moulded readily by injection moulding techniques, and used, inter alia, for the manufacture of gaskets, diaphragms, tubing, a variety of automobile components, footwear components; they can be extruded to form a film of outstanding abrasion resistance.

The possession of a broader endothermic peak corresponds with a lesser sensitivity of viscosity to temperature variation, which makes them particularly suitable for coating textile, leather, paper and similar substrates by processing on calenders or melting and laminating rollers.

In addition they may be soluble in polar organic liquids, e.g. ketones, esters and ethers, e.g. acetone, methyl ethyl ketone, methyl-isopropyl ketone, cyclohexanone, ethyl acetate, butylacetate, tetrahydrofuran and mixtures of these, the resultant solutions, especially those prepared from polyurethanes of NCO:OH less than 1, being valuable for use as adhesives or as coatings, e.g. for fabrics. Thus the polyurethanes can be used as an adhesive for joining materials, especially those of a flexible nature such as fabrics, natural and synthetic elastomers and flexible foams. in particularly in sheet form, to each other or to other substrates, e.g. wood or metal. These adhesives are especially applicable to the manufacture of foam-backed textiles and joining shoe-uppers to soles or may be used to form a coating of polyurethane elastomer on substrates such as wood, metal, leather and textile fabrics, e.g. to give protective clothing and taupaulin.

The invention is illustrated by te following Examples in which parts and percentages are by weight: Example 1 1200 parts of poly-tetramethylene adipate, OH value 56 mg KOH/g were heated to 700C and added to a mixture of 645 parts of 4,4'-diphenylmethane diisocyanate (MDI), 0.1 part of benzoyl chloride, 2 parts of 2,6-di-t-butyl-4-methylphenol and 19 parts of ethylene bis(oleamide) at 70 C. The mixture was stirred at 90-1100C for 2 hours then cooled and the NCO value adjusted to 8.7% by the addition of more MDI.

100 Parts of the product were mixed with a mixture of 1.36 parts of 1,3-butylene glycol and 7.69 parts of tetramethylene glycol (NCO-OH ratio 1.03) and the mixtures poured into a mould and heated at 1100C for 16 hours.

The resulting product was granulated and the viscosity of the product measured over a range of temperatures using an Instron 3211 Extrusion Rheometer ("Instron" is a Registered Trade Mark) with a die of 51 mm. length and circular cross section of 1.25 mm.

diameter at a shear rate of 10 sec. . Also the temperatures at which endothermic peaks occurred were determined by Differential Scanning Calorimetry (DSC) using a du Pont Model 990 Thermal Analyser with a heating rate of 20 C/minute. The remainder of the product was extruded at about 200 C and the temperature of the endothermic peaks of the extrudate, after granulation. redetermined by DSC. A further sample of the extrudate was injection moulded to provide test samples to determine the tensile strength.

Viscosity Measurements (N sec-1) 1700C - too high to measure 1800C - 2.35 x 104 1900C - 7 x 103 200 C - 2 x 103 A"/AT 5.8 x 102 D. S. C. results Found : before extrusion. endothermic peak at 198 C, minor peaks at 145, 220 C.

After extrusion, endothermic peak at 170 C, hardness 86 Shore A tensile strength 52 M NM-2 elongation at break 550% In contrast, a polyurethane obtained in identical manner, save that 9.05 parts of tetramethylene glycol were used in place of the mixture of glycols, had the following properties: Viscosity Meas ur eseles?ts: (N sec') 170 C - too high to measure 180 C 190 C - 6.4 x 200 C - 1.8 x 10 A r 8.5 x 1()2 D.S.C. results endothermic peak before extrusion at 208 C endothermic peak after extrusion at 175. 220"C hardness 88 Shore A tensile strength 47 M NM-2 elongation at break 570C/c Example 2 A polyurethane was obtained in identical manner to Example 1 save that a mixture of: 1,3-butylene glycol 0.81 parts 1,2-propylene glycol 0.81 parts diethylene glycol 0.81 parts tetramethylene glycol 6.62 parts was used in place of the mixtures of glycols. The product had the following properties: Viscosity Measurements: (N sec~l) 1700C 1.41 x 104 1800C 6.8 x 103 1900C 2.2 x 103 200"C 8 x 102 L'l/AT = 4.4 x 102 D. S. C. results endothermic peaks before extrusion 120-230"C " " after extrusion 117-160"C hardness 84" Shore A tensile strength 46 M NM-2 elongation at break 620% We make no claim herein to a thermoplastic polyurethane claimed in Specification No.

1462595 which is the reaction product of (a) 4,4'-methylene bis (phenyl isocyanate) (b) a diol consisting of a polyoxypropylene polyoxyethylene block copolymer having a molecular weight of 1000 to 3000, a pH of 4.5 to 9, a primary hydroxyl content of not less than 50% and a content of alkali metal ion not greater than 25 ppm, said block copolymer having a minimum content of ethylene oxide (E.O.) residues for any given molecular (M.W.) corresponding to:

(c) an extender selected from aliphatic straight chain diols having from 2 to 6 carbon atoms, inclusive, and the bis(2-hydroxyethyl) ethers of hydroquinone and resorcinol, and optionally as a minor constituent, a branched alkylene or aminoalkylene diol having from 3 to 6 carbon atoms, diethylene glycol, dipropylene glycol or polyethylene glycols of molecular weight 200 to 250; the molar proportion of said block polymer (b) to said extender (c) being from 1:1 to 1:12 and the ratio of equivalents of isocyanate to total equivalents of hydroxyl groups being from 1:0.96 to 1:1.10.

Subject to this disclaimer, WHAT WE CLAIM IS: 1. A thermoplastic polyurethane elastomer which is the reaction product of an organic diisocyanate, a diol of molecular weight greater than 800 and a mixture of aliphatic diols of molecular weight below 250 and having 2 to 10 carbon atoms which mixture contains a major proportion by weight of one diol and a minor proportion by weight of one or more different diols, which minor proportion is within the range 1% to 20% by weight of the total diols of molecular weight below 250 in the case of a single different diol or individually in the range 1% to 10% by weight of the total diols of molecular weight below 250 in the case of more than one different diols. the overall NCO:OH ratio of the reactants being within

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

Claims (7)

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

   Example 2 A polyurethane was obtained in identical manner to Example 1 save that a mixture of: 1,3-butylene glycol 0.81 parts 1,2-propylene glycol 0.81 parts diethylene glycol 0.81 parts tetramethylene glycol 6.62 parts was used in place of the mixtures of glycols. The product had the following properties: Viscosity Measurements: (N sec~l) 1700C 1.41 x 104 1800C 6.8 x 103 1900C 2.2 x 103 200"C 8 x 102 L'l/AT = 4.4 x 102 D. S. C. results endothermic peaks before extrusion 120-230"C " " after extrusion 117-160"C hardness 84" Shore A tensile strength 46 M NM-2 elongation at break 620% We make no claim herein to a thermoplastic polyurethane claimed in Specification No.

   1462595 which is the reaction product of (a) 4,4'-methylene bis (phenyl isocyanate) (b) a diol consisting of a polyoxypropylene polyoxyethylene block copolymer having a molecular weight of 1000 to 3000, a pH of 4.5 to 9, a primary hydroxyl content of not less than 50% and a content of alkali metal ion not greater than 25 ppm, said block copolymer having a minimum content of ethylene oxide (E.O.) residues for any given molecular (M.W.) corresponding to:

   (c) an extender selected from aliphatic straight chain diols having from 2 to 6 carbon atoms, inclusive, and the bis(2-hydroxyethyl) ethers of hydroquinone and resorcinol, and optionally as a minor constituent, a branched alkylene or aminoalkylene diol having from 3 to 6 carbon atoms, diethylene glycol, dipropylene glycol or polyethylene glycols of molecular weight 200 to 250; the molar proportion of said block polymer (b) to said extender (c) being from 1:1 to 1:12 and the ratio of equivalents of isocyanate to total equivalents of hydroxyl groups being from 1:0.96 to 1:1.10.

   Subject to this disclaimer, WHAT WE CLAIM IS: 1. A thermoplastic polyurethane elastomer which is the reaction product of an organic diisocyanate, a diol of molecular weight greater than 800 and a mixture of aliphatic diols of molecular weight below 250 and having 2 to 10 carbon atoms which mixture contains a major proportion by weight of one diol and a minor proportion by weight of one or more different diols, which minor proportion is within the range 1% to 20% by weight of the total diols of molecular weight below 250 in the case of a single different diol or individually in the range 1% to 10% by weight of the total diols of molecular weight below 250 in the case of more than one different diols. the overall NCO:OH ratio of the reactants being within

   the range 0.90:1 to 1.10:1.
2. 2. A thermoplastic polyurethane as claimed in claim 1 wherein the diol of molecular weight greater than 800 is a hydroxy-terminated polyester of an aliphatic-o--dicarboxylic acid and a straight-chain or branched aliphatic dlol.
3. 3. A thermoplastic polyurethane as claimed in claim 2 wherein the polyester has a melting point below 60"C and is derived from a glycol having 2 to 8 carbon atoms and an aliphatic dicarboxylic acid having from 4 to 10 carbon atoms.
4. 4. A thermoplastic polyurethane as claimed in claim 1 wherein the diol of molecular weight greater than 800 is a polyethlene glycol, polypropylene glycol or polytetramethylene glycol of molecular weight 1000-2500.
5. 5. A thermoplastic polyurethane as claimed in any preceding claim wherein the organic diisocyanate is dipheny-methane-4,4'-diisocyanate.
6. 6. A thermoplastic polyurethane as claimed in any preceding claim wherein the major portion of diol of molecular weight below 250 is tetramethylene glycol.
7. 7. A thermoplastic polyurethane as claimed in any preceding claim substantially as herein described with reference to Example 1 or Example 2.