PRODUCING THE SAME

The present invention relates to poly(ether esters) which are degradation resistant, and processes for manufacturing the same, and articles produced therefrom.

Thermoplastic polyether based polyesters are generally susceptible to oxidative and hydrolytic degradation. In addition, in the absence of antioxidants, copolyester elastomers are rapidly degraded in air at elevated temperatures. Conventional polyester elastomers are subject to oxidative degradation when exposed to ultra violet light, and as a result of their polar nature, they are also subject to degradation by hydrolysis at elevated temperatures.

US patent 3,023,192 discloses fibers that are formed from copoiyether ester units prepared by the reaction between one or more dicarboxylic acids or their ester forming derivatives, one or more difunctional polyethers and one or more dihydroxy compounds which include lower aliphatic glycols having the general formula:

HO(CH ₂ ) _a OH where a is from 2 to 10.

Representative of the difunctional polyethers which may be used include poly(al ylene oxide) glycols such as: poly(heptamethylene oxide)glycol, poly(hexamethylene oxide) glycol, poly(octamethylene oxide)glycol, poly(nonamethylene oxide)glycol and poly(decamethylene oxide)glycol.

The synthetic fibers formed by the method of US 3,023,192 have an ability for a high degree of elastic recovery and are particularly suitable in the textile

industry. There is no indication however that the copolyether ester elastomers are especially degradation resistant. In fact the polyesters usually incorporate stabilisers in order to stabilise the composition to heat and ultra violet radiation.

A copolyether ester with increased resistance to oxidative degradation is disclosed in US patent 3,856,749. Such copolyether ester compositions are prepared with the use of poly(alkylene oxide) glycols having a carbon to oxygen ratio of about 2.0-4.3. The stability of the composition is achieved by incorporating from 0.01 to 7.0 wt% of a urea linkage between long chain and short chain ester units. Examples of the long chain glycols that are utilized include poly(ethylene oxide) glycol, poly(1 ,2- and 1 ,3-propylene oxide) glycol, poly(tetramethylene oxide) glycol, random or block copolymers of ethylene oxide and 1 ,2-propylene oxide, and random or block copolymers of tetrahydrofuran with minor amounts of a second monomer such as 3-methyltetrahydrofuran. Such polymeric glycols have a molecular weight of from about 400 to 6000. Particularly preferred is poly(tetramethylene oxide)glycol.

Such materials require stabilisers toward hydrolysis and oxidation even for use in relatively mild environments. The limited hydrolytic and oxidative stability, for example prevented the materials for being used for chronic medical implants, and other areas where a hostile environment may exist.

European patent 210281 discloses non-adsorbable high strength sutures or ligatures comprising a poly(ether ester), in which the ester has alkylene oxide groups containing from 1-10 carbon atoms.

It has been found however, that articles with improved degradation resistance can be produced by correct selection of the poly(alkylene oxide) during the process of manufacture. The present invention aims to overcome or at least alleviate one or more of the difficulties associated with the prior art.

According to a first aspect of the present invention, there is provided a degradation resistant poly(ether ester) derived from:

a polyether macroglycol; and a low molecular weight dicarboxylic acid or ester forming species derived therefrom; wherein the poly(ether ester) is prepared from a polyether macroglycol having alkylene ether repeating units containing 6 to 10 carbon atoms.

In a preferred embodiment of the invention, the polyether macroglycol is poly(hexamethylene oxide) glycol, poly(octamethylene oxide) glycol or poly(decamethylene oxide) glycol. Most preferred is poly(hexamethylene oxide) glycol. It has been found that by utilizing these particular polyether macroglycols in accordance with the invention, that the polymers so produced exhibit particular degradation resistance in hostile environments.

The poly(hexamethylene oxide) glycol, or indeed any other required macroglycol, may be prepared in a manner as disclosed in Australian patent 642799. This process involves providing a suitable polyhydroxy compound and reacting the compound in the presence of an acid resin catalyst, such as Nafion- H™. The polyhydroxy compound is not critical and may be for example branched or unbranched, cyclic or linear, substituted or unsubstituted or contain one or more hetero atoms in the main chain. Suitable polyhydroxy compounds may include 1 ,6 hexanediol, 1 ,4-cyclohexanediol, 1 ,8 octanediol, 2,2,3,3,4,4,5,5,- octafluoro-1 ,6-hexane diol, or 1 , 10-decanediol.

This process is usually carried out at a temperature in the range of from 130°C to 220°C, and the degree of polymerisation is controlled by the presence of the catalyst. For the purpose of the present invention, poly(alkylene oxides) having molecular weights of from 400 to 10,000 may be produced. Particularly preferred are poly(hexamethylene oxide) having a molecular weight of from 800 to 1200.

The low molecular weight dicarboxylic acid or ester forming species derived therefrom, may be the product of the reaction of a low molecular weight diol and a dicarboxylic acid, acid halide or anhydride. The diol will usually have a

molecular weight of below about 250. The ester forming dicarboxylic acid derivative itself may be an ester or a half ester of a low molecular weight alcohol.

The poly(ether ester) may be derived from a composition including a low molecular weight dioi. Included among the low molecular weight diols suitable for the preparation of the poly(ether ester) of the invention, are aliphatic, cycloaliphatic, and aromatic dihydroxy compounds. Preferred are diols with 2 to 15 carbon atoms such as butanediol, ethylene, propylene, butylene and tetramethylene glycols. In particular aliphatic diols containing 2 to 8 carbon atoms are preferred.

The poly(ether esters) of the invention are formed by the polymerisation reaction between the poly(alkylene oxide) glycol and the low molecular weight dicarboxylic acid or ester forming species derived therefrom. A low molecular weight diol may be present to provide elastomeric properties for the polymer.

The ester forming dicarboxylic acid derivative may be aliphatic, cycloaliphatic or aromatic with preferably a molecular weight of less than 550, most preferably less than 300. Most preferably, aromatic dicarboxylic acids are used, having from 8 to 16 carbon atoms particularly phenylene dicarboxylic acids, for example phthalic, terephthalic and isophthalic acids or derivatives thereof.

Representative of the aliphatic or cycloaliphatic dicarboxylic acids that may be used include sebacic acid, cyclohexane carboxylic acids, adipic acid, glutahc acid, and succinic acid and or derivatives thereof.

The reaction and the reaction product may also include an antioxidant. Suitable antioxidants that may be used include aryl and diaryl amines, ketone aldehyde amine condensates, and hindered phenol antioxidants.

Suitable diaryl amines include phenyl πaphthylamines and octylated diphenylamine and 4-iso-propoxydiphenylamines. P-phenylenediamine

derivatives such as N,N'-bis-1-methyl-heptyl-p-phenylenediamine and N,N'-di- beta-naphtyl-p-phenylenediamine are also preferred.

Generally, the macroglycol will constitute from 5 to 85% by weight, preferably 10 to 75% by weight of the poly(ether ester); the low molecular weight dicarboxylic acid or ester forming species may constitute from 15 to 95% by weight, preferably 25-90% by weight of the poly(ether ester). The diol may be added in a molar ratio of from 0.1 :1 to 10:1 of the dicarboxylic acid or its derivative, the excess (if any) being distilled off during polymerisation such that the final polymer may include from 0 to 20% by weight of the polymer. The antioxidant is generally present in an amount of from 0 to 5 % by weight.

According to a further aspect of the present invention, there is provided a process for the production of degradation resistant poly(ether ester) which includes reacting: a polyether macroglycol; and a low molecular weight dicarboxylic acid or ester forming species derived therefrom; to form a poly(ether ester), wherein the polyether macroglycol has alkylene ether chain units containing 6 to 10 carbon atoms.

It is most preferred in the processes, to select the polyether macroglycol from poly(hexamethylene oxide) glycol, poly(octamethylene oxide) glycol or poly(decamethylene oxide) glycol. Most preferred is poly(hexamethylene oxide) glycol.

The poly(ether ester) may be manufactured according to known ester interchange reaction processes, for example those described in United States Patent 3,856,749. A preferred procedure may include heating the dicarboxylic ester with a poly(hexamethylene oxide) of molecular weight of from 800 to 1200, and a molar excess of a diol in the presence of a catalyst, at a temperature of from 130° to 290° and a pressure of from 0.5 to 5 atmospheres, preferably ambient pressures until the alcohol from the ester exchange is distilled. This

reaction will generally take from 2 minutes to 2 hours depending upon conditions. Generally the molar ratio of the components may be from 1 mol of acid:0.0025 to 0.85 mol of poly(hexamethylene oxide): greater than 1 mol of diol. The optional antioxidant may be included at any time during the reaction.

Distillation of the excess diol will result in 'polycondensation' to the poly(ether ester). This step is usually conducted at a temperature of from 180°C- 270°C for 1/2 to 2 hours at less than 5mm pressure.

The process is able to produce polymers which may be shaped or formed by conventional methods to make degradation resistant articles of poly(ether ester) based polyesters. Such polyesters are particularly useful for use in harsh degradation producing environments. For example, they have particular application in medical devices, including insulation for medical electrical leads and long term indwelling catheters and vascular prosthesis. Other non-medical applications include long term or severe exposure to degradative environments, such as oil rig or chemical plant hosing. The polyesters also show improved thermal processing through their greater oxidation resistance.

The polymers of the present invention are suitable for harsh environments with a potential use in the broad number of applications, including monofilaments and fibers including optical fibers, vascular grafts, medical implants, surgical prosthesis, sutures, catheters, artificial leather, flexible boots, shoe soles, sporting equipment, cable sheathing and hosing.

The following examples are illustrative of the present invention, and the scope should not be considered to be limited thereto.

EXAMPLE 1

Poly(hexamethylene oxide) of number average molecular weight 950 is dried by heating at 105 °C for 15 hours at 0.1 Torr. Anhydrous butanediol (19.6 g), dimethylterephthalate (30.5 g), the pre-dried polyhexamethylene glycol (51.3 g) and sym-di-β-naphthyl-p-phenylenediamine (0.15 g) are added to a nitrogen blanketed reaction flask at 200°C equipped for efficient mechanical stirring and set up for distillation. After five minutes of stirring, at which time the mixture becomes molten, n-tetrabutyl titanate (0.3ml) is added. Methanol distillation starts almost immediately and is complete within 20 minutes. The temperature is maintained for a further one hour and then is increased over 30 minutes to 250°C. The pressure is then reduced to 0.1 Torr and distillation at reduced pressure is continued for a further 90-120 minutes. The resulting viscous slurry is scraped from the flask under an atmosphere of nitrogen or argon and allowed to cool.

This procedure yields 80.6 g of a polymer, designated as Material A, of inherent viscosity 0.81 dl/g, which is suitable for thermoforming into a degradation resistant article. Material A was compression moulded on a Wabash Press at 180

°C (and a nominal load of 8 Tons) into sheets, from which dumbbell-shaped test pieces were cut using a specially manufactured punch.

COMPARATIVE EXAMPLE 1

A method identical with that described in Example 1 , except that pre-dried poly(tetramethylene oxide) (54 g) of number average molecular weight 1000 replaced the poly(hexamethylene oxide), to prepare the poly(ether ester. This poly(ether ester) is of the type typically used for preparing articles according to the prior art. This polymer, designated as Material B, had an inherent viscosity of 1.04 dl/g and could be thermoformed at 180 °C into sheets, from which dumbbells could be cut.

The comparative mechanical properties are shown below:

Ultimate Tensile Ultimate Strain Stress at 100%

Stress Strain Material A 8.1 MPa 143% 7.8 MPa

Material B 10.4MPa 330% 8.7 MPa

Material A exhibited characteristics expected of a degradation resistant material, whilst Material B, which is representative of the prior art, did not. For example, Material A exhibited good hydrolytic stability when tested by boiling weighted dumbbells for 6 days in pH 7, pH I and pH 13 buffer solutions. After washing with water and drying, the dumbbells showed an average 10%, 87% and 40% decrease in ultimate tensile stress for the three treatments, respectively, whereas the corresponding decreases for Material B were 26%, 100% and 75%, respectively.

The decreases in ultimate tensile stress for dumbbells prepared from a commercial sample of Hytrel (registered trademark) prepared under these conditions were 59%, 96% and 95%, respectively. Dumbbells of Material A also showed good oxidative stability when tested in 50% hydrogen peroxide solution at 37°C for 24 hours. After washing with water and drying, the dumbbells showed an average 19% decrease in ultimate tensile stress, whereas the corresponding decreases for the dumbbells of Material B and of commercial Hytrel were both 94%.

The relative stabilities are shown in Charts 1 and 2.

Chart 1. Polyester Hydrolytic Stability at 100°C (6 days)

pH7(r) pH13 pH1

Chart 2. Poly(ether ester) Stability to Hydrogen

SUBSTTTUTE SHEET (Rule 26)

EXAMPLE 2

A poly(decamethylene oxide) polyester incorporating 52% of the polyol was made using the procedure described in Example 1 (64% polyol) except with the following levels of starting reagents:-

poly(decamethylene oxide) (MW is 960) 39.2g dimethylterephthalate 37.6g butanediol 19.63g sym-di-β-naphthyl-p-phenylenediamine 0.1 Og n-tetrabutyl titanate 0.22ml

This procedure yields 72g of a polymer, designated as material C, which could be compression moulded at 195°C into sheets from which dumbbells were cut.

COMPARATIVE EXAMPLE 2

A poly(tetramethylene oxide) polyester incorporating 52% of the polyol was also made using the procedure of Example 1. The following levels of starting reagents were used:-

poly(tetramethylene oxide) (MW is 980) 107.7g dimethylterephthalate 103.1 g butanediol 55. Og sym-di-β-naphthyl-p-phenylenediamine 0.3g n-tetrabutyl titanate 0.6ml

This procedure yielded 200g of a polymer designated below as Material D.

The comparative mechanical properties were:

Ultimate Tensile Ultimate Strain Stress at 100% Toughness

Strength Strain Material C 11.4 MPa 143% 12.0 MPa 16.5 MPa

Material D 12.4 MPa 165% 12.8 MPa 19.0 MPa

As demonstrated below Material C exhibited characteristics expected of a degradation resistant material, whilst Material D, which is representative of the prior art, did not.

(a) Hydrogen Peroxide Resistance

Material C exhibited good oxidative resistance when heated at 80°C in 50% hydrogen peroxide solution at pH 1.6 for 7 hours. After washing with water and wiping dry, the dumbbells (x5) showed only an average 16% decrease in ultimate tensile stress. Material D and a commercial poly(ester ether) Hytrel (registered trade mark) when subjected to these same conditions were partially digested by the hydrogen peroxide and lost all cohesive strength.

(b) Resistance to Oxygen at Elevated Temperature

The materials were dried to constant weight at 60°C at 0.1 Torr for 12 hours and then heated at 200°C in an atmosphere of pure oxygen using a Mettler thermogravimetric analysis apparatus which enabled continuous monitoring of weight loss. The results in the table below demonstrate that the polyether ester polymers of the invention are significantly more resistant to high temperature oxidation that the prior art materials.

Material Weight Loss in Oxygen at 200°C

1 hour 2 hour 3 hour

C 0.6% 1.2% 1.8%

D (prior art) 1.5% 2.9% 3.9%

(c) Hydrolytic Stability in Strong Acid

Material C exhibited good hydrolytic stability when tested by boiling weighted dumbbells for six days in pH 1 buffer solution. After washing with water, wiping dry and testing for tensile properties, the dumbbells showed an average of 7% decrease in ultimate tensile stress and an average 51 % decrease in ultimate strain. The corresponding decreases for Material D, typical of a prior art material, were 18% in ultimate tensile stress and 80% in ultimate strain.

(d) Resistance to alkali

Material C exhibited good hydrolytic stability when tested by boiling weighted dumbbells for six days in pH 13 buffer solution. After washing with water, wiping dry and testing for tensile properties, the dumbbells showed an average 2% decrease in ultimate tensile stress and an average 56% decrease in ultimate strain for the two treatments respectively. The corresponding decreases for Material D, typical of a prior art material, were 28% in ultimate tensile stress and 60% in ultimate strain.

EXAMPLE 3

A poly(hexamethylene oxide) polyester incorporating 52% of the polyol was made using the procedure described in Example 1 except with the following levels of starting reagents:-

poly(hexamethylene oxide) (MW is 960) 107.9g dimethylterephthalate 103.4g butanediol 54.4g sym-di-β-naphthyl-p-phenylenediamine 0.30g n-tetrabutyl titanate 0.6ml

This procedure yielded 200g of a polymer which was compression moulded at 195°C into sheets from which dumbbells were cut. The polymer had the following mechanical properties:

Ultimate tensile strength 12.0 MPa

Stress at 100% strain 11.7 MPa

Ultimate strain 225%

Toughness 24.5 MPa