GB2203158A

GB2203158A - Hydrophilic polyurethane and method of making same

Info

Publication number: GB2203158A
Application number: GB08707374A
Authority: GB
Inventors: Charles K Kliment; James M Curtis
Original assignee: Tyndale Plains Hunter Ltd
Current assignee: Tyndale Plains Hunter Ltd
Priority date: 1987-03-27
Filing date: 1987-03-27
Publication date: 1988-10-12
Also published as: AU7130587A; GB8707374D0; DE3708953A1; AU583183B2; FR2612194A1

Abstract

Hydrophilic thermoplastic polymers such as polyurethanes are stretched at a temperature above their glass transition point and then cooled to control axial swelling characteristics of the polymer in aqueous media; such polymers are especially useful for intravenous catheters.

Description

HYDROPHILIC POLYURET11ANE AND METHOD OF MAKING SAME This invention relates to hydrophilic polymers and in particular to certain water swellable hydrophilic polyurethanes.

In U. S. Patent No. 3,975,350, there is disclosed a class of polyurethanes which are so formulated as to pro vide high hydrophilicity excellent polymer properties in the wet state and variations from dry to wet state which are tolerably uniform. Generally speaking, such hydrophilic polyurethanes are the product of (a) a polyfunctional resin having an equivalent weight of more than 170 and up to 2000 and a numerical carbon to oxygen or carbon to nitrogen ratio of up to 2.5:1 to 1.2:1 or a numerical carbon to ionic group ratio in said resin of 20:1 to 6::1 and (b) an aliphatic, alicyclic-aliphatic mixed aliphatic-aromatic or an aromatic polyfunctional isocyanate, a nitrile carbonate or mixtures of same of a functionality of 2 or higher in an amount from 0.02 in excess of one equivalent weight of isocyanate times its functionality per equivalent weight of resin times its functionality up to equivalent weight of said isocyanate to said resin.

The polymers aforesaid are useful in medicinal, cov metic and industrial applications. They are also useful as release agents for various active substances and in the production of hydrophilic coatings having reduced surface friction.

One type of polymer embraced within the general type described in the cited patent and with which the invention is particularly concerned, is the product of a polyoxyethylene glycol and an aliphatic diisocyanate. The resulting hydrophilic polyurethane has proved eminently suitable in the fabrication of various body inserts such as catheters and the like. On contact with bodily fluids, the polymers undergo swelling from absorbed moisture thereby producing a snug fit between the insert and tissue. Moreover, the polymers are extremely slippery in the wet state. This means that medical devices or articles made therefrom can be inserted and removed from the body with minimal discomfort to the patient.

Now the swelling of these polymers occurs uniformly, i.e., expansion takes place in all directions. However, uniform swelling is not always desirable. Such is the case, for instance, where tubing made from the polymer E to be used as an intravenous, through the needle, catheter. Here, uniform expansion results in the tubing undergoing considerable elongation after insertion into a vein or artery. This can cause buckling or kinking of the catheter as it adjusts to the axial extension. The elongation can also make it difficult to maintain the tip of the catheter at the desired location within the circulatory system.

A method has now been discovered whereby hydrophilic urethane polymers can be made to undergo differential axial swelling in aqueous media and the provision of sad method and polymers prepared thereby constitutes a prince pal object and purpose of the present invention. Other main objects and purposes include the fabrication of plastic articles from the said polymers. A particular object of the invention is the provision of a catheter which does not swell lengthwise in the presence of aqueous liquids.

As understood herein, differential axial swelling means that swelling is not uniform but will differ along the axes of a plastic article manufactured from the herein polymers.

The objects aforesaid can be realized by first forming a hydrophilic substantially linear thermoplastic polyurethane from the reaction of an aliphatic diisocyanate and a polyoxyethylene glycol. This polymer is then subejected to stretching at a temperature above its glass transition point to promote alignment of the polymer molecules followed by cooling to effect fixing of the aligned molecules. On immersion in a water based liquid, the polymer undergoes swelling in which the ratio of swelling along the stretch axis to swelling along the other axis is controlled by the degree of stretching.

Thus, a tubular or rod member made from a given polymer can be sufficiently stretched whereby there is no axial extension on swelling; even axial contraction on swelling may occur with sufficient stretching. Yet, the stretch polymer will still exhibit radial swelling. Such controlled directional swelling renders the polymers eminently useful for the manufacture of through the needle catheters since they do not exhibit the undesirable elongation as when the swelling occurs uniformly.

The preferred hydrophilic thermoplastic polyurethane herein are prepared by reacting an aliphatic diisocyanate with a resin mixture containing a major amount of a polyoxyethylene glycol having a molecular weight of from about 1000 to about 8000 and a minor amount of diethylene glycol.

Exemplary polyoxyethylene glycols are the various commercial Carbowaxes available in a range of molecular weights from the Union Carbide Corporation. Repre R sentative Carbowaxes are CARBOWAX 1450 and CARBOWAX 8000R Exemplary aliphatic diisocyanates include methylenebis(4-cyclohexylisocyanate), tetramethylene diisocyanate, hexamethylene diisocyanate, decamethylene diisocyanate and the like.

The invention is illustrated in further detail by the following non-limiting examples.

EXAMPLE I A solution of a polyoxyethylene glycol having an average molecular weight of 668 was prepared by combining 1012.1 g (0.253 equivalents) of CARBOWAX 8000R, a polyoxyethylene glycol having a number average molecular weight of 8000 and sold by the Union Carbide Corporation; 407.3 g (0.562 equivalents) of CARBOWAX 1450R, a polyoxyethylene glycol having a number average weight of 1450 and sold by the Union Carbide Corporation; and 216.8 g (4.085 equivalents) of diethylene glycol. The components were mixed with stirring at a temperature of about 7OOC.

After mixing was complete, there was added while maintaining stirring, 633.9 g (4.802 equivalents) of methylenebis(4-cyclohexyliso-cyanate), available asDESMO DURR W from Mobay Chemical Corporation, Pittsburgh, Pennsylvania 15205. During the addition, the temperature decreased to 580C. At this point, 3.4 cc of dibutyl tin dilaurate urethane catalyst was introduced and stirring continued for 1 to 2 minutes while the temperature rose to 0 transferred a 70 C. The reaction mixture was then transferred to a tray and placed in an oven at 1000C for 1 hour and thirty minutes to ensure completion of the reaction. The polymer was removed from the oven and allowed to cool to ambient temperature.

A sample of the polymer was placed in distilled water for 24 hours. The water content of the resulting hydrated polymer amounted to 54.6% by weight.

The above prepared polymer was fed into a normal one- inch barrel thermoextruder of a type common within the medical tubing extrusion industry. A crosshead-type tubing die assembly was employed with a 0.060 inch orifice and 0.030 inch diameter mandrel pin. The melt temperature of the polymer was i03OC. As the tubing exited the die, it was stretched by a strand-pulling device until the outer diameter measured 0.032 inches. The material was then cooled in such a way that relaxation to a shorter length and larger diameter was prevented. After 24 houre of cooling, the tubing was examined for swelling properties. A number of cross-sections were taken and their dimensions were measured optically using a microscope.

Then, the samples were hydrated in distilled water for a period of 24 hours. Next, the dimensions were again measured. The tubing was found to swell +53.0% in inner diameter, +46.8% in outer diameter, and only a negligible +1.68 in length.

The one-inch extruder is manufactured and sold by Killion Extruders, Inc. of Verona, New Jersey 07044.

EXAMPLE 2 A solution of a polyoxyethylene glycol having an average molecular weight of 2646 was prepared by combining 2011.6 g (0.503 equivalents) of CARBOWAX 8000R and 56.3 g (1.060 equivalents) of diethylene glycol. The components 0 were mixed with stirring at a temperature of 70 C. After mixing was complete, there was added while maintaining stirring, 202.2 g (1.532 equivalents) of DESMODURR W; the temperature decreased to about 600C. At this point, 3.4 cc of dibutyl tin dilaurate was introduced and stirring continued for about' 1-2 minutes while the temperature rose 0 to 70 C.The reaction mixture was transferred to a tray and placed in an oven heated to about 1000C; the polymer 0 was kept in the oven at 100 C for 1 hour to ensure com- pletion of the reaction. The tray was removed from the oven and allowed to cool to ambient temperature.

A sample of the polymer was placed in distilled water for 24 hours. The water content of the resulting hydrated polymer was determined and found to be 80.0% by weight.

After hydration, the polymer had swelled about 350t ofits original volume. The polymer was extruded using the same equipment as in Example I, except that a rod die whose orifice measured 0.100 inches was used and the strand was pulled until it was 0.028 inches in diameter. As in Example I, the material was confined at its stretched length as it cooled for 24 hours (to ambient). Cross-sectional pieces were cut for swelling measurements.

The rod's diameter increased by 114.2% during hydration. The samples length was found to have decreased 2.0%. The length contracted slightly because the effect of relaxation in this case was slightly larger in magnitude and opposite in direction as the effect of swelling EXAMPLE 3 This polymer was prepared after the manner of Example I using the following quantities of reactants: CARBOWAX 1450R 819.0 g (1.130 equivalents) Diethylene Glycol 380.0 g (7.153 equivalents) DESMODURR W 1071.5 g (8.117 equivalents) Stannous Octoate 3.4 cc (catalyst) The resulting polyol mixture had an average molecular weight of 289. On immersion in distilled water for 24 hours, the water uptake amounted to 43.7% by weight while the volumetric swelling was about 75%.

A blown film of the polymer was processed on a standard blown film apparatus, but in order to obtain a high blow-up ratio, a smaller than usual die was used.

the blow-up ratio = (2 x layflat dimension of blow film)/ x xdie diameter). The blow-up ratio is the parameter which expresses the degree of post-die enlargement Ofthe film. ] In the process of making blown film, the enlarg#- ment is obtained by extruding a tube, running this tube through a pair of nip rollers which pinch the tube and form an air seal. Next, air is forced into the collapsed tube, through the inside of the die-mandrel. This air in flates the tube. [ This resembles the blowing-up of a b- loon. ] In this way, very thin films can be created.

Often, the tube is alit and spooled to obtain rolls of film. In this case, a high blow-up ratio was used so that the film would be strongly oriented in the direction of its circumference (or if the blown tube was slit, its width).

A two-inch blown film-type die was used. The material was blown to a layflat of 16 inches. The blow-up ratio, therefore, was [ 2 x (16)/(w x 2)), about 5:1. The extrudate was spooled during the extrusion and cooled on the spool for 24 hours. Samples were taken for swellinc measurements.

The change in width due to hydration was -34.6% (the negative value indicates that the width decreased during hydration). The length change measured was +11.3%. The thickness swelled by 140.4%.

From the foregoing, it can be seen that the swelling characteristics of various plastic shapes formed from the herein polyurethane can be controlled by the process of the invention.

Claims

1. A method of making a hydrophilic thermoplastic polymer which undergoes differential swelling in contact with an aqueous liquid, comprising the steps of: (a) providing a water swellable hydrophilic thermoplastic polymer; (b) stretching the polymer of step (a) at a temperature above its glass transition point to promote alignment of the polymer molecules; (c) cooling the stretched polymer of step (b) to produce a stressed water swellable polymer in which the ratio of swelling along the axis of stretch to lateral swelling is controlled by the degree of stretching.

2. The method as claimed in Claim 1 wherein the water swellable hydrophilic thermoplastic polymer is a polyurethane produced by reacting a major amount of a polyoxyethylene glycol having a molecular weight in the range 1000 to 8000 and a minor amount of diethylene glycol with an aliphatic diisocyanate.

3. The method as claimed in Claim 2 wherein the aliphatic diisocyanate is methylenebis(4-cyclohexyldiisocyanate).

4. The method as claimed in any of the preceding claims wherein the polyoxyethylene glycol has a molecular weight of 1450.

5. The method as claimed in any of the Claims 1 to 3 wherein the polyoxyethylene glycol has a molecular weight in the range of 7500 to 8000.

6. The method as claimed in Claims 4 and 5 wherein the polyoxyethylene glycol is a mixture of a polyoxyethylene glycol having a molecular weight of 1450 and a polyoxyethylene glycol having a molecular weight in the range 7500 to 8000.

7. Methods of making hydrophilic thermoplastic polymers which undergo differential swelling in contact with an aqueous liquid as claimed in Claim 1 and as herein described.

8. Hydrophilic thermoplastic polymers which undergo differential swelling in contact with an aqueous liquid whenever made by the method of any of the claims 1 to 7.

9. A stretched rod comprising a hydrophilic thermoplastic polymer as claimed in Claim 8.

10. A stretched film comprising a hydrophilic thermoplastic polymer as claimed in Claim 8.

11. A stretched tube comprising a hydrophilic thermoplastic polymer as claimed in Claim 8.

12. A needle catheter comprising a stretched tube as claimed in Claim 11.