HYBRID POLYURETHANE BLOCK COPOLYMERS WITH THERMOPLASTIC PROCESSABILITY AND THERMOSET PROPERTIES

FIELD OF THE INVENTION

[0001] The present invention relates to novel polyurethane block copolymers, and to methods of manufacturing them. The novel block copolymers of the present invention are formulated with multifunctional chain extenders. The resulting block copolymers are characteπzed by improved mechanical properties such as compression set. They may be used in medical applications, or in industrial applications such as seal and gasket applications, including O- rings, window seals, and automotive gaskets

BACKGROUND OF THE INVENTION

[0002] In general, thermoplastic urethane (TPU) material marketed for gaskets and seals use aromatic diisocyanates to maximize intermolecular forces between the hard segments, which lead to improved compression set properties. However, aliphatic polyurethanes with improved compression set are desirable for their optical properties It is therefore important to improve the intermolecular forces between polymer chains through chemical, physical or ionic crosslinks of aliphatic mateπals.

[0003] Vulcanized rubber performs very well during compression set testing due to the high degree of chemical crosslinks. However, vulcanized rubber is not thermoplastic and can not be extruded or injection molded. Therefore, there is much interest in a good compression set TPU for high compression applications such as seals or gaskets

[0004] Aliphatic diisocyanates based TPUs are desirable over their aromatic based counterparts because they do not discolor from exposure to ultraviolet light. It is known that aromatics provide polyurethane materials with considerably improved compression set properties. However, aliphatic isocyanate based TPUs generally exhibit very poor compression set due to weaker intermolecular forces compared to aromatic isocyanates.

Chemical, physical, or ionic crosslinks are required to improve the compression set of such materials

SUMMARY OF THE INVENTION

[0005] The present invention synthesizes a TPU which will chemically crosslink after it is thermoprocessed and aged or annealed This novel TPU is based on the combination of a diamine chain extender, such as DYTEK A or ethylene diamine, and a multifunctional (functionality > 3) chain extender, preferably with at least one OH group It can be used to improve thermoplastic processability while improving compression set by taking advantage of the different reaction rates of the hydroxyl groups versus the diamines

[0006] During continuous reaction, a structural low molecular weight (MW) polymer using a diamine chain extender may be synthesized to allow for processability A trifunctional polyol chain extender or other multi-functional chain extender may be introduced but not completely reacted (no catalyst is introduced) Residence time in the reactor must not be too long Because of the polymer's low molecular weight, it will be processable After processing, the formed device may be cured at elevated temperatures or by aging to increase the molecular weight by initiating crosshnkmg between unreacted isocyanate groups and residual unreacted hydroxyl groups from the trifunctional or multi-functional chain extenders

[0007] In effect, the present invention provides a hybrid resm, preferably a polyurethane resin, that has both thermoplastic and thermoset properties at different times in its life cycle The initially-formed polyurethane resm behaves as a thermoplastic processable material, while the configured end-use product is thermoset

DETAILED DESCRIPTION OF THE INVENTION

[0008] In one embodiment, this invention provides a block copolymer having improved compression set, which block copolymer compnses a soft segment and a hard segment made from a dnsocyanate, an alkylene diamine chain extender, and a multifunctional chain extender which provides delayed crosslinking

[0009] The multifunctional chain extender feature of this invention has a functionality > 3 and preferably has at least one OH group This multifunctional chain extender may be an aliphatic or aromatic tnol or polyol This multifunctional chain extender may be a tπfunctional polyol chain extender in which there are two primary alcohols and a one secondary alcohol, for instance, a polyether tnol chain extender that has the formula HO - X(OH) - OH wherein X is an polyalkylene oxide moiety, such as VORANOL 230-660, a tπfunctional polyol that has a molecular weight of 250 Preferably, one of the OH groups in said polyether tnol chain extender is a secondary alcohol The multifunctional chain extender may alternatively be a polyether chain extender that has the formula (HaN) _n , - X - (OH) _n wherein X is an polyalkylene oxide moiety and m and n are integers from 1 to 8

[0010] In accordance with the present invention, the block copolymer may compnse 40 98 weight-% soft segment and 2-60% hard segment, in which 70-95% of the chain extender in the hard segment is difunctional and 5-30% is multifunctional

[0011] The hard segment of the block copolymer of this invention may be made with a diisocyanate having the formula OCN - R - NCO Suitable such isocyanates may be alkyl dπsocyanates, arylalkyldπocyanates, alkyl-cycloalkyl dnsocyanates, alkylaryl dusocyanates, cycloalkyl dnsocyanates, aryl dnsocyanates, and cycloalkylaryl dnsocyanates A particularly suitable diisocyanate is isophorone diisocyanate The alkylene diamine chain extender used to make the hard segment prefeiably is one of the formula H ₂ N - R' - NH ₂ in which R is a divalent alkylene moiety having from 2 to 20 carbon atoms A particularly suitable alkylene diamine chain extender is 2-methylpentamethylenediamine, commercially available as DYTEK A (2-methylpentamethylenediamme) from INVISTA GmbH of Hattersheim, Germany

[0012] The present invention also provides a manufacturing method for making the novel block copolymers disclosed herein The method may include, for instance, combining 40-98 weight-% soft segment component with 2-60 weight-% hard segment component, wherein, in said hard segment component, 70-95% of the chain extender is difunctional and 5-30% of the chain extender is multifunctional to form a partially crosslmked article, and maintaining that

partially crosslinked article at or below room temperature for at least 24 hours In a specific example, the method of this invention may include the steps of providing a reaction vessel containing tetrahydrofuran solvent, rapidly adding to said solvent in said reaction vessel, in the absence of catalyst, 45 weight-% PDMS 3345, 35 weight-% isophorone dnsocyanate, 15 weight-% DYTEK A chain extender, and 5 weight-% VORANOL 230-660 chain extender, at 22 ⁰ C, and removing the resulting polymer from the reaction vessel after 15 mmutes of adding the reactants thereto In another specific example, the method may include the step of synthesizing in bulk using continuous reactive extrusion by metering into a twin screw extruder with a screw speed of 200 rpm a formulation made up with 80% PDMS 3345, 15 5% IPDI, 3 3% Dytek A, and 1 2% Voranol and at 19O ⁰ C

[0013] Yet another embodiment of the present invention is the polymeric products descπbed herein, configured as useful articles (e g , as prosthetic spinal discs)

Block Copolymers

[0014] The present invention provides block copolymers, which include a soft segment, a diisocyanate-based hard segment, the hard segment also including an alkylene diamine chain extender and a multifunctional chain extender which provides delayed crosslinkmg The block copolymers of this invention are characteπzed by improved compression set

[0015] The soft segment used in the preparation of the block copolymers of the invention may be a polyfunctional aliphatic polyol, or a polyfunctional aliphatic or aromatic amine such as are commonly used for the preparation of polyurethanes The molecular weight of the soft segment is typically about 200 to 1,000,000, and preferably about 400 to 9,000

[0016] Aliphatic polyol soft segment components may be selected from linear and branched polyalkylene and polyalkenyl oxides, random and block copolymers thereof, polycarbonate polyols, hydroxyl-terminated silicones, random and block copolymers thereof with polyalkylene oxides, linear and branched polyalkenyl and polyalkylene polyols, and mixtures

thereof

[0017] Examples of polyols that are suitable for use in the present invention are polyethylene oxides, polypropyleneoxides, polytetramethylene oxides, random or block polypropylene oxide-polyethylene oxide copolymers, vaπous ethyleneoxide-termmated polyols, random or block polytetramethylene oxide-polyethylene oxide copolymers, polycarbonate diols and tπols, multifunctional hydroxyalkyl- or amme-terminated silicones, random or block sihcone- polyethyleneoxide copolymers, polybutadiene diols and tπols, polyisobutylene diols and tπols, and mixtures thereof

[0018] Amine soft segment components may be selected from the group consisting of amme- termmated homologues of the above polyols, including but not limited to polyamine- termmated alkylene oxides and random and block copolymers thereof, polyamme-termmated silicones, random and block copolymers thereof with polyalkylene oxides and mixtures thereof

[0019] Examples of the amines that are suitable for use in the present invention are multifunctional amme-terminated polytetramethylene oxides, multifunctional amine terminated polyethylene oxides, random or block multifunctional amine terminated polypropylene oxide-polyethylene oxide copolymers, random or block multifunctional amine-termmated polytetramethylene oxide-polyethylene oxide copolymers, multifunctional amme-termmated silicones, random or block amme-termmated silicon polyethylene oxide copolymers and mixtures thereof

[0020] Particularly suitable polydrmethylsiloxanes for making the soft segments of the block copolymers of the present invention are, without limitation, those havm the formula

NH ₂ (CH ₂ ) ₃ -Si(CH ₃ ) ₂ -O-[Si(CH ₃ ) ₂ -O] _n -Si(CH ₃ ) ₂ -(CH ₂ ) ₃ NH ₂ wherein n = 0 to 500 A typical embodiment thereof is PDMS 3345, which is commercially available from Wacker-Chemie GmbH of Munich, Germany

[0021] Suitable polyisocyanates for the preparation of the hard segment of the copolymer of the invention are aromatic or aliphatic polyisocyanates The organic diisocyanates may be selected from the group consisting of alkyl diisocyanates, arylalkyl diisocyanates, cycloalkylalkyl diisocyanates, alkylaryl diisocyanates, cycloalkyl diisocyanates, aryl diisocyanates, cycloalkylaryl diisocyanates, all of which may be further substituted with oxygen, and mixtures thereof

[0022] Examples of suitable polyisocyanates are 4,4'-diphenylmethane dusocyanate, hexamethylene dnsocyanate, dicyclohexylmethane dusocyanate, 2,4-toluene dusocyanate, 2,6-toluene dnsocyanate, hexamethylene-l,6-dnsocyanate, tetramethylene-l,4-dnsocyanate, cyclohexane- 1 ,4-diisocyanate, naphthalene- 1 ,5-diisocyanate, diphenylmethane-4,4'- dπsocyanate, xylylene dnsocyanate, dicyclohexylmethane-4,4'-dnsocyanate, 1 ,4-benzene dnsocyanate, 3,3'-diniethoxy-4,4'-diphenyl dnsocyanate, m-phenylene dnsocyanate, isophorone dnsocyanate, polymethylene polyphenyl dnsocyanate, 4,4'-biphenylene dnsocyanate, 4-isocyanatocyclohexyl-4'-isocyanatate, and mixtures thereof

[0023] The primary chain extender of the hard segment used in the preparation of the copolymers of the invention may be an aliphatic diol or an aliphatic or aromatic diamine such as those known for preparing polyurethanes

[0024] The polyol for the hard segment may be selected from alkylene, cycloalkylene, and arylene diols and mixtures thereof Examples of polyols suitable for the preparation of the hard segment are 1 ,4-butanediol, ethylene glycol, 1 ,6-hexanediol, 1 ,4-cyclohexane dimethanol, phenyl diethanolamme, and mixtures thereof, among others However, other polyols are also suitable

[0025] The diamine of the hard segment may be selected from the group consisting of alkyl, cycloalkyl and aryl amines which may be further substituted with N, O, or halogen, complexes thereof with alkali metal salts, and mixtures thereof Suitable diamines for preparing the hard segment are p,ρ'-methylene dianilme and complexes thereof with alkali metal chlorides, bromides, iodides, nitrites and nitrates, 4,4'-methylene-bis(2-chloroanihne), piperazine, 2-methylpiperazine, oxydianihne, hydrazine, ethylenediamine,

hexamethylenediamine, xylylenediamine, bis(p-aminocyclohexyl)methane, dimethyl ester of 4,4'-methylenedianthramlic acid, p-phenylenediamme, m-phenylenediamine, 4,4'-methylene bis(2-methoxyaniline), 4,4'-methylene bis(N-methylaniline), 2,4-toluenediamme, 2,6- toluenediamine, benzidine, dichlorobenzidine, 3,3'-dimethylbenzidine, 3,3'- dimethoxybenzidine, diansidine, 1,3-propanediol bis(p-aminobenzoate), isophorone diamine, and mixtures thereof

[0026] The copolymer of the invention may be prepared m a wide range of molecular weights Molecular weights may range from 5000 to 1 ,000,000, and preferably from about 10,000 to 100,000.

[0027] The preparation of block copolymers is in general well known to persons skilled in the art. Particularly useful disclosures may be found in US 5,428,123, the contents of which are incorporated by reference herein.

Multifunctional chain extenders

[0028] In accordance with the present invention, a multifunctional chain extender compnsing at least one hydroxyl group is used to create chemical crosslinks after a device or part is fabπcated. The amine groups will quickly react with the di-isocyanate and as long as a catalyst is not used, the reaction rate between isocyanate groups and hydroxyl groups will be slow enough to prevent crosshnkmg during synthesis and processing Only after the material has been configured into a part and cured by aging or at elevated temperature will the reaction complete by forming chemical crosslinks between unreacted hydroxyl and isocyanate groups.

[0029] The multifunctional chain extender of the hard segment used in the preparation of the copolymers of the invention may be an aliphatic or aromatic triol or polyol The multifunctional polyol for the hard segment may be selected from polyether polyols, polyester polyols, acrylic and alkyd polyols, and mixtures thereof.

[0030] Examples of polyols suitable for the preparation of the hard segment are glycerol, tπmethylol propane, tπmethylol ethane, pentaerythπtol, ethanolamine, N- methyldiethanolamine, Mannich polyols, oxypropylated triols, sorbitol (hexahydroxyhexane), 2,2-bis(hydroxylmethyl)-3-propanol ether, and mixtures thereof, among others. However, other multifunctional polyols are also suitable

[0031] Duπng synthesis, a structural polymer can be produced using a soft segment, di- lsocyanate, and a diamine chain extender while a multifunctional functional polyol is 'compounded' into the melt dunng the reaction. Some of the alcohol groups may react, but many if not most of the groups will not react dunng the residence time of the polymer in the extruder The alcohol and excess isocyanate groups will react once they are cured at high temperature after fabrication of a useful article, thus creating chemical crosslinks.

[0032] The strategy of using a trifunctional polyol as a post fabrication crosslmkmg agent improves compression set Although it appears that most crosshnkmg occurred during curing, it is likely that some of the polyol did react and crosslinked duπng synthesis. It is also likely that some crosshnkmg occurs during the processing step of creating compression set discs

[0033] VORANOL 230-660 contains three primary alcohols To control crosslinking during reaction or processing, a trifunctional polyol chain extender may be used in which there are two primary alcohols and a one secondary alcohol. The secondary alcohol would react much more slowly and likely improve the shelf life of the unconfingured polymer The secondary alcohol would then react only during curing at elevated temperatures after a device was fabricated

[0034] Generally, polyurethanes with urea groups synthesized from the reaction of amines with isocyanate, are not ideal for thermoplastic processing due to their elevated melting temperature. In fact, a polyurea-urethanes can have degradation temperatures above its melting point. Therefore, only a small concentration of amine groups can be used withm a given formulation if the mateπal is to be thermoplastic A balance must be made between the

use of reactive amine and hydroxyl groups to obtain the desired effect of post fabrication chemical crosslinks. Enough amine must be used to create a structural material so it can be injection molded or extruded.

Compression Set

[0035] The permanent deformation remaining after release of a compressive stress is defined as Compression Set. Compression set is expressed as the percentage of the original deflection. Compression set is an important property for elastomers and cushioning materials. To evaluate the compression set of the present formulations, a Compression Set apparatus may be assembled based on ISO 815. This includes the design and manufacturing of a mold capable of producing samples required in ISO 815. All of the compression set tests reported herein were performed using 25% strain at 7O ⁰ C for 22 hours

[0036] The test specimen is compressed for a specified time at a specified temperature Compression Set is calculated as the percentage of the original deflection after the material is allowed to recover at standard conditions for 30 minutes. Compression set is calculated using the formula: C = [(h _o - h,) / (h _o - h _n )] * 100 where h _o is the original specimen thickness, h, is the specimen thickness after testing, and h _n is the spacer thickness.

[0037] DEFINITION. In accordance with the present invention, a polymer has "improved compression set" when its compression set can be decreased by at least 5% by aging at 25 ⁰ C for 72 hours.

COMPRESSION SET EXAMPLES

[0038] A strain of 25% may be used for testing Test specimens may be cylindrical discs 29.0 mm in diameter and 12.5 mm in thickness, cut from a slab of the testmg material.

[0039] Compression set discs are fabricated in accordance with the present invention They have a compression set of >98% without elevated temperature curing. When the discs made from the same material are treated at 100 ⁰ C for 24 hours, the compression set is improved to 77%. To determine the effect of aging the samples at room temperature, discs are left at

room temperature for 72 hours before compression set testing. The aged samples exhibit a compression set of 92%. These results are summarized in the following Table.

Compression Tensile Hardness

Lot Set Stren th PSI

10 % Hard Segment, PDMS 3345, Dytek A:Voranol (4:1 )

EXAMPLES Example 1

[0040] In a formulation of this invention, VORANOL 230-660, a trifunctional polyol with a MW of 250, replaces some of the DYTEK A diamine chain extender in a formulation based on PDMS 3345, DYTEK A, and isophorone diisocyanate (IPDI), with a hard segment content of 10%. This example may employ, for instance, a 4: 1 ratio of DYTEK-A to VORANOL.

Example 2

[0041] A formulation according to the present invention consists of 45 weight-% PDMS 3345, 35 weight-% isophorone diisocyanate, 15 weight-% DYTEK A chain extender, and 5 weight-% VORANOL 230-660 chain extender. The formulation is placed in a reaction vessel containing tetrahydrofuran solvent. More specifically, the formulation is rapidly adding to the solvent in the reaction vessel, in the absence of catalyst. One-quarter hour after placing the ingredients in the reaction vessel, they are removed therefrom, and solvent is distilled off.

Example 3

[0042] A polymer having improved compression set in accordance with the present invention is made from 80% PDMS 3345, 15.5% IPDl, 3.3% DYTEK A, and 1.2% VORANOL. The polymer is synthesized in bulk using continuous reactive extrusion by accurately metering the listed ingredients into a twin screw extruder at a temperature of 19O ⁰ C employing a screw speed of 200 rpm.

Industrial applicability

[0043] These materials can be used where TPUs are commonly used for in either medical or industrial applications. In addition, these materials can be used in seal, gasket, or load bearing applications, such as O-πngs, window seals, and automotive gaskets Medical applications include bearing materials in orthopedic applications such as prosthetic spinal discs or hip or knee implants.

[0044] The device or prosthesis m these embodiments configured as an implantable medical device or prosthesis or as a non-implantable disposable or extracorporeal medical device or prosthesis or as an in vitro or in vivo diagnostic device, wherein said device or prostheses has a tissue, fluid, and/or blood-contacting surface In these devices or prostheses, the polymer body may be a dense or microporous membrane component in an implantable medical device or prosthesis or in a non-implantable disposable or extracorporeal medical device or prosthesis or as an in vitro or in vivo diagnostic device, and wherein, when said polymer body comprises a membrane component in a diagnostic device, said component contains lmmuno- reactants

[0045] The device or prosthesis of this invention can comprise a blood gas sensor, a compositional sensor, a substrate for combinatorial chemistry, a customizable active biochip, a semiconductor-based device for identifying and determining the function of genes, genetic mutations, and proteins, a drug discovery device (wherein the drug is complexed to surface- modifying endgroups and is released through diffusion or wherein the drug is associated with, complexed to, or covalently bound to surface-modifying endgroups that degrade and release the drug over time), an immunochemical detection device, a glucose sensor, a pH sensor, a blood pressure sensor, a vascular catheter, a cardiac assist device, a prosthetic heart valve, an artificial heart, a vascular stent, a prosthetic spinal disc, a prosthetic spinal nucleus, a spme fixation device, a prosthetic joint, a cartilage repair device, a prosthetic tendon, a prosthetic ligament, a drug delivery device from which drug molecules are released over time, a drug delivery coating in which drugs are fixed permanently to polymer endgroups, a catheter balloon, a glove, a wound dressing, a blood collection device, a blood storage container, a blood processing device, a plasma filter, a plasma filtration catheter, a device for bone or

tissue fixation, a urinary stent, a urinary catheter, a contact lens, an intraocular lens, an ophthalmic drug delivery device, a male condom, a female condom, devices and collection equipment for treating human infertility, a pacemaker lead, an implantable defibrillator lead, a neural stimulation lead, a scaffold for cell growth or tissue engineenng, a prosthetic or cosmetic breast implant, a prosthetic or cosmetic pectoral implant, a prosthetic or cosmetic gluteus implant, a penile implant, an incontinence device, a laparoscope, a vessel or organ occlusion device, a bone plug, a hybrid artificial organ containing transplanted tissue, an in vitro or in vivo cell culture device, a blood filter, blood tubing, roller pump tubing, a cardiotomy reservoir, an oxygenator membrane, a dialysis membrane, an artificial lung, an artificial liver, or a column packing adsorbent or chelation agent for purifying or separating blood, plasma, or other fluids

MANUFACTURING EXAMPLES

Imection molding of a gasket

[0046] A gasket is processed using injection molding as follows. Polymer produced as in Example 3 is dried by flowing dry air at 18O ⁰ F until the water content is less than 0.01% The dried polymer is then melted in an Arburg 320C Allrounder injection molder and charged into a cavity mold at 9000 psi The injection cycle takes 3-10 seconds with a mold temperature of 8O ⁰ F. Once the gasket is extracted from the mold, it is cured in a 100°C oven for 24 hours to complete crosslinking between unreacted isocyanate groups and the hydroxyl groups from VORANOL.

Compression molding of a spinal disc

[0047] A prosthetic spinal disc is made through compression molding, as follows Polymer produced as m Example 3 is dπed by flowing dry air at 18O ⁰ F until the water content is less than 0.01%. The top platen temperature is set at 19O ⁰ C and the bottom platen is set at 180 ⁰ C A clean steel mold is sprayed with Teflon release agent. The steel frame is placed on the base plate and polymer is placed evenly withm the frame The top plate is then placed above the polymer and the entire mold is placed on the lower platen of the compression equipment. Pressure is increased to 6000 pounds until the polymer melts. The pressure is then increased to 19,000 pounds until polymer exits the side of the mold Pressure is held for another 30

seconds at which time the pressure is relieved and the mold is placed in a bucket of water to cool The polymer block is then removed from the mold and ready for machining into a prosthetic spinal disc. After the spinal disc is machined, final curing is completed by placing the disc in a 100 ⁰ C oven for 24 hours.

[0048] While the invention has been described with reference to the preferred embodiments, it will be understood by those skilled in the art that various obvious changes may be made, and equivalents may be substituted for elements thereof, without departing from the essential scope of the present invention Therefore, it is intended that the invention not be limited to the particular embodiments disclosed but that the invention includes all equivalent embodiments.