Curable compositions

Details Curable compositions Curable compositions

1998-05-26

2002-03-05

Gorr, Rachel (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From reactant having at least one -n=c=x group as well as...

C528S059000, C252S182220, C602S008000

Reexamination Certificate

active

06353077

ABSTRACT:

The present invention relates to curable resin compositions and in particular to isocyariate functionalised resin systems suitable for use in medical applications, such as orthopaedic splinting.
A favoured method for curing isocyanate functionalised resins is to use water curing. Water curing can be achieved by many means, for example the resin being immersed in water, contact with atmospheric moisture or by being sprayed with water after application.
As used herein water curable means that the resin system is capable of hardening to a rigid or semi-rigid structure on exposure to water.
Any isocyanate based resin system depending on the reaction of an isocyanate functional group with water, an amine group or an alcohol group for curing may benefit from the use of catalysts to speed up the curing so that the resin sets in an acceptably short time.
The use of inorganic carbonate catalysts has been proposed with functionalised isocyanate resin systems, however the shelf life may be affected in the presence of any moisture, as the catalyst is in direct contact with the resin and would be set off in the presence of moisture. More recently alternative catalysts based on tertiary amines have been used with isocyanate functionalised resin systems in Patent Application WO88/02636, U.S. Pat. No. 5,027,804 and U.S. Pat. No. 4,427,003.
Reactive tertiary amines are rarely fully chemically incorporated into the polyurethane during the isocyanate-water reaction. In addition, such tertiary amines may be vaporised by the exotherm generated during the polyurethane reaction. Thus, there is the possibility that catalyst may leach out or evaporate from the resin system during cure or after curing. Such amines may have a strong odour and the potential inhalation and absorption toxicity of tertiary amines is well known.
Patent Application WO94/02525 partially addresses the problems encountered with tertiary amine catalysts by modifying reactive tertiary amine catalysts by mixing under reaction conditions a reactive tertiary amine, a polyol and an organic isocyanate compound to give a catalyst which has a higher molecular weight and may therefore be retained more.
Patent Application WO94/05475 discloses a tertiary amine as a polyurethane reaction catalyst, where the catalyst is added to a binder containing isocyanate groups. Lignocellulose fibres are coated with the binder and then shaped into a mat which is pressed under the influence of heat to form a board, where the catalyst is subsequently built into the board.
However such catalysts may still be prone to leaching especially when used in a water curable isocyanate composition.
It may be possible to use a lower level of catalysts to reduce the problems discussed above, however such a catalyst is unlikely to be suitable for rapid cure systems, as would be required for am orthopaedic splinting material.
The present invention seeks to overcome these disadvantages by providing a water curable isocyanate functionalised resin system with catalysts which are not a potential hazard due to leachable or volatile components.
The use of a chemically bound-in tertiary amine catalyst would overcome the problems associated with the leaching of catalyst. By “chemically bound-in” is meant a catalyst that is ionically and/or covalently bound to the curable isocyanate functionalised prepolymer.
Furthermore the use of more than one catalyst may benefit the curing speed of isocyanate functionalised resin systems.
Surprisingly it was found that the curing reaction of a water curable isocyanate functionalised resin, when catalysed by a first and a second catalyst resulted in a greatly increased curing rate of the resin as the two catalysts together showed a synergistic effect.
The synergistic effect described in this invention is the increase in the reaction rate between water and isocyanate functionalised prepolymers in polyurethane/urea synthesis.
Thus according to the present invention there is provided a resin system comprising at least a water curable, isocyanate functionalised prepolymer and a first and second catalyst component wherein the first catalyst is chemically bound-in to the prepolymer and the second catalyst is not chemically bound-in.
Chemically bound-in catalysts include catalysts bonded covalently and/or ionically to the isocyanate functionalised prepolymer.
Preferably the first chemically bound-in catalyst is covalently bound-in to the prepolymer.
Preferably the first catalyst is a tertiary amine catalyst.
Suitable tertiary amine catalysts comprise both a tertiary amine group and an isocyanate reactive group.
The term “isocyanate reactive group” refers to a group which forms a covalent bond when reacted with an isocyanate group (—NCO) under appropriate conditions, these include for example hydroxy and amine groups as well as carboxylic acids, thiols, anhydrides, urethanes, ureas and other such groups with an active hydrogen atom known to one skilled in the art.
Preferably the chemically bound-in tertiary amine catalyst is covalently bound-in to the prepolymer.
The bound-in tertiary amine catalyst may be present at any appropriate location in the isocyanate prepolymer. For example they may be introduced at an end of the isocyanate prepolymer molecules via a capping reaction, they may be present on a side chain extending from the main polymer backbone, or may be part of the polymer backbone itself.
The tertiary amine catalyst may be optionally substituted with substituents which do not substantially adversely affect the reaction of the tertiary amine catalyst with the isocyanate functionalised prepolymer or the catalytic effect of the tertiary amine catalyst when present in the isocyanate functionalised prepolymers of the resin system of the present invention.
Appropriate tertiary amine catalysts for reacting with isocyanates so as to form the prepolymers of the present invention may include but are not limited to the molecules listed below.
1-(2-Hydroxyethyl)pyrrolidine, 1-methyl piperazine,
1-methyl-2-piperidine methanol,
1,4-bis(2-hydroxyethyl)piperazine
2[2-(dimethylamino)ethyl]methyl amino ethanol,
gramine, 3-morpholino-1,2-propanediol,
1,4-bis(3-aminopropyl)piperazine, tropine,
3-aminopropyl morpholine, 4,2-hydroxyethyl morpholine,
3,3-diamino-N-methyl dipropylamine,
1,4-bis(2-hydroxypropyl)-2-methylpiperazine,
1-(2-hydroxypropyl)imidazole, 3-dimethyl amino propanol
and &bgr;-hydroxy-4-morpholine propane sulphonic acid.
The chemically bound-in tertiary amine catalysts may comprise a single species or mixture of species. Further, several species of such bound-in tertiary amines may be present within a prepolymer composition or within one isocyanate functionalised prepolymer molecule.
Any one of the prepolymer molecules may contain a single bound-in tertiary amine catalyst of a single species or more than one tertiary amine catalyst of a number of species.
In addition any one prepolymer molecule may comprise more than one tertiary amine catalyst either present on a side chain, as end groups or part of the polymer backbone, for example when the tertiary amine catalysts comprise two or more isocyanate reactive catalysts and act as chain extenders.
The isocyanates used to react with the tertiary amine catalyst comprising both a tertiary amine group and an isocyanate reactive group may be any suitable isocyanates well known in the art, for example aliphatic, cycloaliphatic, aromatic or heterocyclic isocyanates. Preferably aliphatic isocyanates are used.
Whatever species of tertiary amine containing molecules are utilised to prepare a bound-in catalyst, it is preferred that they comprise less than 10% by weight and more preferably from 0.1 to 5% by weight of the curable composition.
The second catalyst comprises preferably 0.05 to 10% and more prefereably 0.1 to 5% by weight of the curable composition. The second catalyst is preferably water soluble but insoluble in the prepolymer. The second catalyst is preferably a solid inorganic catalyst. For example the second catalyst is aptly a group I or II alkali metal salt and preferably a group I

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