GB1566552A - Swellable polymers - Google Patents

Description

(54) SWELLABLE POLYMERS (71) 1, DONALD JAMES HIGHGATE, a British subject, of Brambles, Wonham Way, Gomshall, Guildford, Surrey GU5 9NZ do hereby declare the invention, for which I pray that a patent may be granted to me and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention concerns a method of making articles comprising polymeric matter, hereinafter termed "polymeric articles".

It is known to make polymeric articles which, by application of heat, can be caused to shrink and/or change shape.

Such articles have been made in the form of sleeves or tubes and have found wide use for protecting and/or joining articles such as subes and cables around which they have been put and then shrunk by heating.

There are circumstances in which it would be desirable to have polymeric articles which could be caused to shrink and/or change shape when immersed in liquids. Such circumstances arise, for example, in marine engineering where it may be desirable to protect and/or join underwater members e.g. tubes. In such circumstances it is generally impracticable to effect any desired shrinkage and/or change of shape by heating since this would usually necessitate heating very large volumes of liquid.

I have now found that polymeric articles e.g. sleeves and tubes can be made which, on immersion in a liquid, will shrink and/or change shape in a predetermined manner but without undergoing degradation.

An article according to the invention is one which is formed of a polymer that will absorb a liquid, which has second dimensions, and which upon absorbing a liquid with substantially no change in temperature will change its dimensions substantially to or towards different, first, dimensions, and which has been made by forming an article having the first dimensions and deforming this article by heat and pressure but without melting to the article having second dimensions, and cooling the article. Thus the invention is based upon the discovery that when an article is formed of a polymer that will absorb a liquid and that article is deformed from its initial (first) dimensions to different dimensions it will revert or tend to revert to its initial first dimensions as a result of subsequent absorption of the liquid.

This reversion is not a temperature effect and so is obtained even when the article is cooled after deformation and even if there is no change in temperature during the reversion step.

The amount of absorption of the liquid must of course be sufficient to achieve substantial or substantially complete reversion to the original dimensions and naturally polymers that will only absorb such trivial amounts of the liquid that there is no significant reversion are excluded from the invention.

Usually the articles will be required to be swellable in water (including aqueous systems) but by suitable choice of polymer articles that will be caused to revert by absorption of other liquids may be obtained, e.g. articles revertable in oils, alcohols or hydrocarbons.

As mentioned, reversion is preferably achieved by water (including aqueous systems) and so the polymer is preferably a hydrophilic polymer. Most polymers will absorb some water, even when the polymers are called hydrophobic polymers.

For instance most polymers, including those that might be considered to be hydrophobic, will absorb up to 5% water but this is insufficient for achieving sub stantial reversion in the invention and instead truly hydrophilic polymers, that is to say polymers that absorb substantial amounts of water should be used. Generally the polymer is highly swellable in water or whichever liquid is to be used for reversion. The polymer however must not be soluble in the chosen liquid.

Suitable polymers are addition polymers or copolymers of monoethylenically unsaturated monomers and, if the polymer is to be water swellable, the monomers should be hydrophilic or the monomer system should contain a sufficient proportion of hydrophilic monomer that the final product is hydrophilic. Examples of monomers having hydrophilic properties are aminoalkyl acrylates and methacrylates, especially those in which the alkyl group is one containing 1 to 4 carbon atoms, e.g. methyl or ethyl. The amino group may be monoor di- substituted and any substituent is preferably a C1 alkyl group e.g. methyl or ethyl. Specific examples are amino ethyl acrylate, dimethylaminoethyl acrylate, methylaminoethyl methacrylate and diethylamino ethyl methacrylate. Hydroalkyl acrylates and methacrylates may also be used as the hydrophilic monomer and in these the alkyl group is preferably of 1 to 4 carbon atoms e.g. methyl or ethyl. A specific example is hydroxymethyl methacrylate.

Preferred hydrophilic monomers include N-vinyl pyrrolidone and other vinyl lactams and acrylamide and methacrylamide and N-substituted derivatives thereof. Substituted acrylamide and methacrylamide derivatives may be mono- or di- substituted and preferred substituents are alkyl, hydroxyalkyl and aminoalkyl (including monoand di-substituted aminoalkyl e.g. dialkylaminoalkyl groups. Preferably any alkyl group present contains 1 to 4 carbon atoms, methyl and ethyl being especially preferred. Examples of such derivatives are N-methylacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-dimethylaminomethylacrylamide, N.N - di methylaminoethylacrylamide and N-methylaminoisopropyl acrylamide.

The polymers are preferably copolymers, two or more hydrophilic monomers, e.g.

as described above, being copolymerised together or one or more hydrophilic monomers being copolymerised with one or more other monomers. Preferably a hydrophilic monomer is copolymerised with an alkyl acrylate or methacrylate, especially one in which the alkyl group has from one to four carbon atoms e.g. methyl or ethyl, or acrylonitrile. Styrene may also be used as a comonomer. Specific examples of suitable copolymers are copolymers of N-vinyl pyrrolidone and methyl methacrylate, of N-vinyl pyrrolidone and hydroxymethyl methacrylate and of N-vinyl pyrrolidone, styrene and acrylonitrile. Copolymers of terephthalic acid and N-vinyl pyrrolidone may also be suitable.

It is greatly preferred that the polymers should be cross-linked and this may be achieved by incorporating di- or polyfunctional cross-linking agents in the monomer system. Examples of suitable crosslinking agents are compounds containing two or more ethylenically unsaturated groups e.g. allyl methacrylate, divinyl benzene, ethylene glycol dimethacrylate and trimethylol propane trimethacrylate. Usually it is desirable that the polymers should be relatively lightly cross-linked, the cross-linking agent being used, for example, in an amount of about 1% by weight of the monomer system.

The article that is subjected to the heat and pressure may be formed directly in a mould and it is most satisfactory actually to effect the polymerisation in the mould.

The polymerisation may be effected by use of a chemical initiator and heating or by use of radiation in which case neither heating nor an initiator is necessary. A particularly satisfactory chemical initiator is azobisisobutyronitrile and other examples are di-isopropylpercarbonate and organic peroxides such as benzoyl peroxide. Heating at temperatures in the range of 30 to 800 C, preferably 35 to 700 C., is generally suitable and it is often desirable to conduct the heating in a series of stages at increasing temperatures. After the basic polymerisation has been conducted a postcure treatment may be effected e.g. by heating the polymer at a temperature of 85 to 95 C, preferably under vacuum. If the polymerisation is to be effected by irradiation various forms of radiation may be used e.g. ionising radiation such as U.V., X or gamma-rays or particulate radiation such as electron or photon beams. Preferably the radiation is ionising gamma radiation from a cobalt 60 source or a beam of electrons. After the basic polymerisation has been completed a postcure treatment may be effected by further irradiation.

Commonly the mixture subjected to the polymerisation will consist of the monomer or monomers, cross-linking agent and any initiator needed but, if desired, a solvent for one or more of the monomers may be included e.g. water.

Conventional additives, desired in the final product, may be included with the matter to be polymerised in the mould or the polymer put into the mould.

The article subjected to the heat and pressure is not necessarily formed directly in a mould. For example, a block of poly mer may be formed in a mould and then machined to give the article subsequently treated or the article may be fabricated by heat-welding together component parts formed of the polymer.

Having formed the article of the chosen, first, dimensions it is then deformed by heat and pressure without melting and, of course, without degradation. The heat and pressure must not be such that the article is actually caused to melt since, if this occurs, the article of deformed configuration will not tend to revert to its original dimensions on immersion in the liquid.

The polymeric composition must be such that the article is malleable on application of heat and pressure such that it can be deformed and the deformed configuration will be retained substantially unchanged on cooling and release of the pressure.

Accordingly deformation is brought about by applying heat and pressure sufficient to soften the composition somewhat without melting and to deform the composition into the desired new configuration.

For any particular composition, suitable conditions of heating and pressure may readily be determined by experiment and will depend upon the temperature at which the composition begins to soften. Normally the heating and pressure is applied with the article in an inert atmosphere.

The change in dimensions from first dimensions to second dimensions may result solely in a change in the size of the article or in a change of the shape of the article or both.

There are, of course, limits of deformation beyond which the article will not tend to return to a close approximation of its original moulded configuration on immersion in a liquid and these limits may readily be determined by experiment. Furthermore, if the articles include bulky portions it may take an appreciable time for the article to become completely swollen in the liquid and regain its original configuration.

If the initial polymeric article i.e. before the application of heat and pressure contains water or other absorbed liquid, this is preferably removed for example by heating under reduced pressure e.g. at 70 to 1100C in a vacuum oven for up to 1 hour, before the configuration of the article is modified by application of heat and pressure. If substantial proportions of such absorbed liquids are allowed to remain, the capacity of the final article to regain its original shape on immersion in a liquid is diminished.

We have found in the invention that, very surprisingly, on immersion in the appropriate liquid the article will change its dimensions snbstantially and that this change will be towards or to the original dimensions of the article, the first dimensions, even if considerable modification was effected during the deformation step.

For example articles can be made according to the invention in which the original size is substantially recovered even if the ratio of one linear dimension of the modified article to the corresponding dimension of the original article is as high as 2.5:1.

It is particularly preferred for the article to be in tubular form in which event the deformation may result from radial stretching, so that reversion causes radial shrinking. Thus the tubular article having the deformed, second, dimension may be applied around a part or parts and water or other chosen liquid may then be applied whereupon the tubular article will shrink into a tight fit on to the part or parts.

Broadly by the invention it is possible to protect or joint parts or fill gaps in parts by applying an appropriate article according to any preceding claim around the part or parts to be protected or joined or within the gap and absorbing the appropriate liquid into the article and thereby causing the article to change to dimensions such that it becomes more tightly fitted around the part or parts or within the gap.

The following examples illustrate the invention.

Example I 10 g of feshly recrystallised acrylamide dissolved in 5 g of distilled water, 20 g of freshly distilled acrylonitrile, 10 g of freshly distilled N-vinyl-2-pyrrolidone and 0.4 g of allyl methacrylate as cross-linking agent were thoroughly mixed, purged with nitrogen, degassed under vacuum and sealed in a mould. Polymerisation was effected by subjecting the mixture to a does of 2.5 M. Rads of ionising gamma radiation from a cobalt 60 source. A post-cure treatment was then carried out by heating at 900 C under vacuum for 24 hours. This treatment removed from the polymer most of the water initially used.

The moulded polymeric article so obtained could be deformed by application of pressure at a temperature of 1000 C and, on cooling and release of the pressure the deformed configuration was maintained and stable. After immersion of the article in water for 6 hours at 150 C (approximately 1 hour per mm. of thickness) the article regained substantially its original moulded configuration Example 2 lOg of freshly recrystallised acrylamide, 20 g of freshly distilled acrylonitrile, 10 g of freshly distilled N-vinyl-2-pyrrolidone, 0.3g of freshly distilled trimethylol propane trimethacrylate as cross-linking agent and 0.03g of azobisisobutyronitrile as initiator were throughly mixed, purged with nitrogen, degassed under vacuum and sealed in a mould. Polymerisation was then effiected by subjecting the mixture to a heating cycle of 24 hours at 350 C, 24 hours at 40"C, 24 hours at 450C, 24 hours at 50"C and 24 hours at 600 C. The mixture was then subjected to a post-cure treatment involving heating at 90"C under vacuum for 24 hours The resulting moulded polymeric article could be deformed under pressure at a temperature of 1600C and on cooling and release of the pressure the deformed configuration was retained and stable. After immersion of the article in water for 12 hours (approximately 2 hours per mm. of thickness) at 15"C the article regained substantially its initial moulded configuration.

WHAT I CLAIM IS: 1. An article which is formed of a polymer that will absorb a liquid, which has second dimensions, and which upon absorbing the liquid with substantially no change in temperature will change its dimensions substantially to or towards different, first, dimensions, and which has been made by forming an article having first dimensions and deforming this article by heat and pressure but without melting to the article having second dimensions, and cooling the article.

2. An artiste according to claim 1 comprising a cross-linked addition polymer of one or more monoethylenically unsaturated monomers.

3. An article according to claim 1 or claim 2 in which the polymer is a hydrophilic polymer that will absorb water and the liquid is water.

4. An article according to claim 3 in which the polymer is a copolymer of two or more monomers one at least of which is selected from aminoalkyl acrylates and methacrylates and N-substituted derivatives thereof, hydroxyalkyl acrylates and methacrylates, acrylamide and methacrylamide and N-substituted derivatives thereof and N-vinyl pyrrolidone.

5. An article according to claim 4 in which the copolymer is a copolymer comprising acrylonitrile and n-vinyl pyrrolidone.

6. An article according to claim 5 in which the copolymer also comprises acrylamide.

7. An article according to any preceding claim which upon absorbing the liquid will change its dimensions to a close approximation to the first dimensions.

8. An article according to any preceding claim in which before the article having first dimensions was deformed the article contained the said liquid and this liquid was removed before the deformation.

9. An article according to any preceding claim having tubular form, and in which the deformation involved radial stretching and the diameter of the article will contract upon absorbing the said liquid 10. A method according to claim 1 substantially as herein described with reference to either of the examples.

11. A method of protecting or joining parts or filling gaps in parts comprising applying an article according to any preceding claim around the part or parts to be protected or joined or within the gap, and absorbing the said liquid into the article and thereby causing the article to change its dimensions such that it besomes more tightly fitted around the part or parts or within the gap.

12. Parts protected, joined or filled by a method according to claim 11.

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

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. 0.03g of azobisisobutyronitrile as initiator were throughly mixed, purged with nitrogen, degassed under vacuum and sealed in a mould. Polymerisation was then effiected by subjecting the mixture to a heating cycle of 24 hours at 350 C, 24 hours at 40"C, 24 hours at 450C, 24 hours at 50"C and 24 hours at 600 C. The mixture was then subjected to a post-cure treatment involving heating at 90"C under vacuum for 24 hours The resulting moulded polymeric article could be deformed under pressure at a temperature of 1600C and on cooling and release of the pressure the deformed configuration was retained and stable. After immersion of the article in water for 12 hours (approximately 2 hours per mm. of thickness) at 15"C the article regained substantially its initial moulded configuration. WHAT I CLAIM IS:

1. An article which is formed of a polymer that will absorb a liquid, which has second dimensions, and which upon absorbing the liquid with substantially no change in temperature will change its dimensions substantially to or towards different, first, dimensions, and which has been made by forming an article having first dimensions and deforming this article by heat and pressure but without melting to the article having second dimensions, and cooling the article.

2. An artiste according to claim 1 comprising a cross-linked addition polymer of one or more monoethylenically unsaturated monomers.

3. An article according to claim 1 or claim 2 in which the polymer is a hydrophilic polymer that will absorb water and the liquid is water.

4. An article according to claim 3 in which the polymer is a copolymer of two or more monomers one at least of which is selected from aminoalkyl acrylates and methacrylates and N-substituted derivatives thereof, hydroxyalkyl acrylates and methacrylates, acrylamide and methacrylamide and N-substituted derivatives thereof and N-vinyl pyrrolidone.

5. An article according to claim 4 in which the copolymer is a copolymer comprising acrylonitrile and n-vinyl pyrrolidone.

6. An article according to claim 5 in which the copolymer also comprises acrylamide.

7. An article according to any preceding claim which upon absorbing the liquid will change its dimensions to a close approximation to the first dimensions.

8. An article according to any preceding claim in which before the article having first dimensions was deformed the article contained the said liquid and this liquid was removed before the deformation.

9. An article according to any preceding claim having tubular form, and in which the deformation involved radial stretching and the diameter of the article will contract upon absorbing the said liquid

10. A method according to claim 1 substantially as herein described with reference to either of the examples.

11. A method of protecting or joining parts or filling gaps in parts comprising applying an article according to any preceding claim around the part or parts to be protected or joined or within the gap, and absorbing the said liquid into the article and thereby causing the article to change its dimensions such that it besomes more tightly fitted around the part or parts or within the gap.

12. Parts protected, joined or filled by a method according to claim 11.