It is already known in the art to make cross linked, block and chain extended hydrogels based on polyethylene oxide or polyethylene glycols by reaction with polyisocyanates, polyacids, polyols and polyamines.

However, in general these cross linked compositions do not flow and generally can only be moulded by reaction injection moulding (RIM) or by related"polymerisation in place"processes, which are slow and expensive processes.

Also a different, existing reaction injection moulding and related technique utilises free radical initiation or irradiation cure which produces radicals which cause polymerisation of double bonds at the terminal positions of ethylene glycol polymers. These radicals initiate a

peroxidation chain process, which is unintended and leads ultimately to damage of PEO based polymers in storage for use and has prevented their adoption as materials for uses requiring a significant shelf life. There are also problems with bio compatibility of such reaction injection moulded hydrogels.

Additionally, the current cross linked polymer hydrogels often have a very poor resistance to crack initiation and crack propagation.

It can therefore be seen that it would be beneficial to provide thermoplastic hydrogels which are capable of being generally moulded under pressure.

It is an aim of the present invention to provide a thermoplastic hydrogel composition which has the ability to flow under moderate shear at particular temperatures below the polymer decomposition temperature.

It is a further object of the present invention to provide a thermoplastic hydrogel composition which can be injection or compression moulded.

It is a further object of the present invention to provide a solvent soluble composition.

Another object of the present invention is to provide a thermoplastic hydrogel composition which is highly bio compatible.

Another object of the present invention is to provide a biodegradable thermoplastic hydrogel.

A yet further object of the present invention is to provide thermoplastic hydrogels which have a high level of water swelling properties after moulding and swelling with water.

A yet further object of the present invention is to provide thermoplastic hydrogels which are made by a synthetic process which does not have to use free radical initiation.

According to a first aspect of the present invention, there is provided a method of producing thermoplastic hydrogels, comprising the steps of reacting one or more from the list; polyethylene oxide, polyol, polyamine, with a polyisocyanate and a polyfunctional amine or alcohol.

Preferably the polyol is polyethylene glycol.

Preferably, the method also comprises the step of end capping unreacted groups with a unit capable of producing hydrogen bonding, z bonding, ionic bonding, hydrophobic bonding and/or phase separation or forming a glassy or crystalline phase separated domain.

Alternatively, according to a second aspect of the present invention, the method also comprises the step of end capping unreacted groups with a unit from a list of: Mono-functional amine

Mono-functional isocyanate A cyclic diacid anhydride A mono-functional acid Mono-functional alcohol Preferably the reaction between one or more from the list polyethylene oxide polyol polyamine and a polyisocyanate is prepared using a range of NCO: OH or NCO : NH2 ratios.

Optionally a biodegradable unit may be incorporated.

The biodegradable unit may be polycaprolactone, poly (lactic acid), poly (glycolic) acid or poly (hydroxybutyric) acid, amine or hydroxyl ended poly (amino) acids (protein or peptide analogues).

The ratios are preferably selected such that, at complete reaction, the product does not form a macrogel.

Preferably the first step reaction is prepared using a range of NCO : OH or NCO: NH2 ratios from 2: 1 to 1: 2.

Optionally where both OH and NH2 groups are used within the single reaction, a range of NCO: (OH+NH2) ratios of 2: 1 to 1: 2.

Most preferably the first step reaction is prepared using NCO: OH or NCO: NH2 ratios of 2.0 : 1 to 1: 1.8 and 1.8 : 1 to 1: 1.8.

Optionally the range of ratios used may be extended by the addition of monofunctional amines, alcohols or isocyanates.

Alternatively, a macrogel is prevented from forming by stopping the reaction before completion.

Preferably, the reaction is stopped by the addition of a monoamine or an amine terminated polymer.

Optionally, the monoamine or an amine terminated polymer is added when the reaction is partially complete.

Alternatively, an amine is admixed at the outset thus removing the possibility of gelation.

Optionally, the amine is added in the form of amine carbonate.

Optionally, products with NCO end groups are subjected to a final curing by immersion in liquid water or steam after moulding.

Preferably, in the second stage the unreacted groups are capped with an amine ended polymer.

Optionally, unreacted NCO groups are endcapped.

Another option is that unreacted OH groups are endcapped.

Preferably, terminal NCO groups are converted into a strongly hydrogen bonding urea group.

Preferably, the unreacted groups are capped by an aliphatic amine.

Optionally, the amine group is attached to a long linear or branched alkyl group or to an aryl-or aralkyl-amine.

Optionally, the amine group is attached to polymers or low molecular weight pre-polymers.

Alternatively, excess OH groups are capped with one or more molecules from the list of ; mono-isocyanate ended aromatic molecules, mono-acid anhydride ended aromatic molecules, mono-isocyanate ended aliphatic molecules, mono-acid anhydride ended aliphatic molecules reaction product of a monoamine with a di (or higher) isocyanate.

The groups used in the endcapping process allow the polymers to interact with physical or chemical cross- linking. The separate molecules or particles therefore bind to each other.

According to the third aspect of this invention there is provided a thermoplastic hydrogel produced by the method of the first and second aspects.

Preferably, the hydrogel is completely polymerised under the specific conditions that are being used.

Preferably, after polymerisation the hydrogel is heated.

Alternatively, after polymerisation the hydrogel is immersed in water liquid or vapour.

Optionally, the end product may be pelletised, pressed, extruded or heat, pressure, injection or compression moulded.

Preferably, the end product incorporates an antioxidant containing two or more hydroxyl groups.

The antioxidant may be internal or external.

Preferably, the antioxidant is ascorbic acid.

Alternatively, the antioxidant is 2,6-di tertiarybutyl4- hydroxanisole.

Optionally the end product can incorporate pigment.

Optionally, the end product can incorporate dye (s).

Optionally the end product may develop opacity when swollen in water thereby behaving as though it contained a light scattering pigment.

Optionally the end product may be blended with a water-soluble compatible solvent or plasticiser An example of the present invention will now be illustrated by way of example only and with reference to the following figure, in which:

Figure 1 shows typical end groups that could be envisaged as being associated in stacks as shown.

In the preferred embodiment, the thermoplastic materials are prepared from mixtures of di (or higher) PEG polyol with a di (or higher) polyisocyanate and/or a di (or higher) polyamine.

First stage materials can also be made from many step- growth reactions amongst which the reaction of PEG polyols with polyacids with removal of reactive-produced water is an option. The production of first stage materials can also be guided by the art of making alkyd resins in the paint industry.

If the product from the first stage reaction is made from a mixture of PEG diol, 1,2, 6-hexantriol and diphenylmethane-4,4-diisocyanate, it can be prepared using a range of NCO: OH ratios from, for example, 2: 1 to 1: 2. At the extremes of these ratios, the 2: 1 will have all NCO unreacted groups and the 1: 2 ratio will have essentially all OH unreacted groups. These compositions are not able to macrogel and will contain only small proportions of low molecular weight branched polymers.

The product is a fluid and suitable for injection, extrusion or compression moulding at temperatures which are typically below 150°C, although temperatures of 200°C to 250°C can be utilised for short periods. It should be noted that only the products with predominantly NCO end groups can be moulded and subjected to final further curing by immersion in liquid water or steam or atmospheric moisture for a suitable period.

It is possible to use intermediate NCO: OH ratios, such as 2: 1 to 1: 1.8 and 1.8 : 1 to 1: 1.8 (and these ranges can be further extended by the addition of mono-functional molecules). As these still provide at complete reaction, fluid systems, which when the end groups, are NCO can be injection moulded and post-cured by water or steam immersion. However, depending on the proportion of tri or higher functional materials, ratios such as 1.6 : 1 to 1: 1.6 form macrogels at as complete a reaction as is possible with the NCO and OH groups present (and more extended ratios are possible if mono-functional amines, alcohols or isocyanates are used in the first stage. The resulting products are not fuseable nor solvent soluble).

It is possible that the products may still be used for the second stage of the process, to give useful end capped products, if the reaction is stopped before it has proceeded as far as possible. This operation is less convenient and more difficult as the degree of completion of the reaction must be determined using, for example, infra-red analysis of the isocyanate absorption peak of the reaction mixture, or by the viscosity of the reaction. Therefore, it is much preferred to use the compositions which cannot macrogel, as they can be taken reproducibly to completion of the first stage without fear of irreversibly solidifying the reactants.

A preferred embodiment is that the first stage product is a heavily branched polyurethane/PEG resin. In this embodiment, the second stage is intended to convert each or a proportion of the terminal groups into a strongly hydrogen bonding urea group. An aliphatic amine could be used and the amine group could be attached to a short or long linear or branched (preferably linear) alkyl group,

such as decyl or stearic or higher polyamines such as polyethylene, or to an aryl or aralkylamine, such as aniline, aminoanthracene or octylaniline. The combination of the urea group and the long aliphatic chain or aromatic ring will promote association and phase separation of these groups with development in the product material of toughness and strength. This will be especially the case where an aromatic diisocyanate has been utilised in stage one.

Figure 1 shows a diagram of a typical end group which could be envisaged as associating in stacks, as shown.

The association of many such end groups should provide increased cohesion and strength to the product.

Once the initial homogeneous mixing has been completed, then the still fluid mix may be poured into suitable containers, such as polypropylene moulds. If desired, a polymerisation (curing) of the finished product can then be completed. In order to provide an oxidation resistant product, it is particularly useful to incorporate a reactive internal antioxidant containing two or more hydroxyl groups, for example, ascorbic acid (alternatively an external anti-oxidants may be used).

Alternatively the antioxidant may be added in earlier during the first stage.

The final product has a number of benefits, in particular there will be no unreacted groups left in the completed product to cause problems, the product will be particularly bio-compatible and there will be little or no toxicity. There is also the benefit that materials made from the final hydrogel product would be comfortable

and re-useable. The final product would also have the benefit of being intrinsically rubbery in the dry state,. and therefore could be used to produce cloths, etc., which would not set rigid when dried out. Also, the thermoplasticity of the final product means that it can be made into a number of forms, for example, strips, sheets or discs. The final product could be heat or solvent laminated onto or between fabrics to provide product impermeable to liquid water but permeable to water vapour. Such material can be used in a wide range of applications such as comfort clothing and bedding etc.

Also, coloured dyes can be put into the final product easily, which cannot be done with similar cross-linked hydrogels.

The final product can be extracted or spun into film or coated onto common non-biological fibres to provide a form of the product which can be knitted, braided or formed by techniques well known to those skilled in the art.

Examples 1. POLYMERS PREPARED BY USING THE ALIPHATIC AMINE ETHYLENEDIAMINE (EDA) AND ALIPHATIC ISOCYANATE DICYCLOHEXYLMETHANE-4, 4'-DIISOCYANATE (DesmodurW). 1,2, 6- HEXANE TRIOL (HT) WAS ALSO USED. THE POLY (ETHYLENE GLYCOL) (PEG) HAD A MEASUED NUMBER AVERAGE MOLECULAR WEIGHT OF 3130 AND THE POLY (PROPYLENE GLYCOL) PPG A VALUE OF 425.

The following compositions were prepared where the symbols carry the usual names.

(a) PUU3130CX (0. (0. 5EDA) mol intended wt actual wt used (g) used (g) PEG 3130 (1) 5.00 5.00 PPG 425 (15) 10.1837 10.188 HT (0.5) 0.10717 0.1071 EDA (0.5) 0. 048g 0.050 DesmodurW (18.11) 7.5950g 7.595 FeCl3 0.02 wt% 4.58mg 4mg Procedure.

The following method of preparation was used for all of the examples that follow. All of the reaction components were either dry as used or else they were dried (i. e. the PEO AND PPG) using a"Rotavap"rotating heated vacuum drier. The dry PEG, PPG and HT were placed in a beaker and heated to 95C and mixed thoroughly with the aid of a glass rod. The anydrous ferric chloride catalyst was then blended in in small increments at a time with stirring ensuring that each small addition was dissolved before the next was added. When an amine was used it was added and blended in a similar fashion. Finally the DesmodurW diisocyanate was added as rapidly as possible with stirring and the reaction allowed to proceed at 95C.

Cured for 20 hours at 95°C. The product was solid at room temperature and thermoplastic at elevated temperatures.

It formed moulded products, by the usual method of pressing between polypropylene moulds, which were readily demoulded when cold.

The moulded product was initially clear but became slightly hazy in water.

The polymer swelled to high degree in tetrahydrofuran but would not dissolve.

(b) PW3130DX (0.5HT (0. 5EDA) mol intended wt actual wt used (g) used (g) PEG 3130 (1) 5.00 5.124 PPG 425 (20) 13.5782 13.580 HT (0. 5) 0.1071 0.1071 EDA (0.5) 0.0480 0.059 DesmodurW (23.3625) 9.7965 9.796 FeCl3 0.02 wt% 5.7mg 6mg Procedure Synthesised in the manner presented above. The product was a soft solid which was thermoplastic. It was a suitable material for further modification by reaction with amine or hydroxyl-containing modifiers as is illustrated for a related composition in the following example in which the proportion of isocyanate-containing component DesmodurW is increased.

The compression method afforded moulded products very easily from this product without further reaction, but the product was very sticky and did not demould in dry state. The moulded product with mould was immersed in water over weekend after which time the moulded product had swollen off it's support. It was soluble in THF.

2. A STAGE1 POLYMER WITH EXCESS OF ALIPHATIC ISOCYANATE AND A LINEAR ALIPHATIC AMINE (0.75 EDA) PUU3130CX (0. 5HT) (0.75 EDA) with excess of DesmodurW mol intended wt. actual wt.

Used (g) used (g) PEG 3130 (1) 5.00 5.00 PPG 425 (15) 10.1837 10.188 HT (0.5) 0.1071 0.1071 EDA (0.75) 0.071 0.072 DesmodurW (44.0) 18.450 18.375 FeCl3 0.02 wt% 4.58mg 5mg Procedure The usual method. The product solidified on cooling but melts when hot.

This product produced a spherical section by the usual method. The product was immersed in water when it fragmented. White sections of polymer were obtained in the product mould. This material was soluble in methanol and precipitated when a little water were added. The product was also soluble in tetrahydrofuran. It is not suitable for the formation of strong mouldings but is used here to exemplify the ready formation of end-capped modified thermoplastic polymers using the following end group modifiers by: 2. a Reaction with benzylamine in the absence of solvent.

2. b Reaction with butylamine in the absence of solvent 2. c Reaction with dibutylamine in the absence of solvent Those expert in the synthesis of polymers would readily see how to extend this procedure to many other simple amine or hydroxyl-containing molecules and to end-capping with many amine and hydroxyl ended low-molecular weight polymers.

2. a Reaction with Benzylamine Wt of the prepolymer with excess isocyanate = 4. 275g Wt of the benzylamine = 1. 00g Procedure Both materials were mixed and allowed to react. at 95°C for half an hour. The materials were in a round bottom flask that was rotated using a rotary evaporator while immersed in an oil bath at 95°C.

The product was thermoplastic and fluid and could be readily moulded into a moulded product that appeared optically transparent though it was fragile and broke when attempts were made to detach it from the mould.

2. b Reaction with Butylamine Weight of the prepolymer = 4.278g Weight of the butylamine = 1.380g

Procedure The reaction was carried out in a beaker placed in an oven at 95°C with stirring manually, using a glass rod.

The polymerising mixture was cured for 2 hours at 95°C.

The product was a brittle, hard, thermoplastic which forms a clear moulded product.

2. c Reaction with Dibutylamine Weight of the stagel polymer = 4. 275g Weight of the benzylamine = 1. 380g The procedure used was the same as described in (2. b).

The product was a sticky, thermoplastic which can be moulded into a moulded product easily but is physically rather weak after immersion in water.

3. PREPOLYMER WITH EXCESS OF OH GROUPS CONTAINING EXCESS HYDROXYL AND UREA UNITS FORMED USING AN AROMATIC AMINE DIPHENYLMETHANE-4, 4'-DIISOCYANATE (DPDA).

PUU3130CX (0. 5HT) with excess of alcohol groups mol intended wt actual wt used (g) used (g) PEG 3130 (1) 10.00 g 10.01 PPG 425 (15) 20.3674 20.376 HT (0.5) 0.2143 0.214 EDA (0.5) 0.3167 0.317 DPDA (10.25) 8.5962 8.63 g FeCl3 0.02 wt% 7.96 mg 8.0 mg

The prepolymer was prepared as above and remained liquid after 5 hours of reaction at 95°C. The mixture could not be gelled and demonstrates the ability of compositions having a suitable excess of one of the reacting groups to provide a stagel polymer without the possibility of gelling in the reaction vessel. On cooling the material solidifies but melts again when heated. It forms a useful basis for either end-capping with desired materials or for preparing reactive mixtures which can be formed into moulded product shapes and subsequently crosslinked by heating. Because of its fast rate of reaction the aliphatic diisocyanate DPDA is a very suitable crosslinking agent.

This prepolymer was used for the following curing reaction: The Prepolymer and Desmodur W Weight of the stage 1 polymer with excess of alcoholic groups =10.0 g DesmodurW added to the same beaker =1.467 g Mixed well. The resulting very fluid material was. poured into a polypropylene tube and cured for 4 hours at 95°C.

The polymer gelled sometime within 2 hours and on cooling provided a strong crosslinked product. This would clearly have been able to be moulded and formed into crosslinked moulded products before the second stage curing.

Incorporation of antioxidant butylated hydroxyl anisole (BHA) and using diphenylmethane-4, 4'-diamine (DPDA) PW5950 BX (0.75 HT) mol intended wt Actual wt used (g) used (g) PEG 5950 (1) 10 10.00 HT (0.75) 0.1691 0.169 PPG 425 (10) 7.1428 7.147 DesmodurW (13.2562) 5.8483 8.63 g BHA (0. 03% by 3 mg 3 mg wt of PEG) DPDA (0.5) 0.1666 0.166 FeCl3 0.02 wt% 4.66 mg 4.0 mg When BHA added to the reaction there was a very slight darkening in the colour. The reaction product was fluid and could be moulded into clear moulded products.

Procedure HT and PPG, FeCl3 and DPDA, BHA and D were mixed in this order and allowed to cure in polypropylene test-tube. mol intended wt actual wt used (g) used (g) PEG 5950 (1) 10 10.02 HT (0.75) 0.1691 0.171 PPG 425 (10) 7.1428 7.147 DesmodurW (13.2562) 5.8483 8.63 g BHA 3% by wt 0.3000 0.305 of PEG)

DPDA (0.5) 0.1666 0.166 FeCl3 0.02 wt% 4.66 mg 6. 0 mg In the case of the very high 3% level of BHA the reaction became immediately very dark but returned to slightly darker yellow than expected without BHA when PEG was added and mixed. No other visual effect was observed and the product set solid when cold and became fluid and mouldable when hot when it could be moulded readily into transparent moulded products.

These results show that the antioxidant BHA can be incorporated into the stagel reaction.

4. THERMOPLASTIC HYDROGELS SUITABLE FOR USE IN CLEAR MOULDED PRODUCTS.

Thermo plastic hydrogelcompositions were made from poly (ethylene glycol), poly (propylene glycol), 1,2, 6- hexane triol, dicyclohexylmethane-4, 4'-diisocyanate and diphenylmethane-4, 4'-diamine (DPDA). The overall composition has a functionality of >2.

Three batches of poly (urethane urea) denoted PUU polymers coded PUU 5950 BX (0.5 HT), PUU 5950 BX (0.6 HT), and PUU 5950 BX (0.75 HT) were prepared by a single step bulk polymerisation method described below. The molar compositions and the weight compositions are given in the next two tables below.

Chemical compositions PUU polymers Polymer unit denoted SOFT BLOCKS HARD BLOCKS TRIOL

as PEG PPG 425 DPDA Desmodur HT W moles (moles) (moles) (moles) (mole s) PUU5950 BX (0.5HT) 1 10 0. 5 12. 8625 0. 5 Batch 1, 2,3 PUU5950 BX (0.6HT) 1 10 0. 5 13. 02 0. 6 Batch 1, 2, 3 PUU5950 BX (0.75HT) 1 10 0. 5 13. 2562 0. 75 Batch 1,2, 3 Ferric chloride catalyst was used as 0.02 wt% of the reactants DesmodurW was used as 5 mol% in excess of stoichiometric quantity The appropriate quantities of hexane triol (HT) and dehydrated PPG 425 weighed into a beaker to which the calculated quantity of ferric chloride catalyst was added. The beaker was then placed in the oven at 95 C.

Within-15 minutes the catalyst dissolved assisted by occasional stirring. The DPDA was then added, mixed and left in the oven. Once the DPDA had dissolved the dehydrated molten PEG was added, mixed thoroughly and left in the oven for few minutes. Finally, the required amount of Desmodur W (dicyclohexylmethane-4, 4'- diisocyanate) was directly weighed into the beaker containing the other reactants, mixed and left in the oven with occasional stirring for 15 minutes. This was then poured into preheated polypropylene moulds and placed in the oven at 95 deg C to cure over 22 hours.

After this period the oven was switched off, the product

was allowed to cool and readily demoulded after quenching in liquid nitrogen.

Weights of reactants used Polymer denoted as SOFT BLOCK HARD BLOCK Triol PEG PPG 425 DPDA Desmodur HT (g) (g) (g) (g) w (g) PUU5950BX (0.5HT) 10 7. 1428 0. 1666 5. 6746 0. 1127 Batchl, 2,3 PUU5950BX (0.6HT) 10 7. 1428 0.1666 5. 7441 0. 1353 Batchl, 2,3 PUU5950 BX (0.75HT) 10 7. 1428 0. 1666 5. 8483 0. 1691 Batchl, 2, 3 Ferric chloride was used as 0.02 wt% of the reactants DesmodurW was sued as 5 mol% in excess of stoichiometric quantity Actual amounts of the materials used were kept close to the calculated values Swelling test.

Slices from polymer billets were cut and three slices of essentially identical thickness were allowed to swell to equilibrium in water at ambient temperature. The swelling (%) calculated by the equation: % swelling = Weight of the swollen slice-weight of the dry slice/weight of the swollen slice. The three test results were averaged.

Test of thermoplasticity.

A small disk of the thermoplastic hydrogel was placed between two polypropylene moulds which when compressed

formed a moulded product shape between their faces. The disk was placed into the female section and the male half of the mould was placed on top. After 10 minutes heating at 95C the ability of the test thermoplastic hydrogel. composition to flow and form a moulded product when cooled to room temperature was evaluated under the pressure between the thumb and forefinger. The mould was cooled and the solid moulded moulded product removed using forceps and then made available for testing.

Average swelling of PUU polymers in water at ambient temperature. Polymer composition Swelling Swelling Average data (pph) data (%) Swelling (%) PUU5950BX (0. 5HT) 253. 6 72 Batch 1 PUU5950BX (0.5HT) 253. 7 72 Batch 2 PUU5950BX (0. 5HT) 244. 8 71 72 Batch 3 PUU5950BX (0.6HT) 246. 6 71 Batch 1 PUU5950BX (0.6HT) 229. 9 70 Batch 2 PUU5950BX (0.6HT) 279. 7 74 71 Batch 3 PUU5950BX 224. 5 69 (0.75HT) Batch 1 PUU5950BX 239. 3 70 (0.75HT) Batch 2

PUU5950BX 222. 7 69 69 (0. 75HT) Batch 3 Swelling test results The results from the swelling tests in water at ambient temperature are summarised in Table 3. Only a small variation in the swelling values was seen in the polymers that contained HT (see Table 3) in spite of the significant change in the amount of the triol used. The visual appearance of the swollen polymers also varied. It was observed that the PUU 5950 BX (0.5 HT) polymer occasionally afforded"frostiness"possibly due to micro stress cracking in the water-swollen state. Polymer PUU 5950 BX (0.6 HT) with slightly increased HT from 0.5 molar to 0. 6 molar showed the effect in an occasional batch. However such"frostiness'in PUU 5950 BX (0. 75HT) was not observed at all. The moulded products produced ~were transparent and the obtained degree of swelling of 69% is a very useful figure for moulded products such as contact lenses.

Some selected results from GPC analysis of PUU polymers.

Note that these are only comparative and not absolute values. Polymer Mn Mn Mn/Mn PUU5950BX 6.603 # 103 1.674 # 104 2.535~0.044 (0.5HT) Batch 1 PUU5950BX 6. 399 x 101. 456 x 104 2. 2750. 038 (0.5HT) Batch 2

PUU5950BX 6.049 x 1. 349 x 104 2. 2310. 059 (0.5HT) Batch 3 The following conclusions can be drawn from the above All polymer compositions investigated were thermoplastic and afforded moulded products when subjected to the compression technique.

'The chemical structure of all the polymer compositions were shown to be similar by the FTIR analysis and reproducible within three batches of a given polymer composition.

GPC analysis Table 4 confirmed good reproducibility among three batches of a given polymer composition.

The polydispersity values of all the polymers were from 2.2-2. 6. These values are quite broad but consistent with that to be expected from a step- growth polymerisation. The Mw and Mn values within three batches of a given polymer composition were quite similar-a desired result and indicates a good reproducibility.

FTIR analysis clearly indicated that free primary amine of DPDA after polymerisation has disappeared and been converted to secondary amine to form a urethane/urea group of the polymer structure.

5. PREPARATION OF THERMOPLASTIC HYDROGELS FROM A POLYURETHANE WITHOUT THE USE OF A DIAMINE AS A COMPONENT OF THE STAGE 1 COPOLYMER The polymers were made according to a closely similar to the procedure described previously. above. The reactants were poly (ethylene glycol) described by the supplier as PEG6000 and meaning a PEG having a number average molecular weight close to 6000.1, 2,6-hexanetriol, and dicyclohexylmethane-4,4'-diisocyanate (DesmodurW) and using anhydrous ferric chloride (0.2mg per g. of reactants) as the catalyst. The molar proportions used are given in Table 4 below. Other compositions made nearer to stoichiometry of the hydroxyl and isocyanate groups crosslinked during the curing reaction so at complete reaction could not provide thermoplastic hydrogels. They would have done so if the reactions had been terminated prior to complete reaction. Preparation PEG6000 1, 2, 6- Desmodur number HEXANETRIOL W 11 MOLE1 MOLE3. 75 1 MOLE 1 MOLE 5. 0 After fours hours cure at 90C the products were cooled demoulded and stored in sealed bags away from air and light. A few of the samples were converted into thin slices and sample slices were evaluated for their ability to thermoform in a"Rosslyn"heat press. At 115C the slices became very fluid and could be pressed into thin films. These became solid at 110C and formed solid pliable hydrogel films.

Cut film samples were allowed to swell in water to equilibrium when they became. clear transparent gels.

They were insoluble in water but swelled to a high degree as given in the table below. Sample Dry weight Swollen % of slice in weight of equivalent g. slice of isocyanate in the preparation 1. 730 3. 845 1. 5 2. 223 2. 282 2. 0 Sample 1 was completely soluble in methanol demonstrating that it was not a crosslinked gel before contact with water when the residual isocyanate groups would have been converted to urea crosslinks.

It can be seen that the embodiments disclosed are both or merely exemplary of the present invention, which may be embodied. in many different forms. Therefore, details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and for teaching one skilled in as to the various uses of the present invention in any appropriate matter. In particular, it should be noted that a wide variety of changes can be made in this process.

For example, pre-polymers with excess OH can be capped with a mono-isocyanate ended aromatic or aliphatic molecule or with a reaction product of a mono-amine with di or higher isocyanate. The low molecular weight amine

could be replaced with a low molecular weight polymeric amine, such as low Mn primary and secondary amine ended nylon polyamide) or polypropylene oxide, poly (butanediol) or low molecular weight polymers producing glassy domains such as end-capped polystyrenes or amine end-capped hydrophobic and crystalline domain forms such as poly (ethylene) units. The reaction can be between such amine ended PEGs and PPGs and di or higher amines and di or higher isocyanates, but done in solvents to allow suitable reduced viscosity to be obtained. Also, to slow down the amine reaction, the amine can be added at the outset as the carbonate version of amine carbonate, resulting from the reaction of amine and carbon dioxide.

Also, stage one hydroxylic excess polymers could be reacted with a phase separating polymer end capped with a group capable of reacting with a hydroxyl such as an anhydride group.

Finally, it should be noted that this end capping process could be applied to a wide variety of polymers, such as polyesters, nylons, polyurethanes, polyureas, polyethers, polyolefins, polyvinyls and poly (meth) acrylates.