CH621562A5 - Process for preparing a copolymer and use thereof for producing mouldings, in particular contact lenses - Google Patents

Description

The invention relates to a process for the preparation of copolymers, which is characterized in that a first hydrophilic monomer of the formula I

R O OH

I II I

CH: = C - O - O - (CHz) n - CH - CH2OH (I),

wherein

R is hydrogen or methyl; and n is an integer from 1 to 4

mean with a second, essentially water-insoluble monomer of the formula II

R O

I II

CH2 = C-C-OR '(II),

wherein

R is hydrogen or methyl; and R 'is alkyl having 1 to 6 carbon atoms, mixed in a molar ratio of 1: 3 to 20: 1 and the mixture is allowed to react in the almost complete absence of water and other diluents until a dimensionally stable copolymer is formed.

Preferred reactants are glyceryl methacrylate and methyl methacrylate.

Similar copolymers of the monomers mentioned are in the publications by H. Yasuda, C.E. Lamazo and L.D. Ikenberry, Makromol. Chem. 118 (1968) 1935 and H. Yasuda, C.E. Lamaza and A. Peterline, J. Polym. Sc. Part A-2, 996 (1971) 1117-1131.

The copolymers described in the first of the above publications were polymerized in a mixed solvent of acetic acid and water (70:30). The solutions were prepared with 5% by weight of total monomer and 95% by weight of solvent and started with approximately 0.5% by weight, based on the monomer weight, of K2 S2O8 and 1% by weight of Na2S20s. The nitrogen in the solution was expelled by blowing nitrogen through the solution. After standing at room temperature for eight to ten days, the polymer was precipitated in water. In these series of experiments, six copolymers were produced, the molar ratio of the methyl methacrylate to the glyceryl methacrylate varying from 95: 5 to 70:30.

The method described in the second of the above publications is similar to the first method, except that the polymerization process was carried out in a non-aqueous solvent using 2,2'-azobis (2-methyl-propionitrile) as an initiator. For reasons that will be discussed in more detail below, the copolymers produced by the abovementioned processes differ from those obtainable according to the invention because of the polymerization method used and the ratio of the components. The copolymers produced according to the publications described above differ fundamentally from those obtainable according to the invention, except that they are also suitable for the production of contact lenses.

For the process according to the invention, the dihydro-xyalkyl acrylate or methacrylate of the formula I is preferably used in a larger amount and the alkyl acrylate or methacrylate is preferably used in a smaller amount.

The copolymers produced by the process according to the invention have properties which are very similar to the “Hema” material described above. As a result, they are well suited for the production of contact lenses and other shaped articles which have to be associated with living tissue, such as, for example, surgical implants. The contact lenses made from the copolymers obtainable according to the invention do not have as many disadvantages as the lenses made from the “Hema” material. Although the present copolymers are soft and pliable, as required for soft contact lenses, they are nevertheless stronger and somewhat stiffer than the "Hema" materials. As a result, they result in an appropriate and s

1"

15

20th

25th

30th

35

40

45

50

55

60

65

621 562

4th

Uniform field of vision, since there is no constantly changing optical surface during eye movement and blinking, which could disturb the eyesight. Since the present copolymers are also stiffer than the “Hema” materials, the lenses produced from the copolymers obtainable according to the invention can be produced with a peripheral curvature that promotes the fluid flow, so that fresh tear fluid reaches the areas covered by the lens can. This liquid provides the eye with oxygen and also removes catabolic products as well as dust or dirt particles that can accumulate under the lens. Another important aspect is that, due to the increased stiffness, lenses can be produced which have a smaller thickness than the lenses produced from the “Hema” materials. The reduced thickness results in a significantly better permeability, which means that the tear fluid can also flow through the lens and around the eye. As a result, the irritations that occur particularly with the “Hema” lenses are avoided. Other advantages of the contact lenses made from the present copolymer are improved cleanability with water and strength that protects them from tearing.

The dihydroxyalkyl acrylate or methacrylate of the formula I which serves as the starting material can be prepared by hydrolysis in the manner described in GB-PS 852 384. In this process, a particular dioxolane alkyl acrylate or methacrylate is hydrolyzed with a dilute aqueous solution of a strong mineral acid over a long period of time at about room temperature, as described below.

The monomers of the formula II are commercially available and do not require any further description. Examples of such connections are u. a. the methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl methacrylate, butyl acrylate and butyl methacrylate, with the methyl methacrylate being the preferred compound.

The molar ratio of the monomer of the formula I to the monomer of the formula II is in the range from 1: 3 to 20: 1. However, it is preferred that the former monomer be present in at least the same molar amount as the latter, and so a preferred molar ratio can be between 1: 1 and 10: 1, most preferably between 1.2: 1 and 2: 1 . When used for contact lenses, the above molar ratio is preferably about 1.5: 1.

Catalysts which can be used are those which have been used in previous production processes for the corresponding monomers. The polymerization takes place in the almost complete absence of water and other diluents. The copolymers produced by mass polymerization have different properties than the copolymers which are produced in solution polymerization processes. The monomers mixed in the absence of a solvent can be kept at an elevated temperature for an extended period of time, after which the resulting polymer can be isolated. The temperature of the polymerization process generally varies between 20 and 60 ° C, preferably between 35 and 42 ° C, the most favorable temperature being about 40 ° C. The catalyst concentration can vary within fairly wide limits, depending on the type of catalyst used in the individual case. However, it is generally between 0.001 and 0.2% by weight, based on the monomer of the formula I, preferably between 0.01 and 0.04% by weight. A preferred catalyst is isopropyl percarbonate in an amount of approximately 0.02% by weight.

example 1

50 g of isopropylidene glyceryl methacrylate, 150 ml of water, 0.3 g of concentrated sulfuric acid and 0.02 g of hydroquinone were stirred at 25 to 30 ° C. for 16 hours. A clear, colorless solution resulted. The sulfuric acid was then neutralized by adding a small amount of solid barium hydroxide. The precipitated barium sulfate would be removed by filtration and washed out on the filter with a little water. The filtrate and the wash water were combined and resulted in 212 ml of a clear colorless solution which had a theoretical content of approximately 20% 2,3-dihydroxypropyl methacrylate in dilute aqueous acetone. The reaction product was isolated by saturating the solution with sodium chloride and extracting it with benzene or ether. After removing the solvent under reduced pressure, the 2,3-dihydroxypropyl methacrylate resulted as a slightly viscous oil.

The preferred comonomer for making the present hydrogel copolymer is glyceryl methacrylate (2,3-dihydroxypropyl methacrylate). This compound can be prepared by the method described in the aforementioned British patent, but is preferably made by the method described by M.F. Refojo in Journal of Applied Polymer Science, Issue 9, (1965) pp. 3161-3170. The process comprises the hydrolysis of the glycidyl methacrylate and the subsequent solvent extraction from the reaction mixture, as described below.

Example 2

100 g of commercially available glycidyl methacrylate (American Aniline and Extract Company, Inc. -GMA), 150 ml of distilled water and 0.25 ml of concentrated sulfuric acid were stirred for 6 days. During this time the reaction vessel was kept in a water bath at 24-29 ° C. In addition to the inhibitor already present in the glycidyl methacrylate, no further inhibitor was added to the reaction mixture.

Glycidyl methacrylate is immiscible with water, however, as the conversion progresses, the solubility increases until a clear solution finally results. In the course of the reaction process, glyceryl methacrylate is formed, which acts as a solubilizer in the unreacted glycidyl methacrylate.

The reaction mixture was neutralized with 10% sodium hydroxide solution and then extracted with 5x100 ml ether. The ether extracts were washed out with 3x20 ml of distilled water and this aqueous solution was washed out again with 50 ml of ether. The combined ether extracts were dried over anhydrous sodium sulfate. The ether was then evaporated on a rotary evaporator with the rotating bottle kept in a cool water bath. The 18.8 g residue from the ether extract consisted largely of glycidyl methacrylate, which could be used to produce further glyceryl methacrylate.

The aqueous extract from the ethereal solution was saturated with sodium chloride. The glyceryl methacrylate separated out as an oily layer over the saturated salt solution. The oily portion was dissolved in methylene chloride. The organic solution was dried with anhydrous sodium sulfate and evaporated without heating in the same manner used for the concentration of the ether extract. After evaporation, 11.6 g of a viscous Haren liquid resulted, which largely consisted of glyceryl methacrylate.

The aqueous reaction medium, which had previously been extracted with ether, separated into two layers after saturation with sodium chloride. The organic layer s

io

15

20th

25th

30th

35

40

45

50

55

60

65

was taken up with methylene chloride and the solution after drying with anhydrous sodium sulfate evaporated in a rotary evaporator using a cool water bath under the rotating container. The yield was 71.6 g of glyceryl methacrylate. The reaction product should also be 1.8 to 2.2% by weight of unreacted glycidyl methacrylate, which is not removed during extraction, and small amounts of other impurities, such as methacrylic acid, glyceryl methacrylate diester and / or glyceryl methacrylate - have included Triester.

It goes without saying that other dihydroxyalkyl acrylates or methacrylates can also be prepared from the corresponding epoxyalkyl esters in the manner described in this example.

It can be assumed that the crosslinking of the dihydroxyalkyl (meth) acrylate / alkyl (meth) acrylate polymer chains which occurs in the subsequent copolymerization with monomers of the formula II is at least in large part due to the presence of unreacted epoxyalkyl ester, which is present in the Dihy -droxyalkyl (meth) acrylate reaction product remains. Typically, a significant amount of unreacted epoxy alkyl ester will remain in the reaction mixture, even after repeated solvent extraction. This is obviously due to the dihydroxyalkyl (meth) acrylate, which acts as a co-solvent for the ester in the aqueous phase. However, if the amount of unreacted ester present in the dihydroxyalkyl (meth) acrylate product is different from the amount necessary to achieve the desired degree of crosslinking, it can be increased by adding epoxyalkyl ester to increase the crosslinking or by reducing the amount of ester in the product to reduce networking. The amount of ester can e.g. can be reduced by further solvent extraction steps as is known in the art.

The amount of epoxy alkyl ester that should be present in the reaction product depends on the degree of crosslinking desired in the final hydrogel product. In general, it can be said that the higher the amount of epoxyalkyl ester, the higher the degree of crosslinking to be achieved, and the lower the amount of ester, the lower the degree of crosslinking. It is generally preferred to have about 1 to 3% by weight of epoxy alkyl ester in the dihydroxyalkyl (meth) acrylate, which is reacted with the alkyl (meth) acrylate. In the preferred glyceryl methacrylate / methyl methacrylate system e.g. the reaction using glyceryl methacrylate containing about 1% by weight glycidyl methacrylate will generally give a copolymer that is hydrated to about 53%, indicating a relatively low degree of crosslinking, while using glyceryl methacrylate containing about 3% glycidyl methacrylate contains, generally provides a copolymer that is approximately 32% hydrated, indicating a relatively high level of crosslinking. A preferred range for the epoxy alkyl ester is from about 1.8 to 2.2% by weight, which in the preferred system results in glyceryl methacrylate / methyl methacrylate copolymers with about 39 to 43% hydration. Although not wishing to be bound by theory, it is possible that the crosslinking reaction occurs through the formation of a free radical on the carbon atom which contains the tertiary hydrogen, namely in the a-position to the epoxy oxygen atoms. The radical for glycidyl methacrylate thus obtained is shown below:

CH3

! I.

CH2 = C-C-O-CH2C-CH2

II \ /

o 0

621562

Small amounts of other contaminants, e.g. Methacrylic acid from a possible acid hydrolysis of the glycidyl methacrylate and / or the dimer or trimer of glyceryl methacrylate, if present, will react with the glyceryl methacrylate / methyl methacrylate system and contribute to a small degree to the crosslinking. However, it is clear that the essential crosslinking agent is the epoxy alkyl ester and that this compound is used effectively to control the degree of crosslinking. Other polymerizable difunctional compounds with only one olefinic double bond while the other functional group is non-olefinic can also be used as a crosslinking agent. Other suitable crosslinking agents are known to the person skilled in the art.

Example 3

A mixture of 56.8 g of 2,3-dihydroxypropyl methacrylate (prepared according to Example 2) and 23.7 g of methyl methacrylate (Rohm and Haas Company, Inc.) (molar ratio 1.5: 1.0) was carefully stirred . Then approximately 3 g of sodium sulfate was added to the mixture with stirring to remove all traces of water. The mixture was then filtered to remove the sodium sulfate and then 15.5 mg (0.02% by weight, based on the 2,3-dihydro-propyl methacrylate) of isopropyl percarbonate were added. The mixture thus formed was carefully stirred and then poured into a large tube.

The tube containing the mixture was then placed in a low temperature bath of dry ice in methylene chloride so that the temperature of the mixture in the tube could be kept between -20 and -30 ° C. The tube was then blown three times with nitrogen, sealed under vacuum and then placed in a bath at a constant temperature of 35 to 40 ° C for the polymerization process. The temperature was held constant for about 4 hours, although after about 90 to 95 minutes the mixture had solidified, indicating that the reaction had taken place. This point in the reaction process is referred to below as the "polymerization time". The tube was then placed in an oven at 75 ° C for 16 hours (overnight). The temperature of the furnace was then raised to 90 ° C. and maintained for one hour. The tube was then allowed to cool.

The polymerization product produced by the present process could be removed from the tube in the form of a solid rod. The resulting material, if formed into thin slices into lenses and placed in water, would become hydrated and have a soft, rubbery consistency.

Examples 4 to 8 The procedure of Example 3 was repeated several times, but the ratio of the 2,3-dihydroxypropyl methacrylate (GMA) to the methyl methacrylate (MMA) was varied. The concentration of the catalyst was adjusted to 0.02% by weight, based on the 2,3-dihydroxypropyl methacrylate, and the polymerization temperature was carefully kept at 40.degree. After the reaction process, the polymerization product was determined according to the following values: water absorption in percent, linear swelling in percent, durometer hardness and appearance in the water-containing state. The quantitative ratios used and the final results are summarized in Table 1 below:

5

5

10th

IS

20th

25th

30th

35

40

45

50

55

60

65

621 562 6

Table 1

example

relationship

water

Linear

«Durometer» -

Appearance

No.

GMA: MMA

admission

Queilung

Hardness (1)

(2)

[%]

m

4th

1: 1

27 to 29

12 to 14

-

very milky

5

1.25: 1

33 to 35

14 to 16

53 to 56

very milky

6

1.5: 1

39 to 42

17 to 19

46 to 49

slightly milky

7

2: 1

43 to 45

20 to 22

39 to 43

something clear

8th

3: 1

50 to 52

25 to 27

-

clear

(1) Durometer: Reading-Shore Durometer Type A-2 (0-60) ASTM D 676

(2) Appearance: Determined by looking through a round button 3 mm thick and 12 mm in diameter through the edge or cross section of the button.

The polymerization product from Example 6 is the preferred material for making contact lenses, although it appears slightly milky when the cross-section of the button is checked. This may be due to a lack of homogeneity which is responsible for the improved stiffness of the hydrated copolymer. The preferred polymer from Example 6 is based on its physical properties (hardness and rigidity), which are excellent for the production of lenses. It has in fact been found that the slightly milky appearance of one of the present polymers is an indication of optimal properties for the production of contact lenses if one looks through the edge or the cross section of the button mentioned above with the dimensions mentioned.

As for the optical clarity of a lens made from the preferred polymers, the appearance of the lenses in the thin sections used (0.05 20 to 0.15 mm) is actually absolutely optically clear.

Examples 9 to 14 The procedure of Example 3 was repeated several times, but the concentration of the catalyst 25 was increased. The temperature during the polymerization process was kept constant at 40 ° C. As a result of increasing catalyst concentration, the shortened reaction time (the time in which a solid forms in the tube containing the monomers) resulted. The results are summarized in Table 2 below.

Table 2

Example No.

catalyst

%

P.Z. (l)

Water absorption [%]

Linear swelling [%]

"Durometer" reading

Appearance

(2)

9

0.02

93

39 to 42

17 to 19

46 to 49

slightly milky

10th

0.03

60

41

20th

46

slightly milky

11

0.04

45

41

18th

47

something clear

12

0.05

34

40

20th

47

something clear

13

0.06

28

41

20th

47

clear

14

0.08

18th

42

20th

46

clear

(1) Polymerization time in minutes

(2) Appearance: Determined by looking through a round button 3 mm thick and 12 mm in diameter through the edge or cross section of the button.

The polymerization product prepared in Example 9 is also preferred for the manufacture of contact lenses, although it also has a slightly milky appearance when viewed through the cross-section of the standard size button.

Examples 15-17 The procedure of Example 3 was repeated several times, except that different temperatures were used and all other conditions were kept constant. The results are summarized in Table 3 below:

Table 3

example

Temp.

p.z.

water

Linear

«Durometer» -

Appearance

No.

° C

(i)

admission

Swelling

Reading (3)

(2)

[%]

[%]

15

40

93

39 to 42

17 to 19

46 to 49

slightly milky

16

43

42

41

20th

47

slightly clear

17th

45

39

42

20th

46

slightly clear

(1) Polymerization time in minutes

(2) Appearance: Determined by looking through a round button, 3 mm thick and 12 mm in diameter through the edge or cross section of the button.

The copolymer from Example 15 is also suitable. Examples 4 to 17 can be seen that it is preferred for the production of contact lenses. From the above of contact lenses it is of great advantage if the ratio

'7

621562

of the 2,3-dihydroxypropyl methacrylate to the methyl methacrylate is approximately 1.5: 1, furthermore the isopropyl percarbonate in a concentration of approximately 0.02% by weight, based on the 2,3-dihydroxypropyl methacrylate, and a reaction temperature of about 40 ° C is used. Networking can also preferably be carried out.

Example 18

A procedure according to Example 3 was repeated, but the methyl acrylate was replaced by the ethyl methacrylate and similar results were obtained.

Example 19

The procedure of Example 3 was repeated, with the methyl methacrylate being replaced by the methyl acrylate and similar results being obtained.

Example 20

The procedure of Example 3 was repeated, except that the 2,3-dihydroxypropyl methacrylate was replaced by the 2,3-dihydroxypropyl acrylate and similar results were obtained.

Example 21

200 g (1.406 mol) of glycidyl methacrylate, 300 ml of water and 0.5 ml of concentrated sulfuric acid were stirred at 24 ° to 29 ° C. for 5 days. The clear solution obtained had a pH of 2.0 and was neutralized to pH 7.0 with 10% sodium hydroxide solution. The solution was then extracted with six 100 ml portions of ether. The aqueous layer was stirred and saturated with sodium chloride, resulting in a two phase mixture which was separated by filtration. The two phase filtrate was then extracted with six 100 ml portions of methylene chloride. The combined extracts were stored in a separatory funnel in a refrigerator overnight to clarify. The organic layer was separated and concentrated under reduced pressure. 118.7 g of a clear viscous liquid were obtained, which mainly contained glyceryl methacrylate but also 2.19% by weight of unreacted glycidyl methacrylate. A portion of this reaction product (62.6 g) was mixed with 26.1 g of methyl methacrylate. This solution was dried by treatment with sodium sulfate and filtering the resulting mixture. The filtrate was mixed thoroughly with 18.2 g of isopropyl percarbonate and placed in four prepared large test tubes. Nitrogen was passed through each tube for two minutes, after which the tubes were cooled to -30 ° C, evacuated, filled with nitrogen three times and sealed tightly under vacuum. After the openings of the tubes were covered with wax, they were placed in a bath at a constant temperature of 40 ° C for 5 hours. The tubes were then placed in an oven at 75 ° C overnight. The next morning the temperature was raised to 90 ° C for one hour. The tubes were then cooled. Trial buttons from this approach showed 39.3% hydration and 17.9% swelling. After subjecting the glyceryl methacrylate to further solvent extraction until it contained only 1.06% unreacted epoxy, it provided a polymer with 52.8% hydration.

As already mentioned, the present hydrogels have properties that make them an excellent material for soft contact lenses. After absorption of water (physiological saline or water containing a physiologically active substance such as bacteriostatics), these hydrogels are soft and flexible, but at the same time tough and resistant to tears. They're a little more rigid than previous connections,

which were used as hydrogel contact lenses. As a result, they retain the contour of the eye better than previous materials and can be made with a thinner cross section, preferably 0.05 to 0.15 mm thick. Because of this thin cross-section, they are essentially more permeable to tear fluid than previous materials.

In addition, the greater hardness prevents the ugly blinking, which in turn prevents a constantly changing optical surface, which produces different and distorted images. Although the material has sufficient flexibility and, if shaped appropriately, it adapts well to the cornea, the lenses are still hard enough to retain their shape and a stream of tear fluid can flow under the lens. This is advantageous because fresh tear fluid and nutrients can constantly reach the areas covered by the lenses and thereby remove catabolic substances that could accumulate under the lenses. In addition, the polymers are sufficiently hard to allow the shape and function of a peripheral curvature of the lenses, which favors this liquid flow very much.

In addition to the above-mentioned uses of the present copolymers, their physiochemical properties are so good that they are suitable for prolonged contact with living tissue, blood and mucous membranes, so that they can be used for medical implants, devices for blood dialysis and the like. In view of this, it is known that blood, for example, decomposes very quickly when it comes into contact with most artificial surfaces. The design of a synthetic surface that does not promote thrombosis and does not have a hemolytic effect on blood is necessary for every prosthesis and device that is used together with blood. The non-ionic hydrogels, such as the hydrogels made by the present method, are known to actually reduce the clumping tendency of the blood.

The present hydrogels are also selectively permeable to water and are therefore suitable for various areas of application, u. a. for dialysis, ultrafiltration and hyper-filtration. In this regard, it is particularly beneficial

that the permeability of these hydrogels can be adjusted for any desired purpose and the size and shape of a diaphragm can be made in situ to form an integral part of a hydrophilic article or device. The good chemical stability of the hydrogels also makes them suitable for electrolytic purposes.

If the copolymers prepared by the process according to the invention, in particular in the form of the hydrogels obtainable therefrom by hydration, are used for dialysis purposes, the dialytic effectiveness can be influenced favorably, for example by creating a system of channels or lines running parallel to the eyes.

This line system can be produced, for example, by introducing fibers or plates made of a material which can be removed after the molding process has been carried out, into the mold into which the copolymer is poured. Suitable for this purpose are, for example, glass fibers which can be removed with hydrofluoric acid to form fluorosilicic acid, and materials which can be melted at temperatures below 100 ° C., such as aliphatic polyesters, which can be melted out. Such diaphragms can be used for industrial dialysis or for the production of artificial kidneys.

Because of their good compatibility with s

10th

15

20th

25th

30th

35

40

45

50

55

60

65

621562

-8th

living tissue, in particular mucosal tissue, the copolymers obtainable according to the invention can also be used for intrauterine devices or pessaries, optionally impregnated with biologically active substances such as medicaments, e.g. Antibiotics. The release of the medication then extends over a longer period of time. In addition, the copolymers obtainable according to the invention can be used for the controlled release of pesticides. The pesticides are gradually released from the copolymer by diffusion. In this way, a significantly lower environmental impact is achieved, especially when using biodegradable pesticides.

B

Claims (3)

621 562 2. The method according to claim 1, characterized in that the molar ratio of the first monomer to the second monomer is set to 1: 1 to 10: 1, preferably 1.2: 1 to 2: 1. 3. The method according to claim 1, characterized in that one uses a monomer of formula I, wherein R is methyl. 4. The method according to claim 3, characterized in that the monomer of the formula used is Ini. 5. The method according to claim 1, characterized in that one uses the monomer of formula II, wherein R and R 'are methyl. 6. The method according to claim 1, characterized in that one carries out the reaction at a temperature of approximately 40 ° C. 7. The method according to claim 1, characterized in that one carries out the reaction in the presence of a catalyst, preferably isopropyl percarbonate, the amount of the catalyst being 0.02% by weight, based on the first monomer. 8. The method according to claim 1, characterized in that 2,3-dihydroxypropyl methacrylate is used as the first monomer and methyl methacrylate is used as the second monomer, the molar ratio of the first monomer to the second monomer being from 1: 1 to 10: 1, preferably to 1.2: 1 to 3: 1, and in particular 1.5: 1. 9. The method according to claim 8, characterized in that 0.02 wt .-% of a catalyst, based on the 2,3-dihydroxypropyl methacrylate, is added. 10. A process for the preparation of a hydrogel of a copolymer, characterized in that the copolymer is prepared by the process according to claim 1 and then hydrated. 11. The method according to claim 10, characterized in that a copolymer hydrogel is produced which appears slightly milky in the form of a round, disk-shaped test specimen with a thickness of 3 mm and a diameter of 12 mm when looking through it. 12. The method according to claim 11, characterized in that the copolymer is prepared from 2,3-dihydroxypropyl methacrylate and methyl methacrylate and swells linearly by 17 to 19% when water is absorbed, 39 to 42% Absorbs liquid and assumes a Shore hardness of 46 to 49. 13. Use of a copolymer produced by the process according to claim 1 for the production of moldings. 14. Use according to claim 13, characterized in that one manufactures contact lenses. 15. Use according to claim 14, characterized in that one produces copolymer hydrogel contact lenses with a thickness of 0.05 to 0.15 mm, namely from a copolymer made of 2,3-dihydroxypropyl methacrylate and methyl methacrylate, which in the Water absorption swells linearly by 17 to 19%, 39 to 42% absorbs liquid and assumes a Shore hardness of 46 to 49. 16. Use according to claim 14, characterized in that contact lenses having a peripheral convex or concave curvature or peripheral multiple curvatures are produced. 17. Use according to claim 13, characterized in that molded articles which have a plurality of through openings are produced. 18. Use according to claim 13, characterized in that one produces a shaped body having the shape of an intrauterine device. 19. Use according to claim 13 or 18, characterized in that one manufactures a molded article impregnated with a medicament. As is already known, the conventional contact lenses are made from methyl methacrylate. Lenses made from this material, known as "hard lenses", have had limited success, however, because many people cannot get used to the presence of the lens in the eye and / or because the lens is a physiological process that is necessary for metabolism the cornea is affected. For many people, small particles and dust that come under the lens and rub against the cornea cause minor irritation. In addition, it has been found that after wearing hard contact lenses for a long time, for example for one to five years, and with varying degrees of success, discomfort develops for many people and forces them to stop wearing the lenses. For this reason, extensive studies have been carried out to develop new material for contact lenses which is free from the disadvantages of the lenses made of methyl methacrylate. A new material is described in U.S. Patents 2,976,576 and 3,220,960. The material described in these patents consists of hydrogel of a slightly cross-linked hydrophilic polymer with a substantial amount of aqueous liquid, e.g. water. The hydrophilic polymer is effectively a copolymer in which the major portion is a polymerizable monoester of an olefinic acid, preferably acrylic and methacrylic acid, with a single olefinic double bond, and the minor portion is a polymerizable diester of one of the acids mentioned, wherein the diester has at least two olefinic double bonds. The copolymer is formed by copolymerization in a solvent medium. In the materials described in the abovementioned patents, a weakly crosslinked polymer, which contains 2-hydroxyethyl methacrylate as the main component and is known as “Hema”, was first used for contact lenses. As a characteristic property, «Hema» can form hydrophilic polymers, which are hydrated with water s 10th 15 20th 25th 30th 35 40 45 50 55 60 65 2nd PATENT CLAIMS 1. Process for the preparation of a copolymer, characterized in that a first hydrophilic monomer of the formula I R O OH ! Il I CH2 = C - C - O - (CH2) n - CH - CH2OH (I), wherein R is hydrogen or methyl; and n is an integer from 1 to 4, with a second, essentially water-insoluble monomer of the formula II R O I II CH2 = C-C-OR '(II), wherein R is hydrogen or methyl; and R 'is alkyl having 1 to 6 carbon atoms, mixed in a molar ratio of 1: 3 to 20: 1 and the mixture is allowed to react in the almost complete absence of water and other diluents until a dimensionally stable copolymer is formed. 3rd 621562 can, for example up to 40 wt .-%, this percentage can of course vary between 35 and 65 wt .-%. This high water content makes the contact lens made of this material much more flexible and softer, so that such a lens can adapt more easily to the curvature of the eye. This is in contrast to the conventional hard lenses, which maintain their rigid original shape and do not adapt to the curvature of the eye. The most important advantage of this soft "Hema" hydrogel lens is that it can be worn with almost the same shape and with almost immediate and lasting comfort, since the cornea, at least initially, is significantly less affected than with conventional hard lenses. A second advantage of the soft «Hema» hydrogel lenses compared to the hard lenses is that less dust and foreign matter can get under the lenses and rub against the cornea. Another advantage of the soft "Hema" hydrogel lenses compared to the conventional hard lenses is the improved peripheral vision, since the lenses have a larger diameter. Despite the advantages of the soft "Hema" hydrogel lenses, there are certain disadvantages that have at least until now prevented these lenses from being widely accepted and used. One of these disadvantages is the lack of clarity in central vision. For many people, the soft "Hema" hydrogel lens does not provide sufficient and permanent vision because the material has a constantly changing optical surface during eye movement and blinking, which may be due to the lens being too soft or not stable enough . A second problem concerns correcting astigmatism. The conventional types of contact lenses can usually correct corneal astigmatism by forming a new surface on the cornea. Due to the extreme flexibility of the soft “Hema” hydrogel lenses, the lens adapts to the shape of the eye and, in most cases, does not form the new surface necessary to correct astigmatism. There have also been other physiological problems with the soft "Hema" hydrogel lenses. These problems include corneal irritation and wrinkles in the membranes of the eye. The exact causes or the meaning of these phenomena are neither known nor are solutions available to remedy them. However, it has already been reported that the tear fluid exchange is minimal with the «Hema» lenses compared to the conventional lenses. This is probably due to the fact that the "Hema" lenses adapt too much to the contour of the eye and therefore prevent the tear fluid from flowing under the edges of the lens. The reduction of the fresh tear fluid is not desirable because it significantly reduces the contact of the eye with oxygen and also increases the accumulation of catabolic substances. In addition, the soft «Hema» hydrogel lenses tend to tear easily and therefore have to be replaced in such a case. It has now been found that copolymers which, according to the invention, are prepared from certain acrylate or methacrylate monomers of different water solubility and which form hydrogels with water are suitable for the production of contact lenses which are free from the disadvantages described above.