Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-03-26
2002-01-29
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S273000, C526S287000, C526S307000, C526S317100, C526S320000, C526S328500
Reexamination Certificate
active
06342570
ABSTRACT:
The present invention relates to novel copolymers based on vinyl lactams, the monomer building blocks of which have a statistical distribution, that are water-soluble and cross-linkable, and are, where appropriate, modified with reactive vinyl monomers, to processes for the preparation of the novel copolymers, to cross-linked water-insoluble copolymers, hydrogels and mouldings produced from the cross-linked water-insoluble copolymers, especially contact lenses, and to processes for the preparation of hydrogels and finished contact lenses using the said cross-linkable water-soluble copolymers.
Vinyl lactam copolymers, such as, for example, vinylpyrrolidone copolymers, have already been known for a relatively long time as material for contact lenses having a high water content. Scafilcon A and Surfilcon A are mentioned here as representative examples. They have proved very successful in practice owing to their high degree of wearer comfort.
U.S. Pat. No. 4,347,198 describes the manufacture of contact lenses where a hydrophilic component, for example N-vinylpyrrolidone, a hydrophobic component, for example methyl methacrylate, a cross-linking agent and an initiator are mixed in a solvent, for example DMSO, and then the whole is cross-linked in a mould. After extraction and equilibration in water, a soft hydrogel contact lens is obtained. Extraction with water is necessary because the solvent and unreacted vinyl monomers have to be removed. Since a polymer swells to different extents, for example in DMSO on the one hand and water on the other, the contact lens assumes its final size only at that stage.
EP 216 074 describes a process for the preparation of hydrogel contact lenses. There, a methacrylate-modified polyvinyl alcohol is used which is copolymerised in DMSO solution with vinyl monomers in a suitable casting mould, for example in the presence of a photoinitiator by irradiation with UV light for approximately 3 hours. After being removed from the mould, the contact lens is extracted with water or physiological saline solution in order to remove the DMSO and unreacted vinyl monomers. In this case too, the contact lens does not receive its final geometry until the final stage owing to the different influences of DMSO and water on its swelling behaviour.
Efforts are being made in various quarters to reduce the reaction times in polymer preparation in order to make lens manufacture more economical. EP 370 827 (Vistakon) describes, for example, the use of boric acid esters of certain difunctional alcohols as solvents for the polymerisation of, in the main, HEMA in a polystyrene casting mould. Polymerisation takes place in only 6 to 12 minutes, again in the presence of a photo-initiator by irradiation with UV light, and yields a gel which then has to be extracted with water.
One disadvantage of the previous processes for the manufacture of contact lenses is the laborious extraction with water or physiological saline solution, which precludes economical contact lens manufacture with short cycle times.
Another disadvantage of the previous processes is, as already mentioned, the relatively slow cross-linking speed in the preparation of polymers in the case of the prior art.
The present invention provides a remedy for those problems since it discloses statistical copolymers that are water-soluble and cross-linkable. The above-mentioned laborious extraction with water or physiological saline solution after cross-linking is omitted in the case of the present invention because cross-linking can be effected, for example, in water. The disadvantage of the relatively slow cross-linking speed is countered by using copolymers instead of monomers as starting material for the manufacture of contact lenses.
The present invention accordingly relates to a water-soluble cross-linkable copolymer comprising a copolymerisation product of a monomer mixture consisting substantially of a vinyl lactam (a) and at least one further vinyl monomer (b) of a different type selected from the group consisting of hydrophobic, hydrophilic and functional vinyl monomers, wherein the monomers are present in the copolymer in the form of statistically distributed building blocks, and, if a functional vinyl monomer is present as a building block in the copolymer, that building block is, where appropriate, modified with a reactive vinyl monomer (c), the reactive vinyl monomer (c) being linked to a building block of a functional vinyl monomer with retention of its vinylic group and with the formation of a covalent bond.
Within the context of the present invention, any reference hereinbefore or hereinafter to a copolymer is always intended to mean a copolymer wherein the monomers are present in the form of statistically distributed building blocks.
A copolymer wherein the monomers are present in the form of statistically distributed building blocks is to be understood as being a copolymer comprising at least two different types of monomer in the case of which, in 98% of all cases, the block size of identical monomer building blocks is in the range of from 1 to 10, preferably in 90% of all cases in the range of from 1 to 7 and more preferably in 80% of all cases in the range of from 1 to 5. Within the context of the present invention, the expression “statistical monomer distribution in a copolymer” or the expression “statistical copolymer” is also used to have the same meaning. A statistical monomer distribution in a copolymer also means that said copolymer is substantially free of homopolymers and block polymers. Statistical copolymers differ in their physical properties from their isomeric homopolymers and block polymers and can, if necessary, accordingly be separated therefrom by physical methods. Statistical copolymers are given their typical characterising features, for example, by their molecular weights, their solubilities, their thermal properties or their NMR spectra
Statistical copolymers can be distinguished from non-statistical copolymers, for example, on the basis of the molecular weight distribution. Statistical copolymers generally exhibit a typical Gaussian molecular weight distribution while non-statistical copolymers do not. The molecular weight range of a statistical copolymer is generally adjustable and depends, inter alia, on the nature and amount of the solvent used. The average molecular weight can be adjusted, for example, to a range of from 1·10
5
to 4·10
5
, for example when copolymerisation is carried out in methanol.
In the present invention, preference is given to copolymers according to claim
1
that comprise a copolymerisation product of a monomer mixture consisting of 30-95 mol % of a vinyl lactam (a) and 5-70 mol % of at least one vinyl monomer (b) and, where appropriate, a reactive vinyl monomer (c).
A preferred copolymer is a copolymer according to claim
1
that comprises a copolymerisation product of a monomer mixture consisting of 50-90 mol % of a vinyl lactam (a) and 10-50 mol % of at least one vinyl monomer (b) and, where appropriate, a reactive vinyl monomer (c).
More strongly preferred is a copolymer according to claim
1
that comprises a copolymerisation product of a monomer mixture consisting of 60-80 mol % of a vinyl lactam (a) and 20-40 mol % of at least one vinyl monomer (b) and, where appropriate, a reactive vinyl monomer (c).
The present invention relates preferably also to a copolymer according to claim
2
wherein the proportion of reactive vinyl monomer (c) is up to 50 mol % of the total amount of vinyl monomer (b) and (c).
Also preferred is a copolymer according to claim
3
wherein the proportion of reactive vinyl monomer (c) is from 5 to 40 mol % of the total amount of vinyl monomer (b) and (c).
Preference is given also to a copolymer according to claim
4
wherein the proportion of reactive vinyl monomer (c) is from 10 to 25 mol % of the total amount of vinyl monomer (b) and (c).
In the case of commercial lenses, the hydrophobic vinyl monomer used is principally methyl methacrylate (MMA). MMA can also be used in the present invention. In general, however, it is pos
Borghorst Sharla
Bothe Harald
Golby John
Hagmann Peter
Herbrechtsmeier Peter
Gorman Robert J.
Meece R. Scott
Novartis AG
Wu David W.
Zalukaeva Tanya
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