Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Nonmechanical aftertreatment
Patent
1998-11-12
2000-12-05
Vargot, Mathieu D.
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Nonmechanical aftertreatment
525 62, 5253278, 525 56, 523106, C08F 812, B29D 1100
Patent
active
061562440
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the preparation of hydrogels that contain hydrolysable side groups and the storage stability of which can be established by controlled hydrolysis. At the same time as the storage stability is established, the hydrogel is sterilised in its final packaging, the salt concentration of the aqueous phase being adjusted preferably to a physiological range.
In the commercial preparation of hydrogels, for example by crosslinking polymers in solution, in order for the process to be economical certain physicochemical properties are required of the starting polymers in respect of, for example, viscosity, crystallisation tendency, solubility and chemical reactivity. Those properties can be positively influenced by using special side groups in a polymer. It is of advantage for an economic process to employ side groups that are used on a large commercial scale and that are favourably priced, but a disadvantage is that such side groups are not always sufficiently stable for the purpose for which the hydrogel is intended.
It is known, for example, that the viscosity of a Mowiol solution (aqueous solution of a partially hydrolysed polyvinyl alcohol, Hoechst AG) is dependent on the one hand on the degree of polymerisation and degree of hydrolysis of the polymer, and on the other hand on the concentration and the temperature (see, for example, the Hoechst AG booklet "Profil eines Polymeren, Polyvinylalkohol Mowiol" (Profile of a polymer, Mowiol polyvinyl alcohol), 1991). If the degree of polymerisation is kept constant, then a solution of a fully hydrolysed polyvinyl alcohol (PVA) will have a higher viscosity than a solution of a partially hydrolysed polyvinyl alcohol. Furthermore, the polarity of the PVA building blocks causes so-called association phenomena, which occur especially in the higher concentration range of fully hydrolysed high- and low-molecular-weight Mowiol types. The result is so-called gelling effects, which render efficient processing difficult and also make commercial processes, for which a high viscosity is prohibitive, impossible.
The present invention relates to hydrogels, especially hydrogels based on crosslinkable polyvinyl alcohols modified by hydrolysable side groups, the storage stability of which hydrogels can be established in a simple process. The invention also relates to a procedure by which, at the same time as the storage stability of the hydrogel is established, the hydrogel can be sterilised in its final packaging and the salt concentration of the aqueous phase can be set in the physiological range.
Hereinbefore and hereinafter, storage stability also signifies dimensional stability and/or mechanical stability, for example of a moulding or especially of a contact lens.
As a result of the present invention it is possible in the preparation of storage-stable hydrogels to use especially PVA prepolymers, which offer advantages in terms of processing technology, such as low viscosity and good processing stability of the prepolymer solution (see in this connection the above-mentioned association phenomena of PVA), but the use of which has not been possible hitherto on account of their lack of stability in respect of hydrolysis and their resultant lack of stability in storage. Furthermore, the mechanical properties of a crosslinked prepolymer, and hence of the hydrogel, can be regulated not only by way of the network density but also by means of the side groups of the prepolymer used.
Accordingly, a hydrogel moulding of the present invention is produced preferably from a PVA prepolymer of which the physicochemical properties have been positively modified by hydrolytically removable side groups. In a process step following the crosslinking, the side groups are hydrolytically removed without there being any significant alteration to the mechanical properties of the hydrogel. The moulding assumes its final geometry in that process step. The process step may preferably proceed in such a manner that the moulding is simultaneously hydrolysed and sterilised
REFERENCES:
patent: 3221083 (1965-11-01), Crandon
patent: 5407062 (1995-04-01), Shannon et al.
patent: 5508317 (1996-04-01), Muller
patent: 5583163 (1996-12-01), Muller
Leder Iris
Muller Achim
Muller Beat
Seiferling Bernhard
Gorman, Jr. Robert J.
Meece R. Scott
Novartis AG
Vargot Mathieu D.
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