Method of forming shaped hydrogel articles including contact lenses using inert, displaceable diluents

#The invention relates to the production of shaped hydrogel articles including soft contact lenses, and more particularly to a method for the direct molding of such articles using a new class of inert, displaceable diluents.

#Until recently, soft contact lenses of the hydrogel type have been manufactured either by lathe cutting or spin casting. In the lathe cutting method, a lens blank or button of a substantially anhydrous hydrophilic polymer (xerogel) is mechanically cut and polished to a lens shape on a fine lathe, and thereafter is contacted with water or saline to hydrate the polymer and form the desired hydrogel lens. The mechanical steps utilized in the lathe cutting operation are similar to those used in the manufacture of hard contact lenses, except that allowance must be made for swelling of the lens during hydration of the polymer.

#In the spin casting method, a small quantity of hydrophilic monomer mixture is placed in a concave, optically polished mold, and the mold is rotated while the monomers are polymerized to form a xerogel lens. The two optical surfaces of the lens are formed simultaneously during polymerization, the outer surface being formed by the concave mold surface and the inner surface being shaped by the joint actions of centrifugal force generated by the rotating mold and surface tension of the polymerization mixture. The lens produced thereby is contacted with water or saline to hydrate the polymer and form a hydrogel lens as in the case of the lathe cut lens.

#To a 5 L three neck round bottom flask are added 728 g (1.255 mol) of dried Photonol 7025 (molecular weight=580 g/mol), 1.5 L of dry acetonitrile, 1.0 g of 4-methoxy phenol (MEHQ) and 0.5 g of stannous octoate (approximately 0.1 mol % relative to diol). After these components are added, the resulting solution is purged with dry O.sub.2 for 30-45 minutes (a gas diffuser is used for this purpose). After the O.sub.2 purge is completed, 365 g (2.35 mol) of isocyanatoethyl methacrylate (IEM) and 730 g of acetonitrile are charged to a 1 L addition funnel (this operation is preferably carried out under N.sub.2).

#The contents of the addition funnel (i.e. the IEM solution) are then added, dropwise with vigorous stirring, to the 5 L round bottom flask. The addition should take about 2-3 hours to complete. After the IEM addition is complete, the addition funnel is rinsed with 50-100 mL of acetonitrile. The progress of the reaction is followed monitored by following the disappearance of the NCO absorption at 2270 cm.sup.-1 in the infrared spectra. The acetonitrile is removed under reduced pressure and the resultant viscous liquid dicapped bisphenol A 890 is used as prepared.

#A total of 200 g (0.05 mol) of dry PEG 4000 is placed into a 1 L three neck round bottom flask equipped with mechanical agitation, and a gas-inlet tube. A dry nitrogen blanket is established in the reaction vessel. To this flask is added 375 g of dry acetonitrile and the PEG 4000 is allowed to sit until it has completely dissolved. Subsequently, two drops of stannous octoate and 500 ppm of MEHQ are added. To a 100 mL addition funnel are added 15.52 g (0.100 mol) of IEM and 50 mL of acetonitrile. After the addition of the IEM is completed, the reaction progress is monitored by following the disappearance of the NCO absorption at 2270.sup.-1 in the infrared spectra. After the reaction is completed, the acetonitrile is removed under reduced pressure and the resultant white waxy dicapped PEG 4000 is used as is.