MXPA97003372A

MXPA97003372A - Clear polymeric compositions optically containing an interpenetra

Info

Publication number: MXPA97003372A
Application number: MXPA/A/1997/003372A
Authority: MX
Inventors: H Askari Syed; H Heidingler Hermann
Original assignee: Pilkington Barnes Hind Inc
Priority date: 1994-11-09
Filing date: 1997-05-08
Publication date: 1998-02-01

Abstract

Described are xerogel optically clear polymer compositions containing an interpenetrant

Description

CLEAR POLYMERIC COMPOSITIONS OPTICALLY CONTAINING AN INTERPENETRANT DESCRIPTION OF THE INVENTION This invention is directed to optically clear xerogel polymer compositions containing an interpenetrant. These compositions are characterized by the presence of hydroxyl functionalities which are blocked with a removable blocking group, which after removal of the blocking groups and the hydration of the composition, will have a water content of at least 10% by weight and preferably from 35 to 70% by weight and modulus of at least 2 Mdina / cm2. This invention also deals with methods for the preparation of optically clear hydrogel compositions containing the hydroxyl functionality and an interpenetrant. Hydrogel polymer compositions and the use of these compositions in ophthalmic devices, especially contact lenses, are well known in the art. Such polymeric hydrogel compositions are typically manufactured as copolymeric, optionally cross-linking systems that are formed in the xerogel state where they are hard materials. This xerogel in the presence of water or another solvent containing water, is hydrated and undergoes a change so that it reaches a hydrophilic state. When hydrated, the resulting polymer composition contains water and therefore becomes softer and more foldable compared to the composition before hydration. The degree of softness and flexibility depends on the amount of water incorporated into the polymer composition after hydration. Additionally, contact lenses derived from polymeric compositions have large amounts of water that provide the user with greater comfort and greater oxygen permeability. Therefore, the technique has generally been directed to the incorporation of large amounts of water in these polymer compositions. However, despite the convenience of incorporating large amounts of water into the hydrogel polymer compositions, a typical problem is encountered as the water content increases, the structural rigidity of the polymer composition, as measured by its modulus, decreases and can reach a point where the structural rigidity is less than desirable, Therefore the hydrogel polymer composition is typically formulated to balance the need for a high water content and for a suitable module and the values achieved for both parameters they often demand sacrifices of ideal values. With respect to the foregoing, it is known in the art that an intßrpßn? trant? incorporated in the polymer composition increases the structural rigidity of the composition by providing a means to obtain a desired level of water content while retaining adequate structural rigidity. However, a problem is found in the area of ophthalmic devices when a large amount of interpenetrant , this is greater than about 1.5% by weight (based on the dry weight of the polymer composition) is incorporated in a hydrogel polymer composition comprising hydroxyl groups. Specifically, it has been found that the use of a high amount of interpenetrant in those compositions renders the resulting composition opaque. Without being bound by theory, it is believed that hydroxyl-comprising polymer compositions have a poor solubility for the interpenetrant and therefore the resulting optical opacity for the compositions arises from the phase separation of the interpenetrant with respect to the polymer. Whatever the case, optically opaque materials can not be used in ophthalmic devices because optical clarity is a critical factor in these devices. In one embodiment, the technique has turned the problem up by including large amounts of organic solvent (eg, about 80-95% by weight or more) such as dimethyl sulfoxide (DMSO) with a chemically modified interpenetrant to include a reactive vinyl group. See for example the European patent application 0 456, 611. The organic solvent acts to solubilize the interpenetrant as well as the monomer% polymer composition and the reactive vinyl group acts to covalently incorporate the interpenetrant into the polymer structure during polymerization. After polymerization the resulting polymer is omarized (this is not a xerogel). The inclusion of large amounts of solvent in the polymer through such methods complicates the process of manufacturing ophthalmic devices from hydrogel materials because such materials typically slip or bend in the xerogel state, and once solvated, they become soft and pliable. makes the machining of materials difficult. Therefore the final shape and other physical characteristics of the polymer article are preferably formed during the xerogel state, ie in the absence of significant amounts of any solvent, the inclusion of large quantities of solvent in the prior art methods to form a composition optically clear polymer that contains an interpenetrant, has as premise the formation of a xerogel composition. In view of the foregoing, the art has been seeking, without success, an optically clear polymer composition comprising hydroxyl groups in the polymer and having incorporated at least 1.5% by weight of an interpenetrant. The invention is directed in part to optically clear xerogel polymer compositions comprising a polymer and at least 1.5% by weight of an interpenetrant (based on the weight of xerogel) wherein 1 polymer comprises blocked hydroxyl functional groups, these being removable. the xerogel polymer compositions are further characterized by forming, upon deblocking and with hydration, a hydrogel polymer composition having a water content of at least 10% by weight and preferably from about 35 to 70% by weight and a modulus of at least 2 M dynes / cm2. Therefore in one of its composition aspect this invention deals with an optically clear xerogel polymer composition comprising: a polymer comprising blocked hydroxyl functional groups and at least 1. 5% of an interpenetrant based on the total weight of the composition of xerog? l polymer where the composition has an optical clarity auficißntß to allow the passage of at least 80% of the visible light through 0. 1 mm thickness of the sample of the composition. In a preferred embodiment, the composition of the polymer described above has ridicule. In another more preferred embodiment, the polymer composition, after deblocking and hydration, has a water content of at least 10% by weight and even more preferably from approximately 35 to 70% by weight of water based on the total weight of hydrated hydroglyph composition and a modulus of at least 2 M dynes / cm2 In another preferred embodiment said composition prepared from polymer xerog? l has a modulus of 2 to 50 M dynes / cm2, and more preferably of 5 to 30 M dynes / cm2 and still more preferable greater than 12M dynes / cm2, a d-elongation both greater than 100% and more preferably greater than 175% and an oxygen permeability greater than about 10 Dk units and more preferably greater than about 18 Dk. In another preferred embodiment, the hydrated hydrogel polymer composition has a water content of 45 to 70% and more preferably 50%. This invention also deals, in part, with the unexpected discovery that the preparation of such optically clear hydrogel polymer compositions can obtained by placing a removable block group on the hydroxyl groups of the monomer component before polymerization and incorporation of an interpenetrant there. After polymerization and incorporation of an interpenetrant, the blocking groups are removed and the xerogel hydrated polymer composition is used in an optically clear hydrogel polymer composition. therefore in one of the aspects of the method, this invention is directed to a method for the preparation of an optically clear xersgel polymer composition comprising a polymer with hydroxyl functionalities, functionalities that are blocked with a removable group, and at least 1.5% by weight of an interpenetrant based on the total weight of the xerogel polymer composition, which method comprises: (a) selecting a monomer composition wherein each component comprises a reactive vinyl functionality and when less than one of the components of the composition comprises at least one hydroxyl functional group; (b) blocking the hydroxyl functionalities in each of the monomer components contained in the hydroxyl selected in (a) with a removable blocking group; (c) combining the monomer composition with when less than 1. 5% by weight of an intrinsic agent based on the total weight of the composition and (d) polymerizing the composition produced in (c) to obtain a clear xerography polymer composition. optically In a preferred embodiment the method described further comprises: (e) removing the blocking groups from the hydroxyl groups; and (f) hydrating the composition produced above in (e). In another preferred embodiment, an effective amount of a crosslinker is incorporated into the monomer composition before the polymerization process (d). As indicated, the invention is partially directed to preparing clear xerogel polymer compositions optically containing an interpenetrant and methods for preparing such compositions. However, before discussing the invention in detail, the following terms will be defined: The term "hydrogel polymer composition" refers to polymer compositions described herein, which, after polymer formation, are hydratable when treated with water, and therefore, they can incorporate water into the polymer matrix without dissolving in the water. typically the incorporation of water is effected by sinking the polymer composition in a water solution for a sufficient time to incorporate at least 10% by weight of water and preferably from 35 to 70% water and more preferably around 50 / in the polymer composition based on the total weight of the polymer composition. The term "xerogel polymer composition" refers to the composition formed in the absence of large amounts of added solvent wherein any solvent in the polymer composition typically represents less than about 5% by weight of the total composition and more preferably less than about 2% by weight of the total composition. % by weight of the total composition. The term "withdrawing blocking group?" refers to any group that is attached to one or more hydroxyl groups by preventing the reactions of these hydroxyl groups and protecting groups that can be selectively removed by conventional chemical and / or enzymatic methods to reestablish the hydroxyl group. The particularly employed removable blocking group is not critical and the preferred groups of beta blockers. Hydroxyl withdrawls include conventional substituents such as benzyl, benzoyl, acetyl, clroacetyl, trichloroacetyl, fluoroacetyl, trifluoroacetyl, t-butylbenzylsilyl and any other group that can be introduced into a functionality and then selectively removed by conventional methods under average conditions compatible with the nature of the product . In a particularly preferred embodiment, the blocking group is a solizable sun blocking group. In another preferred embodiment, the removable blocking group is selected such that upon hydration and removal of the blocking group, changes in the polymer do not occur or are minimal. More preferably, the magnitude of the dimensional change, when measured by the change in ßl percent expansion, is controlled to less than about plus or minus 25% and even more preferably less than about plus or minus 10%. The term "solvolizable" or "solvolizable blocking groups" refers to groups capable of cleavage in a compound containing carboxyl and an alcohol, in the presence of nucleophile, for example a hydroxyl ion in water or a weak base such as ammonia or organic amine or an alcohol with 1 to 4 carbon atoms, preferably solvolizable groups are capable of being solvolized with medium or mild solvolysis conditions, such as in an aqueous solution of a pH greater than 7 to less than 12 and at a temperature less than about 60 °.

Such solvolizables groups that depart or leave are well known in the art and a list is presented in for example the European patent application 0 495 603 Al, US 4, 638, 040 and the accepted US application 08/107, 023, which is Incorporate by reference. The term "interpenetrating" refers to structurally rigid high molecular weight materials, which are soluble, at levels employed, in at least one of the components used in preparing the polymer compositions described above. Such interpenetrants are well known in the art and include, by way of example, siloxane, polyurethane, cellulose acetate butyrate, hydroxypropyl hydroxyethyl cellulose, intergroup blends, as well as chemically modified interpenetrants to include a polymerizable group such as vinyl groups, epoxide groups, isocyanates, etc. (see for example European application No. 0 456 611 and the like such interpenetrants are either commercially obtainable or can be prepared by known techniques from commercially available starting materials.The particular interpenetrant used is not critical, preferably the interpenetrant has a molecular weight of about 1, 000 to 50,000 and more preferably from about 5,000 to 500,000.

The interpentrastrants are considered to be structurally rigid if 1. 5% of the intnerrene increases the modulus of a polymeric composition by at least 1 M dyne / c 2 compared to the same polymer composition in the absence of the interpenetrant. The term "unsaturated ethylene-compatible monomers free of hydroxyl groups" refers to monomers containing neither hydroxyl groups nor blocked hydroxyl groups, which may participate in the polymer formation with a monomer containing blocked hydroxyl groups with a removable blocking group, and which, when incorporated into the polymeric composition provide for the polymer composition, which after solvolysis and hydration, is suitable for use in ophthalmological devices, this is the hydrogel polymer. transparent to transmit visible light. Such ethylenically compatible unsaturated free onomeros free of hydroxyl groups include, d-methyl acrylate, methyl methacrylate, trifluoromethyl methacrylate, trifluoromethyl acrylate, 2,2 ', 2'-trifluoroethyl acrylate, ethyl methacrylate, ethyl acrylate, styrene and the like . Such materials are well known in the art and are available commercially or preparable from commercially available materials. Preferably the ethylenically compatible unsaturated monomers free of hydroxyl groups solubilize in whole or in part the interpenetrant employed. A particularly preferred combination of a non-saturated, ethylenically compatible monomer free of hydroxyl groups and an interpenetrant is methyl methacrylate and cellulose acetate butyrate. Another monomer of the above preferred type is phenoxyethyl methacrylate which also solubilizes cellulose acetate butyrate, although less efficiently than methyl methacrylate. The term "cross-linked agent" refers to a monomer containing at least two reactive groups capable of forming covalent bonds with reactive groups found in at least one of the monomers used to prepare the polymer compositions described above. Suitable reactive groups include, for example, vinyl groups, which may participate in the polymerization reaction, the reactive groups are typically substituents of a suitable structure such as a polyalkylene structure (including halogenated derivatives thereof) a polyalkaline structure, a glycol structure, a glycerol structure, a polyester structure, a polyamide structure, a polyurea structure, a polycarbonate structure, and the like.

Cross-linked agents for use in the preferred compositions described herein, they are known in the art and the crosslinked agent that 3ß employs is not critical. however preferably, the reactive vinyl group is attached to the α-structure of the cross-linked agent by means of an ester linkage such as is found in the acrylate and methacrylate derivatives, such as urethane diacrylate, urethane dimethacrylate, ethylene glycol diacrylate, dimethacrylate ethylene glycol, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, and amines, However, other vinyl compounds include, for example, di and higher vinyl carbonates, higher vinyl di and amides (e.g. CH2 = CHC (0) NHCH2CHaNHC (0) CH = CH2 and the like Preferred crosslinking agents include, by way of example, ethylene glycol dimethacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, tetradecaethylene glycol dimethacrylate, tetradecathylene glycol diacrylate. , allyl methacrylate, allyl acrylate, trimethacrylate propanotrimethylol, trimethylortolopropyl trailate or, 1,3-butanediol dimethacrylate, 1,3-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol dimethacrylate, diacrylate 1.9 nonanodiol, dimethacrylate 1, 10-decanediol, diacrylate 1,10 diecanodiol, dimethacrylate glycol neopentyl, diacrylate glycol neopentyl, 2, 2,2 bis (p- (gamma-methacryloxy-beta-hydroxypropoxy) phenyl) propane, triacrylate pentaerythritol, trimetacrylate pentaerythritol, tetraacrylate pentaerythritol, tetrametacrylate pentaerythritol, 1,4-cyclohexanediol diacrylate, 1,4-cyclohexanediol dimethacrylate, bis-phenol-A-ethoxylated diacrylate, bis-phenol-A-ethoxylated dimethacrylate, bis -phenol-A-dimethacrylate, diacrylate bis-phenol-A, N, N-methylene bis-3-acrylamide, as well as difunctional macromerenes having an approximate molecular weight of 1,000 to 1,000,000. Such materials are well known in the art, and are commercially available or preparable by methods known in the art. The technique. The reticulant agent has at least 2 or more preferably 2 to 6 vinyl functionalities and preferably has an average molecular weight of about 100 to 2.500 (except for the macromers described above). more preferably the vinyl functionalities are methacrylate or acrylate groups attached to a polyoxyalkyl structure (including halsgenated derivatives thereof) a polyalkaline structure, a glycol structure, a glycerol structure, a polyester structure, or a polycarbonate structure or. Formulations The polymer compositions described herein are prepared by first preparing a suitable formulation containing the required components and then polymerizing the formulation. Specifically, the formulations comprise a monomer composition and an interpenetrant. The monomer composition comprises at least one monomer component having a reactive vinyl functionality and at least one hydroxyl functional group wherein the hydroxyl group is blocked with a removable blocking group. Suitable hydroxyl monomer components (before blocking) include hydroxyethyl methacrylate (HEMA), hydroxyethyl acrylate, glycidyl methacrylate, glycidyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, monomethacrylate butanediol, mixtures of such components and the like. Suitable blocking groups include benzyl, benzoyl, acetyl, chloroacetyl, trichloroacetyl, fluoroacetoethyl, trifluoroacetyl, t-butyl biphenylsilyl groups and the like. When the monomer component contains more than one hydroxyl group, for example d-glycidyl methacrylate, the removable blocking groups used may be the same or different group, but for ease of synthesis, they are preferred. The monomer composition may optionally contain one or more compatible unsaturated monomers free of hydroxyl groups. When the monomer composition does not contain such ethylene-free monomers that are free of hydroxyl groups, the composition will preferably comprise monomers containing sufficient hydroxyl so that the resulting hydrogel polymer composition absorbs at least 10% by weight and more preferably from 35 to 70% by weight. In a particularly preferred embodiment, the monomer composition comprises at least about 20% by weight of monomer component or components with a reactive vinyl functionality having at least one hydroxyl functional group wherein the hydroxyl groups are blocked with a removable blocking group and more preferably from about 50 to 100% by weight based on the total weight of the monomer composition and still more preferably from 60 to 100% by weight. The formulation also contains an interpenetrant which is employed in the amount of at least 1.5% by weight based on the total weight of the formulation (in the absence of water) and preferably from about 5 to 60% by weight and more preferably from 5 to 30% by weight. The use of high concentrations of initerpenetrant can decrease the water content of the resulting hydrated polymeric composition. The specific amount of the interpenetrant employed is selected such that the hydrogel polymer composition has a modulus of at least 2 M dynes / cm 2 and preferably 2 to 50 M dynes / cm 2 and still more preferably 2 to 30 M dynes / cm 2. The compositions of this invention are preferably crosslinked and accordingly, one of the components of a preferred formulation is a crosslinking agent. when the reticulant agent is used, it is applied in an amount sufficient to provide a cross-linked product, but preferably in an amount of d 0. 0. 30% by weight, more preferably 0. 1 to 5% by weight and still more than 0. 2 a 3% by weight based on the total weight of the formulation. the use of higher amounts of crosslinker appears to be parallel to polymer compositions having a high modulus but low water content and a lower elongation in percent. the formulation may optionally contain one or more additional components such as initiators, colorants etc, which are conventionally employed in the art.

Eataa formulations and the reactants employed to prepare the formulations are preferably stored and formulated in containers that prevent premature polymerization of one or more of the reactants. For example, the use of amber bottles for the stored reactants inhibits photo-induced polymerization. METHODOLOGY The formulations described above are easily polymerizable by conventional techniques such as thermal, UV, gamma irradiation, or electron beam to induce polymerization, and thus obtain the polymer composition. For example, thermally induced polymerization can be achieved by combining a suitable polymerization initiator in a mixture of monomers under an inert atmosphere (for example argon) and maintaining the mixture at an elevated temperature of about 20 to 75 ° for a period of 48 hours. . Ultraviolet light induced polymerization can be achieved by combining a suitable polymerization initiator in the monomer mixture under an inert atmosphere (eg argon) and maintaining the mixture under a suitable UV source. Preferably the UV-induced polymerization is carried out under ambient conditions for a period of about 5 minutes to 24 hours. Suitable polymerization initiators are well known in the art including thermal initiators such as t-butyl peroxy pivalate (TBPP) neodecanoate t-butyl peroxy (TBPN) benzoyl peroxide, ethyl methyl ketone peroxide, diisopropyl peroxycarbonate and the like and UV initiators such as benzophenone, Daracur 1173 (obtainable from Ciba Geigy Arsley New York E. U) bis-azoisobutyronitrile and the like.

The UV or thermal initiator employed is not critical and sufficient initiator is used to catalyze the polymerization reaction. Preferably, the initiator is used up to about 1% by weight based on the total weight of the composition The polymerization achieved by either electron beams or gamma irradiation does not require the use of initiator and the formulation to be polymerized simply needs to be exposed to the electron beam or gamma irradiation using conventional methods. The polymerization is typically performed in a manner that facilitates the manufacture of the finished contact lenses. For example, the polymerization can be conducted in molds corresponding to the structure of the contact lenses. Alternatively, the polymerization can take place to form a polymer bar that can be machined (turned) to provide contact lenses of suitable dimensions. In this latter embodiment, the polymerization can be conducted in a silylated glass test tube and after polymerization, the test tube is broken to obtain the polymeric rod. The bar in the form of the xerogel can be machined, for example with lathe, cutter, milling machine and consequently the bar can be made contact lenses by cutting small cylinders or buttons of the bar with subsequent turning. In another alternative embodiment, the polymerization can be conducted in a curved base mold to provide a suitable button to form the contact lens. In any case, after the polymerization, a post-curing process is optionally employed to complete the polymerization, which increases the hardness of the polymer. This subsequent process may comprise heating the polymer to a temperature of about 60 to 120 ° for a period of 2 to 24 hours, alternatively, the post-curing stage may employ gamma irradiation of about 0. 1 to 5 Mrad. Combinations of these two procedures can be used.

The polymer compositions described above, preferably in the described contact lens forms, are subjected to removal of the removable blocking group and hydrolysis. The conditions for removing the block depend, of course, on the block used and the ability to select the conditions relative to the blocking group used is within the technique. either during or after the removal of the blocking group, the composition is subjected to conventional hydration to provide a hydrated form of the composition. In a particularly preferred embodiment, the removable blocking group is a solvolizable blocking group and the solvolysis of the groups and the hydration of the polymer composition occur simultaneously. The solvolysis is preferably carried out by suspending the contact lens in an aqueous solution in the presence of a nucleophile, for example, hydroxyl ion in water or a weak base such as ammonia or an organic amine or an alcohol with 1 to 4 carbon atoms, preferably solvolizable groups are capable of being under mild conditions, such as aqueous solutions with a pH greater than 7 to less than about 12 and a temperature of 10 to 60β. Under these conditions, hydration of the polymer material also occurs. however, if desired, a separate hydration step may be used. the hydration continues until the polymer composition is completely hydrated, which in the present case means that the water content of the hydrogel is approximately 36 to 70% by weight. In another embodiment, water may be included in the polymerization step resulting in the direct inclusion of water in the polymer composition. Utility. The described xerogel polymer compositions are suitable for use in medical and non-medical applications as a water absorbent useful for many applications. After incorporation of the water, the polymeric compositions are particularly suitable for use in ophthalmic devices, such as contact lenses to provide the required optical clarity, water content, high strength, no deterioration in time, a release or expedition of the hydrated water relatively slow when exposed to air, and good optical properties, including transparency. When formed in contact lenses, the lenses are typically sized to be approximately 0. 02 to 0.15 millimeters thick and preferably 0. 05 to 0.10 millimeters thick (all thickness is measured in the xerogel array). Now the invention will be illustrated by means of example that are provided by way of illustration and without limitation. In the following examples the following abbreviations are presented: BPAGMA = dimethacrylate bis phenol -A-2-hydroxypropyl CAB = cellulose acetate butyrate cm = centimeter EGDMA = ethylene glycol dimethacrylate EWC = equilibrium water content EX33 = Esperox 33 (M. R) (t-butylperoxineodecanoate) GMA = glycidyl methacrylate HCEGMA = glyceryl methacrylate di-trichloroacetate ester = linear expansion Mdins = megadines min = minute mm, = millimeter MMA = methyl methacrylate ppm = parts per million EXAMPLES n Examples Following the values of the polymeric compositions are established for the equilibrium water content EC, the linear expansion and the properties tesoros (this is the tensile strength, the percentage of elongation, and the module). Unless otherwise stated, those values were determined as follows: Measurement of Balancing Water Content The EWC value was determined by immersing the polymer samples in a saline solution of phosphate buffer overnight. The samples were removed, lightly dried with paper and weighed. The hydrated samples were placed in a 60ß vacuum oven overnight. The next day the sample was reweighed- The equilibrium water content was calculated by the following formula: EWC = X - Y / X where X = mass of the hydrated polymer Y = mass of the dehydrated polymer The EWC is ever mentioned as% water. Measurement of the Linear Expansion The linear expansion factor is determined by measuring the diameter of the xerogel polymer sample using the Nikon apparatus. Profile Projector V-12 (obtainable from Nippon Kagaku K. K. Tokyo, Japan). the sample is immersed in the overnight in a saline solution of phosphate buffer. The diameter is remeasured in a phosphate buffer exit solution. The linear expansion is calculated using the following equation LE = X / Y where X = diameter of the hydrated polymer Y = initial polymer diameter (dry) Measurement of the tensile properties From a disc or a lens a sample is cut in the form of dumbbell the sample is inspected under a microscope for cuts and nicking. If observed, the sample is discarded. Then the bulk of the sample is measured. The sample is then placed between the jaws of an Instron tensile tester (obtainable from Instron Corp. Canton Mass. E. U.) or an equivalent instrument. The initially used grip separation is 10 mm. The sample is placed under outlet during the measurement to prevent drying. The experiment starts with the cross head speed of 5 mm / in. The Instron records the force required to pull the sample as a function of the displacement of the transverse head. This information is converted to a tension - effort line. The experiment continues until the sample is broken. From the trace or tension stress diagram, the following is calculated Tensile strength The maximum effort the sample can withstand before it breaks; Elongation: The amount of extension (expressed as a percentage of the original length / separation of grip) that the sample suffers before breaking.

Module: is the slope of the initial linear portion of the stress-strain curve. Usually the experiment is repeated in 5 samples of the polymer bath itself and the average standard deviation is noted. Comparative Example A and Example 1 illustrate that blocking the hydroxyl groups in the hydrophilic monomer is essential to prepare an optically clear xerogel polymer composition incorporating an interpenetrant. Examples 2-3 exemplify that the dimensional change occurring during hydration can be controlled by selection of the polymer composition with respect to the removable blocking group. Examples 4-21 illustrate other examples of polymer compositions of this invention. Example 22 illustrates improvements in the amount of surface wettability achieved for the ophthalmic devices molded from polymer compositions made by the method of the invention. COMPARATIVE EXAMPLE A AND EXAMPLE 1 Two xerogel polymer compositions were prepared by incorporating an interpenetrant into the polymer composition, polymer compositions in the form of hydroxyl-containing hydrogel. Specifically, the first composition, Comparative Example A, was prepared so that the hydroxyl functionalities on the glycidyl methacrylate were not blocked with a removable blocking group during polymer formation, On the contrary in Example 1, the hydroxyl groups were blocked with a removable blocking group (this being the trichloroacetate). Specifically, the formulations for comparative example A and example 1 are set forth in table 1. TAB LA 1 Monom A MMA / CAB BPAGMA EX33 example 1 HCEGMA 2. 19 g 0. 274 107g (17. 72g) amin, comp, GMA 4. 38g 0. 548g 107g (12. 58) 1 MMA / CAB = 30% p. butyrate acetate in methyl methacrylate 2 BPAGMA = dimethacrylate bis phenol-A 2-hydroxypropyl (l: 2 p: p BPAGMA in DMSO) 3 EX 33 = Esperox 33 4 HCEGMA = glyceryl methacrylate di-trichloroacetate ester (stored at least - 5 ° C and preferably at -5 ° C) Each of the formulations was prepared by combining the monomer A with both the methyl methacrylate / cellulose acetate butyrate composition and the crosslinker (BPAGMA). The composition was then mixed for 1 hour and then the gas was removed for 6 minutes. At this point, the initiator (EX 33) was added to the composition and the formulation was again subjected to removing the gas, this time for 30 seconds. The loss of gas was done in order to avoid contamination of the reaction vessel with oxygen, which can have an adverse effect on the degree of polymerization. the resulting formulation was polymerized and cured in a programmable oven increasing 10"per minute in the following manner to provide a xerogel polymer composition: 1) 40V 2 hours 2) 55/2 hours 3) 70V 2 hours 4) room temperature / 4 Subsequently, the xerogel polymers of the comparative example a and of Example 1 were subjected to hydrolysis using a 5% solution of ammonium hydroxide, in the saso of Example 1, which resulted in the removal of the blocking groups (via solvolysis) and hydration of the polymer composition The clarity / opacity of the resultant polymer compositions are set forth in Table II TABLE II OPTICAL PROPERTY POLYMER OPTICAL PROPERTY LIKE XEROGEL AS HYDROGEL COMPOSITION A optically optically opaque opt. 1 light op.c., or clear Other physical properties for the polymer of example 1 were determined as follows: tensile strength = 13.8 plus minus 5.8 M dynes / cm2, both percent ongation = 211 plus minus 89, modulo = 22. 1 plus minus 12. 3 and an EWC = 52. 3 plus minus 2. 5. The results of this comparison establish that the hydrogel polymer compositions contain an interpenetrant which requires the blocking of the hydroxyl groups on the monomers prior to the polymerization with the object of achieving optical clarity in either the xerogel or the hydrogel composition. The physical properties of the polymer of example 1, establish that this polymer has values of tensile strength, percent elongation, modulus and EWC suitable for use in ophthalmic devices. Examples 2 and 3 EXAMPLES 2 AND 3 The following examples illustrate the selection of removable blocking group that can be made to control the dimensional change that results from hydrating the polymeric composition. Specifically, the formulations for examples 2 and 3 are set forth in Table III below: TABLE III HCEGMA MMA / CAB BPAGMA EX33 EXEM 2 94. 24% 5. 236% 0. 523% 0. 4% EXAM 3 89. 22% 9. 345% 0. 9345% 0. 4% HCEGMA = di-trichloroacetate ester of glyceryl metasyrilat (stored at at least -5o and preferably at -5β) MMA / CAB = 30% p > P butyrate acetate cellulose and methyl methacrylate BPAGMA = dimethacrylate bis-phenol-A-2 hydroxypropyl (1: 2 p: p BPAGMA in DMSO) EX33 = Esperox 33 (MR) These formulations were polymerized and cured in the manner described above for the comparative example A and example 1, to obtain optically clear xerogel polymer compositions. After that, the xerogel polymers of examples 2 and 3 were subjected to hydrolysis using a 5% solution of ammonium hydroxide which resulted in both removal of the blocking groups (via solvolysis) and hydration of the polymer composition. The resulting compositions were both optically clear and had the physical properties set forth in the following Table IV T A B L A IV Ex Modulo Tena% Elong EWC Exp. Linear 2 4. 4-1. 1 3. 1-1. 6 117-28 64, 4-0. 9 22. 2% 3 12. 5-1. 7 14. 8-6. 7 140-40 51. 2-0. 7 5. 5? Í Modulo = in Mdinas / cm Tension = in Mdinas / cm The second value indicates the variation of more or less In both cases the percentage of the linear expansion remained less than 25% evidencing a degree of expansion control produced by hydration. The example 3 in particular, exemplifies a polymer composition having approximately 50% water that undergoes minimal expansion during hydration. Therefore, in selecting the removable blocking groups with respect to the amount of water to be absorbed, it is possible to provide a polymer composition having little dimensional change during hydration. EXAMPLES 4-21 The following examples present optically clear polymeric compositions, both xerogel and hydrogel, within the scope of the present invention. These polymer compositions were prepared in the manner described and hydrated in a manner similar to that described above. The formulations employed to prepare such polymer compositions are described in Table V, which follows: T A B V HCEGMA MMA / CAB BPAGMA EX33 Example 4 94 8 0. 5 0. 4% weight Example 5 97 8 0. 5 0. 4 Example 6 94 8 1. 0 0. 4 Example 7 97 8 1. 0 0. 4 Example 8 94 12 0. 5 0. 4 Example 9 97 12 0. 5 0. 4 Example 10 94 12 1. 0 0. 4 Example 11 97 12 1. 0 0. 4 Example 12 96 11 0. 4 0. 4 Example 13 98 11 0. 4 0. 4 Example 14 96 13 0. 4 0. 4 Example 15 98 13 0. 4 0. 4 Example 16 96 11 0. 4 0. 4 Example 17 98 11 0. 4 0. 4 Example 18 96 13 0. 4 0. 4 Example 19 98 13 0. 4 0. 4 Example 20 97 12 0. 4 0. 4 Example 21 96 11 0. 4 0. 4 HCEGMA = Glyceryl methacrylate di-trichloroacetate ester (stored at -5β); MMA / CAB = 30% p: cellulose acetate butyrate in methyl methacrylate; BPAGMA = dimethacrylate bis-phenol-A-2-hydroxypropyl (1: 2 p: p BPAGMA in DMSO); EX33 = Esperox 33 (M.R.) In examples 4-21 HCEGMA, MMA / CAB and BPAGMA are indicated in amounts referred to weight. EXAMPLE 22 The purpose of this example is to illustrate the best in surface wettability of molded ophthalmic devices (contact lenses) made by the methods of this invention compared to the prior art methods. Specifically, when the polymerization of the monomer mixture is conducted in a polypropylene mold, the hydrophobic nature of the mold tends to orient the molecules during polymerization so that the resulting polymer surface contains a more hydrophobic nature than the interior of the polymer. This difference can be quantified by comparing the contact angle of the polymer surface to the surface formed by turning the polymer so that the interior of the polymer is exposed, typically, when the hydroxyl groups of the monomer are not blocked prior to polymerization, the resulting polymer composition will have a significant increase in the contact angle of the surface formed during the polymerization encountered with the contact surface angle d formed after the polymerization by turning. The increase in the contact angle corresponds to a reduction in surface wetting.

In the present case, a polymeric composition formed in accordance with the description was tested for its angle d? contact both on the surface formed during the polymerization and in opposition to the contact angle of a surface formed after the polymerization by the action of a lathe. In both cases, the contact angle was d? 40 * more or less 2 showing that there was no reduction in surface wettability between the surface formed during the polymerization and the interior of the polymer. Without being limited to any theory, it is believed that the blocking groups employed in the hydroxyl groups of this invention alter the hydrophilic nature of the monomer to a more hydrophobic nature thus allowing the orientation of the groups on the surface of the polymer. After the formation of the polymer, removal of these blocking groups exposes the hydroxyl groups on the surface of the polymer. In any case, the improved surface in its wettability is a beneficial attribute of the polymers of this invention. Following established procedures, other optically clear polymeric compositions containing an interpenetrant and hydroxyl group can be prepared simply by substituting the appropriate uit reactant for the surfactant mentioned in the previous examples. For example, a polymer composition using EGDMA can be prepared by simply replacing the BPAGNA crosslinker with the ßl EGDMA crosslinker.

In this case 0. 0355 grams of EGDMa can replace 0274 grams of the BPAGMA / DMSO crosslinker. Other substitutions can be made immediately as well known in the art.

Claims

CLAIMS 1. An optically clear xerogel polymer composition comprising: a polymer comprising blocked hydroxyl functional groups and at least 1. 5% by weight of an interrognent based on the total weight of the xerogel polymer composition wherein the composition has sufficient optical clarity to allow the passage of at least 80% of visible light through 0. 1 millimeter dß thickness of the sample of the composition.
2. The composition of the polymer according to claim 1, wherein the composition is crosslinked. The polymer composition according to claim 1, wherein the polymer composition after unblocking and hydrating, has a water content of about 35 to 70% by weight based on the total weight of the hydrated hydrogel polymer composition and a module of at least about 2M dyne / cm2 4. - The xerogel polymer composition according to claim 1, wherein the composition comprises from 5% by weight to about 60% by weight of an interpenetrant. 5. The xerogel polymer composition according to claim 4, wherein the interpentant has a molecular weight of about 1,000 to 50,000, 000. 6. The xerole polymer composition according to claim 5. , wherein the interpenetrant has a molecular weight of about 5,000 to 500,000. 7. The xerogel polymer composition according to claim 1, wherein the interpenetrant is selected from the group consisting of siloxane, polyurethane, butyrate, cellulose acetate, cellulose, hydroxy ethyl cellulose, hydroxy propyl cellulose, and hydroxyethyl hydroxypropyl cellulose. 8. The xerogel polymer composition according to claim 1, wherein the composition is optically clear enough to allow passage of at least 90% of the visible light through a sample of 0. 1 mm thick of the composition. 9. An optically clear cross-linked xeroge polymer composition comprising: about 70 to 95% by weight of the methacrylate hydroxyl di-trichloroacetate functional group? of glyceryl based on the total weight of the composition, and from about 1.5 to 30% by weight of the cellulose acetate butyrate based on the total weight of the composition; from about 0. 1 to 30% by weight of a crosslinking agent based on the total weight of the composition 10. An ophthalmic device comprising a polymer composition according to claim 1. 11. The ophthalmic device according to claim 10 wherein said device is a contact lens. 12. A method for the preparation of an optically clear xerographic polymer composition comprising a polymer having hydroxyl functionalities, which are blocked with removable blocking groups, and at least about 1.5% by weight of an interpenetrant based on in the total weight of the xerogel polymer composition wherein the polymer composition has sufficient optical clarity to allow the passage of at least 80% of the visible light through a 1-millimeter gruea of the composition, which method comprises (a) selecting a monomer composition wherein each component thereof comprises a vinyl functionality rßaß1 - («rß and at least one of the components of the composition comprises at least one hydroxyl functional group, (b) blocking the hydroxyl functionalities in each of the monomer components containing hydroxyl selected in * a (with a removable blocking group; ) combining the monomeric composition with at least 1.5% by weight of an interpenetrant based on the weight of the composition; and (d) polymerizing the composition produced in (c) to provide an optically clear polymer composition. 13. A method for the preparation of an optically clear hydrogel polymer composition comprising a polymer having hydroxyl functionalities and at least about 1.5% by weight of an interpenetrant based on the total weight of the xerogel polymer composition wherein the polymer composition has sufficient clarity to allow the passage of at least 80% of the visible light through a sample of 0. 1 millimeter thick of the composition, method comprising: (a) selecting a monomer composition e wherein each component thereof comprises a reactive vinyl functionality and at least one of the component β comprises at least one hydroxyl functional group; ..... (b) block the hydroxyl functionalities in cad * dß loar hydroxyl-containing monomer components selected in (a) with a removable blocking group; (c) combining the monomer composition with at least 1.5% by weight of an interpenetrant based on the total weight of the composition; (d) polymerizing the composition produced in (c) to provide an optically clear xerogel composition; (e) removing the blocking groups from the hydroxyl groups; and (f) hydrate the composition produced in step (e) previous. 14. - The method according to claim 1 wherein the blocking groups d? the monomer components are solvolizable blocking groups. 15. - The method d? according to claim 1 wherein the solvolizable blocking groups is selected from the group consisting of d and C acyl blocking groups and haloacyl d 2 to 8 carbon atoms. 16. - The method according to claim 13, wherein the blocking group is a haloaeyl blocking group of the formula X3CC (0) 0 wherein each X is independently selected from the group consisting of fluoro and chloro. 17. - The method according to claim 1 wherein the blocking groups are selected to reduce the change? dß volume in the polymer composition during hydration. 18. - The method according to claim 13, wherein the polymerization process of step (d) is carried out in the presence of water or a solvent containing water. 19. - The method according to claim 13 wherein the interpenetrants comprise one or more polymerizable groups. 20. A method for increasing the wettability of the surface of a polymer molded against or together with a hydrophobic mold material wherein the polymer is derived from monomers having a hydroxyl functionality, which method comprises (a) blocking the functional β-hydroxyl laß in each of the monomer components containing hydroxyl and used to prepare the polymer; (b) polymerizing the monomer produced in step (a) above to obtain a polymer composition; (c) removing the blocking groups from the hydroxyl groups.