CA1204407A - Dimensionally stable contact lens materials and method of manufacture - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Improved contact lens materials are obtained from copolymers containing a siloxanyl alkyd ester vinyl monomer and another unsaturated monomer by exposing the materials to high energy radiation thereby reducing the amount of unreacted monomer and residual contaminants.

Description

glue . . . . . .
Background Go the Invention In recent years hard contact lens materials having improved oxygen permeability have been developed. Certain such materials are set forth in United States Patent 3,808,178 which describes contact lenses fabricated from a copolymer of a polysiloxanyl acrylic ester and an alkyd acrylic ester. Other such hard contact lens materials have been developed. It is sometimes difficult to obtain good dimensional stability in contact lenses made from siloxanyl alkyd ester vinyl monomers Dimensional stability is an important property of hard contact lenses and affects both accurate vision correction and wearer comfort. It is known that changes in the dimensions of hard lenses can occur rapidly shortly after cutting and finish-in or over a prolonged period of time. Such changes can be of various types. Changes to the base curve or outer curve of a contact lens which changes are uniform are known as "steepening" or "flattening" depending upon the direction of change. A non-uniform change in lens dimension is termed "war page".

Ye ~2C~ 7 1 Dimensional changes of the type noted above can result

2 from one or more factors which include the relief of internal ,

3 stress or strain incurred during manufacture or the wakeup or

4 loss ox material within the lens. The prior art has developed processes for handling internal stress and strain problems as 6 by the use of careful annealing of lens blanks.
7 Dimensional stability difficulties have been encountered with gas permeable contact lenses prepared from co or higher 9 polymers containing a siloxanyl alkyd ester vinyl monomer. These difficulties may result from the differences in the reactivity 11 ratios between various monomers employed in the materials and 12 the chain transfer reactions during polymerization. Contact 13 lenses produced from such materials can contain significant 14 portions of unrequited monomer or monomers. This can lead to dimensional instability when these monomers leave the material.
16 The monomers can leave the lenses shortly after making the lenses 17 or over a long period ox time. When the monomers leach out 18 during use, this can have toxicological consequences.

Summary of the Invention 21 It has now been found that the dimensional stability of 22 polymeric materials useful as contact lenses and containing 23 a siloxanyl alkyd ester vinyl monomer can be greatly increased.
24 The materials can be polymerized by any of the known methods.
Such polymerization normally leaves 4% by weight or less, such 26 as typically 1 to 2%, residual unrequited monomer, mixture of ~2~4~
~702 1 monomers, oligimers and other low molecular weight materials 2 which would ordinarily leach out or exude on normal contact 3 lens use and all of which are referred to as unrequited monomer 4 in this application. In a second step, the polymerized material is treated with high energy radiation to increase the 6 degree of polymerization of the unrequited monomer and thereby 7 increase the dimensional stability of the material.
8 It is an object of this invention to provide a contact 9 lens material having good dimensional stability and which can be formed into contact lens blanks and contact lenses by con-11 ventional methods which blanks and lenses have good dimensional 12 stability and minimized unrequited monomer.
13 It is still another object of this invention to provide a 14 method for improving the dimensional stability of contact lens polymeric materials formed at least in part from siloxanyl 16 alkyd ester vinyl monomer.
17 It is still another object of this invention to use high 18 energy radiation to treat polymeric materials useful for form 19 in contact lenses, the blanks or the lenses formed from such material, with high energy radiation to improve dimensional 21 stability.
22 According to the invention a method is provided for imp 23 proving dimensional stability of polymeric materials useful 24 in forming contact lenses. The method comprises selecting a polymeric maternal polymerized from a siloxanyl alkyd ester ~204~07 1 vinyl monomer and at least one comonomer and having a minor 2 amount of unrequited monomer therein. This polymeric material 3 is then exposed to high energy radiation to reduce the amount 4 of unrequited monomer and increase dimensional stability in a second or post polymerization step. The resulting material 6 exhibits good dimensional stability.
7 Preferably the radiation is in the form of gamma rays with 8 an absorbed dosage of from 0.005 Megarads to 10 Megarads and ; 9 more preferably in the range of from 1 to 4 Megarads. Prey-drably the material is irradiated when in the form of lens 11 blanks having thicknesses of up to 1/4 inch although higher 12 thicknesses can be irradiated. The material in bulk form or the 13 final lens can be irradiated if desired.
14 It is a feature of this invention that the high energy radiation acts to sterilize the material which may be in the 16 form of contact lenses or blanks. Not only is dimensional 17 stability improved but in many cases physical properties are 1~1 pry O
18 Lowe since higher degrees of polymerization are obtained 19 when the second polymerization step is used.

21 Description of Preferred Embodiments 22 Contact lens materials are normally polymerized as in 23 rods and then rough cut to form lens blanks or lens buttons 24 which are then machined to final lens dimensions. The process 25 of this invention can be carried out at any stage of the contact 0~4~)7 1 lens manufacture. For example the rods, buttons or lenses 2 can be exposed to radiation. The lenses or buttons which are 3 normally 3/16 inch whey irradiated, can be successfully if-4 radiated to increase the degree of polymerization and drive the polymerization reaction closer to 100% reaction without 6 deteriorating the desirable physical properties of the material.
7 The high energy radiation useful in the present invention 8 generally has an energy per particle or per quantum of from 9 about 15 million electron volts (Movie.) to about 0.003 Movie.
Any of the known high energy radiation sources can be used 11 as for example those listed below:
12 Energy per Particle Radiation Wavelength or per quantum 14 x-ray 0.008-40 A 1.5-0.003 million electron volts (Movie.) O
16 gamma ray 0.0014-1.6 A 9.0-0.008 Movie.
17 accelerated electrons 5xlO 2-.08xlO 2 A 15-0.25 Movie.
18 neutron particles 5xlO 2-.O~xlO 2 A 15-0.25 Movie.
19 alpha particles 5xlO-2-.08xlO-2 A 15-0.25 Movie.
When using gamma rays, the absorbed dosage is preferably 21 in the range of from 0.005 Megarads to 10 Megarads and more 22 preferably in the range of from 1 to 4 Megarads. When using 23 x-rays, the absorbed dosage is within the ranges given for 24 gamma rays while when using electron beam irradiation, the absorbed dosage is preferably in the range of from 0.005 I I

1 Megarad to 1 Megarad. The time of exposure to irradiation 2 can vary greatly depending upon the particular materials and 3 the type of irradiation. For example, gamma radiation can be 4 carried out for periods of hours as for example 24 hours while i 5 electron beam radiation can be obtained in seconds. Prey-6 eerily the polymeric materials irradiated have been polymerized 7 by conventional polymerization reactions such as free radical 8 reactions to 4X by weight residual or unrequited monomer or 9 less and normally there remains from 1 to 2% by weight of us-reacted monomer prior to the irradiation step. The irradiation 11 step preferably carries the degree of polymerization sub Stan-12 tidally to completion greatly reducing or eliminating any amount 13 of unworked monomer present in the polymer.
14 Whole radiation to polymerize various polymeric materials is known, it is not believed known to use radiation as a 16 second step in the polymerization of contact lenses or contact ; 17 lens materials. Curing of thin coating formulations for wire 18 insulation and modification of polymeric surfaces through 19 graft polymerization is known in other areas. As long as 20 years ago it was reported in the literature Journal Polymer 21 Science 44 295 (1960) that the effects of gamma radiation on 22 polymethylmethacrylate and polyethylmethacrylate were very 23 dependent on the amount of residual monomer present in a 24 sample polymer. It has also been found that x-ray irradia-lion of polymethylmethacrylate orthopedic cement results in ~149~t)7 28/7~2 1 s~gn1ficant decrease on residual me~hylmethacrylate content 2 (American Chemical Society, Organic Coatings and Plastics, 37 3 to 205 and 210 1977).
4 In all cases the irradiation prowess is preferably carried out at room temperature in an inert atmosphere. Gamma radian 6 lion may be obtained from conventional commercl~l sources such 7 as cobalt 60 and sesame 137. X-ray radiation with energies 8 above whose ox the bonds of the polymeric material can be 9 easily obtained.
The polymer maternal useful in the present invention 11 is preferably a highly oxygen permeable contact lens compost-12 lion as known for example and described on U.S. Patent 13 3,808,178 issued April 30, 1974 entitled "Oxygen Permeable 14 Contact Lens Composition, Methods and Article of Manufacture".
That patent describes rompos~tions of matter specially adapted 16 for the production of contact lenses and hang increased Perle-17 ability and comprises solid copolymers of comonomers consist-18 in essentially of: (a) about 10 to 60 parts by weight of a 19 polysiloxanyl alkyd ester of the structure I ray 1 'I 9 21 A - -Sue (Sheehan C- SHEA
22 PA m Y
23 Hun:
24 (1) X and Y are selected from the class consisting of 2P12.~ I 7 1 Clucks alkyd groups phenol groups and Z groups, 2 (2) Z us group of the structure 4 Sue _ PA _ m 6 I is selected from the class consisting of Cluck alkyd 7 groups and phenol groups, 8 I R us selected from the class consisting of methyl 9 groups and hydrogen,

(5) m us an integer from one to five, and 11 (6) n is an integer from one to three; and 12 (b) about 40 to 90 parts by weight of an ester of a Cluck moo-13 hydric ~lkanol and an acid selected from the class consisting 14 of acrylic and methacryl~c acids.
The preferred lens materials for treatment with high 16 energy radiation in accordance with this invention are materials 17 ox the type generally described in United States patent 4,152,508 which 18 issued May 1, 1979 entitled "Improved Silicone-Containing Hard Contact 19 Lens Materials" invented by Edward J. Ellis and Joseph C. Solomon and assigned to the same assignee as the present invention.
21 Generally the preferred formulation is an oxygen permeable 22 herds machinable dimensionally stable hydrophll~c contact lens ~,~

04~V7 1 material of high transparency consisting essentially of a 2 polymer formed from (a) 30-80% by weight of a siloxanyl alkyd 3 ester monomer having the following formula:

6 R4~~Si-~Hz~-o- C - C = Chihuahuas g Assay I
I
11 where Al is selected from the class of hydrogen or methyl 12 groups, "a" is an integer from one to three, "b" and "c" are 13 integers from zero to two, "d" is an integer from zero to 14 one, A is selected from the class of methyl or phenol groups, R2 is selected from the class of methyl or phenol groups, 16 R3 and R4 represent either no group(cycllc ring from "c" to "d") 17 or methyl or phenol groups, 18 (b) 5 to 60% by weight of an itaconate moo- or dip ester, 19 (c) 1 to 60 parts by weight of an ester of a Cluck moo-hydric or polyhydric alkanol or phenol and an acid selected 21 from the class consisting essentially of acrylic and methacrylic 22 acid, 23 (d) 0.1 to 10% by weight of a cross-linking agent, 24 (e) 1 to 20% by weight of a hydrophilic monomer to impart hydrophil;c properties to the surface of the contact lens material 26 of this invention.

go 1 Generally the copolymers useful in this invention can 2 be formed from 10 to 90% by weight ox a siloxanyl alkyd ester 3 monomer or mixtures thereof, and from 10 to 90% by weight of an or 4 itaconate ester from 10 to 90% by weight of an acrylate or methacrylate ester. Mixtures of an itaconate ester with 6 an acrylate or methacrylate ester totaling 10 to 90% by

7 weight are generally preferred since they exhibit the broader

8 balance of lens properties. Other necessary ingredients as

9 known in the art such as initiators, cross-linking agents, wetting agents, colorants and the like can be added to the 11 polymeric materials as is known.
12 The general formula for useful polymeric materials is as 13 hollows:
14 The siloxanyl alkyd ester monomers useful in this invention preferably have the following formula:

17 A it 19R4~0~Si-O-S~-(CH2)a-0-C-C=CH2 A isle -21 Assay I

23 Where Al is selected from the class of hydrogen or methyl 24 groups, "a" is an integer from one to three, I'm" and "c" are integers from zero to two, A is selected from the class of 26 methyl or phenol groups, R3 and R4 represent either no group 27 (cyclic ring from "c" to "d") or methyl or phenol groups, 28 "d" is an integer from zero to one.

-10-~2044~)7 1 Representative s;loxanyl alkyd ester monomers which could 2 be utilized in this invention include 3methacryloyloxymethyl pentamethyldisiloxane 5 Ho SHEA Al Ho SHEA 0-Si-CH2-0-C-C=CH2 9methacryloyloxypropyl tris(trimethylsilyl)siloxane

11 Ho

12 CH3-5~i-CH3

13 SHEA SHEA
SHEA- I Ho -C=CH2 16 CH3-Si-CH3 I
19methacryloyloxymethyl heptamethylcyclotetrasiloxane 22 Sue SHEA 0/ ~H2-0-C-C=CH2 SHEA 'SHEA

~Z~44(~7 8/7~2 1 methacryloyloxypropyl heptamethylcyclotetraslloxane 4 C ~sjCH3 6 OH Ho 8 Ho SHEA I H 0-C-C=CH2 8 Swahili SHEA SHEA
The itaconate esters useful in the present invention have 11 the following structure:

13 SHEA = C

14 SHEA
OWE
I
17 X and Y are the same or different and are hydrogen, methyl 18 or phenol groups. Representative moo- and dip itaconate 19 esters include methyl itaconate 21 dim ethyl itaconate 22 phenol itaconate 23 diphenyl taco Nate 24 methyl phenol itaconate The fracture strength adding material is an ester of ~7C2 1 a Cluck mandrake or polyhydric alkanol, or phenol and an : 2 acid selected from the class consisting of acrylic and moth-3 acrylic acid. Such esters include:
4 methyl methacrylate methyl phenylacrylate 6 phenol methacrylate 7 cyclohexyl methacrylate - 8 Examples of cross-linking agents include polyfunctional 9 derivatives of acrylic acid methacrylic acid, acrylamide, methacrylamide and multi-Yinyl substituted benzenes, including 11 but not limited to the following:
12 ethylene glycol d;acrylate or dimethacrylate 13 diethylene glycol diacrylate or dimethacrylate 14 tetraethylene glycol diacrylate or dimethacrylate polyethylene glycol diacrylate or dimethacrylate 16 trimethylolpropane triacrylate or trimethacrylate 17 Bisphenol A diacrylate or dimethacrylate 18 ethoxylated Bisphenol A diacrylate or dimethacrylate 19 pentaerythritol in- and tetraacrylate or methacrylate tetramethylenediacrylate or dimethacrylate 21 Mullen bisacrylamide or methacrylamide 22 dim ethylene bisacrylamide or methacrylamide 23 N,N'-dihydroxyethylene blsacrylamide or methacrylamide 24 hexamethylene bisacrylamide or methacrylamide decamethylene bisacrylamide or methacrylamide 26 divinely Bunsen _ _ _ ~2~4~4V7 3/70~

1 The wettable surface is provided by the inclusion of hydra- ', 2 Philip neutral monomers, hydrophil;c kink monomers and 3 hydrophilic anionic monomers and mixtures of these.
4 The classes of these compounds are hydrophilic acrylates and methacrylates, acrylamides, methacrylamides, and vinyl 6 lactams. Representative hydrophilic neutral monomers include:
7 2~hydroxyethyl acrylate or methacrylate 8 N-vinylpyrrolidone 9 acrylamide methacrylamide 11 glycerol acrylate or methacrylate 12 2-hydroxypropyl acrylate or methacrylate 13 polyethylene glycol monoacrylate or methacrylate 14 The kink monomers either can be initially in their charged form or are subsequently converted to their charged form after 16 formation of the contact lens. The classes ox these compounds 17 are derived prom basic or cat ionic acrylates, methacrylates, 18 acrylamides, methacrylam;des, vinylpyridines, vinylimidazoles, 19 and diallyldialkylammonium polymerizable groups. Such monomers are represented by:
21 N,N-dimethylaminoethyl acrylate and methacrylate 22 2-methacryloyloxyethyltrimethylammonium chloride and 23 methyl sulfate 24 2-, 4-, and 2-methyl-5-vinylpyridine 2-, 4-, and 2~methyl-5-vinylpyridinium chloride and 26 methyl sulfate ~2044~7 l ~-(3-methacrylamidopropyl)-N,N-dimethylamine 2 N-(3-methacrylamidopropyl)-N,N,N-trimethylammoniumm ; 3 chloride 4 l-v;nyl- and 2-methyl-l~vinyl~midazole l-vinyl- and 2-methyl-l-vinylimidazolium chloride 6 and methyl sulfate 7 N-(3-acrylamido-3~methylbutyl)-N,N-dimethylamine 8 N-(3-acrylam~do-3-methylbutyl)-N,N,N-trimethylammoopium : 9 chloride lo N-(3-methacryloyloxy-2-hydroxylpropyl)-N,N,N-trimeethyl-if ammonium chloride 12 diallyldimethylammonium chloride and methyl sulfate 13 The anionic monomers either are in their neutral form initially 14 or are subsequently converted to their anionic form. These classes of compounds include polymerizable monomers which contain 16 car boxy, sulfonate~ and phosphate or phosphonate groups. Such 17 monomers are represented by:
18 acrylic acid lo methacrylic acid I sodium acrylate and methacrylate 21 vinylsulfonic acid 22 sodium vinylsulfonate 23 p-styrenesulfonic acid 24 sodium p-styrenesulfonate 2-methacryloyloxyethylsulfonic acid v Jo ~2~:1144~)7 ~8/702 1 3-methacryloyloxy-2-hydroxypropylsulfonic acid 2 2-acrylamido-2-methylpropanesulfonic acid 3 al7ylsulfonic acid 4 2-phosphatoethyl methacrylate The copolymers described in thus invention are prepared 6 by radical polymerization through the incorporation of a free 7 radical initiator. The initiator is chosen from those 8 commonly utilized to polymerize vinyl type monomers and would 9 include the following representative initiators:
2,2'-azo-bis-isobutyronitrile 11 4,4'-azo-bis-(4-cyanopentanoic acid) 12 t-butyl peroctoate 13 bouncily peroxide 14 laurel peroxide methyl ethyl kitten peroxide 16 diisopropyl peroxycarbonate 17 The free radical initiator is normally used in amounts of from 18 0.01 to 2% by weight of the entire compound.
19 The materials of this invention can be polymerized directly in a suitable mold to form contact lenses. The materials are 21 all thermosetting and thus various methods of fabrication can 22 be used. It is preferable to polymerize into sheet or rod stock 23 from which contact lenses may be machined.
24 It us preferred to use the conventional approach when forming contact lenses such as used for polymethyl methacrylate sty '702 1 (PUMA). In this approach, the formulations are polymerized 2 directly into a sheet or rod and the contact lens blanks are 3 cut as buttons, discs or other preformed shapes which are then 4 machined to obtain the lens surfaces and the final lens form.
The resulting polymeric stock of buttons possesses the optical 6 qualities necessary to produce aberration-free oxygen permeable, ; 7 hard contact lenses in accordance with this invention.
8 Of course when referring to the-polysiloxanyl alkyd 9 ester vinyl monomer in the polymers of this invention, more than one can be used in place of a single monomer as is true 11 with each of the monomeric recitations. Thus one or two 12 itaconate esters can be used in place of a single ester if 13 desired.
14 The following examples are given to illustrate the invent lion and are not to be considered limiting thereof:

3lZ0~4~7 2 A hard, oxygen permeable contact lens formulation was pro-3 pared prom a comonomer mixture of dim ethyl itaconate (DIM), 4 methyl methacrylate (MA), methacryloyl oxypropyl tris(trimethyl-5 sill) selection (TRIP), methacrylic acid (MA), and tetraethylene 'I
6 glycol dimethacrylate (TEGDM) using the free radical initiator 7 2,~'-azobisisobutyronitrile (AIBN). The formulation components 8 (shown in TABLE I in parts by weight) were thoroughly mixed, 9 transferred to test tubes, stopper Ed, degassed, then filled with nitrogen. The test tubes were then placed on a water bath at 11 40C and allowed to polymerize for two days. The tubes were 12 then placed in a 60C oven for an additional two days, after 13 which the solid rods are removed from the tubes. The rods were 14 then subjected to conditioning for approximately eighteen hours at 100C under vacuum then slowly cooled to room temperature 16 to produce a stress-free material. The conditioned rods were 17 then machined to discs of the size 3/16" by 1/2", which are of 18 the conventional form for hard polymethyl methacrylate lens lug blanks.
The finished discs were then subjected to gamma radiation 21 in a Gamma Cell 200 instrument (made by Atomic Energy of Canada 22 Limited of Ottawa, Canada). The cell contained 1230 curies of 23 Cobalt 60 in the form of 20 pencils which produced a central 24 dose rate of 2.12 x 105 fads per cm3 per noun. The discs were I irradiated under a nitrogen atmosphere and the total time of 26 exposure was adjusted to produce a total dose absorbed in the 27 material of from 1x106 fads (lMR) to 5x1O6 fads (5 MY).

~2~4407 1 Both irradiated and non-irradiated discs were subjected 2 to distilled water extraction for 6 hours at 75C. The extract 3 was diluted to loom with distilled water and ultra violet 4 absorbency measurements were performed at three wavelengths.
The data in TABLE I clearly demonstrate the ability of gamma 6 radiation to significantly reduce the content of extractable 7 (residual) material i.e. unrequited monomer, in the lens blanks.

_19_ 12~44?Q7 ' 702 TABLE I
2 FORMULATION (parts by weight) 3 DIM 27. 5 4 MA 2 7.5 TRIP 45.0 6 TO GYM 3.0 7 MA 5.0 8 AIBN 0. 2 1 0 Sample wet gut, US Absorbency . of extract Radiation level ems (grams) 205 no 215 no 245 no nanometers) O MY, control 3.343 û.775 0.395 0.0795 MY 3.330 0.214 0.122 0.025 2 MY 3.400 0.089 0.052 0.015 3 MY 3.410 0.075 0.041 0.0115 4 MY 3.4û9 0.045 0.0225 0.009 MY 3.371 0.0315 0.015 0.003 I

~;2(114~7 ~702 2 The hard, oxygen permeable lens formulation given in TABLE
3 II was prepared using the experimental procedures detailed in 4 Example I. The lens blanks were gamma irradiated under a vitro-5 gun atmosphere to various total delivered dosages. Contact ', 6 lenses were prepared from these discs utilizing techniques 7 which are common in the manufacture of hard contact lenses.
8 The test lenses were standardized to the following prescript 9 lion:
Base curve radius 7.95 mm 11 Power -7.0 dotters 12 Central thickness 0.12 mm 13 Diameter 12 mm 14 The base curve of each lens was noted after manufacture and no-checked after two days immersion in distilled water. The change 16 in the base curve radius as a function of radiation dosage is 17 presented in TABLE II and illustrates the effectiveness of the 18 gamma radiation process as a means of imparting dimensional 19 stability to contact lens.

~Z~14~07 t702 TABLE II

Formulation (parts by weight) DIM 27.5 MA 27.5 TRIP 4~.0 TEGDM 5,0 MA 5.0 AIBN 0.2 Original Base curve* Dimensional Radiation dosage base curve, mm After soak, mm change, mm O MY, control 7.94 7.96 8.04-8.08 0.09-0.12 flattening 3 MY 7.94-7.96 7.97-8.01 0.03-0.05 flattening 5 MY 7.94-7.96 7.94-7.97 0.00-0.02 flattening**

* average of several test lenses ** within acceptable limits ~Z04407 EXAMPLE I I I
2 The hard, oxygen permeable lens formulations given in 3 TABLE III were prepared using the experimental procedures de-4 tailed in Example I. The lens blanks were gamma irradiated under a nitrogen atmosphere to various total delivered dosages.
6 Compressive strength at yield was determined using a TUNIS-7 OLSEN testing machine under the following conditions:
8 Sample size - 3/16" x 1/2"
9 Temperature - 73~F
Testing rate - 0.05 inhuman 11 Multiple determinations were made and the average values are 12 reported in TABLE III. It is evident from the data that the 13 compressive strength of the lens materials is significantly 14 improved by radiation treatment at total levels as low as 2 Megarads.

~2C~44~7 ', Formulation (parts by weight) A B C
DIM 27.5 27.5 27.5 MA 27.5 27.5 27.5 TRIP 45.0 45.0 45.0 TEGDM 3.0 4.0 5.0 MA 5.0 5.0 3.0 DMAEM* - - 2.0 AIBN 0.2 0.2 0.2 * dim ethyl amino ethyl methacrylate Compressive strength at yield (psi) Sample MY 2 MR4 MY 6 MY 8 MY 10 MY
_ Aye 13,340 13,240 13,290 13,450 13,500 B10,965 12,430 12,270 12,170 12,020 12,120 C9,270 12,070 11,710 12,320 12,220 11,920 Average deviation + 200 Sue ~2~Q~

2 The hard oxygen permeable lens formulation given in Table 3 III was prepared using the procedure detailed in Example I. The lens blanks were irradiated with both electron beam and with 5 gamma while under a nitrogen atmosphere. i' 6 Standard permeability samples in the form of piano contact 7 lenses were machined from these samples to the following prescript 8 lion:
g Base curve radius - 8.00 mm Power - Piano 11 Central Thickness - .20 mm 12 Diameter - 12.0 mm 13 Permeability was measured in an instrument designed after 14 ASTM D1434-66 wherein one side of the sample is subjected to pure oxygen at a pressure of one atmosphere above atmospheric.
16 The oxygen that permeates through the lens sample is allowed 17 to expand on the other side of the sample against atmospheric 18 pressure in a capillary tube plugged with a droplet of mercury.
19 Rate of motion of the mercury plug is easily converted into volume of paramount per unit time.
21 The system was calibrated by measurements made on materials 22 of known permeability.
23 Multiple determinations were made and average values are 24 reported in Table IV. This table shows that useful 2 Perle-ability values are maintained after irradiation.

-~2C~4407 TABLE IV
.
Megarads Radiation Dose Radiation Type Permeability*
0 - 1~8 .005 Electron Beam 119 I " " 134 .1 " " 118 1 Gamma 119 2 " 119 3 " 115 4 " 114 " 110 *Permeability is given as 101 cm3-mm/sec,cm2,cmHg .

I

SUE

1 Chile specific examples of this invention have been shown 2 and described, many variations are possible. Such variations 3 include the use of mixtures of monomers within the components 4 to make up the required percentages of each. For example, two or more siloxanyl alkyd ester monomers can be used instead 6 of a single such monomer for that component of the system.
7 Similarly, two or more cross-linking agents can be used.
8 Conventional additives to the lenses such as colorants, tints 9 and the like may also be employed within the normal ranges of such materials. In all cases, high energy radiation is used 11 to act as a second step or post polymerization in an attempt 12 to substantially completely polymerize polymeric material and 13 thus improve dimensional stability and lower unrequited monomer 14 to 1/2% by weight or less.
It is preferred that the contact lenses of the present 16 invention and the materials from which they are made have an 17 oxygen permeability in the range of from 38 to 500 cm3mm/cm2/
18 sec. cm Hug x 10-1 and a Rockwell hardness value of from 100 19 to 125 ASTM d-785 R scale and be formed of a polymer of dim ethyl itaconate, methylmethacrylate, methacryloxyloxypropyl iris 21 (trimethylsilyl) selection, methacrylic acid and tetraethylene 22 glycol dimethacrylate. Such lenses can be worn in the eye 23 of a user for long time periods.

Claims (25)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A method of improving dimensional stability of polymeric materials useful for hard contact lenses, said method comprising selecting a polymeric material formed from a siloxanyl alkyl ester vinyl monomer and at least one other organic unsaturated comonomer copolymerized to a solid state having a minor amount of unreacted monomer and exposing said material to high energy radiation to reduce the amount of unreacted monomer and improve dimensional stability.

2. A method in accordance with the method of claim 1 wherein said polymeric material is an oxygen permeable material.

3. A method in accordance with the method of claim 1 wherein said polymeric material consists essentially of a polymer formed from (a) 30-80% by weight of a siloxanyl alkyl ester monomer having the following formula:

where R1 is selected from the class of hydrogen or methyl groups, "a" is an integer from one to three, "b" and "c" are integers from zero to two, "d" is an integer from zero to one, A is selected from the class of methyl or phenyl groups, R2 is selected from the class of methyl or phenyl groups, R3 and R4 represent either no group(cyclic ring from "c" to "d") or methyl or phenyl groups, (b) 5 to 60% by weight of an itaconate mono- or di- ester, (c) 1 to 60 parts by weight of an ester of a C1-C20 mono-hydric or polyhydric alkanol or phenol and an acid selected from the class consisting essentially of acrylic and methacrylic acid, d) 0.1 to 10% by weight of a cross-linking agent, e) 1 to 20% by weight of a hydrophilic monomer to impart hydrophilic properties to the surface of the contact lens material of this invention.

4. A method in accordance with clam 3 wherein said siloxanyl alkyd ester monomer (a) is present in an amount of from 40 to 55% by weight, said itaconate ester (b) is present in an amount of from 20 to 40% by weight, said ester (c) is present in an amount of from 20 to 40% by weight, said cross-linking agent is present in an amount of from 0.1 to 10% by weight, and said hydrophilic monomer is present in an amount of from 1 to 20% by weight of the entire composition.

5. A method of improving dimensional stability of materials useful for hard contact lenses, said method comrpising selecting a polymeric material which is a solid copolymer of comonomers consisting essentially of:
(a) about 10 to 60 parts by weight of a polysiloxanyl-alkyl ester of the structure wherein:
(1) X and Y are selected from the class consisting of C1-C5 alkyl groups, phenyl groups and Z groups, (2) Z is a group of the structure (3) A is selected from the class consisting of C1-C5 alkyl groups and phenyl groups, (4) R is selected from the class consisting of methyl groups and hydrogen, (5) m is an integer from one to five, and (6) n is an integer from one to three; and (b) about 40 to 90 parts by weight of an ester of a C1-C20 monohydric alkanol and an acid selected from the class consisting of acrylic and methacrylic acids, said copolymer having a small amount of unreacted monomer, and exposing said copolymer to high energy radiation to reduce the amount of unreacted monomer and improve dimensional stability.

6. A method of improving dimensional stability of materials useful for hard contact lenses, said method comprising selecting a solid copolymeric material from a siloxanyl alkyl ester vinyl monomer and monomer selected from the group consisting essentially of itaconate ester, acrylate ester, methacrylate ester and mixtures thereof, said material having unreacted monomer present therein, and treating said material with high energy radiation to reduce the amount of unreacted monomer and improve dimen-sional stability.

7. A method in accordance with the method of claim 6 wherein said siloxanyl alkyl ester vinyl monomer has the following formula:

where R1 is selected from the class of hydrogen or methyl groups, "a" is an integer from one to three, "b" and "c" are integers from zero to two, A is selected from the class of methyl or phenyl groups, R2 is selected from the class of methyl or phenyl groups, R3 and R4 represent either no group (cyclic ring from "c" to "d") or methyl or phenyl groups, "d" is an integer from zero to one.

8. In a method of making oxygen permeable hard contact lenses from polymeric materials formed from two or more monomers where one of said monomers is a siloxanyl alkyl ester and having less than about 4% by weight unreacted monomer present therein, the improvement comprising treating said materials with high energy radiation in the range of from 15 Me.v. to 0.003 Me.v. to reduce the amount of unreacted monomer and improve dimensional stability.

9. A method in accordance with the method of claim 1 wherein said high energy radiation is gamma radiation and said polymeric material absorbs from 0.005 Megarads to 10 Megarads of said radiation.

10. A method in accordance with the method of claim 3 wherein said high energy radiation is gamma radiation and said polymeric material absorbs from 0.005 Megarads to 10 Megarads of said radiation.

11. A method in accordance with the method of claim 5 wherein said high energy radiation is gamma radiation and said polymeric material absorbs from 0.005 Megarads to 10 Megarads of said radiation.

12. A method in accordance with the method of claim 6 wherein said high energy radiation is gamma radiation and said polymeric material absorbs from 0.005 Megarads to 10 Megarads of said radiation.

13. A method in accordance with the method of claim 1 wherein said high energy radiation is selected from the class consisting of x-ray radiation, gamma ray radiation, accelerated electron radiation, neutron particle radiation and alpha particle radiation.

14. A method in accordance with the method of claim 3 wherein said high energy radiation is selected from the class consisting of x-ray radiation, gamma ray radiation, accelerated electron radiation, neutron particle radiation and alpha particle radiation.

15. A method in accordance with the method of claim 5 wherein said high energy radiation is selected from the class consisting of x-ray radiation, gamma ray radiation, accelerated electron radiation, neutron particle radiation and alpha particle radiation.

16. A method in accordance with the method of claim 6 wherein said high energy radiation is selected from the class consisting of x-ray radiation, gamma ray radiation, accelerated electron radiation, neutron particle radiation and alpha particle radiation.

17. A method in accordance with the method of claim 3 wherein said polymeric material contains no more than about 4% by weight of unreacted monomer prior to said exposure to high energy radiation and less than 1/2% by weight of un-reacted monomer after exposure to said high energy radiation.

18. A method in accordance with the method of claim 5 wherein said polymeric material contains no more than about 4% by weight of unreacted monomer prior to said exposure to high energy radiation and less than 1/2% by weight of un-reacted monomer after exposure to said high energy radiation.

19. A method in accordance with the method of claim 6 wherein said polymeric material contains no more than about 4% by weight of unreacted monomer prior to said exposure to high energy radiation and less than 1/2% by weight of un-reacted monomer after exposure to said high energy radiation.

20. A method in accordance with the method of claim 8 wherein said polymeric material contains no more than about 4%
by weight of unreacted monomer prior to said exposure to high energy radiation and less than 1/2% by weight of unreacted monomer after exposure to said high energy radiation.

21. The improved polymeric product having good dimensional stability produced by the process of claim 1.

22. The improved polymeric product having good dimensional stability produced by the process of claim 3.

23. The improved polymeric product having good dimensional stability produced by the process of claim 5.

24. The improved polymeric product having good dimensional stability produced by the process of claim 6.

25. method in accordance with the method of claim 1 wherein said polymeric material contains no more than about 4%
by weight of unreacted monomer prior to said exposure to high energy radiation and less than 1/2% by weight of unreacted monomer after exposure to said high energy radiation.