Thermoplastic silicone-containing composition are useful as a hydrogel contact lens material. The compositions are based on polymers including a siloxane segment and a highly hydrophilic segment.

BACKGROUND OF THE INVENTION 
The present invention generally relates to thermoplastic 
silicone-containing materials useful as a hydrogel contact lens material. 
Hydrogels represent a desirable class of materials for many biomedical 
applications including contact lenses. Hydrogels are hydrated, 
cross-linked polymeric system that contain water in an equilibrium state. 
Silicone hydrogels are a known class of hydrogels and are characterized by 
the inclusion of a silicone-containing material. Typically, a 
silicone-containing monomer is copolymerized by free radical 
polymerization with a hydrophilic monomer, with either the 
silicone-containing monomer or the hydrophilic monomer functioning as a 
crosslinking agent (a crosslinker being defined as a monomer having 
multiple polymerizable functionalities) or a separate crosslinker may be 
employed. Such silicone hydrogels, based on polyurethanes, are disclosed 
in U.S. Pat. No. 5,034,461, for example. An advantage of silicone 
hydrogels over non-silicone hydrogels is that the silicone hydrogels 
typically have higher oxygen permeability due to the inclusion of the 
silicone-containing monomer. Because such hydrogels are based on monomers 
polymerizable by free radical, these materials are thermosetting polymers. 
The present invention provides a class of silicone hydrogel materials that 
are thermoplastic. These materials can be cast into articles such as 
contact lenses by methods other than free radical polymerization, for 
example, by compression molding or injection molding. The materials 
include a silicone-containing moiety and a highly hydrophilic moiety, thus 
the materials exhibit relatively high oxygen permeability while being able 
to absorb and retain water. When cast into contact lenses, the materials 
are optically clear, and the materials are stable at relatively high 
temperatures. 
SUMMARY OF THE INVENTION 
This invention provides a thermoplastic silicone-containing composition, 
useful as a hydrogel contact lens material, represented by the formula 
(I): 
##STR1## 
wherein M is a hydrophilic radical derived from a hydrophilic 
ethylenically unsaturated monomer and having a molecular weight of about 
500 to 5000; 
each R is independently selected from an alkylene group having 1 to 10 
carbon atoms wherein the carbon atoms may include ether, urethane or 
ureido linkages therebetween; 
each R' is independently selected from hydrogen, monovalent hydrocarbon 
radicals or halogen substituted monovalent hydrocarbon radicals wherein 
the hydrocarbon radicals have 1 to 18 carbon atoms which may include ether 
linkages therebetween; 
a is an integer equal to or greater than 1; 
each Z is independently a divalent urethane or ureido segment; 
and x is greater than or equal to 1, and y is greater than or equal to 1. 
The invention further relates to contact lenses formed on the 
above-described silicone-containing composition. 
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The thermoplastic polymers of this invention include units of the general 
formula (I), represented above. 
The thermoplastic polymers include a silicone-containing segment. More 
particularly, this silicone-containing segment is derived from 
polysiloxanes endcapped with hydroxyl or amino radicals: 
##STR2## 
wherein each A is hydroxyl or amino radical; each R is independently 
selected from an alkylene group having 1 to 10 carbon atoms wherein the 
carbon atoms may include ether, urethane or ureido linkages therebetween; 
each R' is independently selected from hydrogen, monovalent hydrocarbon 
radicals or halogen substituted monovalent hydrocarbon radicals wherein 
the hydrocarbon radicals have 1 to 18 carbon atoms which may include ether 
linkages therebetween, and 
a is an integer equal to or greater than 1. 
Preferred R' radicals include: alkyl groups, phenyl groups, 
fluoro-substituted alkyl groups and alkenyl groups. Preferred R' radicals 
are alkylene, preferably butylene. Preferably, a is about 10 to about 100, 
more preferably about 15 to about 60. 
The thermoplastic polymers also include a highly hydrophilic segment, 
represented by the "M" moiety in Formula (I). More particularly, this 
hydrophilic segment can be prepared from an ethylenically unsaturated 
hydrophilic monomer, preferably an amino-substituted (meth)acrylamide or 
an N-vinyl lactam. Most preferred hydrophilic monomers are 
N,N-dimethylacrylamide (DMA) and N-vinyl pyrrolidone (NVP). The "M" moiety 
in Formula (I) is conveniently derived from prepolymers of the 
aforementioned hydrophilic monomers, such prepolymers being endcapped with 
hydroxyl or amino radicals as in Formula (II): 
EQU A'--(M').sub.n --(A").sub.m 
wherein: 
A' is derived from a chain transfer agent and includes a terminal hydroxyl 
or amino radical; 
A" is derived from an ethylenically unsaturated monomer that includes a 
terminal hydroxyl or amino radical; 
M' is derived from the hydrophilic ethylenically unsaturated monomer, such 
as the preferred DMA and NVP; 
m is an integer of 1 or greater, and preferably 1; and 
n is about 5 to 50. 
A" in Formula (II) is derived from a chain transfer agent. More 
specifically, the hydrophilic ethylenically unsaturated monomer M' is 
polymerized in the presence of the chain transfer agent which serves to 
control the molecular weight of the resultant polymer and provides 
hydroxy- or amino- functionality to the resultant polymer. Suitable chain 
transfer agents include mercapto alcohols (also referred to as 
hydroxymercaptans) and aminomercaptans. Preferred chain transfer agents 
include 2-mercaptoethanol and 2-aminoethanethiol. Accordingly, the chain 
transfer agent forms a terminal end of the hydrophilic polymer, with the 
hydroxy radical (in the case of a mercapto alcohol) providing the 
resultant polymer with terminal hydroxyl functionality, and the amino 
radical (in the case of a aminomercaptan) providing the resultant polymer 
with terminal amino functionality. Generally, the molar ratio of chain 
transfer agent to this hydrophilic monomer precursor will be about 1:5 to 
about 1:100. 
The ethylenically unsaturated hydrophilic monomer and the chain transfer 
agent are copolymerized with another monomer having ethylenic unsaturation 
and a hydroxy- or amino-radical (A" in Formula (II)). Accordingly, this 
additional monomer is also copolymerized with the hydrophilic monomer and 
also provides terminal hydroxy- or amino-functionality to the resultant 
polymer. Suitable monomers include alcohol esters of (meth)acrylic acid 
such as 2-hydroxyethylmethacrylate (Hema), allyl alcohol, amino esters of 
(meth)acrylic acid such as 2-t-butyl-aminoethylmethacrylate, and 
allylamine. Generally, this hydroxy- or amino-containing ethylenically 
unsaturated monomer will be at a 1:1 molar ratio to the chain transfer 
agent. 
Representative reaction schemes for these hydrophilic precursors of Formula 
(II) are illustrated as follows: 
nDMA+HOCH.sub.2 CH.sub.2 SH+CH.sub.2 .dbd.C(CH.sub.3)COOCH.sub.2 CH.sub.2 
OH.fwdarw.HOCH.sub.2 CH.sub.2 S-(DMA)n--CH.sub.2 C(CH.sub.3)COOCH.sub.2 
CH.sub.2 OH 
nDMA+H.sub.2 NCH.sub.2 CH.sub.2 SH+CH.sub.2 .dbd.C(CH.sub.3)COOCH.sub.2 
CH.sub.2 NHC(CH.sub.3).sub.3 .fwdarw.H.sub.2 NCH.sub.2 CH.sub.2 
S-(DMA).sub.n --CH.sub.2 C(CH.sub.3)COOCH.sub.2 CH.sub.2 NH 
C(CH.sub.3).sub.3 
nNVP+HOCH.sub.2 CH.sub.2 SH+CH.sub.2 .dbd.CHCH.sub.2 OH.fwdarw.HOCH.sub.2 
CH.sub.2 S-(NVP)n--CH.sub.2 CH.sub.2 CH.sub.2 OH 
nNVP+H.sub.2 NCH.sub.2 CH.sub.2 SH+CH.sub.2 .dbd.CHCH.sub.2 NH.sub.2 
.fwdarw.H.sub.2 NCH.sub.2 CH.sub.2 S-(NVP)n--CH.sub.2 CH.sub.2 CH.sub.2 
NH.sub.2 
where (DMA).sub.n is 
##STR3## 
and (NVP).sub.n is 
##STR4## 
Such synthesis methods will generally involve thermal polymerization by 
methods generally known in the art. Representative detailed syntheses of 
preferred precursors of Formula (II) are described in the Examples. 
The aforementioned silicone-containing segment and hydrophilic segment are 
linked via "hard" segments, represented by "Z" in Formula (I). These 
"hard" segments are based on urethane/urea chemistry. More specifically, 
these "hard" segments are based on diisocyanates that react with hydroxyl- 
or amino-functionality, respectively, of the silicone-containing segments 
and hydrophilic segments. 
Generally, any diisocyanate may be employed. These diisocyanates may be 
aliphatic or aromatic, and include alky, alkyl cycloalkyl, cycloalkyl, 
alkyl aromatic and aromatic diisocyanates preferably having 6 to 30 carbon 
atoms in the aliphatic or aromatic moiety. Specific examples include 
isophorone diisocyanate, hexamethylene-1,6-diisocyanate, 
4,4'-dicyclohexylmethane diisocyanate, toluene diisocyanate, 4,4'-diphenyl 
diisocyanate, 4,4'-diphenylmethane diisocyanate, p-phenylene diisocyanate, 
1,4-phenylene 4,4'-diphenyl diisocyanate, 1,3-bis-(4,4'-isocyanto methyl) 
cyclohexane, and cyclohexane diusocyanate. Other examples are 
diisocyanates which are the reaction product of a diisocyanate and a 
short-chain diol at a 2:1 molar ratio. 
The "hard" segments forming the "Z" moiety in Formula (I) are preferably 
further based on a relatively low molecular weight diol or glycol. These 
include an alkyl diol, a cycloalkyl diol, an alkyl cycloalkyl diol, an 
aryl diol or an alkylaryl diol having 1 to 40 carbon atoms and which may 
contain ether, thio or amine linkages in the main chain. Specific examples 
include 2,2-(4,4'-dihydroxydiphenyl)propane (bisphenol-A), 
4,4'-iso-propylidine dicyclohexanol, ethoxylated and propoxylated 
bisphenol-A, 2,2-(4,4'-dihydroxydiphenyl)pentane, 
1,1'-(4,4'-dihydroxydiphenyl)-p-diisopropyl benzene, 1,3-cyclohexane diol, 
1,4-cyclohexane diol, 1-4-cyclohexane dimethanol, neopentyl glycol, 
1,4-butanediol, 1,3-propanediol, 1,5-pentanediol, diethylene glycol and 
triethylene glycol. Especially preferred are alkyl and oxyalkylene diols 
having 1 to 10 carbon atoms. 
Accordingly, a preferred class of thermoplastic polymers may be represented 
by the formula (III): 
##STR5## 
wherein: M is the hydrophilic radical derived from a hydrophilic 
ethylenically unsaturated monomer, as in Formula (I); 
R, R' and a are as previously defined; 
each X is independently a urethane or ureido linkage; 
each R.sup.2 is independently a divalent residue of a diisocyanate; 
each R.sup.3 is independently a divalent residue of a diol or glycol; 
and x is greater than or equal to 1, and y is greater than or equal to 1. 
Methods for forming thermoplastic urethane or urea polymers are known in 
the art, and representative synthesis is illustrated in the Examples. 
The polymers can be cast into shaped articles, such as contact lenses, by 
methods such as injection or compression molding. More specifically, the 
polymers are charged to a mold cavity having the desired shape of a 
contact lens and then cured to form a thermoplastic polymer, with the 
addition of heat to facilitate curing if desired. The mold may be formed 
of two mold sections, one mold section shaped to form the anterior lens 
surface and the other mold section shaped to form the posterior lens 
surface two mold sections, and may be either plastic or metal. A 
polymerization initiator may be included in the material charged to the 
mold to facilitate curing, for example, thermal curing. 
When used in the formation of contact lenses, it is preferred that the 
subject thermoplastic polymers, when hydrated, form hydrogels having water 
contents of at least 5 weight percent and more preferably at least 10 
weight percent. Furthermore, it is preferred that such hydrogels have a 
Young's modulus of elasticity from about 20 g/mm.sup.2 to about 150 
g/mm.sup.2, and more preferably from about 30 g/mm.sup.2 to about 100 
g/mm.sup.2, and a tear strength of at least 2 g/mm.

As an illustration of the present invention, several examples are provided 
below. These examples serve only to further illustrate various preferred 
embodiments of the invention and should not be construed as limiting the 
invention. 
EXAMPLE 1 
Synthesis of Hydroxyl-Terminated 12Repolymer of Formula (II) Based on DMA 
To a dried 500-ml round bottom flask was added N,N-dimethylacrylamide (DMA, 
79.2 g/0.799 mole), 2-hydroxyethylmethacrylate (Hema, 13 g/0.0998 mole) 
and anhydrous tetrahydrofuran (THF, 200 ml). The contents were flushed 
with nitrogen and 2-mercaptoethanol (7.8 g/0.0998 mole) and 
2,2-azobisisobutyronitrile (AIBN, 0.8 g/0.5 mole % of DMA) were added. The 
mixture was heated at 60.degree. C. for 5 hours and poured into a beaker 
containing ether to precipitate the product. The hydroxyl-equivalent 
weight as determined by titration (addition of excess isophorone 
diisocyanate to react with OH groups in the prepolymer, and then addition 
of excess di-n-butylamine to react with isocyanate groups, followed by 
titration with HCl) was 480. 
EXAMPLE 2 
Synthesis of Thermoplastic Polymer of Formula (I) 
To a dried 3-neck round bottom 500-ml flask was added the 
hydroxyl-terminated prepolymer of Example 1 (4.8284 g/0.00504 mole) and 30 
ml of dry methylene chloride. The mixture was stirred until complete 
dissolution. Then, .alpha., .omega.-bis(hydroxybutyl) polydimethylsiloxane 
having an average molecular weight of about 5000 (PDMS, 20.3886 g/0.00504 
mole), diethylene glycol (2.1441 g/0.0202 mole), isophorone diisocyanate 
(IPDI, 6.7243 g/0.03025 mole), dibuytltin dilaurate (0.1032 g) and 200 ml 
of methylene chloride were added. The contents were refluxed under 
nitrogen. Samples of the reaction product were taken periodically for 
measurement of IR spectrum, and the reaction was terminated after about 
120 hours when the isocyanate peak (about 2270 cm.sup.-1) disappeared from 
IR spectrum of the reaction product. The solvent was then stripped with 
methylene chloride under vacuum to give the polymeric product (number 
average molecular weight Mn 11400, molecular weight MW 43175 using 
polystyrene standard). 
EXAMPLE 3 
Film Samples 
Before stripping the product solution of Example 2 in methylene chloride, 
films were cast from this solution onto glass plates, followed by 
evaporating the solvent under vacuum. The films were optically clear. The 
films were placed in borate buffered saline solution to yield hydrogel 
films. The hydrogel films were optically clear and had a water content of 
22 weight percent. Mechanical properties of the films were determined on 
an Instron Model 4500 using ASTM methods 1708 and 1938, tensile modulus of 
63 g/mm.sup.2 and a tear strength of 20 g/mm.sup.2. Oxygen permeability 
was 269 Dk units. 
The hydrogel films were dried and then heated in water at 80.degree. C. for 
4 hours. After re-drying, there was no loss in weight, indicating the 
hydrogels were stable up to this temperature. 
EXAMPLE 4 
Contact Lens Casting 
The thermoplastic resin obtained in Example 2 was ground into a fine 
powder. It was then poured into an a plastic mold made of Ultem.TM. resin, 
having a molding surface to provide an anterior contact lens surface, and 
then another plastic mold having a molding surface to provide a posterior 
contact lens surface was placed on top of each anterior mold to form a 
molding cavity therebetween. The two molds were clamped between plates, 
and then placed between two preheated platens and compressed at 
147.degree. C. for 1 hour. The lenses were released from the molds and 
placed in borate buffered saline. All hydrogel lenses thus obtained were 
visually clear. 
The following examples illustrate synthesis of other hydrophilic 
prepolymers suitable for the subject thermoplastic polymers. 
EXAMPLE 5 
Synthesis of Hydroxyl-Terminated Prepolymer of Formula (II) Based on DMA 
To a dried 500-ml round bottom flask was added N,N-dimethylacrylamide (DMA, 
94.78 g/0.95 mole), 2-hydroxyethylmethacrylate (Hema, 3.27 g/0.0251 mole) 
and anhydrous tetrahydrofuran (THF, 200 ml). The contents were flushed 
with nitrogen and 2-mercaptoethanol (1.97 g/0.0251 mole) and 
2,2-azobisisobutyronitrile (AIBN, 0.8 g/0.5 mole % of DMA) were added. The 
mixture was heated at 60.degree. C. for 20 hours and poured into a beaker 
containing ether to precipitate the product. The product was vacuum dried 
to yield 92 grams. Size exclusion chromatography indicated Mn 2926, MW 
7466, with a polydispersity of 2.55. The hydroxyl-equivalent weight as 
determined by titration (addition of excess isophorone diisocyanate to 
react with OH groups in the prepolymer, and then addition of excess 
di-n-butylamine to react with isocyanate groups, followed by titration 
with HCl) was 1870. 
EXAMPLE 6 
Synthesis of Hydroxyl-Terminated Prepolymer of Formula (II) Based on NVP 
A prepolymer was prepared as in Example 5 employing the following amounts 
of reactants: N-vinylpyrrolidone (NVP), 86.43 g/0.78 mole; allyl alcohol, 
5.79 g/0.0997 mole; mercaptoethanol, 7.79 g/0.099 mole; and AIBN, 0.5 mole 
% of NVP). The reactants were polymerized for 150 hours, and the 
hydroxyl-equivalent weight as determined by titration was 594. 
EXAMPLE 7 
Synthesis of Hydroxyl-Terminated Prepolymer of Formula (II) Based on DMA 
A polymer was prepared as in Example 5 employing the following amounts of 
reactants: N,N-dimethylacrylamide (DMA, 100 g/1.009 mole); 2-hydroxyethyl 
methacrylate (Hema, 10.69 g/0.0841 mole); 2-mercaptoethanol (6.57 g/0.0841 
mole); and 2,2-azobisisobutyronitrile (AIBN, 1.64 g/0.01 mole). The 
product was vacuum dried to yield 109.6 grams. Size exclusion 
chromatography indicated Mn 1483, MW 3416, with a polydispersity of 2.30. 
Many other modifications and variations of the present invention will be 
evident to the skilled practitioner in the field in light of the teachings 
herein. It is therefore understood that, within the scope of the claims, 
the present invention can be practiced other than as specifically 
described.