Silicone containing acrylic star polymers

Acrylic star polymers containing polysiloxanylalkyl ester groups in their arms and terminal organo groups containing a polymerizable carbon-carbon double bond are useful for improving polymer compositions for contact lenses.

FIELD OF THE INVENTION 
This invention relates to novel star polymers containing polysiloxanyl 
groups in their arms which can be used in combination with other polymers 
to improve the properties of the other polymers, for example to impart an 
improved combination of oxygen permeability and hardness in 
polysiloxanylalkyl acrylic polymers used for contact lens applications. 
BACKGROUND OF THE INVENTION 
U.S. Pat. Nos. 3,808,178 and 4,120,570, issued to N. E. Gaylord in 1974 and 
1978 respectively, concerns linear random copolymers of polysiloxanyl and 
alkyl acrylates and methacrylates which have increased oxygen 
permeability, as compared to the alkyl methacrylates alone for example. 
Use of the polymers in contact lenses for correcting visual defects of the 
human eye is taught. Further modifications of such polymers with an 
itaconate ester, and preferably including a crosslinking agent and a 
hydrophilic monomer, are disclosed in U.S. Pat. No. 4,152,508 issued to E. 
J. Ellis et al. (1979). 
U.S. Pat. No. 4,254,248 issued to G. D. Friends et al. (1981) concerns 
acrylate and methacrylate soft contact lenses using as a comonomer 
polysiloxanes end-capped with polymerizable unsaturated groups. The 
copolymers have high tear strengths and a high modulus of elasticity. Such 
comonomers are also disclosed in U.S. Pat. No. 4,189,546 issued to W. G. 
Deichert et al. (1980) to make polymeric shaped articles for biomedical 
applications. 
U.S. Pat. Nos. 4,659,782 and 4,659,783 issued to H. J. Spinelli in 1987 
teach the preparation of acrylic star polymers with crosslinked acrylic 
cores and acrylic arms. Such star polymers can contain reactive functional 
groups, including carbon-carbon double bonds as disclosed in U.S. Pat. No. 
4,810,756 to Spinelli (1989). The incorporation of the star polymers into 
other polymer compositions to give improved properties is disclosed. The 
use of functionalized star polymers in clear or filled acrylic sheet or 
castings is referred to in U.S. Pat. No. 4,810,756. 
In the prior art, as represented for example by the above Gaylord patents, 
improvements in one polymer property, such as oxygen permeability, are 
frequently gained at the expense of another property, such as hardness or 
machineability. Optical clarity must remain unaffected as well. Improved 
methods and materials which can provide polymeric contact lens 
compositions having improved combinations of properties remain highly 
desirable. 
An object of this invention is a novel acrylic star polymer which is 
compatible with and can be used in polymer compositions for contact lenses 
to provide improved properties. Another object is a novel star polymer 
which can be incorporated into polysiloxanyl-, alkyl-(meth)acrylate 
copolymers during bulk polymerization of the copolymer to provide a novel 
combination of oxygen permeability and hardness and not adversely affect 
optical clarity. 
SUMMARY OF THE INVENTION 
This invention provides a novel silicone-containing acrylic star polymer 
comprised of a crosslinked core derived from one or more (meth)acrylate 
monomers and attached to the core a plurality of linear copolymeric arms 
with an unattached free end which arms are derived from one or more 
(meth)acrylate monomers, wherein about 5 to 100% by weight of the 
(meth)acrylate monomers from which the arms are derived are one or more 
polysiloxanylalkyl esters, preferably of the formula: 
##STR1## 
wherein D and E are selected from the group consisting of C.sub.1 -C.sub.5 
alkyl groups, phenyl groups and a group of the structure 
##STR2## 
where A is selected from the group consisting of C.sub.1 -C.sub.5 alkyl 
groups and phenyl groups; R.sub.2 is selected from the group of hydrogen 
and methyl; "m" is an integer from one to five; and "n" is an integer from 
one to three. 
As used herein the term "(meth)acrylate" refers to methacrylate and/or 
acrylate groups. 
Preferably at least 5 of said arms are present, and most preferably 
substantially all of said arms have their unattached ends terminated with 
an organo group containing a polymerizable carbon-carbon double (olefinic) 
bond. Such double bonds permit the star to copolymerize with other olefin, 
especially (meth)acrylic, monomers to form copolymers of the olefin 
monomers and the star polymer. Such copolymerization chemically 
incorporates the star polymer into the copolymer, as compared to simply 
physically mixing the star with another polymer or with the other monomers 
prior to polymerization of the other polymer. Such chemical incorporation 
results in improved resistance to extraction and greater reinforcement of 
properties, such as toughness, in the polymer combination.

DETAILED DESCRIPTION OF THE INVENTION 
Also preferred in this invention are silicone-containing acrylic star 
polymers which comprise: 
a. a crosslinked core comprising a polymer derived from a mixture of 
monomers comprising 
i). 1-100% by weight of one or more monomers, each having at least two 
groups, 
##STR3## 
ii). 0-99% by weight of one or more monomers, each having one group, 
##STR4## 
in which each R.sub.3 is the same or different and is --H, --CH.sub.3, 
--CH.sub.2 CH.sub.3, --CN, or --COR',and Z is O or --NR' and 
b. attached to the core at least 5 polymer chains that are derived from a 
mixture of monomers comprising 
i). 15-90% by weight of one or more monomers having the formula 
##STR5## 
and mixtures thereof wherein: X is --CN, --CH.dbd.CHC(0)X' or --C(0)X'; Y 
is --H, --CH.sub.3, --CN or --CO.sub.2 R, provided, however, when X is 
--CH.dbd.CHC(O)X', Y is --H or --CH.sub.3 ; X' is --OSi(R).sub.3, --R, 
--OR or --NR'R"; each R is independently selected from C.sub.1-10 alkyl, 
alkenyl, or alkadienyl or C.sub.6-20 cycloalkyl, aryl, alkaryl or aralkyl, 
any of said groups optionally containing one or more ether oxygen atoms 
within aliphatic segments thereof and optionally containing one or more 
functional substituents that are unreactive under polymerizing conditions; 
and each of R, and R' is independently selected from C.sub.1-4 alkyl; and 
ii. about 10-100% by weight, preferably 15 to 50, of one or more 
polysiloxanylalkyl esters having the formula 
##STR6## 
where D and E are selected from the class consisting of C.sub.1 -C.sub.5 
alkyl groups, phenyl groups, and groups of the structure 
##STR7## 
where A is selected from the class consisting of C.sub.1 -C.sub.5 alkyl 
groups and phenyl groups; R.sub.2 is selected from the group of hydrogen 
and methyl; m is an integer from one to five; and n is an integer from one 
to three, and 
c. the unattached ends of said arms having a terminal organo group 
containing a polymerizable carbon-carbon double bond. 
Representative monofunctionally polymerizable monomers of the a.(ii.) group 
include, but are not limited to the following: methyl methacrylate 
(abbreviated herein as MMA), butyl methacrylate, ethyl methacrylate, 
methyl acrylate, ethyl acrylate, methacrylic acid, acrylic acid, 
hydroxyethyl methacrylate, hydroxyethyl acrylate, glyceryl methacrylate, 
sorbyl acrylate and methacrylate; 2-(dimethylamino)ethyl methacrylate, 
2-(dimethylamino)ethyl acrylate; 3,3-dimethoxypropyl acrylate; 
3-methacryloxypropyl acrylate; 2-acetoxyethyl methacrylate; p-tolyl 
methacrylate; 2,2,3,3,4,4,4-heptafluorobutyl acrylate; methylene 
malononitrile; ethyl 2-cyanoacrylate; N,N-dimethyl acrylamide; 
4-fluorophenyl acrylate; 2-methacryloxyethyl acrylate and linoleate; 
propyl vinyl ketone ethyl 2-chloroacrylate; glycidyl methacrylate; 
3-methoxypropyl methacrylate; 2[(1-propenyl)oxylethyl methacrylate and 
acrylate; phenyl acrylate; 2-(trimethyloloxy)ethyl methacrylate; allyl 
acrylate and methacrylate. Preferred monomers include methyl methacrylate, 
glycidyl methacrylate; sorbyl methacrylate; ethyl acrylate, butyl 
acrylate; sorbyl acrylate; 2-(trimethylsiloxy)ethyl methacrylate; 
2-methacryloxyethyl acrylate, 2-acetoxyethyl methacrylate; and 
2-(dimethylamino)ethyl methacrylate. Methyl methacrylate is most preferred 
because of its availability, cost and performance among other things. 
Representative polysiloxanylalkyl ester.monomers which can be employed 
include: pentamethyldisiloxanylmethyl methacrylate, 
heptamethyltrisiloxanylethyl acrylete, 
tris(trimethylsiloxy)-gamma-(methacryloxypropyesilane which is abbreviated 
as TRIS, phenyltetramethyldisiloxanylethyl acrylate, 
phenyeetetraethyldisiloxanylether methacrylate, 
triphenyldimethyldis.eeoxanylmethyl acrylate, 
isobueylhexamethyltrisiloxanylmethyl methacrylate, 
methyedi(trimethylsiloxy)-methacryloxymethylsilane, 
n-propyloctamethyltetrasiloxanyl propye methacrylate, 
pentamethyldi(trimethylsiloxy)acrylexymethylsilane, 
t-butyltetramethyldisiloxanylethylacrylate, 
n-pentylhexamethyltrisiloxanylmethyl methaerylate, and 
tri-i-propyltetramethyltrisiloxanylethylacrylate. 
Examples of core monomers having at least two pelymerizable alpha, beta 
unsaturated acid esters or amedes as mentioned in a.(i.) above are: 
ethylene dimeteracrylate; 1,3-butylene dimethacrylate; tetraethylene 
glycol dimethacrylate; triethylene glycoe dimethacrylate; 
trimethylolpropane trimeacrylate; 1,6-hexylene dimethacrylate; 
1,4-butylene dimethacrylate; ethylene diacrylate; 1,3-butylene diacrylate; 
tetraethylene glycol diacrylate; triethylene glycol diacrylate; 
trimecylolpropane triacrylate; 1,6-hexylene diacrylate; and 1,4-butylene 
diacrylate. 
Other useful known ingredients and polymerization techniques will be found 
in U.S. Pat. No. 4,417,034--Webster, in columns 2-9 which is incorporated 
herein by reference. 
In the preparation of the acrylic star block copolymers of the present 
invention, good use can be made of the known "group transfer" 
polymerization process of the general type described in part by Farnham 
and D. Y. Sogah, U.S. Pat. No. 4,414,372 and by O. W. Webster, U.S. Pat. 
No. 4,417,034 and in U.S. Pat. Nos. 4,508,880, Webster, Apr. 2, 1985, and 
4,524,196 Farnham and granted June 18, 1985. 
"Group transfer" initiators that are useful polymerization include but are 
not limited to the following: 
1-(2-trimethylsiloxy)ethoxy-1-trimethylsiloxy-2-methylpropene, 
methoxy-[(2-methyl-1oxy]trimethylsilane; (trimethysilyl)isoronitrile; 
ethyl 2-(trimethylsilyl)acetate; methyl 2-(tributylstannyl)propanoate; 
[(2-methyl-1ohexenyl)oxy]tributylstannane; trimethylsilyl ile; methyl 
2-methyl-2-(trimethylgermanyl) anoate; 
[(4,5-dihydro-2-furanyl)oxy]trimethylne; 
[(2-methyl-1-propenylidene)bis(oxy)]bismethylsilane][(2-methyl-1-[2-methox 
ymethoxy)xyl]-1-propenyl)oxy]trimethylsilane; methyl 
(trimethylxilyloxy)-1-propenyl)oxylate; 
[(1-(methoxymethoxy)-2-methyl-1-propenyl) 
silane; [(2-ethyl-1-propoxy-1-butenyl) 
ilane; ethyl 2-(trimethylstannyl) 
[(2-methyl-1-butenylidene)bis(oxy)]bismethylsilane]2-(trimethylsilyl)propan 
enitrile; (trimethylgermanyl)acetate; 
[(1-((1-dec-2-enyl)-1-propenyl)oxy]-trimethylsilane; phenyl 
2-(triethylsilyl)acetate; [(2-methyl-1-cyclohexeneyl)ox 
[(1-methoxy-2-methyl-1oxy]phenyldimethylsilane. 
Acrylic star polymers are high molecular polymers that have a multitude of 
linear, acrylic arms radiating out from a central core. The cores are 
highly crosslinked segments of difunctional acrylates or copolymers of 
monofunctional and difunctional acrylates. The arms are linear polymers 
that can be homopolymers, copolymers, or block polymers, and may have 
functional groups located at the end of the arms (or in some cases 
distributed along the chain). The manner in which star polymers of the 
present invention can be prepared include the "arm-first", "core-first", 
and "arm-core-arm" methods, as described for example in Spinelli U.S. Pat. 
No. 4,810,756, which is incorporated herein by reference. 
Typically, the molecular weight of the arms of the star polymers of this 
invention can range from 1,000 to 20,000. The preferred range based on 
performance and handling is from 5,000 to 14,000. The number of arms per 
star is dependent on the composition and process used to make the star. 
The number of arms that are present in a star can be determined by 
dividing the molecular weight of the entire star by the molecular weight 
of the arms from which it was made. The number of arms can range 
preferably from 5 to 5,000. A more preferred range is 10 to 200. The 
molecular weight of both the arms and the star can be determined by using 
standard analytical techniques, such as gel permeation chromatography, 
light scattering, and osmometry. Factors affecting the number and length 
of arms in star polymers of the present invention are the same as known 
and described in U.S. Pat. No. 4,810,756 the disclosure of which is 
incorporated above. 
Known conventional gas permeable lens formulations include slightly 
crosslinked copolymers of MMA and TRIS. The ratio of the two monomers is 
adjusted to optimize a balance of properties. As the level of TRIS monomer 
is increased, the permeability of the contact lens increases, but the 
hardness and flex resistance decreases. The amount of TRIS which can be 
used is limited by the minimum hardness that is acceptable for 
manufacturability. Typically, a minimum Shore D hardness of 70 is needed 
for good manufacturing (machineability) of lenses. This, in copolymers of 
the prior art, normally results in a maximum oxygen permeability (DK) of 
about 40. 
Hard polymers, such as PMMA, are not very soluble in highly permeable 
monomers, such as TRIS. It has been found that if the polymer is made into 
a block polymer of the TRIS silicone monomer, for example, and MMA, then 
the block copolymer can be dissolved or dispersed into the TRIS monomer. 
With this procedure, solutions of hard polymers in the silicone monomer 
have been made and copolymerized to make lenses with outstanding 
properties. In general, the use of the block polymer structure 
significantly improves the ease of making the polymer solutions. Other 
soluble hard polymer/permeable monomer mixtures may also be used. 
Useful star polymers of this invention include but are not limited to the 
following (The values given represent the weight percent of each monomer 
in the polymer. A double slash indicates a separation between blocks, and 
a single slash indicates a random copolymer or random composition in a 
specific block. In each case EGDM is the core monomer.): 
______________________________________ 
Block Next to 
Molecular Weight 
Composition Double Bond* 
Arm Mn 
______________________________________ 
TRIS//MMA//EGDM TRIS 8,600 
37.3//55.1//7.6 
PENTA//MMA//EGDM 
PENTA 9,900 
38.8//56.8//4.4 
TRIS//MMA//EGDM TRIS 10,000 
36.6//55.2//8.2 
TRIS//MMA//EGDM TRIS 10,200 
77.9//15.0//7.1 
TRIS//MMA//EGDM TRIS 10,000 
22.9//70.0//7.1 
TRIS//MMA//EGDM TRIS 9,200 
9.7//83.0//7.3 
PENTA//MMA//EGDM 
PENTA 14,200 
17.3//79.2//3.5 
MMA//TRIS//EGDM MMA 10,200 
23.2//69.6//7.2 
MMA//TRIS//EGDM MMA 8,000 
9.3//82.5//7.2 
MMA/TRIS//EGDM RANDOM 10,300 
24.3/68.6//7.1 
MMA/TRIS//EGDM RANDOM 10,300 
42.9/43.4//13.7 
MMA/TRIS//EGDM RANDOM 10,300 
60.0/26.4//13.6 
MMA/TRIS//EGDM RANDOM 10,300 
68.4/18.2//13.4 
______________________________________ 
MMA = methyl methacrylate 
TRIS = 3tris(trimethylsiloxy)silanepropyl methacrylate 
EGDM = ethyleneglycol dimethacrylate 
PENTA = 3methacryloxypropylpentamethyldisiloxane 
*i.e. in the form of an alphamethylstyrene organo group containing a 
carbon--carbon double bond, the group is linked to the end of the arm by 
urethane linkage formed by the reaction of an isocyanate group and a 
hydroxy group. 
Especially preferred star polymers include: 
______________________________________ 
Block Next to 
Molecular Weight 
Composition Double Bond Arm Mn 
______________________________________ 
TRIS//MMA//EGDM TRIS 10,000 
36.6//55.2//8.2 
TRIS//MMA//EGDM TRIS 10,000 
22.9//70.0//7.1 
TRIS//MMA//EGDM TRIS 9,200 
9.7//83.0//7.3 
PENTA//MMA//EGDM 
PENTA 9,900 
38.8//56.8//4.4 
______________________________________ 
Included in the composition of the star polymers, especially in the arms, 
may also be some (meth)acrylate monomers whose function is to improve 
wetting or deposit resistance, in lens polymers for example. Examples of 
these monomers include: methacrylic acid, acrylic acid, dimethylaminoethyl 
methacrylate, diethylaminoethyl methacrylate, glyceryl methacrylate. Other 
polymers containing such monomers may be mixed with the polymers of this 
invention or in lens compositions as well. 
The polymerizable double bond can be in an organo group that is attached to 
the ends of the arms of the stars and may be in the form of a 
methacryloxy, an acryloxy, a styrenic, an alphia methyl styrenic, an 
allylic, a vinylic, or other olefinic groups. It can be attached to star 
polymer by reacting a functional group on the star arm with compounds that 
contain a polymerizable double bond and react with said functional group. 
Such compounds include, for example, any that has a second functional 
group that can react with the first functional group and contain a 
polymerizable double bond. Examples of such functional groups that can be 
present on the star polymer include hydroxy, carboxylic acid, epoxy and 
aziridine. The functional group may intially be present in blocked form, 
which requires the removal of the blocking group before attachment of the 
polymerizable double bond group. The functional group may be incorporated 
in the arm polymer through either a functional initiator or a functional 
terminal monomer. Examples of the second functional groups include epoxy, 
hydroxy, acid, aziridine, isocyanate, acid chloride, anhydride, and ester. 
Initiators having blocked hydroxyl groups which can be used include 
1-(2-trimethylsiloxyethoxy)-1-trimethylsiloxy-2-methyl propene and 
1-[2-(methoxymethoxy)ethoxy]-1-trimethylsiloxy-2-methylpropene. Blocked 
hydroxyl monomers which can be used include 2-(trimethylsiloxy)ethyl 
methacrylate, 2-(trimethylsiloxy)propyl methacrylate, and 
3,3-dimethoxypropyl acrylate. When the polymerization is completed, the 
blocking group is removed by hydrolysis to give a hydroxy functional 
polymer. Examples of hydroxy functional monomers which can be blocked 
include: 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 
hydroxypropyl acrylate, and hydroxypropyl acrylate. 
Upon unblocking, the hydroxy group is then reacted with compounds that can 
attach a polymerizable double bond group to the polymer. Examples of these 
include: 2-isocyanatoethyl methacrylate, methacryloyl chloride, acryloyl 
chloride, alpha-methylstyrene isocyanate, acrylic acid, methacrylic acid, 
anhydrides of acrylic and methacrylic acid, maleic anhydride, and esters 
of acrylic and methacrylic acids in transesterification reactions. 
Blocked acid initiators which can be used include 
1,1-bis(trimethylsiloxy)-2-methyl propene and 
1,1-bis(trimethylsiloxy)propene. Blocked acid monomers which can be used 
include trimethylsiloxy methacrylate and 1-butoxyethyl methacrylate. When 
the polymerization is completed, the blocking group is removed to give an 
acid functional polymer. Acid 5 monomers which can be used include acrylic 
acid, itaconic acid, and methacrylic acid. 
The acid group is then reacted with compounds that can attach a 
polymerizable double bond group to the polymer. Examples of these include: 
glycidyl acrylate and methacrylate, aziridinyl acrylate and methacrylate, 
the hydroxy esters of acrylic and methacrylic acid. 
The star polymers of this invention, used alone, or self-polymerized, or 
when copolymerized with other (meth)acrylic monomers through the terminal 
carbon-carbon double bonds on the arms, have utility in polymer 
formulations, especially those of U.S. Pat. Nos. 4,861,840, 3,808,178 and 
4,120,570, for use in such diverse applications as release coatings, 
contact lenses, ocular membranes, intraocular implants, sizing agents, 
electronics adhesives, gas and liquid separation membranes, prostheses, 
and etching resists. 
Test Methods 
Oxygen Permeability 
Oxygen permeabilities are determined using standard techniques, such as in 
ASTM-D-1434, as described for example in U.S. Pat. No. 3,808,178 at Column 
4, lines 36-44. 
The values given are the diffusion constants: 
##EQU1## 
Hardness 
A Shore D hardness tester was used in the conventional manner (e.g. ASTM 
E448-82) to determine hardness of buttons made either from a button mold 
or cut from a tube. A suitable tester is a Model D Hardness Tester from 
Shore Instrument and Manufacturing Co., Inc. 
Swelling 
A faced button was weighed and soaked in a container in heptane or ethyl 
alcohol for 18 hours. The container was placed in a water bath at room 
temperature. The button was taken out and wiped dry with a paper towel. 
The different in weight of the button before and after soaking is recorded 
and the percentage increase in weight is calculated based on the original 
weight of the button. 
COMATIVE EXAMPLES 
(Not of the Invention) 
This describes the preparation of a conventional contact lens made with the 
random copolymerization of monomers. 
Formulation 
The following materials were mixed together: 51.8 gm of methyl 
methacrylate, MMA, 36.0 gm of 3-tris(trimethylsiloxy)silanepropyl 
methacrylate, TRIS, 7.0 gm of N-vinyl pyrolidone, NVP, 5.0 gm of 
tetraethyleneglycol dimethacrylate, TEGMA, and 0.2 gm of "Vazo-52", a 
commercial free-radical initiator. The solution was poured in button 
molds, tubes, or in a caste base curve radius type mold. 
Methods of Polymerization 
Method 1: Thermal polymerization. The mixture was heated in the mold at 
30.C for 44 hours, then 4 hours at 45.C, finally 24 hours at 110.degree. 
C. 
Lens Manufacturing 
A lathe cut lens from the samples using standard production procedures. 
Results 
The above formulation was used to make lens that had a Shore D hardness of 
75 and a DK of 17.0. 
A series of six more polymers, and lenses thereof, was made and tested in 
substantially the same manner while varying the ratio of the TRIS and MMA 
monomers with the same amounts of NVP and TEGMA. The results are as 
follows: 
______________________________________ 
Formulation 
Comparison (Wt. in gms) Properties 
Run TRIS MMA DK Hardness 
______________________________________ 
1 36 51.8 17 75 
2 48 39.8 35 70 
3 53 34.8 34.5 64 
4 55 32.8 36.9 60.5 
5 60 27.8 47.3 58 
6 66 21.8 70.0 54.0 
7 70 17.8 Too soft 
______________________________________ 
The above table shows results that are typically obtained with conventional 
random copolymerization of a hard monomer MMA and a permeable monomer 
TRIS. Lenses made with the formulations of Comparisons 4, 5, 6 and 7 are 
considered to be of inferior commercial quality. They were too soft to 
properly cut and lathe, were easily scratched, and were solvent sensitive, 
i.e., they had over 15% solvent swelling. 
The results from Comparisons 1 to 7 are exemplary for lenses made from a 
random copolymerization of hard monomer such as MMA and a permeable 
monomer such as TRIS. These results show that as the level of permeable 
monomer is increased, the oxygen permeability is increased, but the 
hardness of the lens decreases. 
In the above formulations the N-vinyl pyrrolidone was added to improve the 
wetting characteristics of the finished lens. Other wetting monomers that 
could have been used include methacrylic acid, acrylic acid, hydroxyethyl 
methacrylate, and glyceryl methacrylate. It is thought that their use at 
less than 10% does not affect either the permeability or hardness of the 
lenses. 
The tetraethylene glycol dimethacrylate was added to crosslink the lens and 
improve the swell resistance of the finished lens. Other crosslinking 
monomers that could have been used include ethyleneglycol dimethacrylate, 
diethyleneglycol dimethacrylate, and trimethylolpropane trimethacrylate 
TMPTMA. It is thought that their use at less than 8% does not affect 
permeability. 
Others monomers, such as hexafluorobutyl methacrylate, styrene, 
t-butylstyrene, etc. can be used to improve some properties, such as 
deposit resistance. Their use at less than 10% of the total composition 
does not significantly affect either permeability or hardness. 
Preparation Procedure for Lenses Made with Star Polymers of the Invention 
I. Mixing Procedure 
All liquid ingredients were weighed and mixed in screw-on-cap bottle, 
shaken and stirred for a while. The solid star powder (from Examples 1 or 
2) is weighed and added to the liquid monomer ingredients in small 
portions. In order to disperse the power in the bulk of the mixture, after 
each addition the mixture was stirred using a magnetic stirrer, the bottle 
then capped and sealed properly, tumbled on a roller mill until the 
solution was clear and homogeneous (from several hours to several days). 
The initiator and any color were added and tumbled for half an hour, then 
poured in molds or tubes. 
Polymerization Procedure 
Thermal Polymerization 
Solutions were poured in, nitrogen flushed aluminum tubes, capped and put 
in a water bath for 44 hours at 30.degree. C. Then heated in an oven for 4 
hours at 45.degree. C, finally the temperature was raised to 110.degree. C 
for 24 hours. Sometimes an extra 24 hours at 130.degree. C was used. The 
tubes were cooled to room temperature and the rods were punched out. The 
rods were ground to the half inch diameter and cut to buttoms. These 
buttoms were then cut and lathed into lenses. 
The Ultraviolet Method 
After the solution is prepared, it was poured in UV-transparent button 
molds and placed in a UV box. Nitrogen and vacuum was applied 
alternatively. Irradiation was applied for 45 minutes under nitrogen 
atmosphere. The molds were then removed and heated for two hours at 
90.degree. C, then the temperature was raised to 110.degree. C for 20 
hours. Buttons were punched out of the molds and faced. 
Lens Manufacturing 
A lathe was used to cut lenses using standard production procedures. 
EXAMPLES 
In the examples that follow, the compositions are expressed in terms of the 
weight ratios of the ingredients based on total weight of the composition. 
Example 1 TRIS//MMA//EGDM 36.6//55.2//8.2 STAR 
This describes the preparation of a star polymer that has arms composed of 
a block of TRIS [3-methacryloxypropyltris(trimethylsiloxy)silane] monomer 
units and a block of MMA monomer units. The core is derived from 
ethyleneglycol dimethacrylate. There is an organo group containing a 
double bond located at the ends of the arms next to the TRIS block. 
A 1 liter flask was equipped with a mechanical stirrer, thermometer, 
N.sub.2 inlet, drying tube outlet and additional funnels. TRIS, 60.54 gm; 
THF, 38.38; p-xylene, 3.01 gm; tetrabutylammonium m-chlorobenzoate, 300 
microliters of a 1.0 M solution; and bis(dimethylamino)methylsilane, 400 
microliters, were charged to the flash. Initiator, 
1-(2-trimethylsiloxy)ethoxy-1-trimethylsiloxy-2-methylpropane, 4.19 gm was 
injected and the TRIS block of the arms was polymerized. Feed I [THF, 5.62 
gm; tetrabutylammonium m-chlorobenzoate, 300 microliters of a 1.0 M 
solution]was then started and added over 60 minutes. Feed II to form the 
attached MMA block [methyl methacrylate, 91.30 gm; THF, 146.88 gm] was 
started and added over 15 minutes. Feed III to form the core of the lining 
ends of the arms [ethyleneglycol dimethacrylate, 13.56 gm] was started at 
30 minutes after the end of Feed II and added over 10 minutes. At 100 
minutes after the end of Feed III, the reaction was quenched with 
methanol, 3.56 gm; water, 1.98 gm; dichloroacetic acid, 7 microliters to 
deactivate the living polymer. It was refluxed for 3 hours to unblock by 
hydrolysis the blocked hydroxyl groups. Solvent, 279.8 gm, was distilled 
off while 378.12 gm of toluene was added. Distillation was continued until 
the vapor temperature equaled approximately 108.degree. C. Then dibutyltin 
dilaurate, 55 microliters; and alpha-methylstyrene isocyanate (TMI from 
Am. Cyanamid), 5.57 gm, were added and refluxed for 3 hours. This put a 
reactive double bond in an organo group at the end of each arm of the star 
from the reaction of the isocyanate group with the hydroxyl groups to form 
a urethane linkage. Methanol, 0.62 gm, was added and refluxed 30 minutes. 
The polymer solution was then poured into methanol. The solid star polymer 
precipitated out and was dried. 
This made a star polymer of TRIS//MMA 40//60 arms with a polymerizable 
double bond at the end of the arms. The arms have a Mn of about 10,000. 
The star has a Mw of 240,000. 
Example 2 TRIS//MMA//EGDM 22.9//70.0//7.1 STAR 
This describes the preparation of a star polymer that has arms composed of 
a block of TRIS and a block of MMA. The core is from ethyleneglycol 
dimethacrylate. A double bond is contained at the ends of the arms next to 
the TRIS block. 
A 1 liter flask was equipped with a mechanical stirrer, thermometer, 
N.sub.2 inlet, drying tube outlet and addition funnels. 
3-Methacryloxypropyltris(trimethylsiloxy)silane, 76.79 gm; THF, 18.74; 
p-xylene, 4.66 gm; tetrabutylammonium m-chlorobenzoate, 500 microliters of 
a 1.0 M solution; and bis(dimethylamino)methylsilane, 500 microliters, 
were charged to the pot. Initiator, 
1-(2-trimethylsiloxy)ethoxy-1-trimethyl- siloxy-2-methylpropene, 8.43 gm 
was injected and the TRIS block of the arms was polymerized. Feed I [THF, 
5.62 gm; tetrabutylammonium m-chlorobenzoate, 300 microliters of a 1.0 M 
solution]was then started and added over 60 minutes. Feed II to form the 
MMA blocks [methyl methacrylate, 234.3 gm; THF, 391.2 gm, and 
bis(dimethylamino)methylsilane, 500 microliters] was started and added 
over 15 minutes. To form the core Feed III [ethyleneglycol dimethacrylate, 
24.02 gm] was started at 30 minutes after the end of Feed II and added 
over 10 minutes. At 100 minutes the reaction was quenched with methanol, 
5.92 gm; H.sub.2 O, 2.47 gm; dichloroacetate acid, 15 microliters to 
deactivate the living polymer. It was refluxed for 3 hours to unblock the 
hydroxyl groups in the initiator end of the arms. Solvent, 699.8 gm was 
distilled off while 888.12 gm of toluene was added. The flask was 
distilled until the vapor temperature equaled approximately 108.C. Then 
dibutyltin dilaurate, 155 microliters; and a methylstyrene isocyanate (TMI 
from Am. Cyanamid), 7.61 gm, were added and refluxed for 3 hours. This 
puts a reactive styrene double bond in a group at the end of each arm of 
the star. Methanol, 0.62 gm, was added and refluxed 30 minutes. Butanol, 
5.1 gm, was added and refluxed 30 minutes. The polymer solution was then 
poured into methanol. The solid star polymer precipitated out and was 
dried. 
This made a star polymer of TRIS//MMA of 25//75 with a polymerizable double 
bond in a group at the end of each arm. The arms have a Mn of about 
10,000. The star has a Mw of 280,000. 
Examples 3-10 
Using the star polymer of Example 1, polymers of the following formulations 
was prepared and made into lenses using the above described preparation 
procedure: 
__________________________________________________________________________ 
Formulation Properties 
Vazo- Hard- 
No. 
TRIS 
MMA STAR 
NVP 
MAA TMPTMA 
52 DK ness 
__________________________________________________________________________ 
3 35 35.3 
15 5 5 4.5 0.2 25 83 
4 50 22.8 
20 7 -- -- 0.2 47.2 
-- 
5* 
45.5 
15.7 
24.3 
-- -- 5 0.2 58 76.2 
6 53.7 
7.5 
27.5 
6.5 
-- 4.6 0.2 91.0 
78 
__________________________________________________________________________ 
*Example 5 also used 6.0% hexafluorobutyl methacrylate and 3.5% glyceryl 
methacrylate in its formulation. 
This Example used the start polymer that was prepared in Example 2. 
__________________________________________________________________________ 
Formulation Properties 
No. 
TRIS 
MMA STAR 
MAA TEGMA 
Vazo-52 
DK Hardness 
__________________________________________________________________________ 
7 29 15.8 
45 5 5 0.2 61 82 
__________________________________________________________________________ 
The following Examples used the star polymer made in Example 1. 
__________________________________________________________________________ 
Formulation Properties 
Vazo- Hard- 
No. TRIS 
VIN* 
MMA STAR 
NVP 
MAA TMPTMA 
52 DK ness 
__________________________________________________________________________ 
8 27.4 
27.4 
5.5 25 4 5 5.5 0.2 67 79 
9 34.8 
20 5.5 25 4 5 5.5 0.2 69 80 
10** 
-- 48.8 
5 25 5 5 5 0.2 52 83 
__________________________________________________________________________ 
*VIN = 
3[3methacryloxypropyl-1,3,3-tris(trimethyl-siloxy)-1-methyl-1-vinyldisilo 
ane 
**Example 10 also used 6.0% hexafluorobuty1 methacrylate in its 
formulation. 
Examples 3 to 10 clearly show the advantages of star polymers of the 
inention used in contact lens formulations. All of the lenses made in 
these formulations were hard, easy to cutand lathe, resistant to 
scratches, and had less than 15% solvent swell. The combinations of 
hardness and oxygen permeability of lenses made with these materials are 
significantly greater than those obtained with random copolymers as listed 
in Comparisons 1-7. The Figure plots the results of Comparison Runs 1-6 
with Examples 3, 5, 6 and 7. 
The use of stars did not adversely affect the optical clarity or hardness 
values of the lenses.