BRIEF SUMMARY OF THE INVENTION
The invention relates to optical elements whose optical
properties can be readjusted over extended periods of time. In one embodiment, an
intraocular lens is used whose optical properties can be changed multiple times
BACKGROUND OF THE INVENTION
Approximately two million cataract surgery procedures are
performed in the United States annually. The procedure generally involves making
an incision in the anterior lens capsule to remove the cataractous crystalline lens
and implanting an intraocular lens in its place. The power of the implanted lens
is selected (based upon pre-operative measurements of ocular length and corneal
curvature) to enable the patient to see without additional corrective measures (e.g.,
glasses or contact lenses). Unfortunately, due to errors in measurement, and/or
variable lens positioning and wound healing, about half of all patients undergoing
this procedure will not enjoy optimal vision without correction after surgery.
Brandser et al, Acta Ophthalmol Scand 75:162-165 (1997
Oshika et al., J. Cataract Refract Surg 24:509-514 (1998
). Because the power of prior art intraocular lenses generally cannot be
adjusted once they have been implanted, the patient typically must choose between
replacing the implanted lens with another lens of a different power or be resigned
to the use of additional corrective lenses such as glasses or contact lenses. Since
the benefits typically do not outweigh the risks of the former, it is almost never
Recently, a new type of intraocular lens has been described
which permits post-operative manipulation of the optical properties of the lens.
This allows for post-operative adjustment of the lens to achieve optimal vision
quality for the patient. The post-operative manipulation is accomplished through
the polymerization of modifying composition ("MC") in specific regions of the lens
by external stimuli, such as light. By polymerizing the MC in specific regions,
the optical qualities of the lens can be adjusted until the desired optical properties
are achieved. To prevent further changes in the optical properties, however, any
remaining MC is then polymerized throughout the lens, "locking-in" the properties.
Unfortunately, this prevents further adjustment of the
lens at a later time. For example, if the lens were implanted in a child, it would
not be possible to readjust the lens to compensate for changes in vision due to
aging or the like. In this case, the patient would have to choose between surgery
to replace the lens or to use other corrective devices, e.g., glasses.
Thus, a need exists for an intraocular lens whose optical
properties can be adjusted on more than one occasion.
SUMMARY OF THE INVENTION
The invention relates to optical elements whose optical
properties can be modified post-fabrication and adjusted multiple times. In a specific
embodiment, an intraocular lens whose optical properties can be adjusted post-implantation
more than once is used. In particular, the present invention provides use of a blend
of a stimulus absorber and a stimulus initiator in an optical element for delaying
the initiation of polymerisation of a modifying composition (MC) until a predetermined
level of intensity of stimulus is reached, wherein the optical element comprises
a first polymer matrix and said MC dispersed therein, said MC being capable of undergoing
The optical properties of the elements are adjusted by
the localized stimulus-induced polymerization of a modifying composition ("MC")
which is dispersed in the optical element. When the MC is polymerized in a specific
region of the element, the optical properties of the element are changed. This is
accomplished by changing the refractive index of the element in the area where polymerization
has occurred, or by changing the shape of the element, or both. One key aspect of
the invention is that this is accomplished with out the addition or removal of material
from the element.
As noted above, the polymerization of the MC is stimulus-induced.
Typically, this refers to photopolymerization; however, other external stimuli may
be used. The stimulus-induced polymerization is caused by the presence of one or
more initiators which, when exposed to the proper stimulus, induces or initiates
polymerization of the MC.
The invention relates to controlling the conditions under
which the initiators start polymerization of the MC. It has been found that through
the use of various stimulus-absorbing compounds combined with the initiator compounds,
it is possible to control the conditions under which the polymerization reaction
occurs. Thus, it is possible to control the conditions such that any external stimuli
present in the normal environment encountered by the element will not cause polymerization
of the MC.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a plot of light intensity versus wave length
showing the levels for ambient sunlight and the ANSI MPE level.
FIGURE 2 is a plot of UV absorber versus wave length for
a UV absorber and initiator combination useful in practice of the invention.
Figure 3 is a cross section of a portion of an optical
element for use in the invention.
Figure 4 is a cross section of an optical element for use
in the present invention upon exposure to UV light.
Figure 5 is a cross section of a portion of an optical
element for use in the invention after exposure to UV light.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to optical elements whose optical
properties can be continuously modified or adjusted over its useful life. This adjustment
is accomplished in a self-contained system that is without the addition or removal
of material from the element.
Typical optical elements for use in the invention include
data storage elements, including compact disks, digital video disks; lenses, including
but not limited to spectacle lenses; contact lenses, intraocular lenses; mirrors,
prisms, and the like. In the preferred embodiment, the optical element is an intraocular
The optical element is typically prepared from a first
polymer matrix which gives shape to the element as well as many of its physical
properties such as hardness, flexibility and the like.
The optical element also contains a MC dispersed therein.
This MC may be a single compound or a combination of compounds that is capable of
stimulus-induced polymerization, preferably photopolymerization.
The nature of the first polymer matrix and the MC will
vary depending upon the end use contemplated for the optical element. However, as
a general rule, the first polymer matrix and the MC are selected such that the components
that comprise the MC are capable of diffusion within the first polymer matrix. Put
another way, a loose first polymer matrix will tend to be paired with larger MC
components and a tight first polymer matrix will tend to be paired with smaller
Upon exposure to an appropriate energy (e.g., heat
or light), the MC typically forms a second polymer matrix in the exposed region
of the optical element. The presence of the second polymer matrix changes the material
characteristics of this portion of the optical element to modulate its refraction
capabilities. In general, the formation of the second polymer matrix typically increases
the refractive index of the affected portion of the optical element. After exposure,
the MC in the unexposed region will migrate into the exposed region over time. The
amount of MC migration into the exposed region is time dependent and may be precisely
controlled. If enough time is permitted, the MC components will re-equilibrate and
redistribute throughout optical element (i.e., the first polymer matrix,
including the exposed region). When the region is re-exposed to the energy source,
the MC that has since migrated into the region (which may be less than if the MC
were allowed to re-equilibrate) polymerizes to further increase the formation of
the second polymer matrix. This process (exposure followed by an appropriate time
interval to allow for diffusion) may be repeated until the exposed region of the
optical element has reached the desired property (e.g., power, refractive
index, or shape). At this point, because of the presence of the UV absorber, no
further polymerization occurs until the element is exposed to the specific wave
length and intensity. Thus, in the case of an intraocular lens, the lens may be
exposed to natural light and the like without further changes in the lens. If adjustment
are needed because of aging or changes in the patient's health, for example, the
lens can be adjusted by exposure to an appropriate energy source.
The first polymer matrix is a covalently or physically
linked structure that functions as an optical element and is formed from a first
polymer matrix composition ("FPMC"). In general, the first polymer matrix composition
comprises one or more monomers that upon polymerization will form the first polymer
matrix. The first polymer matrix composition optionally may include any number of
formulation auxiliaries that modulate the polymerization reaction or improve any
property of the optical element. Illustrative examples of suitable FPMC monomers
include acrylics, methacrylates, phosphazenes, siloxanes, vinyls, homopolymers and
copolymers thereof. As used herein, a "monomer" refers to any unit (which may itself
either be a homopolymer or copolymer) which may be linked together to form a polymer
containing repeating units of the same. If the FPMC monomer is a copolymer, it may
be comprised of the same type of monomers (e.g., two different siloxanes)
or it may be comprised of different types of monomers (e.g., a siloxane and
In one embodiment, the one or more monomers that form the
first polymer matrix are polymerized and cross-linked in the presence of the MC.
In another embodiment, polymeric starting material that forms the first polymer
matrix is cross-linked in the presence of the MC. Under either scenario, the MC
components must be compatible with and not appreciably interfere with the formation
of the first polymer matrix. Similarly, the formation of the second polymer matrix
should also be compatible with the existing first polymer matrix. Put another way,
the first polymer matrix and the second polymer matrix should not phase separate
and light transmission by the optical element should be unaffected.
As described previously, the MC may be a single component
or multiple components so long as: (i) it is compatible with the formation of the
first polymer matrix; (ii) it remains capable of stimulus-induced polymerization
after the formation of the first polymer matrix: and (iii) it is freely diffusable
within the first polymer matrix. In preferred embodiments, the stimulus-induced
polymerization is photo-induced polymerization.
In general, there are two types of intraocular lenses ("IOLs").
The first type of an intraocular lens replaces the eye's natural lens. The most
common reason for such a procedure is cataracts. The second type of intraocular
lens supplements the existing lens and functions as a permanent corrective lens.
This type of lens (sometimes referred to as a phakic intraocular lens) is implanted
in the anterior or posterior chamber to correct any refractive errors of the eye.
In theory, the power for either type of intraocular lenses required for emmetropia
(i.e., perfect focus on the retina from light at infinity) can be precisely
calculated. However, in practice, due to errors in measurement of corneal curvature,
and/or variable lens positioning and wound healing, it is estimated that only about
half of all patients undergoing IOL implantation will enjoy the best possible vision
without the need for additional correction after surgery. Because prior art IOLs
are generally incapable of post-surgical power modification, the remaining patients
must resort to other types of vision correction such as external lenses (e.g.
glasses or contact lenses) or cornea surgery. The need for these types of additional
corrective measures is obviated with the use of the intraocular lenses used in the
The intraocular lens used in the present invention comprises
a first polymer matrix and a MC dispersed therein. The first polymer matrix and
the MC are as described above with the additional requirement that the resulting
lens be biocompatible.
Illustrative examples of a suitable first polymer matrix
include: polyacrylates such as polyalkyl acrylates and polyhydroxyalkyl acrylates;
polymethacrylates such as polymethyl methacrylate ("PMMA"), a polyhydroxyethyl methacrylate
("PHEMA"), and polyhydroxypropyl methacrylate ("HPMA"); polyvinyls such as polystyrene
and polyvinylpyrrolidone ("NVP"); polysiloxanes such as polydimethylsiloxane; polyphosphazenes,
and copolymers of thereof
U.S. Patent No. 4,260,725
and patents and references cited therein provide more specific examples
of suitable polymers that may be used to form the first polymer matrix.
In preferred embodiments, the first polymer matrix generally
possesses a relatively low glass transition temperature ("Tg") such that
the resulting IOL tends to exhibit fluid-like and/or elastomeric behavior. In applications
where flexibility is important (e.g., intraocular lenses or contact lenses), the
Tg will generally be less than 25°C preferably less than 20°C. Where rigidity
is important, the Tg will be much higher, e.g., 25°C to 50°C.
The first polymer matrix is typically formed by cross-linking
one or more polymeric starting materials wherein each polymeric starting material
includes at least one cross-linkable group. Illustrative examples of suitable cross-linkable
groups include but are not limited to hydride, acetoxy, alkoxy, amino, anhydride,
aryloxy, carboxy, enoxy, epoxy, halide, isocyano, olefinic, and oxine. In more preferred
embodiments, each polymeric starting material includes terminal monomers (also referred
to as endcaps) that are either the same or different from the one or more monomers
that comprise the polymeric starting material but include at least one cross-linkable
group. In other words, the terminal monomers begin and end the polymeric starting
material and include at least one cross-linkable group as part of its structure.
Although it is not necessary for the practice of the present invention, the mechanism
for cross-linking the polymeric starting material preferably is different than the
mechanism for the stimulus-induced polymerization of the components that comprise
the MC. For example, if the MC is polymerized by photo-induced polymerization, then
it is preferred that the polymeric starting materials have cross-linkable groups
that are polymerized by any mechanism other than photoinduced polymerization.
An especially preferred class of polymeric starting materials
for the formation of the first polymer matrix is polysiloxanes (also known as "silicones")
endcapped with a terminal monomer which includes a cross-linkable group selected
from the group consisting of acetoxy, amino, alkoxy, halide, hydroxy, and mercapto.
Because silicone IOLS tend to be flexible and foldable, generally smaller incisions
may be used during the IOL implantation procedure- An example of an especially preferred
polymeric starting material is bis(diacetoxyulethylsdyl)-polymethysiloxane (which
is polydimethylsiloxane that is endcapped with a diacetoxymethylsilyl terminal monomer).
The MC that is used in fabricating IOLs is as described
above except that it has the additional requirement of biocompatibility. The MC
is capable of stimulus-induced polymerization and may be a single component or multiple
components so long as: (i) it is compatible with the formation of the first polymer
matrix; (ii) it remains capable of stimulus-induced polymerization after the formation
of the first polymer matrix; and (iii) it is freely diffusable within the first
polymer matrix. In general, the same type of monomers that is used to form the first
polymer matrix may be used as a component of the MC. However, because of the requirement
that the MC monomers must be diffusable within the first polymer matrix, the MC
monomers generally tend to be smaller (i.e., have lower molecular weights)
than the monomers which form the first polymer matrix. In addition to the one or
more monomers, the MC may include other components such as initiators and sensitizers
that facilitate the formation of the second polymer matrix.
Because of the preference for flexible and foldable IOLs,
an especially preferred class of MC monomers is polysiloxanes endcapped with a terminal
siloxane moiety that includes a photopolymerizable group. An illustrative representation
of such a monomer is:
X - Y - X1
wherein Y is a siloxane which may be a monomer, a homopolymer or a copolymer formed
from any number of siloxane units, and X and X1 may be the same or different
and are each independently a terminal siloxane moiety that includes a photopolymerizable
group. Illustrative examples of Y include:
- m and n are independently each an integer and
- R1, R2, R3, and R4, are independently
each hydrogen, alkyl (primary, secondary, tertiary, cycle), aryl, or heteroaryl.
In preferred embodiments, R1, R2, R3, and R4,
is a C1-C10 alkyl or phenyl. Because MC monomers with a relatively
high aryl content have been found to produce larger changes in the refractive index
of the lens for use in the invention, it is generally preferred that at least one
of R1, R2, R3, and R4 is an aryl, particularly
phenyl. In more preferred embodiments. R1, R2, R3
are the same and are methyl, ethyl or propyl and R4 is phenyl.
Illustrative examples of X and X1 (or X1
and X depending on how the MC polymer is depicted) are:
- R5 and R6 are independently each hydrogen, alkyl, aryl,
or heteroaryl; and
- Z is a photopolymerizable group.
In preferred embodiments R1 and R6
are independently each a C1 and C10 alkyl or phenyl and Z
is a photopolymerizable group that includes a moiety selected from the group consisting
of acrylate, allyloxy, cinnamoyl, methacrylate, stibenyl, and vinyl. In more preferred
embodiments, R5 and R6 is methyl, ethyl, or propyl and Z is
a photopolymerizable group that includes an acrylate or methacrylate moiety.
In especially preferred embodiments, an MC monomer is of
the following formula:
wherein X and X1 are the same and R1, R2, R3,
and R4 are as defined previously. Illustrative examples of such MC monomers
include dimethylsiloxane-diphenylsiloxane copolymer endcapped witli a vinyl dimethylsilane
group; dimethylsiloxane-methylphenylsiloxane copolymer endcapped with a methacryloxypropyl
dimethylsilane group; and dimethylsiloxane endcapped with a methacryloxypropyldimethylsilane
group. Although any suitable method may be used, a ring-opening reaction of one
of more cyclic siloxanes in the presence of triflic acid has been found to be a
particularly efficient method of making one class of MC monomers for use in the
invention. Briefly, the method comprises contacting a cyclic siloxane with a compound
of the formula:
in the presence of triflic acid wherein R5, R6, and Z are
as defined previously. The cyclic siloxane may be a cyclic siloxane monomer, homopolymer,
or copolymer. Alternatively, more than one cyclic siloxane may be used. For example,
a cyclic dimethylsiloxane tetramer and a cyclic methyl-phenylsiloxane trimer are
contacted with bismethacryloxypropyltetramethyldisiloxane in the presence of triflic
acid to form a dimethyl-siloxane methyl-phenylsiloxane copolymer that is endcapped
with a methacryloxylpropyl-dimethylsilane group, an especially preferred MC monomer.
As discussed above, the stimulus-induced polymerization
requires the presence of an initiator. The initiator is such that upon exposure
to a specific stimuli, it induces or initiates the polymerization of the MC. In
the preferred embodiment, the initiator is a photoinitiator. The photoinitiator
may also be associated with a sensitizer. Examples of photoinitiators suitable for
use in the practice of the invention are acetophenones (e.g., substituted haloaceto
phenones and diethoxyacetophenone); 2, 4-dichloromethyl-1,3,5-triazines; benzoin
methyl ether; and O-benzoyl oximino ketone.
Suitable sensitizers include p-(dialkylamino aldehyde);
n-alkylindolylidene; and bis [p-(dialkyl amino) benzylidene] ketone.
Alternatively, the MC for use in the invention may comprise
multifunctional acrylate based monomers having the general formula:
wherein Q is an acrylate based compound used to create the acrylate monomer; A
and A1 are the same or different and have the general structure:
wherein R7 and R8 are alkly, haloalkyl, aryl, haloaryl, and
X and X1 contain moieties capable of stimulus induced polymigration,
preferably photopolymerizable groups and N and M are integers.
In one embodiment the macromer has the general structure
wherein R9 R10 and R11a are independently selected
from the group consisting of alkyls, haloalkyls, aryls, and haloaryls and n and
m are integers and X and X1 are as defined above.
Another key component for use in the invention is a stimulus
absorbing compound. These compounds regulate the level of external stimulus needed
to initiate the polymerization of the MC.
In the preferred embodiment, the stimulus-absorbing compound
is a light-absorbing compound, more preferably a UV absorber. UV absorbers useful
in the practice of this invention include benzotriazole compounds having the general
and mixtures thereof, wherein X is selected from the group
consisting of H, alkoxy radicals preferably containing 1 to about 6 carbon atoms,
and halogen, R1 is selected from the group consisting of H and alkyl
radicals, preferably containing 1 to about 8 carbon atoms, provided that at least
one of X and R1 is other than H, and R2 is an organic radical,
preferably an alkenyl radical, with a terminal double bond. The alkoxy radical is
preferably selected from the group consisting of methyl radical and t-alkyl radicals
containing 4 to about 6 carbon atoms. The present compositions, including the covalently
bonded ultraviolet light absorbing component preferably are capable of absorbing
ultraviolet light in the range of about 300 nm. to about 400 nm.
As with the photoabsorber, the preferred photoinitiator
useful in the practice of the invention are UV-sensitive photoinitiators. Particularly
preferred photoinitiators are x-alkyl/benzoins having the general formula or structure:
wherein R1 is H, alkyl radical, aryl radical,
substituted alkyl, or substituted aryl radical, and R2 is H, alkyl radical,
aryl radical, substituted alkyl or substituted aryl radical; R3 and R4
are phenyl or substituted phenyl. Specific examples of R4 and R2
groups include methyl, phenyl trifluoropropyl, ethyl and cyano propyl. Phenyl substituents
from the R3 and R4 groups may include alkyl, alkoxy, halogen,
alkyaryl, cyano alkyl, haloalkyl and N, N dialkyl amino. Photoinitiator useful in
the practice of the invention include Irgacure 819, Irgacure 184, Irgacure 369 and
Irgacure 651 all available from Ciba Specialty Chemicals Inc.. Where clarity is
required, such as in optical elements, Irgacure 651 is preferred.
Also useful in the practice of the invention are photoinititators
having two initiators linker by a short polymer backbone. One such compound is Benzoin
polydimethyl siloxane Benzoin (B-pdms-B) wherein two benzoin moieties are linked
by a dimethyl siloxane bridge. The compound has the general formula:
Synthesis of these compounds is described in
United States Patent No. 4,477,326
The relative amounts of UV absorber and initiator will
vary depending upon the desire degree of absorbence for the specific application.
Generally the' ratio of photoinitiator to UV absorber will range from about 6:1
to about 25:1. Generally, the relative amounts of photoinitiator and UV absorber
can be calculated using the formula:
wherein T is transmittance, A is absorbence,
is the extinction coefficient for the UV absorber, b1 is the path length
of the light and c1 is the concentration of the UV absorber.
b2, and c2 are as defined above except that they relate to
the photoinitiator. In practice, it has been found that the actual absorbence is
generally less than the predicted values such that the amount use should generally
be al least 1.5 times the calculated amount.
The photoinitiator and UV absorber are combined with the
polymers, monomers or macromers to be polymerized or cross-linked. In one embodiment,
the photoinitiator is bound to the macromers. In other embodiments, the photoinitiator
remains free in the mixture.
While the above illustration is stated in terms of ultraviolet-based
initiators and absorbers, the same principles apply to other initiator/absorber
combinations. For example, the initiator may be activated by infra-red radiation.
In that case, an infra-red absorbing compound must be used to control the activation.
The same is true for other stimulus sources, such as light.
A key advantage of the optical element used in the present
invention is that an element property may be modified post-fabrication. In the case
of an IOL, for example, the modification may be made after implantation within the
eye. For example, any errors in the power calculation due to imperfect corneal measurements
and/or variable lens positioning and wound healing may be modified in a post surgical
outpatient procedure. Additionally, corrections due to physical changes in the patient
over time can also be made.
In addition to the change in the element's refractive index,
the stimulus-induced formation of the second polymer matrix has been found to affect
the element's power by altering the shape of the element in a predictable manner.
For example, in one embodiment, formation of the second polymer matrix changes the
thermodynamic equilibrium in this element. This in turn promotes the migration of
the MC which in turn can cause a change in the curvature of the lens. As a result,
both mechanisms may be exploited to modulate an IOL property, such as power, after
it has been implanted within the eye. In general, the method for implementing an
optical element for use in the invention having a first polymer matrix and a MC
dispersed therein comprises:
-  (a) exposing at least a portion of the optical element to a stimulus
whereby the stimulus induces the polymerization of the MC. This step may be shipped
if the element possesses the desired initial properties;
 (b) determining that a change in optical properties is required or
-  (c) exposing or reexposing at least a portion of the element to a stimulus
whereby the stimulus induces polymerization of the MC to cause a change in optical
properties of the element;
-  (d) waiting for a period of time;
-  (e) evaluating the performance of the element.
After exposure to an external stimulus, the element may
need to be reexposed to stimulus until the desired optical properties are achieved.
In another embodiment, wherein an optical element's properties
need to be modified, a method for modifying the element comprises:
 (a) exposing a first portion of the optical element to a stimulus
whereby the stimulus induces the polymerization of the MC; and
 (b) exposing a second portion of the lens to the stimulus.
The first element portion and the second element portion
represent different regions of the lens although they may overlap. Optionally, the
method may include an interval of time between the exposures of the first element
portion and the second element portion. In addition, the method may further comprise
re-exposing the first element portion and/or the second element portion any number
of times (with or without an interval of time between exposures) or may further
comprise exposing additional portions of the element (e.g., a third element
portion, a fourth element portion, etc.)
In general, the location of the one or more exposed portions
will vary depending on the type of refractive error being corrected. For example,
in one embodiment, the exposed portion of the IOL is the optical zone which is the
center region of the lens (e.g., between about 4 mm and about 5 mm in diameter).
Alternatively, the one or more exposed lens portions may be along IOL's outer rim
or along a particular meridian. In another embodiment, different regions of a spectacle
lens can be exposed to a stimulus thereby creating a bifocal spectacle lens. In
preferred embodiments, the stimulus is light. In more preferred embodiments, the
light is from a laser source.
Once the desired correction is made, there is no need for
further exposure to the stimulus to "lock in" the shape or properties. The presence
of the absorber compound will prevent further changes in the element until the element
is exposed to a stimulus of the correct frequency and intensity. This allows the
optical element to be used once the initial adjustment is made and, if needed, the
optical properties can be readjusted, in situ. In the case of an intraocular
lens, this means that after the initial adjustment, the patent can return for future
adjustment due to factors such as age or the like, over the life of the lens. In
another embodiment, spectacles can be created whose corrective qualities can be
repeatedly adjusted, eliminating the need for new lenses as the patient's vision
Through the focused use of external stimulus, such as UV
light, it is possible to cause polymigration of the MC in specific regions of the
optical element. This includes controlling the depth of the second matrix as well
as where the matrix is located in relation to the center of the element. Figures
3 through 5 illustrate this concept.
Figure 3 shows a portion of a cross section of an optical
element for use in the invention showing the first polymer matrix, 11 and the modifying
composition 12 dispersed within the first polymer matrix.
Figure 4 reflects the exposure of the optical element to
UV light in a predetermined pattern, duration and intensity. The UV absorber in
the exposed region prevents polymerization of the MC until the absorption level
of the UV absorber is exceeded. Then the inhibitor is triggered resulting in polymerization
of the MC to form a second polymer matrix. Formation of the matrix, however, only
occurs when the absorbence capacity of the UV absorber has been exceeded. There
it is possible to limit the depth of the second polymer matrix by limiting the intensity
and duration of the exposure to UV light. Figure 5 represents such a limited matrix
formation. The second polymer matrix only expands part way through the optical element
with optical properties different than the unmodified regions. Further exposures
of the optical element to UV light can then be used to alter the optical properties
As noted above, those adjustments can be made during the
course of the initial adjustment or can occur weeks or years later. Thus, as the
needs of the users change over time, the optical properties can be adjusted without
the need for surgery or the like.
The readjustable properties of the optical element can
also lead to novel data storage devices. By controlling the region where the second
polymer matrix is found, it is possible to record data in three dimensions and then
add or change the data stored at a later time.
The following examples are offered by way of example and
are not intended to limit the scope of the invention in any manner.
A series of siloxane slabs were prepared as reflected in
the tables below. In the control experiments, Part A consisted of a silicone polymer
Silicone MED 6820. Part B was prepared by mixing Silicone 6820 with a catalyst Pt-divinyltetramethyldisiloxane
complex. Parts A and B were separately degassed to remove any air and then blended
together- The mixture was then degassed and placed into a 1 mm thick mold where
it was held in a Carver press for 48 hours at approx. 1000 psi and at 40° C.
The experimental sections were prepared in the same manner
except that a blend of modifying composition, UV absorber and UV initiator was first
prepared and then added to Part A. The proportions of the components were as listed
in Table I. The modifying composition (identified as CalAdd in Table I) was methacrylate
endcapped dimethylsiloxane diphenylsiloxane copolymer with a Mn of from 700 to 1000.
In the table below, the initiators used consisted generally
of the following compounds, Irganox 651, a commercially available UV initiator made
by Ciba Specialty Chemicals, Inc.; Initiator B-pdms-B which is a blend of dual benzoin
structures having the general structure
wherein n ranges from 2 to 28, and B-L4-B which has the same general structure as
above except with n=2 only. Use of these initiators are preferred for applications
where clarity is essential such as optical elements. In other applications where
clarity is not essential, the use of other initiators such as Irgacure 369 is acceptable.
Again, the key is to use an initiator that is triggered in the desire range of wavelengths
and does not require an intensity in excess of prescribed safety standards.
In the experiments recited in the table below, the ultraviolet
absorbing compound used is UV AM (2-(2'-hydroxy-3'-tert-butyl-5'-vinylphenyl)-5-chloro-2H-benzotriazole),
a commercially available absorber. While the use of UVAM is preferred, other ultraviolet
absorbing compounds may be used.
In the experiments reported in Table I, polymer slabs were
prepared as described above. Sections of the slab were then taken and exposed to
light at 365nm for 30 to 120 minutes at intensities ranging from 0.0 to 8 milliwatts
per square centimeters. The transmission and absorbence of the UV light through
the section was determined by Differential Photocalorimetric Analyzer and reported
in the table as 10% Transmittance and &Dgr;H (heat of polymerization).
Part A Wt%
Part B Wt%
Irg 651 Wt%
B-L4-B Wt %
10 % T