FIBRES OPTIQUES AVEC REVETEMENT DE DIORGANOPOLYSILOXANE ET PHOTO-INITIATEUR CATALYTIQUE

OPTICAL FIBRES WITH COATING OF DIORGANOPOLYSILOXANE AND CATALYTIC PHOTOINITIATOR

Abrégé anglais

60SI-740
OPTICAL FIBERS WITH COATINGS OF
DIORGANOPOLYSILOXANE AND CATALYTIC PHOTOINITIATOR
Abstract of the Disclosure
Novel coating compositions for coating
optical fibers are provided which utilize ultraviolet
radiation-curable epoxy-functional or vinyl-functional
diorganopolysiloxanes on a core of high transparency
silica glass together with a catalytic amount of a
photoinitiator, to form flexible, loosely adherent,
and environmentally stable primary coatings. Such
coatings assist in preventing attenuation of light
impulses transmitted through the core fiber or reduce
the level of signal "noise". Use of the particular
coating compositions allows high-speed production of
such optical fibers.

Revendications

- 33 - 60SI-740
The embodiments of the invention in which an
exclusive property or privilege is claimed are defined
as follows:
1. A coated optical fiber comprising:
(a) a core of high transparency silica glass;
and
(b) a coating deposited on said core
comprising an ultraviolet radiation-curable silicone
coating composition comprising (i) a diorganopoly-
siloxane comprising units of the formula RR'SiO, wherein
R is hydrogen or monovalent hydrocarbon radical of from
1 to 8 carbon atoms, R' is hydrogen, a monovalent
hydrocarbon of from 1 to 20 carbon atoms, a monovalent
organic radical of from 2 to 20 carbon atoms having
epoxy or vinyl functionality, or a branched
organosiloxane derived from a vinyl MQ resin, a
sufficient amount of R' is said epoxy or vinyl
functionality to permit crosslinking, and a sufficient
amount of R' is said MQ resin to control viscosity, and
(ii) a catalytic amount of a photoinitiator.
2. A coated optical fiber as defined in claim
1, wherein said diorganopolysiloxane is epoxy-functional
and said photoinitiator comprises, alone or in
combination with a free-radical photoinitiator, a diaryl
iodonium salt of the formula,
<IMG>
wherein X is selected from the group consisting of SbF6,
AsF6, PF6, and BF4 and wherein R" is a monovalent

- 34 - 60SI-740
alkyl or haloalkyl radical of from 4 to 20 carbon
atoms and n is a whole number equal to 1 to 5,
inclusive.
3. A coated optical fiber as defined in
claim 2, wherein said diaryl iodonium salt is a
bis(dodecylphenyl)iodonium salt.
4. A coated optical fiber as defined in
claim 2, wherein the photoinitiator is a combination
of a bis(dodecylphenyl) iodonium salt and diethoxy-
acetophenone.
5. A coated optical fiber as defined in
claim 2, said diorganopolysiloxane has up to about 20%
by weight epoxy-functional groups.
6. A coated optical fiber as defined in
claim 5, wherein said epoxy-functional groups are
limoneneoxide groups.
7. A coated optical fiber as defined in
claim 5, wherein said diaryl iodonium salt is selected
from bis(4-n-tridecylphenyl) iodonium hexafluoro-
antimonate and bis(4-n-dodecylphenyl) iodonium
hexafluoroantimonate.
8. A coated optical fiber as defined in
claim 2, wherein said coating composition also
contains component (iii) in an amount sufficient to
lower the viscosity of a reactive diluent selected
from polyepoxide monomers or aromatic glycidyl ethers.
9. A coated optical fiber as defined in
claim 8, wherein said reactive diluents are selected
from the group consisting of limonenedioxide,
<IMG>,

- 35 - 60SI-740
<IMG> ,
<IMG> .
10. A coated optical fiber as defined in
claim 2, wherein the coating has a higher refractive
index than the silica glass, and said diorganopolysiloxane
is comprised primarily of polymeric units of the formulae,
<IMG>, and <IMG>.
11. A coated optical fiber as defined in
claim 1, wherein said diorganopolysiloxane is a
terpolymer comprised of dimethylsiloxy, methylhydrogensiloxy,
and methylvinylsiloxy units.
12. A coated optical fiber as defined in
claim 11, wherein the photoinitiator is selected from
the group consisting of perbenzoate esters and
polyaromatic photosensitizers of up to 20 carbon atoms
having at least two benzene rings which may be fused or
bridged by an organic radical or hetero-radical.

- 36 - 60SI-740
13. A coated optical fiber as defined in
claim 12, wherein the refractive index of the coating is
greater than 1.5 and said diorganopolysiloxane also
contains diphenylsiloxy units.
14. A method for high-speed production of a
coated optical fiber comprising:
(1) applying to a core fiber of high
transparency silica glass an ultraviolet radiation-
curable silicone coating composition comprising (i) a
diorganopolysiloxane comprising units of the formula
RR'SiO, wherein R is hydrogen or a monovalent hydro-
carbon radical of from 1 to 8 carbon atoms, R' is
hydrogen, a monovalent hydrocarbon radical of from 1 to
20 carbon atoms, a monovalent organic radical of from 2
to 20 carbon atoms having epoxy or vinyl functionality,
or a branched organosilane derived from a vinyl MQ
resin, a sufficient amount of R' is said epoxy or vinyl
functionality to permit crosslinking, and a sufficient
amount of R' is said MQ resin to control viscosity, and
(ii) a catalytic amount of a photoinitiator; and
(2) exposing said coated core fiber to
ultraviolet radiation of sufficient intensity and for a
sufficient period of time to cure said coating
composition on said core fiber to form a flexible,
loosely adherent, environmentally stable coating
thereon.
15. The method of claim 14, wherein said
diorganopolysiloxane is epoxy-functional and said
photoinitiator comprises, alone or in combination with a
free-radical photoinitiator, an iodonium salt having the
formula,
<IMG>

- 37 - 60SI-740
wherein X is selected from the group consisting of
SbF6, AsF6, and BF4 and wherein R" is a monovalent
alkyl or haloalkyl radical of from 4 to, 20 carbon atoms
and n is a whole number equal to 1 to 5, inclusive.
16. The method of claim 15, wherein said
diaryl iodonium salt is a bis(dodecylphenyl) iodonium
salt.
17. The method of claim 15, wherein the
photoinitiator is a combination of a bis(dodecylphenyl)
iodonium salt and diethoxyacetophenone.
18. The method of claim 15, wherein said
diorganopolysiloxane has up to about 20% by weight
epoxy-functional groups.
19. The method of claim 18, wherein said
epoxy-functional groups are limoneneoxide groups.
20. The method of claim 18, wherein said
diaryl iodonium salt is selected from bis(4-n-tri-
decylphenyl) iodonium hexafluoroantimonate and
bis(4-n-dodecylphenyl) iodonium hexafluoroantimonate.
21. The method of claim 14, wherein the
application step (1) is accomplished by drawing the core
fiber through a mass of said silicone coating
composition and immediately thereafter through an
orifice which regulates the coating thickness, and said
exposure step
(2) is accomplished continuously with step (1) by
drawing the coated fiber through a curing chamber
equipped with an ultraviolet radiation source
immediately after the coating step (1).
22. The method of claim 15, wherein said
coating composition also contains component (iii) in an
amount sufficient to lower the viscosity of a reactive
diluent selected from polyepoxide monomers or aromatic
glycidyl ethers.
23. The method of claim 22, wherein said
reactive diluents are selected from the group consisting
of limonenedioxide,

- 38 - 60SI-740
<IMG>
24. The method of claim 15, wherein the
coating has a higher refractive index than the silica
glass, and said diorganopolysiloxane is comprised
primarily of polymeric units of the formulae,
<IMG>
25. The method of claim 14, wherein said
diorganopolysiloxane is a terpolymer comprised of
dimethylsiloxy, methylhydrogensiloxy, and methyl-
vinylsiloxy units.

- 39 - 60SI-740
26. The method of claim 25, wherein the
photoinitiator is selected from the group consisting of
perbenzoate esters and polyaromatic photosensitizers of
up to 20 carbon atoms having at least two benzene rings
which may be fused or bridged by an organic radical or
hetero-radical.
27. The method of claim 26, wherein the
refractive index of the coating is greater than 1.5 and
said diorganopolysiloxane also contains diphenylsiloxy
units.

Description

~ 60SI-740
Since the discovery of a suitable light source in
the laser around 1960, the only technical obstacle to
lightwave communications over great distances was the
development of a suitable ~ransmission medium. Air, or
S example~ although penetrable by light, was unsuitable
because rain, fog, and other atmospheric conditions could
weaken (or "att~nuate") the light signal. Development of
the glass fiber lightguide, or optical fiber, provided an
excellent and relatively inexpensive transmission medium.
Modern optical fibers typically consist o~ a core
o~ high transparency silica glass, which transmits the
light, surrounded by a transparent coating of lower
re~ractive index than the core. The coating acts
as an internal mirror, reflecting the light back into the
core and thus preventing loss of the light signal outside
the optical path.
While the lower refractive index coating
theory has provided serviceable lightguides for relatively
short-distance telecommunications (e.g., building-to-
building or intramural), for lons-distance telecommunica-
tions (e~g., transcontinental), where many lightguides may
be bundled together, the problem o~ signal "noise" becomes
more important than signal attenuation. To a partic~lar
information-carrying lightwave, any incidental lightwaves
(carrying other information) or signals disrupting to the
first lightwave are "noise" ~rom which the desired informa-
tion must be extracted. It has been found that signal
noise can be minimized in lightwave transmissions by
coatings of hi~he_ refractive index than the core fiber.

~s~
- 3 - 60SI-740
There is thus a continuing search for coating
materials having either a higher or a lower refractive
index than the core fiber material. For silica glass
optical fibers, the reference point is 1.47, the
refractive index of silica glass fiber. Suitable
materials will have refractive indices lower,
pr~ferably less than 1.45, or higher, preferably
greater than 1.50.
In the production of fiber optics cable for
telecommunications, the material used for primary
coatings must be very flexible, must not adhere too
closely to the glass fiber core (to permit joining and
other manipulations), and must maintain its integrity
and optical characteristics in changeable environments,
including temperature cycles of from -60 to -~80C.
Many fiber optics proclucers have adopted
heat~curable polydimethylsiloxane coatiny compo~itions
as the primary lightguide coatings. The uncoated
optical fiber is typically drawn through the silicone
composition, then through an eight-inch over at 800C
for curing. The time required to fully cure the
silicone composition has become the limiting factor in
increasing line speeds in producing optical fibers:
Since higher oven temperatures (or longer ovens) cause
oxidation of the silicone and also begin to affect the
drawn fibers, line speeds cannot be increased beyond
about 30 meters/minute with commercially available
thermally cured silicone coatings.
The desire to attain higher production speeds
has led optical fiber producers to investigate
ultraviolet radiation (UV)-curable materials, but a
coating composition having a combination of properties
comparable to the silicone materials has not as yet
been found.

~2 ~ 8Z 1 60SI-740
-- 4
It has now been discovered that certain UV-curable
polysiloxane compositions provide novel coating materials
for optical fibers which exhibit the desired combination
of proper~ies for optical fiber cladding layers. The
discovery includes both low refractive index and hiyh
refractive index compositions, all of which cure rapidly
on brief exposure to ultraviolet radiation, thus ofering
significant advantages in safety, cure rat~, and cost
over thermally cured silicone materials.
SUMMARY OF THE INVENT ION
Accordingly, it is an object of the present
invention to provide a aster curing alternative to
thermally cured polydimethylsiloxane compositions or
the primary coating layer of optical fibers.
It is a further object of the present invention
to provide a coating material ~or optical fibers which
2Q is easily and safely applied, and which ma~ be cured by
brief exposure to ultraviolet radiation.
It is a further object of the present invention
to provide novel low refractive index coating compositions
and high refractive index coating compositions.
I* is a further object of the present invention
tG provide coated optical fibers which are efficiently
and inexpensively produced and can be adapted to a wide
30 variety of lightwave telecommunications usés.

~25682~ 605I-740
It is a fuxther object o~ the present invention
to provide a method for applying a primary coating to an
optical fiber core which will allow increased production
line speeds while providing a cured coating which is
flexible~ not closely adherent to the core fiber, and
capable of withstanding dramaLi~ changes in environmental
conditions~
These and other objects are accomplished herein
by an ultraviolet radiation-curable coating composi-
tion comprising (A) a diorganopolysiloxane comprising units
of the formula RRISio, wherein R is hydrogen or a monova-
lent hydrocarbon radical of from 1 to 8 carbon atoms and
R' is hydrogen, a monovalent hydrocarbon radical o~ from
1 to 20 carbon atoms or a monovalen~ organic radical o~
Erom 2 to 20.carbon atoms having vinyl or epoxy ~unc--
tionality, and (B) a catalytic amount of a photoinitiator.
Also contemplated by the present invention is an
op-tical fiber comprising:
(A) a core of high transpar~ncy silica glass; and
IB) a coating layer deposited on said core
comprising an ultraviolet radition-curable silicone
coating composition comprising (il a diorganopolysiloxane
comprising unitq o~ the ~ormula RR'Sio, wherein R is
hydrogen or a mono~alent hydrocarbon radical of from 1 to
8 carbon atoms and R7 is hydrogen, a monovalen~ hydrocarbon
radical of from 1 to 20 carbon atoms or a monovalent organic
radical of from ~ to 20 carbon atoms having ~inyl or epoxy
functionality, and ~ii) a catalytic amount of a photo-
initiator; said coa~ing layer having a refractive index
higher or lower than said silica glass.

60SI-740
_ 6
Another feature of the present invention is a
method for the high-speed production of an optical fiber
comprising:
(1) Applying to a core fiber of high transparency
silica glass an ultraviolet radiation-curable silicone
coating composition comprising (i) a diorganopolysiloxane
comprising units of the formula RR'SiO, wherein ~ is
hydrogen or a monovalent hydrocarbon radical of from 1 to
8 carbon atoms and K' is hydrogen, a monovalent hydro-
carbon radical of from 1 to 20 carbon atoms or a monova-
lent organic radical o~ from 2 to 20 carbon atoms having
vinyl or epoxy functionality, and ~ii) a catalyt.ic a~lount
o~ a photoinitiator; and
(2) Exposing said coated core fiber to ultraviolet
radiation of sufficient intensity and for a sufficient
period of time to cure said coating composition on said
core fiber to form a flexible, loosely adherent, environ-
mentally stable coating thereon, which coating layeris of a lower or higher refractiYe index than the
core fiber.
4 A method for advantageously controlling the
refractive index and viscosity of the disclosed polysi-
loxane coating materials is also contemplated.
For the purposes of the present invention, the
term l'loosely adherent" refers to a desired property of
the primary coating lay~r o~er a glass optical fiber
meaniny that the coating layer does not adhere so strongly
to the core fiber as to inhibit the common mechanical
operations performed with optical fibers, such as joining.

60SI-740
_ 7
- The texm does not reer to the optical relationship between
~he core and the cladding (primary coating) layer. The term
"environmentally stable" refers to the ability of the
coating material of the present invention to maintain
its integrity and optical characteristics through en-
vironmental changes to which fibers are routinely
exposed, particularly cycles in temperature between the
extremes of about -60C and ~80C.
D~TAILED DESCRIPTION OF THE INVENTION
The coated optical fibers of the presen-t invention
are prepared by ~pplying a rapidly curable, UV-curable,
epoxy-~urlctional or vinyl-functional silicone coating
composition to a trarlsparent silica glass fiber and then
subjecting i~ briefl~ to ultraviolet radia~ion. The
coated optical fibers of the present invention exhibit
all of the desired properties seen in thermally cured
polydimethylsiloxane-coated fibers while providing the
increased production capability, reduced e~ergy expenses,
and safety of ultraviolet radiation curing.
Ultraviolet radiation IW~ is one of the most
widely used types of radiation because of its low cost,
ease of maintenance, and low potential ha~a~d to
industrial users. W -curable compositions not only
exhibit a very short curing time ~ut also avoid the high
energy costs, environmental restrictions and safety
hazards associated with the use of heat-curable materials.
The W-curable compositions employed in the p~e~ent
invention are basically comprised of two components~
an epoxy-functional or ~inyl-functional organopolysiloxane
base polymer combined with (ii) a photoinitiator capable
3S of promoting rapid cure of the composition on exposure
to ultraviolet radiatio~.

60SI-740
~l2~
The epoxy-functional organopolysiloxane base
polymers contemplated by the present invention are com-
prised of units having the general Iormula RR'SiO, where
R is hydrogen or a monovalent hydrocarbon radical of from
1 t~ 8 carbon atoms and where R' can be the same as R or
a monovalent organic radical of from 2 to 20 carbon atoms
having epoxy functionality. The epoxy-silicone polymer
may have up to about 20% by weight epoxy-functional groups
and must be capable of curing, or cross-linking, when
combined with a suitable photoinitiator and exposed to
ultraviolet radiation. The cured polymeric composition
must be of a lower or higher refractive index than the
optical fiber core and exhibit 1exibility, loose adhesion
to the core fiber, ~nd ~nvironm~ntal stability.
Preferred epoxy-Eunctional polydiorganosiloxanes
contemplated by the present invention are more specifi~
cally dialkylepoxy-chainstopped polydialkylalkylepoxysi-
` loxane copolymers wherein the polysiloxane units contain
lo~er alk~l substituents, notably, methyl groups. Theepoxy functionality is obtained when certain of the
hydrogen atoms on the polysiloxane chain of a
polydimethyl-methylhydrogensiloxane copolymer are
reacted in a hydrosilation addition reaction with other
organic molecule5 which contain both ethylenic unsatura-
tion a~d epoxide functionality. Ethylenically unsaturated
species will add to a polyhydroalkylsiloxane to form a func-
tion~lized polymer in the presence of catal~tic amounts of a
precious metal catalyst. Such a reaction is the cross-
linking mechanism for other silicone compositions,however, in the present invention, a controlled amount
of such cross-linking is permitted to take place in a
silicone precursor fluid or intermediate, and this is
referred to as "pre-crosslinking". Pre-crosslinklng of

~ 60SI-740
_ g
the precursor silicone fluid means that there has been
partial cross-linking or cure of the compasition and
sffers the advantages to the present invention of
enabling swift W -initiated cure with :Little expense
for energy and elimination of the need for a solvent.
The UV-curable epoxy-functional silicone inter-
mediate fluid comprises a pre-crosslinked epoxy-
functional dialkylepoxy-chainstopped polydialkyl-alkyl-
epoxy silicone copolymer fluid which is the reactionproduct of a vinyl- or allylic-functional epoxide and
a v.inyl~~unctional siloxane crosslinking Eluid havlng
a viscosity o~ approximately l to lO0,000 centipoise
at 25C with a hydrogen-functional siloxane precursor
fluid having a viscosity of approximately l to lO,000
centipoise at 25C in the presence of an effective
amount of precious metal catalyst for facilitating an
addition cure hydrosilation reaction between the
vinyl-functional crosslinking fluid, ~inyl-functional
epoxide, and hydrogen-Eunctional siloxane precursor
fluid.
The unsaturated epoxides contemplated
ar~ any of a number of aliphatic or cycloali-
2S phatic epoxy compounds having olefinîc moietieswhich will readily undergo addition reaction to
-SiH-functional groups. Examples of such
compounds include l-methyl~4-isopropenyl cyclo-
hexeneoxide (limoeneoxide; SC~I Corp.); 2j6 dimethyl
2,3-epoxy-7-octene (SCM Corp.) and 1/4-dimethyl-4-
vinylcyclohexeneoxide (Viking Chemical Co.~. Limoneneoxide
is pre~erred.
~5

` ~2~ 60SI-740
_ 10 _
O "
The precious metal catalys~ for the hydrosilation
reactions involved in the present invention may be
selected from the group of platinum-metal complexes
which inclu~es complexes of ruthenium, rhodium,
5: palladium, osmium, iridium and platinuIn. Examples of
such hydrosilation catalysts suitable for the purposes
herein are described in U.S. 3,220,972 lLamoreaux),
U.S. 3,715,334 (Karstedt), U.S. 3,775,452 (Karstedt) and
U.S. 3,814,730 (Karstedt)
.
In the present invention, the vinyl-Eunct:ional
siloxane cro~slinking f}uid can be selected from the
group consisting oE dimethylvinyl-chai~stopped linear
polydimethylsiloxane, dimethylvinyl chainstopped
polydimethyl-methylvinyl siloxane copolymer, tetravinyl-
tetramethylcyclotetrasiloxane and tetramethyldivinyldi-
siloxane. The hydrogen-functional siloxane precursor
fluid can be selected from the group consisting of
tetrahydrote~.am2thyl-cyclotetrasiloxane, dimethylhydrogen-
chainstopped linear polydimethylsiloxane, dimethylhydrogen-
chainstopped polydimethyl-methylhydrogen siloxane
copolymer and tetramethyldihydrodisiloxane.
Preferred photoinitiators for the epoxy-functional
base polymers of the present invention include iodonium
salts having the general formula,
\ Y~j

60SI-740
~æ~
~ 11
wherein X is selected from SbF6, AsF6" PF5, or BF4 and
wherein R" is a monovalent alkyl or haloalkyl radical
of from 4 to 20 carbon atoms and n is a whole number
equal ~o 1 to 5, inclusive. These compounds have been
S found to be highly efficient in promoting ~he W -initated
cationic ring-opening curing mechanism for epoxy-functional
polysiloxanes, as disclosed in U.S~ 4,279,717 IEckberg
et al.) . -
Preferred of the iodonium salt photoinitiators
utilized with the epoxy-functional silicones of the
present invention are diaryl iodonium salts derive& from
"linear alkylate" dodecylbenzene. Such salts have the
general formula,
~S~+X~
wherein X equals SbF6, AsF6, PF6 or BF4. These bis(~-
dodecylphenyl) iodonium salts are very effective
initiators for ~he W cure of a wide ~ariety of epo~y-
functional silicones.
"L~near alkylate" dodecylbenzene is known commer-
cially and is prepared by Friedel-Craft alkylation cf
benzene with a C(ll 13~ a-olefin cut. Consequently,
the alkylate contains a preponderance of branched chain
dodecylbenzene, but there may in fact be large amounts
of other isomer~ of dodecylbenzene such as ethyldecyl-

~ 2 5~ 60SI-740
benzene, plus isomers of undecylbenzene, tridecylbenzene,
etc. Note, however, that such a mixtux2 is responsible
for the dispersive character of the linear alkylate derived
catalyst and is an aid in keeping the material fluid.
These catalysts are free-flowing, viscous fluids at room
temperature.
The preferred bis(dodecylphenyl) iodonium salts
are alkane-soluble and water-insoluble, and they dis-
perse well in the preferred epoxy-functional polysiloxanes
utilized in the coating compositions of the present
invention. Bis(4-n-tridecylphenyl) iodonium hexafluor-
oantimonate and bis(4-n-dodecylphenyl) iodonium
hexa~luoroankimonate are most preerred.
The vinyl-functional base polymers contemplated
herein are actually photoreactive terpolymers capable of
curing on exposure to W radiation in the presence or
certain radical photoinitiators. The terpolymers are
mixed dimethylvinyl- and trimethyl-chainstopped linear
polydimethyl-methylvinyl-n,ethylhydrogensiloxane terpoly-
mer fluids and can be synthesized by acid equilibration
of polymethylhydrogen siloxane fluid, tetramethyl-
tetravinylcyclotetrasiloxane (methylvinyl tetramer) andoctamethylcyclotetrasiloxane ~dimethyl tetramer).
These vinyl-functional terpolymers are curable
i~ the presence of polya~omatic photosensitizers having
at least ~wo benzene rings which may be fused or
bridged by organic radicals or hetero rad cals such as
oxa, thio, and the like. Preferred among these photo-
sensitizers are benzophenone and t-butylanthra~uinone.

~2 ~ ~ 60SI-740
The terpolymers may also be cured in the presence
of certain perbenzoate esters having the general formula:
R3-o_o-c ~
where R3 is a monovalent alkyl or aryl group and 2 is
hydrogen, alkoxy, alkyl, halogen, nitro, amino, primary
and secondary amino, amido, and the like. The nature
of Z will affect the stability of the peroxy bond, and
electron-poor substitutent stabilizing the peroxy bond,
and an electron-rich substituent making the peroxy bond
more reactive~ Pre~erred perbenzoate esters lnclude
t-butylperbenzoate and its para-substituted derivatives,
including t-butylper~p-nitrobenzoate, t-butylper-p-
methoxybenzoate, t-butylpex-p-methylbenzoate, and t-butylper-
p-chlorobenzoate. The photoreactive polysiloxane ter-
polymers of the present invention/ and photoinitiators
effectively used therewith, are disclosed in Canadian
Patent Application Serial Number ~ o~ filed
~/oY~nl er 30, /~ ~If
The amount o photoinitiator employed is not
critical, so long as proper curing is effected. As with
any catalysts, it is preferable to use the smallest
effective amount possible; howe~er, for purposes of
illustration, catalyst levels of the aforementioned
compounds from about 1% to 5~ by weight have been found
suitable. Com~inations of photoinitia~ors ~re also
contemplated.
--
._
.. ... _ .. -- .. . . . .. ....... .... .. .. ._ ,. . _ _ _ ._ .. , . ... , . . _._ ... ~ _ . _. . __ .. . _ .. ...
~ ~ .

60SI-740
- 14-
The epoxy-functional and vinyl-functional poly-
siLoxanes described above typically have a low refractive
index, i.e., less than 1.47, where the non-epoxy or non-
~inyl substituents along the siloxane polymer chain are
S hydrogen or lower alkyl. The refractive index of the
polysiloxanes can be raised by for.~ulating polymers
which also contain diphenylsiloxy units.
As discu~sed previously, an epoxy-functional
10 polydiorganosiloxane may be obtained by reacting a vinyl-
functional epoxide with a SiH-containing polydiorgano-
siloxane, such as polydimeth~l~methylhydrogen siloxane
copolymer. To achieve a higher refractive index, a
diphenylsiloxy-containing and SiH-containing polysiloxane
15 can be synthesized by co-hydrolysls of diphenyldichloro
silane, dimethyldichloro silane, and methylhydrogendi-
chloro silane, and this polymer could theoretically be
reacted with a vinyl-functional epoxide to obtain epoxy
functionality on the polymer. However, small quanities
20 of acid residues associated with, and very difficult to
remove from, such linear high-phenyl SiH polymers act to
open the oxirane ring of the epoxides, resulting in poly-
siloxanes which are not photoreactive. A further
difficulty with this approach is that in order to raise
25 the refractive index above 1.50, the polymer must contain
more than 30 mole percent (greater than 50 weight percent)
diphenylsiloxy unitst making the high-phenyl polysiloxanes
vexy costly.
An important feature o~ the present invention is
the di~cover~ of a cost~effective way to produce W -curable
epoxy-functional silicones having a refractive index greater
than 1.47, making the present compositions suitable for
a wider range of fiber o~tic coati.ng applications. In

~2~ 60SI-740
- 15
preferred features of the invention, high refracti~Je index
compositions are prepared by reacting a SiH-containing
polysiloxane with both a vinyl-functional aromatic com-
pound of from l to 20 carbon atoms (to obtain on-chain
5 aromatic substituents) and vinyl-functional epoxides
(to obtain epoxy-functional substituents).
The vinyl-functional aromatic compound contains
at ]east one aromatic ring and at least one aliphatically
lO unsaturated site capable of reacting via hydrosilation
addition with an SiH group to form a car~on-silicon bond.
Ethenylbenzene (styrene) is most preferred, however many
other vinyl aromatic compounds will suggest themselves to
per ons skilled in this art, and ~hese are intended to be
15 included herein.
In reactions with SiH-containing polysiloxanes, the
vinyl aromatic compound and the unsaturated epoxide
may be introduced simultaneously (and compete or hydride
20 reaction sites) or, preferably, in tandem, which allows
more control over the degree of epoxy ~unctionality and
refractive index of the final product. Since raising the
refract.ive index o~ the composition is the chief purpose
of employing such vinyl aro~atic compounds, reacting
25 these compounds first and adding epoxy functionality
second is most preferred. The exact relative amounts of
vinyl aromatic compound and ~inyl-functional epoxide
employed will vary over a wide range, depending on the
r~fractive index desired and the degree of reactivity
30 desired. By judicious selection of the reactant~, their
amounts, and the reaction conditions, high refractive index
epoxy-functional silicones which are tailored to specific
requirements may be produced~ In view of this, simple
experimentation with the processing perameters is contem-
35 plated.
,

60SI-740
-16 -
Combination of the iodonium salt photoinitiators
with other known photoinitiators is also comtemplated.
Preferred among such catalyst blends are combinations
of iodonium salts with free-radical photoinitiators such
as acetophenone derivatives. Even (1:1) blends of diaryl
iodonium salts with diethoxy acetophenone are most preferred.
The present W -curable silicone coating composi-
tions are applied to the optical fibers by methods well
10 known in the art. Typically, for example, uncoated
optical fibers are drawn through a coating solution and
then in-line through a curing chamber. ~s discussecl above,
the curing step has been found heretofore to be the limit-
ing factor in the speed at which the coating operation can
15 be perormed. U~e of epoxy-functional silicone coating
compositions c~red by brief exposure to ultraviolet radia-
tion in accordance with the present discovery provides
a flexible, loosely adherent, environmentally stable
primary coating on the silica glass core fiber which can
20 be applied at increased line speeds and without subjecting
the coating material or fiber of high oven temperatures.
With the increased line speeds made possible with
the compositions o~ the present invention, it has been
25 di~covered (see, i.e., Examples 1-3, infra.) that the
viscosity of the coating compositions becomes an additional
property which the industrial producer of optical fibers
must be concerned with. In general, it is seen that
viscosities below about 1000 cps do not permit "we~ting"
30 ~oating) of the fiber where the production speed is high,
at viscosities greater $han about 10,000 cps, entrainment
of air bubbles in the coating occurs, leading to imperfections
in the primary coating that cause signal attenuation.

~;25~
- 17 - 60SI-740
~ or the epoxy-functional silicones produced
via hydrosilation addition of vinyl-functional epoxides
to an SiH-containing polysiloxane, the viscosity of the
final product has been hard to predict, as it is
dependent no only on the viscosity of the
SiH-containing precursor but also on the degree of
epoxy functionality. For example, a 90 cps precursor
fluid containing 1 weight percent methylhydrogensiloxy
units converted to an epoxy-functional silicone
incorporating
18 weight percent limoneneoxide has a viscosity of
about 400 cps; while a 200 cps precursor fluid
containing 10 weight percent methylhydrogensiloxy unit
converts to an epoxy-functional silicone of 3,000 cps
viscosity and a 200 cps precursor fluid containing 6
weight percent methylhydrogensiloxy units incorporating
11.7 weight percent limoneneoxide has a viscosity oE
100 cps.
It has now been discovered that simultaneous
addition of a vinyl MQ silicone resin and the vinyl-
functional epoxide to a given SiH-containing
polysiloxane provides products where the viscosity is
dependent on the resin content. The vinyl MQ resins
contemplated are polysiloxanes having primarily
monofunctional ~M) units or tetrafunctional (Q) units
The vinyl groups of the resin compete with the
vinyl-functional epoxide for available hydride sites in
the polysiloxane. The resin is thereby incorporated
into the epoxy-functional polysiloxane product.
The vinyl MQ resins are made up of M units
having the formula Y3Sio1/2 and Q units having the
formula sio4/2, with the ratio of M to Q units being
roughly 0.5 to 1.0 and preferably about 0.65. The Y groups
may be, independently, the same or different monovalent
hydrocarbon radicals of no more than 2 carbon atoms, and

60SI-740
_18 _
at least 1 Y group must be vinyl. Such radicals include,
for example, methyl, ethyl, vinyl or etnynyl. Methyl
and vinyl are preferred~ A general discussion of these
resins is found in Chapters 1 and 6 of Noll, Chemistry
and ~echnoloqy of Silicones (2nd Ed., 19683.
In features of the present invention which make
use of the foregoing discovery, the final W -curable
polysiloxane product will contain pendent siloxy groups
corresponding to the incorporated MQ resins. For these
polysiloxanes, the definition o the R' radical in the
formulas described above would be expanded to include
a branched org~nosiloxane radical comprised of from 1 to
200 Q siloxy units oE the ormula SiO4/2 and M siloxy
units having the Eormula Y3SiOl/2, wherein Y is a monova-
lent hydrocarbon radical of 1 or 2 carbon atoms. It is
understood also that the terms "diorganopolysiloxane'l
and "organopolysiloxane ~ase polymer" as used herein to
describe the epoxy~ and vinyl-functional polymer products
of the invention are broad enough to cover such branche~
polysiloxane pendent groups.
Where high refractive index materials are desired,
a further method for modifying the viscosity of the
coating compositions, which also introduces refractive
index-raising aromatic groups into the system, is to
employ aromatic glycidyl ethers as reactiv diluents.
The aromatic glycidyl ether reactive diluents also pro-
vide additional epoxy functionality and so may enhance
the curing characteristic~ of the present coatin~
compositions, as was disco~ered for silicone paper
r~lease compositions by the addition o~ epoxy polymers
in Canadian Patent Applicatio~ Serial Number ~28~142
filed May 13, 1983.
3S

~1 60SI-740
19 _
In order that persons skilled i.n the art may better
understand the practice of the inventi.on, the following
examples are provided by way of illust.ratiQn, and not by
way of limitation.
EXAMPLES 1-3
Three epoxy-functional silicone coating composi-
tions were prepared for optical fiber coating trials as
follows:
Sample 1
_
5 parts by weight of a 250 cps dimethylv:inyl-
chainstopped polydimethylsiloxane fluid, 320 parts by
weight o~ limoneneoxide, and 1 part by weight of a
platinum catalyst (platinum-octyl alcohol complex) were
added to 1,000 parts by weight of toluene. 1,000 parts
by weight of a 150 cps dimethylhydrogen-chainstopped
polydimethyl-methylhydrogen silox~ne copolymer fluid
containing abou~, 8.7 weight percent _SiH groups were
added slowly to the stirring mixture at room temperature
over 1 hour. The reaction mixture was then refluxed at
1~0C for 21 hours, at which point 30 parts by weight
of n-hexene were added and refluxing continued for 4
hours more. The solvents were stripped under a vacuum
at 130C to yield a 1,000 cps limoneoxide-functional
polysiloxane fluid containing about 17.2 weight percent
limoneneoxide groups.
~ .
.~

~2 ~ 60SI-740
20 -
o
Samples 2_& 3
Two other limonenPoxide-func~ional products
designated Sample 2 and Sample 3 were ,prepared following
the same procedure as for Sample 1~ above. Sample 2 was
a 680 cps fluid containing approximately 14O0 weight
percent limoneneoxide groups; Sample 3 was a 700 cps
fluid containing approximately 11.7 weight percent
limoneneoxide groups.
All three compositions were combined with 1.5
weight percent o bis(dodecylphenyl) iodonium
hexa~luoroantimonate cationic pho~oinitiator.
lS Each coating composition was applied to 10 mil
diameter pure silica glass fiber immediately after it
was drawn. The coating device consisted of a small cup
fitted with a 0.025-inch orifice at its base. Coating
was accomplished by pulling the drawn optical fiber down
through the test composition, then through the orifice
to regulate coating thickness. The coated fiber was
passed immediately through a nitrogen-inerted curing
chamber where it was exposed to a single ocused
300 watt, 10 inch long Fusion Systems "H" ultraviolet
lamp. The coated iber was finally wound on a taKe-up
roll.
The coated fibers were observed to make sure the
coating was fully cured. The line speed was gradually
increased in order to determine the line speed at which
the coa~ing on the ~iber would not cure completely,
~ha~ is, in oxder to discovex the point a~ which line
speed surpassed cure rate.
, .

- 60SI-740
~25~
With each of the samples studied, the coating
compositions still cured completely at line speed at
which the coating rate was surpassed. In other words,
"wetting" (coating) of the op~ical fiber by the silicone
fluids ceased at line speeds where complete curing was
still observed. For the ~hree sample compositions,
complete curing was ob~erved under the following condi~
tions:
Loss of Wetting Coating Thickness
lOCompositions(meters/min.l ~microns)
Sample 1 50 125
Samp}e 2 30 120
Sample 3 33 120
The~e results compare favorably with the maximum line
speed of approximately 30 meters per minute observed
with commercially available heat-curable silicone systems.
XAMPI,~S ~-7
~ 00 pbw o~ linear 60 ~ps dimethylhydrogen-chain-
stopped polydimethyl methylhydrogensiloxane fluid con-
taininy 10 weight percent methylhydrogensiloxy units
were dissolved in 600 p~w ~exane. To this solution
~containing l.0 mole of active SiH groups) were added
152 pbw limoneneoxide (1 mole), about 25 ppm platinum
in the form of a soluble complex catalyst, and varying
levels of a vinyl MQ silicone resin. The reaction
mixtures were reflu~ed for four hours, after which the
unreacted SiH was removed by reaction with hexene.
Stripping the solvents, unreacted limoneneoxide, and
hexane under vacuum resulted in the following epoxy
functional poiymers:

- 22 - 60SI-740
~ Limonene- ~ MQ Viscosity
Compositions oxide* resin** (cPs)
Sample 4 19.6` 0.0 340
Sample 5 18.5 7.6 900
Sample 6 14.3 11.5 1976
Sample 7 16.1 12.8 3800
* Weight percent limoneneoxide incorporated in
polymer.
** As weight percent resin solids after stripping
solvents.
Cure was evaluated by blencliny 100 parts by
weight (pbw) of each sample w.ith 1.5 pbw diethoxy
acetophenone and 1-5 pbw (Cl2~l25Ph)2IsbF6 (a
~ree-radical/cation.ic co-catalyst system disclosed for
curing epoxy-functional silicones in the
aforementioned Canadian Application Serial Number
428,142, filed May 13, 1983). The complete coating
compositions were manually applied as 2 mil coatings
on polyethylene kraft paper using an adhesive coater
and exposed to two focused medium pressure mercury
vapor ultraviolet lamps in a PPG 1202 ultraviolet
processor. Cure was evaluated qualitatively at
various conveyor speeds (varying exposure time), UV
intensities, and cure environments, with the following
results:

~ ~ ~ 60SI-740
- 23 -
o
W Power ~ure Line ~
~le (Watts) AIM (meters/sec) Cure
4 400 Air 2.0 E~cellent cure-no ~r~ no
migration, gocd adhesion
- 4 300 N2 2.0
400 Air 2.0 "
400 N2 2.5 "
300 N2 2.5 '~n~ed' - easily
r~d off ~ strate
6 400 Air 2.0 Cured - fa~ adhesion to
subs~ate
6 400 N~ 2.0 Excellent cure no ~ ar -
good adhesion
7 400 Air 2.0 Excellent cure - no ~ ~r,
good adhesion
7 400 N2 2.0 "
It can be seen by comparisons with the control
composition (Sample 4) that incorporation of vinyl MQ
resins, while allowing formulation of epoxy-functional
silicone compositions within a specific target viscosity
range, does not make a signiicant qualitative difference
n cure.
EXAMPLE 8
90 pbw of a 10,000 cps epoxy-~u~ctional poly-
siloxane incorporating 11.3 weight percent limoneneoxide
were blended with 10 pbw of 1,2-epoxy dodecane (ViXolox,
1~, Viking Chemical Co.)., resulting in a 4200 cps blend.
The dual catalyst of Examples 4-7 was added and the
complete composition applied to a 10 mil optical fiber
by the same method as in Examples 1-3, above, up to a
drawing speed of 60 meters/minute. At this speed, the
coating became too thin (less than 80 microns) and the
fiber entering the coating bath was so ho~ that thermal

oOSI-740
~2~
- 24 -
degradation (smoking) of the coating composition was
apparent; however, the coating still cured at this speed
on exposure to a 300 Watt W source. These results
indicate that using the compositions of the present inven-
tion, line speeds for production of optical fibers may bedoubled with the proper formulation. In addition, it is
evident from this example that the omega-epoxy C(8 11)
aliphatic hydrocarbons preferred as cure-enhancing
. reactive diluents as disclosed in the aforementioned
Canadian Patent Application Serial Number 428,142, filed
May 13, 1984, are useful as viscosity controlling agents
for the optical fiber coating compositions herein.
EXAMPLES 9-12
200 pbw of a linear 75 cps trimethyl-chainstopped
polydimethyl-methylhydrogensiloxane fluid having 44.9
weight percent methylhydrogensiloxy units (1.5 moles of
active SiH groups) were disbursed in 400 pbw hexene with
126 p~w styrene (1.27 moles). 0.35 pbw platinum catalyst
were added, the reaction mixture was agitated and slowly
heated to 60C, at which point an exotherm occurred,
taking the temperature to 75C be~ore falling back to
around 65~C, where is was maintained for 1 hour. Infrared
analysis showed 0.23 moles unreacted SiH, indicating that
essentially complete addition of the styrene had taken
place. 60 pbw limoneneoxide were then added (0.4 moles)
and the reaction mixture returned to 69C and maintained
at this temperature, with agitation, for 64 hours. The
produc~ exhibi~ed only .007 moles of unreacted SiH, which
was removed by brief reaction with hexene. The solvents
and unreacted monomers were stripped to yield a viscous
~luid product (11,680 cps) having a refractive index of
1.492. This fluid, desi~nated Sample 9, incorporated
33.0 weight percent styrene and 13.1 weight percent

60SI-740
~ 25
linomeneoxide. Three other compositions were prepared in
similar fashion to give the following.
~igh~ % ~ight % Viscosit~ Refractive
~ Styrene Limon~ide (cps) Index
Sample 9 33.0 13.1 11,680 1.4920
Sa~ple 10 32.9 14.4 3~100 1.4902
Sample 11 29.1 29.1 88,000 1.4930
Sample 12 31.8 22.1 21,000 1.4970
Blends of the above polymers with cresyl glycidyl
ether (DY 023, Ciba Geigy) were prepared to yield the
following compositions:
~4ight ~ Visoosity Refractive
G~sitions D~ 023 ~ Index ~_
155a~pla 9A 20~0 1,200 1.4990
Sample lOA 25.0 2,500 1~4992
~ple llA 25.0 3,600 1.5080
Sample lZA 25.0 1,680 1.5030
The W cure characteristics of the above ~-phene~hyl-
and lim~neneoxide-substituted polysiloxane fluids described
above were qualitatively tested by adding 4 weight percent
of a 1:1 blend of diethoxyacetophenone and (Cl~H25Ph)2ISbF6,
coating the ca~alyzed mixtures onto polyethylene kraft
substrates and then exposing the coated substrates to
W radiation as described pre~iously.
The following results were observed:
\
~"~

- 2 6 ~ ç~82~- 6 0 S I 7 4 0
2~ ~2 ~
~ 3
~ ~0 ~ ~
o ~
,
,q
U~ o o o o o o o o
tq sl ~ ~ ~ ,i ,i ,~
C~
~ ~
a
Q
~ z~
c~ ~
u~
w
c x u~
o~ ~
-
~3
~ ~ o o o o o o o o
~ 3 o o o o ~ o o o
O O
E~
a~
U~

60SI-740
~:25~
- 27 -
It was observed that the diaryl salt catalyst
was much more soluble in the ~-phene~hyl epoxy-functional
silicones than in the low refractive i.ndex epoxy-functional
silicones described in prior examples. This would permit
highex concentrations of the catalyst if needed for faster
cure. In addition, the presence of ~-phenethyl sub-
stituents evidently affords fast cure with lower epoxy
loads, and the above-descri~ed e-ther blends evidently
cure equally well in air or inert atmospheres, making
the high refractive index compositions very efficient
coating materials.
! ~ high cu~e sp~ed c~n be maintained with as much as
25~ of the c~esyl glycidyl ether present. Other aromatic
epoxy monomers such as bisphenol A diglycidyl ether or
epoxy novolak resins are expected to be compatible with
the epoxy-functional silicones as well.
EXAMPLE 13
A low refractive index (below 1.43) polysiloxane
composition was prepared as follow~:
60 pbw of a trimethy~-chain~topped polydimethyl
hydrogen siloxane fluid ~25 cps), 84 pbw sym-tetramethyl-
tetravinylcyclotetrasiloxane, and 1056 pbw octamethylcyclo-
tetrasiloxane were agitated for 17 hours under a nitrogen
atmosphere.at 100C in the presence of 6 pbw Filtrol 20
acid equilibration catalyst. 6 pbw of MgO were added to
neutralize the acid and the mixture held an additional
hour at la0C, at which point the neutralized reaction
product was stripped at 165C under 48 mm Hg vacuum for
2 hours. 829 pbw of the fluid product were treated with
20~8 pbw benzophenone, stirred or 15 minutes at 70C,
then cooled to below 50C. 40 pbw t-butylperbenzoate

60SI-740
~J~L
28-
were added and the complete mixture stirred 10 minutes
before filtering to remove the solid Filtrol and MgO,
giving a 1800 cps fluid product.
The composition was applied to polyethylene kraft
paper at a 2 mil thickness, then exposed to 40Q watts
total W lamp power in a PPG 1202 proce~sor. Curing a~
different line speeds afforded the following results~
Curing
10 Line Speed ATM Cure
50 ft/min. AIR Some smear, otherwise well cured
100 ft/min. N2 Well cured to smear-free coating;
thick section cured OK
200 ~t/min. N2 Slight smear detected, but otherwise
satisfactory
15 300 ft/min- N2 Partially cured ~ easily smeared
and rubbed o~
400 ft/min. N2 Surface cure only ("skin" formed)
The same CQr.position was applied to a 10 mil
diameter optical ~iber as described previously, then
cured by exposure to a single Fusion Systems 300 ~att
"H" lamp in an inert atmosphere. The material wetted the
fiber satisfactorily up to a drawing speed of about 35
meters/minute. A well-cured 140 micr~n thick coating was
obtained. At greater ~peeds, coating thickness rapidly
diminished, although the material appeaxed to cure
completely at speeds above 40 mekers/minute.
It is expected that high refractive index vinyl-
functional polymers, W -curable in the presence of
perbenzoate catalysts, may be prepared, in accordance with
disclosure herein, which are comprised of four different
units, e.g., methylvinyl^, diphenyl r ~ dimethyl-, and
methylhydrogen-siloxy unit~.

60SI-740
_29 _
EXAMPLE 14
300 pbw styrene (2.88 moles) were added to 800 pbw
toluene and a pla~inum complex catalyst: (furnishing 25 ppm
platinum to the complete mixture)~ The solution was heated
to 80C, at which point 400 pbw trimethyl-chainstopped
linear polydimethyl-methylhydrogensiloxane fluid (21 cps
viscosity~ having 69 weight percent methylhy~rogensi.loxy
units (4.61 moles SiH total) were slowly added over a
4 hour period as the reaction mix~ure was held at a
temperature of 81-84C. After stirring a ~ hour,
289 pbw limoneneoxide ~1.9 moles) were added and the
reaction mixture refluxed at 82C ~or 17 hours, then 90C
for 22 hour~, ~t which point unreacted SiH-containing
units were down to about 2.4 weight percent. Unreacted
SiH was removed by xeaction with hexane, and the product
was stxipped at 140C under vacuum for 40 minutes to yield
888 pbw of a 18,800 cps fluid. Assuming quantitative
addition of styrene, the product, designated Sample 14,
included 31.9 weight percent styrene and 25.4 weight
percent limoneneoxide. The refractive index of this
material was 1.503,
Coating compositions of suitable viscosities were
prepared by blending Sample 14 with various epoxy-~unctional
reactive diluents selected from the following:
____ _ _ _ ,

60SI-74 0
- 30 -
DY023 ~Ciba Geigy) = c~3~~CEI2CH2~CH~CH2
cresyl glycidyl et:her
CY179 (Ciba Geigy~ a
\OCH2 -C~Or~/
EPON 825 ~Shell Chemicals) =
H2C-CH-CH2-O ~ clcH3)2 ~ O-CH2-~H!CH2.
E~ch composition was catalyzed with 5 weight percent of
a 1:1 blend o~ diethoxyacetophenone and (C~2H25Ph)2~SbF6;
the for~ulations are outlined below:
DY023 CY179 Epon Refractive
Compositions ~Wt.%) (Wt.%) 825(Wt.~) Index
14A 10 10 1 O 506
14B 10 10 1 513
1~C 20 2Q 1 51~
The compositions were coated on polyethylene kraft
substrates at 3 coating tbickness of 1 mil, then cured in
a PPG QC1202AN processox as pre~iously described. The
cure perormance was racorded as follows:
~~
,

~Zi~
- 31 - 60SI-740
Composi- UV Powers Line Speed
tions Atm. (Watts) (meters~sec.) Cure
5ample 14 Air 400 1.0 Excellent cure,
good anchorage.
Sample 14 Air 600 2.0 "Skin-cure"
Sample 14 Air 600 2.0 Excellent cure,
good anchorage.
Sample 14A Air 400 1.5 Excellent cure.
Sample 14A Air ~00 2.0 Surface cure only.
Sample 14A N2 400 2.0 Surface cure only.
Sample 14A Air 600 2.5 Excellent cure.
Sample 14B Air 400 1.5 Excellent cure,
good anchorage.
Sample 14B Air ~00 2.0 Evidence of
surface cure.
Sample ~B ~ir 600 2.0 Excellent cure.
Sample l~C Air ~00 1.5 Smear-free, yood
anchorage.
Sample 14C Air 400 2.0 Surface cure only.
Sample 14C Air 600 2.5 Excellent cure.
Modifications and variations in the present
invention are obviously possible in light of the
foregoing disclosure. For instance, it is anticipated
that limonenedioxide (or other polyepoxide monomers)
will prove to be a useful epoxy-functional diluent for
high refractive index epoxy-functional polysiloxane
compositions in light of the working examples. Also,
modification of the epoxy-functional or vinyl-functional
polysiloxane compositions described herein with
additives to enhance the curing characteristics, such as
disclosed in commonly assigned Canadian Appln. S.N.
428,142, filed May 13, 1983, and Canadian Appln. S.N.
469,075, filed November 30, 1984 may be advantageous

~L2~ . 60 sI -740
;
- 32 -
in particular situations. It is understood, however,
that these and other incidental changes in the particular
embodiments of this invention are within the full
intended scope of the appended claims.