Photocurable halofluorinated acrylates

Details Photocurable halofluorinated acrylates Photocurable halofluorinated acrylates

2001-06-13

2003-03-18

Ashton, Rosemary (Department: 1752)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acid esters

C526S252000, C570S123000, C570S142000, C570S153000, C430S270100

Reexamination Certificate

active

06534671

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a novel class of halofluorinated acrylates and more particularly to chlorofluorinated or bromofluorinated acrylates characterized by achlorofluorinated alkylene moiety with acrylate functions at both terminals. These chlorofluorinated or bromofluorinated acrylates may be photocured in the presence of a photoinitiator into transparent polymers useful as optical waveguiding materials.
The use of photocuring technology has grown rapidly within the last decade. Photocuring involves the radiation induced polymerization or crosslinking of monomers into a three dimensional network. The polymerization mechanism can be either radical or cationic. Radical initiated polymerization is the most common. Most commercial photocuring systems consist of multifunctional acrylate monomers and free radical photoinitiators. Photocuring has a number of advantages including: a 100% conversion to a solid composition, short cycle times and limited space and capital requirements.
Photocuring technology has recently been applied in planar waveguide applications. See, B. M. Monroe and W. K. Smothers, in Polymers for Lightwave and Integrated Optics, Technology and Applications, L. A. Hornak, ed., p. 145, Dekker, 1992. In its simplest application, a photocurable composition is applied to a substrate and irradiated with light in a predetermined pattern to produce (the light transmissive) or waveguide portion on the substrate. Photocurring permits one to record fine patterns (<1 um) directly with light. The refractive index difference between the substrate and the light transmissive portion of the substrate can be controlled by either regulating the photocurable composition or the developing conditions.
Because of the dramatic growth in the telecommunications industry there is a need to develop photocurable compositions for optical waveguide and interconnect applications. In order to be useful in these applications, the photocurable composition must be highly transparent at the working wavelength and possess low intrinsic absorption and scattering loss. Unfortunately, in the near-infrared region, among which the 1300 and the 1550 nm wavelengths are preferred for optical communications, conventional photocurable materials possess neither the required transparency or low intrinsic absorption loss.
The absorption loss in the near-infrared stems from the high harmonics of bond vibrations of the C—H bonds which comprise the basic molecules in conventional acrylate photopolymers. One way to shift the absorption bands to higher wavelength, is to replace most, if not all, of the hydrogen atoms in the conventional materials with heavier elements such as deuterium, fluorine, and chlorine. See, T. Kaino, in Polymers for Lightwave and Integrated Optics, Technology and Applications, L. A. Hornak, ed., p. 1, Dekker, 1992. The replacement of hydrogen atoms with fluorine atoms is the easiest of these methods. It is known in the art that optical loss at 1300 and 1550 nm can be significantly reduced by increasing the fluorine to hydrogen ratio in the polymer. It was recently reported that some perfluorinated polyimide polymers have very low absorption over the wavelengths used in optical communications. See, S. Ando, T. Matsuda, and S. Sasaki, Chemtech, 1994-12, p.20. Unfortunately, these materials are not photocurable.
U.S. Pat. No. 5,274,174 discloses a new class of photocurable compositions comprised of certain fluorinated monomers such as diacrylates with perfluoro or perfluoropolyether chains which possess low intrinsic absorption loss. It is, therefore, possible to make low loss optical interconnects from a photocurable system include these materials.
Fluorine substitution in the polymer structure, however, also induces some other less desirable changes in the polymer's physical properties. One such change is the decrease in refractive index. For a highly fluorinated acrylate photopolymer, the refractive index decreases to the 1.32 region when the H/F mole ratio reaches 0.25. For optical interconnect applications, to avoid loss of light, it is important that the refractive index of the core of a planar waveguide approximate and preferably match that of the optical fiber (generally 1.45). Another problem with fluorine substitution in the polymer is the decrease of the surface energy of the resulting photopolymer film which results in its reduced adhesion to other materials like substrates.
It is also important to be abovel to precisely control and fine tune the refractive index of the photopolymer at the working wavelength in optical waveguide and interconnect applications. A desired index of refraction can be produced by mixing photocurable monomers with different refractive indices. Most photopolymers made from conventional photocurable monomers have refractive indices in the region of 1.45-1.55. Depending on the application, it is often desirable to lower a photopolymer's refractive index. One way to do this is to mix low refractive index fluorinated monomers with conventional hydrocarbon-based monomers. Unfortunately this is difficult to accomplish because of the incompatibility or insolubility of the different monomer systems. Thus, there is a need for photocurable compositions which: (i) possess low optical loss in the near-infrared region, (ii) possess a refractive index approaching traditional optical fibers; and (iii) are compatible with both conventional hydrocarbon-based and highly fluorinated monomers.
DESCRIPTION OF THE INVENTION
The photocurable monomer of the invention is a di-, tri- or tetra-acrylate which contains a chlorofluorinated or bromofluorinated alkylene chain and has the formula:
wherein 0 in an integer of from 2-4; X is H, F, CH
3
or Cl and is preferably H, or Cl.
R=—CH
2
R
F
CH
2
—,
and
R
F
=—(CF
2
CFX
1
)
a
CF
2
—, —(CF
2
CFX
1
)
a
—(CFX
2
CF
2
)
b
—, —(CF
2
CFX
1
)
a
—(CF
2
CFX
2
)
b
CF
2
—, and —(CF
2
CFX
1
)
a
—(CH
2
CY
1
Y
2
)
b
—(CF
2
CFX
1
)
d
CF
2
—.
wherein X
1
is Cl or Br; X
2
is F, Cl or Br; Y, and Y
2
are the same or different and are H, CH
3
, F, Cl or Br; and a, b, and c are the same or different and are integers of from 1-10 and preferably integers of from 1-7.
In the preferred embodiments, the above mentioned monomers contain chlorofluorinated or bromofluorinated alkylene chains which comprise chlorotrifluoroethylene or bromotrifluoroethylene repeating units and at least two terminal acrylate groups.
These monomers contain much less hydrogen than conventional photocurable monomers such that their inherent carbon-hydrogen bond absorption is greatly reduced. In addition, the introduction of chlorine or bromine atoms into the molecule offsets the effect of fluorine on the refractive index of the monomer producing a material with an index of refraction between about 1.40-1.48 As a result, the monomers of the invention are particularly useful in optical applications in the 1300-1550 nm wavelength region. The monomers are also compatible with both conventional hydrocarbon-based and highly fluorinated monomers. Because of this compatibility, it becomes possible to fine tune the refractive index and other physical properties of photocurable compositions containing these photocurable monomer.
In a second embodiment, the invention relates to a photocurable composition comprising at least one photocurable monomer of the invention and a photoinitiator.
In another embodiment, the invention relates to a process for producing an optical device containing a light transmissive region comprising:
a) applying a film of a photocurable composition comprising a photocurable monomer of the invention and a photoinitiator to a substrate; b) imagewise exposing said composition to sufficient actinic radiation to form exposed and unexposed areas on the substrate; and c) removing the unexposed portions of the composition.
In still another embodiment, the invention relates to an optical device comprising a light transmissive region wherein said light transmissive region comprises a photocurable composition of the inventio

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