Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1998-05-04
2001-09-11
Ashton, Rosemary E. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S916000, C430S923000, C522S068000, C568S328000, C568S330000, C568S375000
Reexamination Certificate
active
06287749
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to compounds useful for initiating polymerization of ethylenically unsaturated compounds, and in particular to compounds useful for initiating polymerization upon exposure to radiation and to methods for using the same.
BACKGROUND OF THE INVENTION
Ethylenically unsaturated compounds, such as acrylate derivatives, can be polymerized by exposure to actinic radiation, typically ultraviolet light, in the presence of a photoinitiating system. Photoinitiating systems include a photoinitiator, which is a compound capable of forming mono-radicals (molecular fragments having one unpaired electron) upon exposure to radiation. The mono-radicals can be formed via various mechanisms, such as &agr;-cleavage or hydrogen abstraction, when the photoinitiator is exposed to radiation. An example of a conventional mono-racial formed by an &agr;-cleavage mechanism is illustrated below:
The resultant mono-radicals can initiate polymerization by reacting with the desired compound to be polymerized to form active growing polymer chains.
Numerous mono-radical forming photoinitiators are commercially available. Despite their advantages, conventional mono-radical forming photoinitiators can suffer various disadvantages. For example, during free racial polymerization, the rate constant for termination (k
t
) can be several orders of magnitude larger than the rate constant for propagation (k
p
) (“Principles of Polymerization,” G. Odian, McGraw-Hill, N.Y., 1970, page 171-2), particularly during the early stages of polymerization when the viscosity of the polymerization medium can be low. Premature termination can occur, for example, if the active radical polymer chain couples with another polymer chain or with an initiator radical. Premature termination can in turn adversely impact cure rates, molecular weight and molecular weight distribution of the resultant product, and the like.
Still further, cured articles formed using mono-radical photoinitiators can include residual fragment molecules. Residuals present in the cured article can create offensive odors and can degrade the physical properties of the article, such as light fastness, coloration, and resistance to oxidative degradation. In addition, residuals can be extracted or leach out of the cured article or migrate to the surface of the article.
SUMMARY OF THE INVENTION
The present invention is directed to compounds useful in radiation curing of photopolymerizable compounds. In contrast to conventional photoinitiators, which form mono-radicals with just one active site, the compounds of the invention are capable of forming biradicals, that is, at least two molecular fragments having one unpaired electron, upon exposure to radiation. Because at least two active sites can be formed, during free racial polymerization, the rate constant for termination can be reduced because various termination mechanisms observed in conventional mono-radical systems can eliminated or minimized. For example, attack of another propagating radical can lead to formation of a macroradical, which can further initiate polymerization, instead of resulting in termination as in the case with conventional mono-radical initiators.
As a result, the compounds can be used to form polymers with increased molecular weights and/or narrower molecular weight distributions. Still further, the compounds can provide increased polymerization rates as compared to convention mono-radical photoinitiators. In addition, articles prepared using the compounds of the invention can have minimal or no residual fragment molecules, and thus can exhibit reduced odors, improved physical properties, and reduced amounts of extractable and migratable compounds. The compounds of the invention are also currently believed to provide “dark cure,” that is, continued cure after the radiation source is removed.
The compounds of the invention have the general formula
wherein:
R
1
and R
2
are each independently selected from the group consisting of lower alkoxy, lower alkyl, nitrile, aryl, hydroxy, and oxygen, with the proviso that if either R
1
or R
2
is oxygen, the other of R
1
or R
2
does not exist;
R
3
, R
4
, R
5
, R
6
, R
7
and R
8
. are each independently selected from the group consisting of hydrogen, lower alkoxy, lower alkyl, nitrile, aryl, and halogen, or R
7
and R
8
together can represent C2 to C10 alkylene, oxaalkylene, or azaalkylene, or when B is not present, R
6
and R
7
together with the carbon atoms to which they are attached can form a fused aromatic ring, or when B is C, R
7
and B together with the carbon atom to which R
7
is attached can form a fused aromatic ring;
B is selected from the group consisting of C, C═O, N—R
11
, O, S, and C(R
9
) (R
10
), wherein R
9
and R
10
are each independently selected from the group consisting of hydrogen, lower alkoxy, lower alkyl, nitrile, aryl, and halogen; R
11
is selected from the group consisting of hydrogen, lower alkyl, aryl, and —C(O)R
12
; and R
12
is selected from the group consisting of lower alkyl, lower alkoxy, aryl, and aryloxy;
m is 0, 1 or 2; and
n is 0 or 1.
The present invention also provides photopolymerizable compositions which include the compounds of Formula (I) above as a component thereof, and methods for the use of the compounds of Formula (I) in photopolymerization systems.
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Bowers, Jr. Joseph Stanton
Eubanks John R. I.
Hoyle Charles E.
Jonsson E. Sonny
Nagarajan Rajamani
Alston & Bird LLP
Ashton Rosemary E.
First Chemical Corporation
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