Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1998-06-05
2001-02-13
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S908000, C522S162000, C522S169000, C522S168000, C522S170000, C522S182000, C522S183000, C522S100000, C522S031000, C522S014000, C522S015000, C522S025000, C523S109000, C523S115000, C523S116000, C523S118000, C523S300000
Reexamination Certificate
active
06187836
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to polymerizing compositions having cationically active and free radically active functional groups.
Acrylate and methacrylate-based compositions polymerize via a one-step free radical mechanism. “Hybrid” compositions featuring both cationically and free radically polymerizable components have been proposed as well. Epoxy resins are typically used as the cationically polymerizable component, and offer the advantage of reduced shrinkage relative to acrylate and methacrylate-based compositions. The hybrid composition polymerizes initially to form a moldable “gel” that can be shaped and compacted. As the polymerization proceeds, the gel forms a hard solid.
SUMMARY OF THE INVENTION
The inventors have discovered that one problem with hybrid compositions is that it is difficult to control the amount of time between formation of the gel and formation of the hardened solid. To address this problem, the inventors have discovered polymerizable hybrid compositions, and methods for polymerizing the free radically active and cationically active functional groups of such compositions, in which the onset of cationic polymerization can be controllably delayed to extend the time between formation of the moldable gel and formation of the hardened solid. The net result is enhanced processing flexibility.
Accordingly, in a first aspect, the invention features a photopolymerizable composition that includes: (a) a cationically active functional group; (b) a free radically active functional group; and (c) a photoinitiation system. Examples of preferred photopolymerizable compositions are dental compositions such as dental adhesives, dental composites (including dental restoratives and prostheses), and dental sealants.
The photoinitiation system is capable of initiating, at a reaction temperature less than about 40° C., free radical polymerization of the free radically active functional group after a finite induction period T
1
and cationic polymerization of the cationically active functional group after a finite induction period T
3
, where T
3
is greater than T
1
. T
1
and T
3
are measured relative to administration of the first dose of actinic radiation which occurs at T
0
. The photoinitiation system includes: (i) a source of species capable of initiating free radical polymerization of the free radically active functional group and cationic polymerization of the cationically active functional group; and (ii) a cationic polymerization modifier. The amount and type of modifier are selected such that in the absence of the modifier, cationic polymerization of the cationically active functional group is initiated under the same irradiation conditions at the end of a finite induction period T
2
(also measured relative to T
0
), where T
2
is less than T
3
.
As used herein, a “cationically active functional group” refers to a chemical moiety that is activated in the presence of an initiator capable of initiating cationic polymerization such that it is available for reaction with other compounds bearing cationically active functional groups. A “free radically active functional group” refers to a chemical moiety that is activated in the presence of an initiator capable of initiating free radical polymerization such that it is available for reaction with other compounds bearing free radically active functional groups.
“Initiation of polymerization” after a “finite induction period” means that after a finite period of time has elapsed, an exotherm (as measured by differential scanning calorimetry) occurs, reflecting initiation of the polymerizable groups. Initiation (and thus a successful polymerization) of the cationically polymerizable groups is said to have occurred if the area under the resulting exotherm peak is greater than 5% of the area of the corresponding peak for a control composition lacking the modifier but irradiated under the same conditions set forth in the Examples, infra.
The term “composite” refers to a filled dental material. The term “restorative” refers to a composite which is polymerized after it is disposed adjacent to a tooth. The term “prosthesis” refers to a composite which is shaped and polymerized for its final use (e.g., as crown, bridge, veneer, inlay, onlay or the like) before it is disposed adjacent to a tooth. The term “sealant” refers to a lightly filled composite or to an unfilled dental material which is polymerized after it is disposed adjacent to a tooth. Each of these materials is suitable for temporary or permanent use.
Suitable components of the photopolymerizable composition include epoxy resins (which contain cationically active epoxy groups), vinyl ether resins (which contain cationically active vinyl ether groups), and ethylenically active unsaturated compounds (which contain free radically active unsaturated groups). Examples of useful ethylenically unsaturated compounds include acrylic acid esters, methacrylic acid esters, hydroxy-functional acrylic acid esters, hydroxy-functional methacrylic acid esters, and combinations thereof. Also suitable are polymerizable components that contain both a cationically active functional group and a free radically active functional group in a single molecule. Examples include epoxy-functional acrylic acid esters, methacrylic acid esters, and combinations thereof.
A preferred material for component (i) of the photoinitiation system is an onium salt, e.g., an iodonium salt. The photoinitiation system preferably contains a photosensitizer as well, e.g., a visible light sensitizer. The term “visible light” refers to light having a wavelength of about 400 to about 1000 nanometers. Examples of suitable photosensitizers include alpha diketones.
The cationic polymerization modifier is preferably selected such that the photoinitiator system has a photoinduced potential less than that of 3-dimethylaminobenzoic acid in a standard solution of 2.9×10
−5
moles/g diphenyliodonium hexafluoroantimonate and 1.5×10
−5
moles/g camphorquinone in 2-butanone. The modifiers typically are bases having pk
b
values, measured in aqueous solution, of no greater than 10. Particularly preferred are modifiers in which the type and amount of modifier are selected such that cationic polymerization of the cationically active functional group after a finite induction period T
3
proceeds at a rate that is greater than the rate in the absence of the cationic polymerization modifier under the same irradiation conditions.
Examples of suitable cationic polymerization modifiers include aromatic amines (e.g., t-butyldimethylaniline); aliphatic amines (e.g., trimethyl-1,3-propane diamine, 2-(methylamino)ethanol, and combinations thereof); aliphatic amides; aliphatic ureas; phosphines (e.g., aliphatic and aromatic); salts of organic or inorganic acids (e.g., sulfinic acid salts); and combinations thereof.
In a second aspect, the invention features a method of polymerizing a photopolymerizable composition that includes exposing the composition to a source of actinic radiation (preferably a source of visible radiation) at a reaction temperature sufficiently high to initiate the polymerization reaction. Preferably, the reaction temperature is less than 40° C. Suitable photopolymerizable compositions include the compositions described above. Also suitable are photopolymerizable compositions that include a cationically active functional group, free radically active functional group, and photoinitiation system (as defined above), but which are not necessarily capable of polymerizing at temperatures less than 40° C. The method is particularly useful for photopolymerizable compositions in the form of dental adhesives, dental composites, dental sealants, and combinations thereof, in which case the method includes applying the photopolymerizable composition to a surface and conducting, polymerization within the oral cavity at temperatures less than 40° C.
In one embodiment, the photopolymerizable composition is continuously exposed to actinic radiation beginning at T
0
. In another embodiment, th
Jacobs Dwight W.
Oxman Joel D.
Trom Matthew C.
3M Innovative Properties Company
McClendon Sanza
Seidleck James J.
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