Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-02-02
2002-03-12
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...
C522S178000, C522S049000, C522S050000, C522S039000, C560S055000, C560S096000, C560S097000, C560S098000
Reexamination Certificate
active
06355702
ABSTRACT:
TECHNICAL FIELD
This invention is directed to multifunctional acyclic monomers which are cured to provide adhesives, coatings and restorative materials, and when cured, affix or coat electronic components or affix optical components, e.g., lenses and prisms, in assemblies.
BACKGROUND OF THE INVENTION
Multifunctional (meth)acrylates have been broadly used as photopolymerizable resins in a wide range of applications including adhesives, coatings, restorative materials, information storage systems and stereolithography. Highly cross-linked networks formed from these resins have desirable properties for these applications such as high strength, and very good moisture resistance and the networks are formed by rapid curing. A conventional monomer is hexane diol diacrylate (HDODA) which has the structure
When a conventional resin is used to affix or coat an electronic component in an assembly and the assembly becomes inoperative, it is impossible to repair the assembly by replacing an inoperative component or to recover or recycle operative components of an inoperative assembly. Moreover, conventional resins are unuseful to temporarily fix components, e.g., optical components such as lenses and prisms, in an assembly. The cured resin is therefore characterized as not being reworkable, i.e., polymer network cannot readily be removed from the substrate by thermal or other treatment.
SUMMARY OF THE INVENTION
It is an object of the invention herein to provide a curable monomer which provides advantages of conventional acyclic monomers of rapid curing and cured compositions which have high strength and very good moisture resistance, and which, in addition, when cured, are reworkable through thermal decomposition.
The term “reworkable through thermal decomposition” is used herein to mean thermally degradable at a temperature of not more than 250° C. to provide decomposed product that is completely soluble in aqueous NaOH or aqueous NH
4
OH, thereby to allow repair, replacement, recovery or recycling of components affixed or coated using the cured resin.
To this end, the invention in a first embodiment herein is directed at compounds containing unsaturated aliphatic hydrocarbon moieties which are linked to each other by a tertiary oxycarbonyl containing acyclic moiety, which when cured provide cross-linked networks which are reworkable through thermal decomposition enabling controlled and selective decomposition of the networks. These compounds may be referred to as the monomers herein.
The term “aliphatic hydrocarbon” is used herein to mean an open chain of carbon atoms which may be straight chain or branched. The term “acyclic” is used herein to define the linking moiety as not being and not containing any alicyclic, aromatic or heterocyclic group; this limitation is important since the presence of such group would increase the difficulty of decomposition. The term “tertiary oxycarbonyl” is used to mean the tertiary ester group
where R′ is alkyl. Polymers formed from monomers with tertiary ester group are more readily decomposed than polymers from monomers with primary or secondary ester groups. The tertiary ester group is subject to breakdown into carboxylic acid and alkene at the temperatures contemplated for use for thermal degradation described hereinafter.
In a second embodiment of the invention herein there is provided a photopolymerizable composition comprising compound of the first embodiment herein and a photoinitiation effective amount of a photoinitiator.
DETAILED DESCRIPTION
The unsaturated aliphatic hydrocarbon moieties of the compounds of the first embodiment herein can be alkenyl, dienyl or alkynyl and are preferably C
2-10
alkenyl and very preferably are
where R is hydrogen or methyl (so the compound is a diacrylate or dimethacrylate).
Preferably the tertiary oxycarbonyl moiety is
where each R′ is the same or different and is C
1-4
alkyl and where each R′ very preferably is methyl.
Preferably the linking moiety, i.e., the group linking the two unsaturated aliphatic hydrocarbon moieties, is
where n ranges from 1 to 30, more preferably from 1 to 6, and very preferably is 3, 4, 5 or 6. The group
acts as a spacer between two tertiary oxycarbonyl moieties and n may be referred to as the spacer length.
Preferably the compounds of the first embodiment have the structure
where R is hydrogen or methyl and n ranges from 1 to 30, very preferably from 1 to 6, and most preferably is 3, 4, 5 or 6. Thus, important compounds have the above structural formula where R is hydrogen and n is 4, where R is hydrogen and n is 6, where R is methyl and n is 4 and where R is methyl and n is 6. The monomers of the formula (I) are normally liquids.
The monomers of the formula (I) can be prepared according to the following reaction scheme
where n and R are as defined above, Et
3
N is triethylamine, 4-DMAP is 4-(dimethylamino)pyridine, THF is tetrahydrofuran and R.T. is room temperature. The Et
3
N functions as an acid acceptor. The 4-DMAP functions as a catalyst. The THF is the reaction solvent. The temperatures are used according to the following sequence: The diol, Et
3
N and 4-DMAP are dissolved in the THF under a nitrogen atmosphere and the solution is cooled to 0° C. Then the acryloyl chloride or methacryloyl chloride in THF is added dropwise and after a period of stirring is allowed to warm to room temperature whereupon stirring is continued. We turn now to the diol starting material. 2,5-Dimethyl-2,5-hexanediol (to provide monomer where n=2) is commercially available. The other diols can be prepared by conversion of ester groups of alkanedioic acid esters to tertiary alcohols by a Grignard reaction, e.g., by reaction of &agr;, &ohgr;-dimethyl carboxylates, e.g., dimethyl adipate, dimethyl suberate, dimethyl sebacate, dimethyl pimelate, dimethyl azelate, or dimethyl glutarate, with methylmagnesium bromide; this reaction can be carried out by starting with a solution of carboxylate in tetrahydrofuran at 0° C., adding the methylmagnesium bromide dropwise, then allowing the reaction to warm to room temperature, stirring and recovering the diol.
We turn now to the embodiment of the invention where a curable composition is provided comprising monomer herein and a photoinitiation effective amount of a photoinitiator. These compositions are prepared by adding photoinitiator to monomer liquid, e.g., in an amount of 0.5 to 10% by weight of the monomer. A preferred photoinitiator is 2-methyl-4′-(methylthio)-2-morpholinopropiophenone which has the formula
Other photoinitiators include, for example, rose bengal peroxy benzoate, substituted benzophenones and substituted hydroxy benzoins.
We turn now to the curing of the curable compositions of the second embodiment of the invention. Curing is readily carried out by exposing a film (e.g., from 50 nm to 5 mm thick, preferably from 50 nm to 0.1 mm thick) to UV light. The source of the UV light can be, e.g., a UVEXS Model 15609 (123 mW/cm
2
) at a distance of from 0.1 to 10 cm. Other sources of UV light include, for example, mercury lamps and lasers and other conventional sources of UV light. Significantly higher rates of polymerization were observed for diacrylates than for dimethacrylates, e.g., the polymerization rate for a diacrylate was observed to be up to 20 times the polymerization rate of the corresponding dimethacrylate. The curing time is related to thickness of body of composition being cured. For a film of 0.05 mm, diacrylates cured in 30 seconds and dimethacrylates cured in 240 seconds. A correlation between spacer length and double bond conversion was observed in that the higher double bond conversions were observed for diacrylates where n is 6 or 8 compared to n being 2 or 4 and that higher double bond conversions were observed for dimethacrylates where n is 4, 6 or 8 compared to where n is 2. Where n=2, the Tg (glass transition temperature, i.e., softening point) of the polymer network was about the same for diacrylate and dimethacrylate but in the other cases of n that were observed, the Tg for p
Ober Christopher K.
Ogino Kenji
Cornell Research Foundation Inc.
McClendon Sanza L
Seidleck James J.
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