Polysulfide-based toughening agents, compositions containing same and methods for the use thereof
View Patent ↗In accordance with the present invention, there are provided toughening agents which are useful for improving the performance properties of epoxy-based adhesive formulations. For example, epoxidized polysulfides have been found to be useful toughening agents of component level underfill adhesive compositions. Invention materials are liquid rubbers which provide improved fracture toughness while maintaining satisfactory capillary flow properties. Invention materials can be synthesized in neat (solventless) reactions from readily available low-cost raw materials and isolated in high yields. They have linear and branched telechelic structures with terminal epoxide functional groups, and are prepared without substantially increasing the molecular weight of the starting polysulfide materials. Invention materials are compatible with common epoxy formulations and may be used without purification. At low levels of incorporation, they provide adhesives that meet the minimum fracture toughness (Gq>2.0 lb/in) and capillary flow specifications (flow time<180 seconds) for many commercial underfill applications. In accordance with a further embodiment of the present invention, there are provided adhesive compositions comprising invention compounds and methods for use thereof. In additional embodiments of the present invention, there are provided methods for the preparation of invention toughening agents, methods for adhesively attaching a device to a substrate, and assemblies comprising first article(s) adhered to second article(s).
1. An epoxidized polysulfide liquid rubber having an epoxy equivalent weight in the range of about 300 up to about 7000, and a viscosity at 25° C. in the range of about 300 up to about 30,000 milliPascal-seconds; wherein said epoxidized polysulfide liquid rubber is prepared by subjecting a mixture of a thiol-terminated polysulfide liquid rubber, an alkenyl- or alkynyl-functional epoxy monomer, and a free radical catalyst to a temperature of no greater than about 60° C. for a time in the range of about 1 up to about 24 hours.
2. An adhesive formulation comprising:
a curable epoxy resin,
a curing agent,
at least one toughening agent comprising an epoxidized polysulfide liquid rubber having an epoxy equivalent weight in the range of about 300 up to about 7000, and a viscosity at 25° C. in the range of about 300 up to about 30,000 milliPascal-seconds; wherein said epoxidized polysulfide liquid rubber is prepared by subjecting a mixture of a thiol-terminated polysulfide liquid rubber, an alkenyl- or alkynyl-functional epoxy monomer, and a free radical catalyst to a temperature of no greater than about 60° C. for a time in the range of about 1 up to about 24 hours; and
optionally, a filler.
3. The adhesive formulation of claim 2 wherein said curing agent is selected from the group consisting of anhydrides, amines, imidazoles, amides, thiols, carboxylic acids, phenols, dicyandiamide, urea, hydrazine, hydrazide, amino-formaldehyde resins, melamine-formaldehyde resins, amine-boron trihalide complexes, quaternary ammonium salts, quaternary phosphonium salts, tri-aryl sulfonium salts, di-aryl iodonium salts, diazonium salts, and combinations of any two or more thereof.
4. A method for adhesively attaching a device to a substrate, the method comprising dispensing an adhesive formulation according to claim 2 onto a substrate and/or a device or between the substrate and the device to form an assembly, and exposing the assembly to conditions sufficient to cure the adhesive.
5. An assembly produced by the method of claim 4 .
6. A method for adhesively attaching a first article to a second article, the method comprising:
(a) applying a formulation according to claim 2 to the first article,
(b) bringing the first article and the second article into intimate contact to form an assembly wherein the first article and the second article are separated only by the adhesive formulation applied in step (a), and thereafter,
(c) subjecting the assembly to conditions suitable to cure the adhesive formulation.
7. An assembly produced by the method of claim 6 .
8. A method for encapsulating an electronic component, the method comprising:
applying a formulation according to claim 2 to the component, and
curing the formulation.
9. An article prepared according to the method of claim 8 .
10. A method for encapsulating an electronic component, the method comprising curing a formulation according to claim 2 after application of the composition to the component.
11. An article prepared according to the method of claim 10 .
12. An article comprising an electronic component adhesively attached to a circuit board, wherein the electronic component is adhesively attached to the board by a cured aliquot of a formulation according to claim 2 .
13. A cured aliquot of a formulation according to claim 2 .