Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2002-03-19
2004-03-30
Hightower, P. Hampton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S125000, C528S126000, C528S128000, C528S170000, C528S171000, C528S172000, C528S173000, C528S185000, C528S188000, C528S220000, C528S229000, C528S350000, C528S351000, C528S480000, C528S490000, C528S491000, C528S50200C, C528S50200C, C427S256000, C427S287000, C427S372200, C427S375000, C525S420000, C525S422000, C525S425000, C525S437000, C428S221000, C428S323000, C428S324000, C428S325000, C428S326000, C428S327000, C428S337000, C428S338000, C428S339000, C428S411100, C428S412000, C428S419000, C428S458000, C428S
Reexamination Certificate
active
06713597
ABSTRACT:
BACKGROUND OF INVENTION
This disclosure relates to the preparation of polyimides.
Polyimides, which include polyetherimides, are thermoplastic polymers with a number of desirable properties such as high strength, high toughness, excellent chemical resistance and high temperature stability due to a high glass transition temperature. They are typically high viscosity materials and the high viscosity combined with the high glass transition temperature can hinder the use of polyimides, particularly polyetherimides, in blends, composites, and coatings.
For example, because of the high glass transition temperature of polyimides, blending may require that the components be heated to a temperature above the decomposition temperature of many polymers. The high viscosity can hinder intimate mixing of components, creating blends and composites with large domains of polyimide or polyetherimide and inconsistent properties. Powdered forms of polyimide and polyetherimide are available, but these non-reactive powders do not overcome the problems associated with high temperature and high viscosity materials. Additionally, the high toughness and high strength of polyimide and polyetherimide makes conventional milling of polyimide and polyetherimide pellets expensive. There currently appears to be no known methods for making a friable polyimide powder.
Polyimides and polyetherimides have been prepared by a variety of processes. The two basic processes used for making these polymers are the so-called “melt polymerization” process and the “solution polymerization” process. The melt polymerization process involves combining an aromatic dianhydride, an organic diamine and an optional catalyst and heating the mixture under an inert atmosphere to form a homogeneous melt. Water formed during the polymerization reaction is removed at a temperature of up to 350° C., and the final stage of the reaction is advantageously conducted under reduced pressure to facilitate removal of water.
Solution polymerization is generally conducted by reacting an aromatic dianhydride and an organic diamine in an inert solvent at temperatures up to about 200° C. With this procedure, water formed during the reaction is typically removed by azeotropic distillation. The resulting polymer is generally recovered by mixing the reactant solution with a precipitant, such as methanol. The reaction solvents employed for solution polymerization reactions are selected for their solvent properties and their compatibility with the reactants and products. High-boiling, nonpolar organic solvents have been preferred. Dipolar, aprotic solvents and phenolic solvents have also been used.
In another process polyimides can be made by reacting an aromatic dianhydride with an organic diamine in an inert solvent to form a prepolymer-solvent mixture, removing the solvent from the mixture by thin-film evaporation and heating the resulting prepolymer (e.g., in an extruder) to a temperature above its glass transition temperature to form the desired polyimide product.
Finally, polyimides and polyetherimides can be prepared by reacting substantially equimolar amounts of dianhydride and diamine and an optional termination agent in a high boiling aprotic solvent under imidization conditions to form an insoluble polyimide prepolymer, separating the insoluble polyimide prepolymer and then melt polymerizing the insoluble polyimide prepolymer under imidization conditions to result in a high molecular weight polyimide.
SUMMARY OF INVENTION
A process for the preparation of a reactive, friable polyimide powder comprises dissolving an aromatic dianhydride and an organic diamine in a high-boiling, aprotic organic solvent to form a reaction solution; heating the reaction solution under imidization conditions to form an insoluble, reactive polyimide and to effect substantially complete distillation of the water of reaction out of the reaction solution; and separating the insoluble, reactive polyimide from the reaction solution to form a reactive, friable polyimide powder.
DETAILED DESCRIPTION
A process for the preparation of a reactive friable polyimide powder comprises dissolving an aromatic dianhydride and an organic diamine in a high-boiling, aprotic organic solvent to form a reaction solution; heating the reaction solution under imidization conditions to form an insoluble reactive polyimide and to effect substantially complete distillation of the water of reaction out of the reaction solution; and separating the insoluble reactive polyimide from the reaction solution to form a reactive friable polyimide powder. The reactive friable polyimide powder may be further processed by drying, milling or a combination of drying and milling. Drying reduces the amount of solvent remaining in the reactive polyimide powder. Milling the reactive polyimide powder reduces the particle size. The reactive friable polyimide powder may be used to make previously unavailable composites, coatings, films, hollow fibers, and blends. The particulate size of the powder can be controlled by the selection of reaction conditions, milling conditions or a combination of reaction and milling conditions. Particulate size is preferably less than or equal to about 100 microns.
The reactive friable polyimide powder is highly suitable for the production of composite materials. It can be contacted with a substrate by methods known in the art suitable for use with powders. Optionally an additional polymer powder may also be mixed with the reactive friable polyimide powder. The substrate/polyimide powder or substrate/polyimide powder blend is then heated to a temperature above the softening point, melting point or glass transition point of the reactive friable polyimide powder or polyimide powder blend. Upon heating, the reactive friable polyimide powder or powder blend flows, resulting in good coverage of the substrate, and may also proceed to polymerize further, resulting in a higher molecular weight polyimide composite. The reactive friable polyimide powder or powder blend is especially suitable for use with powder coating methods, whereby the reactive friable polyimide powder (or blend) is applied to a substrate, then heated to a molten or semi-molten state. The reactive friable polyimide powder (or powder blend) flows to coat the substrate and may further polymerize to form a very high molecular weight polyimide coating.
The reactive friable polyimide powder may be used in combination with other polymers to form previously unavailable blends. The small particle size and presence of reactive functional groups allows a more intimate mixing with other polymers and facilitates the preparation of polymer blends.
Reactive friable polyimide powder comprises repeating structural units having the general formula (I)
wherein V is a tetravalent substituted or unsubstituted aromatic monocyclic or polycyclic linker having about 5 to about 50 carbon atoms. Suitable substitutions include, but are not limited to, ethers, epoxides, amides, esters, and combinations thereof. Preferred linkers include, but are not limited to, tetravalent aromatic radicals of formula (II), such as
wherein W is a divalent moiety selected from the group consisting of —O—, —S—, —C(O)—, —SO
2
—, —SO—, —C
y
H
2y
—(y being an integer from 1 to 5), and halogenated derivatives thereof, including perfluoroalkylene groups, or a group of the formula —O—Z—O— wherein the divalent bonds of the —O— or the —O—Z—O— group are in the 3,3′, 3,4′, 4,3′, or the 4,4′ positions, and wherein Z includes, but is not limited, to divalent radicals of formula (III)
R in formula (I) includes but is not limited to substituted or unsubstituted divalent organic radicals such as: (a) aromatic hydrocarbon radicals having about 6 to about 20 carbon atoms and halogenated derivatives thereof; (b) straight or branched chain alkylene radicals having about 2 to about 20 carbon atoms; (c) cycloalkylene radicals having about 3 to about 20 carbon atoms, or (d) divalent radicals of the general formula (IV)
wherein Q includes but is not limited to a diva
General Electric Company
Hampton Hightower P.
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