Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2000-12-21
2002-09-03
Woodward, Ana (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C525S432000, C525S436000
Reexamination Certificate
active
06444783
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to selected block copolyimide compositions each of which can be processed as a melt and is semicrystalline. In preferred embodiments, these block copolyimides exhibit recoverable crystallinity upon cooling from their respective melts.
BACKGROUND OF THE INVENTION
Polyimides constitute a class of valuable polymers being characterized by thermal stability, inert character, usual insolubility in even strong solvents, and high glass transition temperature (T
g
) among others. Prior art discloses that their precursors have heretofore been polyamic acids, which may take the final imidized form either by thermal or chemical treatment.
Polyimides have always found a large number of applications requiring the aforementioned characteristics in numerous industries, and currently their applications continue to increase dramatically in electronic devices, especially as dielectrics.
Different aspects regarding polyimides and copolyimides may be found in a number of publications, such as for example:
Sroog, C. E.,
J. Polymer Sci.
: Part C, No. 16 1191 (1967).
Sroog, C. E.,
J. Polymer Sci.: Macromolecular Reviews
, Vol. 11, 161 (1976).
Polyimides
, edited by D. Wilson, H. D. Stenzenberger, and P. M. Hergenrother, Blackie, USA: Chapman and Hall, New York, 1990.
Several terms are defined below which are used in accordance with the present invention of high performance block polyimides that possess simultaneously the following desirable properties: high thermal stability, such that they can be processed in the melt, and which in preferred embodiments exhibit recoverable semicrystallinity upon crystallization from the melt.
The term “melt-processible polyimide” means that the polyimide has sufficiently high thermoxidative stability and sufficiently low melt viscosity at temperatures at or above the melting point of the polyimide such that the polyimide can be processed in the melt to form a shaped object (e.g., extruded into a pellet, etc.) without the polyimide undergoing any significant degradation.
The term “DSC” is an acronym for differential scanning calorimetry, a thermal analysis technique widely used for accurately determining various thermal characteristics of samples, including melting point, crystallization point, and glass transition temperature. The acronym “DSC” is employed in text that follows below. The following definitions of slow, intermediate, and fast crystallization kinetics and related terms are based upon behavior of a given sample during DSC analysis under slow cooling, quench cooling, reheat, etc. scans during the DSC analysis (see infra for details).
The term “slow crystallization kinetics” means that the crystallization kinetics are such that, for a given copolyimide sample, the sample, when subjected to DSC analysis, essentially does not show any crystallization during slow cooling (i.e., cooling at 10° C./minute) from its melt but does exhibit a crystallization peak on subsequent reheat. Furthermore, no crystallization occurs upon quench cooling.
The term “intermediate crystallization kinetics” means that the crystallization kinetics are such that, for a given copolyimide sample, when subjected to DSC analysis, the sample exhibits some crystallization on slow cooling and furthermore does exhibit some crystallization on reheat after slow cooling. Furthermore, there is no strong evidence for crystallization occurring upon quench cooling.
The term “fast crystallization kinetics” means that the crystallization kinetics are such that, for a given copolyimide sample, when subjected to DSC analysis the sample does exhibit crystallization peaks in both slow and quench cooling and furthermore no observable crystallization peak is seen on subsequent reheat of a given sample following slow cooling. After quench cooling, there may be some crystallization exhibited on reheat.
The term “melt of a polymer” means the polymer exists as the melt in a liquid or substantially liquid state. If the polymer is crystalline or semicrystalline, a melt of the polymer is necessarily at a temperature greater than or equal to its melting point (T
m
).
The term “recoverable semicrystallinity” and/or “recoverable crystallinity” refers to behavior occurring in a semicrystalline or crystalline polymer and specifically means the behavior that occurs when the polymer, upon heating to a temperature above its melting point and subsequent slow cooling to a temperature well below its melting point, exhibits a melting point in a reheat DSC scan. (If a melting point is not observed during the reheat DSC scan, the polymer does not exhibit recoverable crystallinity. The longer a sample is below T
m
but above T
g
, the greater probability it has to crystallize.)
The term “semicrystalline polymer” means a polymer that exhibits at least some crystalline characteristics and is partially but not completely crystalline. Most or all known polymers having crystalline characteristics are semicrystalline, but not totally crystalline, since they also have at least some amorphous characteristics. (Hence the term crystalline polymer is technically a misnomer in most or all instances where it is used, but nevertheless this term is often used.)
The term “uncapped copolyimide (random or block)” means a copolyimide that is the reaction product of a set of monomers (e.g., dianhydride(s) and diamine(s)) that does not include an endcapping agent.
Some significant advantages of melt processing in accordance with the present invention include processing without a solvent such that tedious and costly solvent recycling is unnecessary and can be eliminated. High thermal stability is not only essential for processing in the melt at temperatures of greater than or equal to 350° C. but also is required for polyimides used in high temperature applications. Semicrystalline polyimides are often highly desirable in comparison to otherwise comparable polyimides that are amorphous, since the former in relation to the latter often exhibit superior properties, such as having better mechanical properties (e.g., especially higher modulus), capability for use at higher temperatures without property degradation (e.g., better solder resistance, modulus retention), higher solvent resistance, higher creep viscosities (e.g., lower tendencies for distortion of a film or other structure with time), and lower coefficients of thermal expansion.
In order for a semicrystalline polyimide to be considered melt-processible, the polyimide must possess a melting point at or below a temperature in the range of about 385° C.-395° C., which temperature range is a practical limit for melt processing due to both equipment capabilities/limitations and to avoid any significant thermal degradation of the polyimide. Furthermore, the polyimide also must possess a sufficiently low melt viscosity (i.e., less than or equal to a maximum of about 10
8
poise (which is equal to 10
7
Pascal-seconds), but preferably 10
4
poise (which is equal to 10
3
Pascal-seconds) or less, depending on polymer melt temperature and shear rates of the melt processing equipment). Copolymerization can be used to lower the melting temperature of a polymer (e.g., polyimide) but usually results in loss of crystallinity. Prior art polyimide compositions have been unable to achieve suitable reduction in the melting points (T
m
s) of the copolymeric compositions while simultaneously maintaining high degrees of semi-crystallinity in the copolymeric compositions. In the compositions of this invention, both suitable melting temperatures and high degrees of semi-crystallinity are achieved by judicious choice of comonomers and endcapping agents, and their relative amounts in each block of these block copolyimide compositions.
Polyimides that exhibit a melting point in an initial DSC heat scan and which are thereby attributed to have crystalline characteristics are disclosed in Kunimune, U.S. Pat. No. 4,923,968 to Chisso Corporation. While the copolyimides disclosed in this patent may be crystalline or semicrystalline until heated to temperatures above their me
Auman Brian C.
Dodd John R.
Kreuz John A.
E. I. du Pont de Nemours and Company
Woodward Ana
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