Melt-processible, thermoplastic random copolyimides having recoverable crystallinity and associated processes

A method of preparing a melt-processible polyimide composition by melt polymerization comprising the steps of:

• (a) blending, to substantial homogeneity, components comprising:
• (I) 93 to 98 mole parts of an aromatic dianhydride component consisting essentially of:
• (A) 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA);
• and
• (B) 4,4 -oxydiphthalic anhydride (ODPA);
• (II) 100 mole parts of an aromatic diamine component selected from the group consisting of 1,3-bis(4-aminophenoxy)benzene (APB-134), 3,4′-oxydianiline (3,4′-ODA);
• 3,4′-oxydianiline (3,4′-ODA) and 4,4′-oxydianiline (4,4′-ODA) in combination;
• 3,4′-oxydianiline (3,4′-ODA) and 1,4-diamino-benzene (PPD) in combination;
• 1,3-bis(4-aminophenoxy)benzene (APB-134) and 4,4′-oxydianiline (4,4′-ODA) in combination;
• and 1,3-bis(4-aminophenoxy)-benzene (APB-134) and 1,4-diaminobenzene (PPD) in combination;
• and
• (III) 4 to 14 mole parts of at least one endcapping component;
• wherein the dianhydride component has a molar ratio of 3,3′,4,4′-biphenyltetra-carboxylic dianhydride/4,4′-oxydiphthalic anhydride (BPDA/ODPA) of greater than or equal to 60/40 but less than or equal to 95/5;
• the components (I), (II) and (III) being in substantially solventless form and the blending step producing a substantially solventless component blend;
• the blending step being carried out at a temperature below the melting point of any of components (I), (II) and (III);
• the components (I) and (II) being present in the component blend in a molar ratio of (I):(II) from 0.93 to 0.98;
• the component (III) being present in the component blend in a molar ratio (III):(II) of 0.04 to 0.14;
• (b) heating the substantially solventless component blend produced in step (a) to a predetermined melt processing temperature at which the (I) aromatic dianhydride component and the (II) aromatic diamine component are melted and react to form a melt of a polyimide;
• the predetermined melt processing temperature being less than the temperature at which the polyimide melt chemically decomposes;
• (c) mixing the component blend and the polyimide melt produced therefrom during the heating step (b);
• (d) removing water of reaction from the component blend and the polyimide melt produced therefrom during the heating step (b);
• (e) forming the polyimide melt into an article having predetermined shape;
• and
• (f) cooling the article having predetermined shape to ambient temperature;
• wherein the polyimide exhibits a melting point in the range of 330° C. to 385° C. and the polyimide exhibits recoverable crystallinity as determined by DSC analysis.