Polyimide compositions, and in particular, polyimide compositions comprising two polymers are disclosed herein.
Polymer blends are widely employed in a range of applications. For example, substitution of metal parts with parts made from plastic materials (polymer compositions) results in parts having lighter weight and similar or improved performance properties. In many applications, such as parts used under an automobile hood, plastic materials with a high heat resistance are required. Frequently though, plastic materials having a high heat resistance are difficult to mold. Blending polymers is one approach to achieving a thermoplastic composition with a desired set of physical properties such as high heat resistance, melt viscosity, and processability. Polymer blends may comprise miscible polymers, immiscible polymers or a combination of miscible and immiscible polymers. Blends comprising immiscible polymers have two or more phases and such blends may be compatible or incompatible. Incompatible blends of immiscible polymers can suffer from phase separation as demonstrated by delamination or the formation of skin-core layered structures during polymer processing operations, especially injection molding. The term, “delamination,” as used when referring to such materials, describes visually observed separation of a surface layer giving a flaking or onion skin effect. Incompatibility may also result in poor mechanical properties and marginal surface appearance (streaking, pearlescence, etc.). Compatible blends of immiscible polymers typically do not show any delamination and can result in acceptable end-use properties.
Miscible polymer blends, on the other hand, may offer desirable end-use properties and the advantage of tailoring product properties intermediate of the individual components across the miscible composition range. Miscible blends do not suffer from delamination and generally have consistent physical properties.
So while a miscible blend of two polymers is generally desirable it can be difficult to achieve. Blends of two polymers of a same or similar class might be expected to have a better chance of miscibility. However, polymers from the same class are frequently immiscible and form multiphasic compositions. For example, ACUDEL 2000 from Solvay is an immiscible blend of two polysulfones—PPSU and PSU. In addition, many such examples of immiscible blends of polymers in the same class exist in the literature. Thus, polymer miscibility is difficult to predict, even within the same class of polymers.
For the foregoing reasons there remains an unmet need for non-delaminated polymer blends, e.g., blends essentially free of delamination, which are either miscible blends or immiscible, but nonetheless compatible, blends. More particularly, there remains an unmet need to develop blends having high heat resistance, and methods of forming such polymer blends.