*4.1.2. Melt mixing*

For mixing in solution, the polymer matrix must be soluble in at least one solvent. This is problematic for many polymers. Melt mixing is generally applicable and fairly simple, especially when used in the case of thermoplastic polymers. In the melt spinning process, carbon nanotubes are mechanically dispersed in the polymer matrix using a high-shear mixer at high temperature [26]. This approach is simple and compatible with existing industrial technologies. Shear forces destroy CNT aggregates and prevent their formation.

The disadvantage of this method is that this method produces a dispersion of carbon nanotubes in the polymer matrix, which is significantly worse than the dispersion that can be achieved by mixing in solution. In addition, carbon nanotubes should be smaller because of the high viscosity of the composites with a higher content of carbon nanotubes.

#### *4.1.3. In-situ polymerization*

Using this method, carbon nanotube or nanostructured silicon carbide is dispersed in the monomer followed by polymerization. Moreover, a higher percentage of fillers can be easily dispersed, and they form a strong interaction with the polymer of the matrix. This method is used for the preparation of composites with polymers that cannot be processed by mixing in solution or melt mixing, for example insoluble and thermally unstable polymers.

In the case of using a polyimide matrix, which is obtained by polycondensation, it is expedient to use the in-situ polymerization method.
