What are the dielectric properties of prepreg and core or difference between them? How do we choose copper layers to have prepreg and core between them as dielectric in same muti layer PCB?
The prepreg-separated layers have more glue and less glass fibre between them.
But these are minor details. The most important difference is in the thickness. For example, if you had to route a 100Ω impedance differential pair on a core with the ground on the opposing layer, you needed a ridiculous trace width of 100mil to get to that impedance. Just because the ground is 1.6mm away. (I saw this once in a commercial USB hub which was murky for other reasons, too, and soon dead, too.)
On a prepreg-separated layer, the ground is only 0.2mm away and you can route the same pair with 8mil trace width.