why bakelite (thermosetting plastic) is rigid and polyethene (thermosoftening plastic) is flexible??

Answer 1

Polyethylene and other thermoplastic polymers have relatively little cross-linking. Thermosetting polymers (not really plastics) have a high degree of cross-linking between the polymer chains, which produces a rigid physical structure that is difficult to deform.

Answer 2

Its all to do with the miolecular structure and boiling points of the materials. If you are asking that then you will probably find it very very hard to understand. Have a look at some school chemistry books aas they touch on it