Are all plastics of the same kind or are there different types of plastics, having different properties?
No!
There are different types of plastics which have difference in their properties. In broad classification the plastics have been grouped into two types:
a) Thermoplastic: Which are softened by heat and can be molded to get various shapes . ex: Polythene, polystyrene , PVC etc.
b). Thermosetting Plastic: Which are not changed by further heating if once it has been given a shape. Ex: Bakelite, Melamine, polyesters etc.