Among the following, the correct statement(s) about polymers is(are)

The correct statement(s) about polymers are:
1. Teflon is prepared from tetrafluoroethene by heating it with persulphate catalyst at high pressure.
2. PVC are thermoplastic polymers.

Let us analyze each of the given statements step-by-step to understand why they are correct or incorrect:

Statement 1: The polymerization of chloroprene gives natural rubber.
This statement is incorrect.
Natural rubber is a polymer of isoprene (2-methyl-1,3-butadiene), specifically cis-1,4-polyisoprene. On the other hand, the polymerization of chloroprene (2-chloro-1,3-butadiene) gives synthetic rubber known as Neoprene (polychloroprene).

Statement 2: Teflon is prepared from tetrafluoroethene by heating it with persulphate catalyst at high pressure.
This statement is correct.
Teflon (Polytetrafluoroethylene or PTFE) is manufactured by heating tetrafluoroethene (${\text{F}}_2\text{C}={\text{CF}}_2$) with a free radical catalyst such as ammonium or potassium persulphate under high pressure.

Statement 3: PVC are thermoplastic polymers.
This statement is correct.
Polyvinyl chloride (PVC) is a long-chain linear polymer held together by weak intermolecular forces. It softens on heating and hardens on cooling, making it a classic example of a thermoplastic polymer.

Statement 4: Ethene at 350 - 570 K temperature and 1000 - 2000 atm pressure in the presence of a peroxide initiator yields high density polythene.
This statement is incorrect.
The conditions mentioned (335 - 343 K to 570 K temperature, 1000 - 2000 atm pressure, and peroxide catalyst) yield Low Density Polythene (LDP) via free radical addition. In contrast, High Density Polythene (HDP) is synthesized at lower pressures (6 - 7 atm) and temperatures (333 - 343 K) using a Coordination Catalyst such as the Ziegler-Natta catalyst (${\text{(C}}_2{\text{H}}_5{\text{)}}_3\text{Al}+{\text{TiCl}}_4$).