Low density polythene and high density polythene,both are polymers of ethene but there is marked difference in their properties. Explain.

(N/A) Low density polythene $(LDPE)$ and high density polythene $(HDPE)$ are both polymers of ethene $(CH_2=CH_2)$,but they are synthesized under different conditions,leading to distinct structural features.
$LDPE$ is obtained by the polymerization of ethene under high pressure $(1000-2000 \ atm)$ and temperature $(350-570 \ K)$ in the presence of traces of dioxygen or a peroxide initiator. It has a highly branched structure,which results in low density and flexibility.
$HDPE$ is formed by the addition polymerization of ethene in the presence of a catalyst like triethylaluminium and titanium tetrachloride ($Ziegler-Natta$ catalyst) at low pressure $(6-7 \ atm)$ and temperature $(333-343 \ K)$. It consists of closely packed linear molecules,which results in high density and greater mechanical strength.