好得意bor....@@

In Fact, LDPE (low density polythene) and HDPE (high density polythene) are not made by only adjusting the temperature and pressure on polymerization of ethene. They are separately made by using different initiator /catalyst (Mahantan's AL textbook mixes the two terms) and different reaction conditions.

To make LDPE, ethene is polymerized at 200°C and 1000 atm in the presence of a peroxide as initiator. The polyethene molecules made in this way are highly branched and thus the molecules are packed loosenly and the density is low.

To make HDPE, ethene is polymerized in a lower temperature and a low pressure in the presence of Ziegler-Natta catalyst. The reaction mechanism is totally different from the above one. The polythene molecules are packed more closely which form a crystalline structure with high density.

正常的
做咩要調番轉= =