IC Explaining polymer properties © Oxford University Press 2011 Explaining polymer properties

IC Explaining polymer properties © Oxford University Press 2011 There are two types of poly(ethene):  Low density poly(ethene), LDPE.  High density poly(ethene), HDPE.

IC Explaining polymer properties © Oxford University Press 2011  The two types of poly(ethene) are both made from ethene but each has its own properties.  LDPE is not as strong as HDPE but it is more transparent. LDPE is flexible and HDPE is stiff.  This is because they are made under different conditions.

IC Explaining polymer properties © Oxford University Press 2011 LDPE is made at a temperature of 100–300°C and pressure of 1500–3000 atm. An oxygen or peroxide initiator is used in the reaction.

IC Explaining polymer properties © Oxford University Press 2011 LDPE polymer molecules have side branches. The branches prevent the polymer molecules from lining up in a regular pattern, so the density is lower.

IC Explaining polymer properties © Oxford University Press 2011 HDPE is made at a temperature of 300°C and pressure of 1 atm. An aluminium-based metal oxide catalyst is used in the reaction.

IC Explaining polymer properties © Oxford University Press 2011  HDPE polymer molecules have few side branches.  Its molecules line up in a pattern, so the density is higher.  The molecules are held together more strongly, so HDPE is stronger and has a higher melting point than LDPE.