Factors that affect polymer properties:

1. Chain length: Longer chains get tangled with and stick to each other, making them harder to separate. This means polymers with longer chains have a higher melting point, strength and toughness

2. Cross-linking: Cross linking permanently attaches the chains to each other, increasing the rigidity, strength and hardness

3. Plasticizers: Plasticizers block the formation of intermolecular bonds by sitting between chains. This leads to the formation of a weak but flexible polymer.

4. Crystallinity: When a polymer is crystalline, it will be tightly packed with the chains parallel to each other. This leads to strong intermolecular forces between the chians, causing increases in strength and melting point.