Question

You must select a high stiffness polymer. How do you expect the tensile modulus of the following polymers compare:

1) Atactic PVC having an average molecular weight of 500,000 g/mol

2) Isotactic PVC having an average molecular weight of 500,000 g/mol

a) 2 will have a greater tensile modulus than 1

b) 1 will have a greater tensile modulus than 2

c) They exhibit about the same tensile modulus

Answer 1

b) 1 will have greater tensile modulus than 2

Atactic polymers are amorphous in nature while isotactic polymers are semi-crystalline. This is because atactic polymers have a random arrangement of molecules while isotactic polymers have semi-ordered arrangement. Due to this structure atactic polymers are stiff compared to isotatic polymers.