Which of the following will increase the strain to failure of polymers?  a. cross-linking of the molecules b. Increased molecular length  c. Addition of a plasticizer  d. Increase degree of crystallization

The strain to failure of polymers can be increased by:

a. Cross-linking of the molecules: Cross-linking involves the formation of bonds between polymer chains. This process can increase the toughness of a polymer, making it more resistant to deformation and failure.

b. Increased molecular length: Longer polymer chains can entangle more, which can increase the toughness of the polymer. This can make the polymer more resistant to deformation and failure.

c. Addition of a plasticizer: Plasticizers are additives that increase the flexibility of a polymer. They work by reducing the intermolecular forces between polymer chains, allowing them to slide past each other more easily. This can increase the strain to failure of the polymer.

d. Increase degree of crystallization: Crystallization refers to the arrangement of polymer chains in a highly ordered, regular pattern. While this can increase the stiffness and strength of a polymer, it can also make the polymer more brittle and decrease its strain to failure. Therefore, increasing the degree of crystallization may not necessarily increase the strain to failure of a polymer.