Which of the following is a primary effect of cross-linking in polymers?

• A. Cross-linking decreases the molecular weight of polymers.
• B. Cross-linking converts polymers into linear chains.
• C. Cross-linking makes polymers more soluble in organic solvents.
• D. Cross-linking increases the rigidity and thermal stability of polymers.

Answer: (D)

Verified step by step guidance

1. Understand what cross-linking means in the context of polymers: it is the formation of covalent bonds between different polymer chains, creating a network structure rather than isolated linear chains.
2. Recognize that cross-linking does not decrease molecular weight; instead, it effectively connects polymer chains, which can increase the overall molecular network size.
3. Note that cross-linking does not convert polymers into linear chains; it actually links chains together, often creating a three-dimensional network.
4. Consider the solubility aspect: cross-linked polymers tend to be less soluble in solvents because the network structure restricts the polymer chains from dissolving easily.
5. Conclude that the primary effect of cross-linking is to increase the rigidity and thermal stability of polymers by restricting chain mobility and enhancing structural integrity.