Polymer Chemistry
Build long molecular chains and connect structure to material properties.
Reactive groups connect. Monomers consume functional groups and build repeat units through a chain or network.
In step growth any two chain ends can join, so at p = 0.62 the Carothers equation gives Xₙ = 1/(1−p) = 2.6. Long chains appear only near complete conversion; about 14.4% of the original monomers are still unreacted.
Xₙ = 1/(1−p) applies to ideal, stoichiometric step-growth (condensation) polymerization, where p is the fraction of functional groups reacted. Chain-growth polymerization builds long chains early and follows different statistics. The chains are schematic; real properties also depend on molecular weight distribution, tacticity, branching, crystallinity, additives, and processing history.
Make the chemistry yours.
Answer from the model, then use the explanation to connect the particle picture to the chemical rule.