Alkanes, which are saturated hydrocarbons, cannot be used to make polymers because they lack the necessary functional groups for polymerisation reactions. Polymers are long chain molecules formed by the repetition of smaller units called monomers. To form polymers, monomers must have reactive functional groups that can undergo polymerisation reactions, such as addition or condensation reactions.

Alkanes consist solely of carbon and hydrogen atoms arranged in a single bond chain. Each carbon atom in an alkane is surrounded by four other carbon atoms or hydrogen atoms, forming a stable and unreactive structure. Alkanes do not have functional groups such as double bonds, triple bonds, or electronegative atoms like oxygen or nitrogen, which are required for polymerisation reactions.

In contrast, monomers used to make polymers typically contain functional groups such as double bonds, triple bonds, or reactive chemical groups like hydroxyl (-OH), amino (-NH2), or carboxylic acid (-COOH) groups. These functional groups enable the monomers to undergo polymerisation reactions, where the multiple bonds can break and form new bonds with adjacent monomers, creating long polymer chains.

Therefore, alkanes alone cannot be used as monomers to make polymers due to their lack of reactive functional groups. Instead, other types of monomers with suitable functional groups, such as alkenes, alkynes, or monomers containing heteroatoms, are typically used for polymerisation reactions to form polymers.