Do you always need a diol + dicarboxylic acid, i.e. the two functional groups in order to make a polyester? Not sure where else I can ask. Thanks.
Edit: I mean; can you make a polyester from just a normal -ol and carboxylic acid.
> Edit: I mean; can you make a polyester from just a normal -ol and carboxylic acid.
You can make an ester with these but not a polymer. Once the alcohol has reacted with the acid the units do not have any more functional groups that could react with other units to create a chain. To create a polymer that each unit needs two functional groups/ have group than can react with more than one other unit (i.e. alkenes/alkynes)
The most common forms of [condensation polymerization](https://en.wikipedia.org/wiki/Condensation_polymer) are polyesters and polyamides.
This happens two ways. The first is as an alternating copolymer (ABABAB…) where one monomer has two acids and the other monomer has two alcohols (or in the case of a polyamide, two amines).
The second way is a single monomer with an acid on one end and an alcohol (or amine) on the other. Amino acid chains are an example of a polyamide which is made this way.
There needs to be two reacting points on each monomer so that the reaction will keep going and form a long chain.