Condensation polymers form when monomers join together, releasing small molecules like water as byproducts. They typically involve two different functional groups (e.g., -OH and -COOH).

Dacron (polyester) is made from ethylene glycol and terephthalic acid, with the reaction:

$$\begin{gathered} \mathrm{HO}-R-\mathrm{OH}+\mathrm{HOOC}-\mathrm{R\text{'}}-\mathrm{COOH} \\ \to [-O-R-O-C(=O)-\mathrm{R\text{'}}-C(=O)-]n+H_{2}O \end{gathered}$$

Neoprene, Acrylonitrile, and Teflon are addition polymers, formed without byproduct loss.

Final Answer: Dacron