Acetal polymers, which are widely used for engineering applications, can be represented by the following reaction, the polymerization of formaldehyde:

Formaldehyde is a gas at room temperature and is commercially available as a 37% solution in water, which is called formalin. As a gas, it polymerizes into a white powder called Paraformaldehyde.

Explanation:

Para-formaldehyde (PFA) is the product of formaldehyde formed by a polymerization degree of 8-100 units. Due to decomposition, it has the smell of formaldehyde. Para-formaldehyde forms white precipitate, if it is stored in the cold. Formalin contains little monomeric formaldehyde and mostly it forms a short chain of poly formaldehyde. To limit the excess of polymerization, a small quantity of methanol is used.