Addition is the name given in chemistry to a process in which a new substance is formed from two other substances without any by-products. In addition polymerisation, molecular components or monomers with different structures are linked to create high polymers with the migration of hydrogen atoms. This type of polymerisation is generally carried out by subjecting the monomers to heat and pressure. Two significant groups of plastics are manufactured by this process nowadays: polyurethanes and epoxy resins. Condensation polymerisation can take place when the reactants each have two functional groups that can combine with each other by producing water. Staudinger 1961, 108 writes: “Condensation polymerisation is characterised by a chemical reaction between two compounds with groups that are of the same or different kinds but are reactive, in which [...] there are low-molecular by-products such as water, alcohols, ammonia, hydrochloric acid or similar substances. [...] It is an absolute technical necessity for the by-products of the reaction to be removed in the condensation process [...] for the reaction to go smoothly and successfully. The list of technically important plastic groups that are manufactured by the condensation polymerisation process includes the following: 1) the group of phenol formaldehyde resins (= typical duroplasts [e.g. Bakelite]), 2) polyamides (nylon and perlon) and linear polyesters (particularly polycarbonates as thermoplastics) and 3) crosslinked polyesters as lacquer and casting resins. [...] (An addition to this list, editor’s note) silicones”.