[tony]

In the production of Polyurethane, a disocyanate (O=C=N-(CH2)xN=C=O where x can be a number from 3-8) is used to react with a diol (ethane-1,2-diol) and in the process a polymer formed has a polymer with a linkage -OCONH-.

Is the polymerisation addition or condensation?

I have found website/book that argue that it is addition since there is no elimination of smaller molecules. Others argue it is condensation poly as the reaction is a step growth instead of chain growth.

[movies]

According to IUPAC, you have to lose a small molecule to have a condensation reaction:

http://www.iupac.org/goldbook/C01238.pdf

[HP]

I know this polymerization reaction is called "migration polymerization" because theres only a migration of H-athom to NCO group to form uretane group.