Yet, the actual structure of a PU chain can be much more
complex and it is dependent not only on the type of employed
raw materials but also on the conditions adopted for the polyaddition
process, e.g., which feedstocks were charged earlier and which
were charged later, stoichiometry of reaction, process temperature and
time, as well as possible presence and amount of polyaddition
catalyst used. The process conditions are responsible for the fact that
PU macromolecules can comprise also biuret groups, allophanate
ones, carbodiimide or azaheterocyclic isocyanurate structures, or oxa-
zolidone ones. The majority of additionally created structures are
polar in their nature. This adds to the nature of carboxyl, urethane
and ether or ester groups which are typical for anionomers. Hence,
the polarity of resultant PUs becomes considerable and those materials
offer better solubility in water (as compared to insoluble nonionic
polyurethanes) and in polar organic solvents, e.g., N,N-dimethylaceta-
mide, dimethylformamide, acetonitrile, dimethylsulfoxide. When a
PU anionomer is not completely water soluble, it is usually capable
of forming aqueous emulsions or dispersions, and it can form
specific polymer gels in the presence of organic solvents