Cationic polymerization of aldehydes

Cationic polymerizations of formaldehyde, higher aliphatic aldehydes and haloaldehydes are discussed. The polymerization is initiated by Lewis and Brønsted acids but is dominated by the fact that in almost all cases the polymers precipitate and crystallize from the solution. As a consequence the polymerizations become diffusion controlled sometimes even at low conversions. This phenomenon is not limited to cationic polymerization but additionally the growing ends are readily occluded and cationic initiators are adsorbed on the precipitated polymer. The morphology and the degree of swelling of the precipitated polymer plays an important role upon the rate of polymerization and conversion of monomer to polymer. As expected, polymerizations of aliphatic aldehydes are more readily carried out by cationic initiators than the polymerization of haloaldehydes; this may be caused by the difference in the initiation mechanism.