Cationic polymerization of aldehydes

Abstract

Cationic polymerizations of formaldehyde, higher aliphatic aldehydes and haloaldehydes are discussed. The polymerization is initiated by Lewis and Bronsted 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. ZUSAMMENFASSUNG:Die kationische Polymerisation von Formaldehyd, hoheren aliphatischen Aldehyden und Halogenaldehyden wird diskutiert. Die Polymerisation wird mit Lewis-Sauren und Bronsted-Sauren initiiert, wird aber beherrscht von der Tatsache, daD in fast allenr Fallen die Polymeren ausfallen und aus der Losung auskristallisieren. Die Folge ist, daD die Polymerisationen diffusionskontrolliert werden und dies in einigen Fallen sogar bei kleinen Umsatzen. Diese Erscheinung ist nicht auf die kationische Polymerisation beschrankt, doch kommt hier h.inzu, da13 die wachsenden Enden leicht okkludiert werden und kationische Initiatoren von dem ausfallenden Polymeren absorbiert werden. Die Morphologie und das AusmaD der Quellung des ausgefallenen Polymeren spielt eine wichtige Rolle in bezug auf die Polymerisationsgeschwindigkeit und den Umsatz des Monomeren zum Polymeren. Wie zu erwarten, lassen sich aliphatische Aldehyde leichter als Halogenaldehyde mit kationischen Initiatoren polymerisieren; dies kann in dem Unterschied des Startmechanismus begriindet sein.

Stable organic cation salts: Ion pair equilibria and use in cationic polymerisation

“…Generally speaking stable salts have been useful mainly from a preparative point of view, and an understanding of the detailed kinetics and mechanisms of aldehyde pot2a-nerisations is still only at the speculative stage (124).…”

Controlled cationic copolymerization of benzaldehyde with isobutyl vinyl ether using base‐assisting system

“…2,5,6 Cationic polymerization of aldehydes is generally difficult compared to vinyl polymerization due to lower ceiling temperatures. 7 Thus, there are few examples of cationic polymerization, 8,9 and even fewer attempts at synthesis of polymers with well-defined structures. Homopolymerization of aromatic aldehydes is known to be especially difficult.…”

Cationic Copolymerization of o-Phthalaldehyde and Functional Aliphatic Aldehydes

“…Boron trifluoride diethyl etherate (BF 3 OEt 2 ) gave the highest yield of polymerizations among the Lewis acids tested. This catalyst has been reported as highly active to aldehyde polymerizations. , Copolymer yields from chloroform and toluene were significantly lower than those from DCM. Other boron trihalides and triethyl aluminum catalysts did not catalyze the copolymerization reaction.…”

“…−78 °C, and their freezing point. The solvent must also dissolve the trimer form of the aliphatic aldehyde comonomer even though the trimer itself does not homopolymerize . Precipitation of the comonomer trimer would decrease the concentration of free monomer from the reaction solution.…”