Ionic Polymerization via C O Bonds

Polymerization by opening of C = O bonds was investigated many years ago in the case of formaldehyde. As may be expected from its polar mesomeric structure formaldehyde can polymerize both anionically and cationically  

Anionic polymerization can be initiated with tertiary phosphines or amines, with organometallic compounds or with alcoholates. With all of these, initiation occurs by nucleophilic attack on the positive carbonyl carbon atom  

Cationic polymerization of formaldehyde (which should be carried out under the driest possible conditions to avoid transfer reactions) can be initiated with protic acids, Lewis acids (see Sect. 3.2.1.1), or other compounds that yield cations such as acetyl perchlorate or iodine  

Polymers of formaldehyde with semiacetal end groups are thermally unstable they decompose at temperatures as low as 150°C, splitting off monomeric formaldehyde. Upon acetylation of the hydroxy end groups, thermal stability up to 220°C is achieved alkylations also provides stability against alkali, but not against acids 

Other carbonyl compounds, such as acetaldehyde or propionaldehyde can also be polymerized to high-molecular-weight products however, their stability is lower than that of polyoxymethylenes with protected end groups. 

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