Abstract
Abstract The cause of the polymerizability of formaldehyde in liquid carbon dioxide was studied in connection with the preparation conditions of the monomer. A liquid carbon dioxide solution of the monomer was prepared by two different methods, by means of the pyrolysis of α-polyoxymethylene and by means of that of the hemiformal of polyethylene glycol, under a carbon dioxide stream. By adding various sodium salts to the pyrolysis system of α-polyoxymethylene, the polymerization rate, without the addition of any catalyst, of the monomer thus obtained was found to decrease with an increase in the pKa value of the conjugated acid of the salt. The polymerization rate also decreased with the amount of sodium carbonate added. The hemiformal of polyethylene glycol was prepared by bubbling the gas evolved by the pyrolysis of paraformaldehyde into polyethylene glycol. The amount of acid present in the hemiformal thus obtained increased linearly with the pyrolysis time. The polymerization rate of the monomer obtained by the pyrolysis of the hemiformal increased in proportion to the acid content in the hemiformal. On the basis of these results, the initiation mechanism in the polymerization of formaldehyde without any additional initiator in a liquid carbon dioxide solution was discussed.
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