Phthalaldehyde was found to undergo cyclopolymerization with ease by several cationic catalysts and by γ‐ray irradiation. The polymer was composed entirely of the dioxyphthalan unit, as confirmed by infrared spectroscopy and ready decomposition to monomer. The enhanced polymerizability of phthalaldehyde as compared with other aromatic aldehydes was explained in terms of the intermediate‐type or, preferably, concerted propagation scheme. The conversion reached a saturation value of 87% in about 1 hr in methylene chloride at −78°C, indicating an equilibrium polymerization. The ceiling temperature of the polymerization was −43°C, as estimated from the relation between the saturation yield and polymerization temperature. The enthalpy and entropy of propagation were −5.3 kcal/mole and −23.0 eu, respectively. Since the molecular weight of the polymer was proportional to conversion, the propagating chain end was considered to be “living” in this system. The rate constant for propagation was calculated to be 0.18 1/mole‐sec in methylene chloride at −78°C with BF3OEt2 catalyst.
Polymerization of o-vinylbenzaldehyde was carried out at 0°C with BFaOEt2 catalyst. The polymers obtained as white powders were soluble in common organic solvents, and were not cleaved by treatment with dilute hydrochloric acid. The degree of polymerization was 20-30. The polymer contained approximately 20% of the pendent vinyl group and 5% of the pendent aldehyde group. The rest of the monomer unit was presumably the cyclized unit. On the basis of these structural data, a cationic propagation scheme of o-VBA was proposed, in which the neighboring aldehyde group reacted overwhelmingly with the growing cation to form a cyclic unit and the intramolecular cyclization of the neighboring vinyl group with the cation was competitive with the intermolecular propagation. This scheme was consistent with that expected from the cyclopolymerization schemes of o-divinylbenzene and o-phthalaldehyde.
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