Polymerization of aromatic aldehydes, 11. Polymerization of 3-(o-formylphenyl)propionaldehyde and o-phenylenediacetaldehyde

Polymerization of 3-(o-formylphenyl)propionaldehyde ( 4 ) and o-phenylenediacetaldehyde ( 5 ) were performed with several ionic catalysts. The cationic polymerization of 4 yielded polyacetals which contained a seven-membered cyclic unit ( 7 ) in mole fractions of 0,3–0,5. The uncyclized unit ( 6 ) contained the pendant aromatic aldehyde. Apparently, the aromatic aldehyde group reacted during the course of the intramolecular cyclization. Polymerizations of 5 with BF₃·O(C₂H₅)₂, lithium tert-butoxide, or Al(C₂H₅)₃-TiCl₄ as catalysts, similarly gave polyacetals containing a seven-membered cyclic unit ( 10 ) in mole fractions of 0,5–0,8. The extent of cyclization decreased with increase in temperature in the cationic polymerization, resulting in a difference of ?7,5 kJ mol^?1 (?1,8 kcal mol^?1) between the activation energy of intramolecular cyclization and that of intermolecular propagation. The polymerization with Al(C₂H₅)₃ as catalyst gave a polyester via propagation involving a hydride shift.