Cationic polymerization of 2-methyl-1.3-dioxepane

2-Methyl-1.3-dioxepane was polymerized in 1.2-dichloroethane with triethyl oxonium tetrafluoroborate and boron trifluoride as initiators. This polymerization involves a monomer-polymer equilibrium and the polymer consists of regularly alternating tetrahydrofuran and acetaldehyde units. The thermodynamic parameters for the polymerization were determined from the temperature dependence of the equilibrium monomer concentration as follows: ΔH_SS = ?2.1 ± 0.3 kcal/mole and ΔS⁰_SS = ?8.9 ± 1.3 cal/mole deg. The ceiling temperature for the 1 mole/1. solution is ?37°C. The attempted polymerization of 2.2-dimethyl-1.3-dioxepane gave only a crystalline cyclic dimer.