Cationic Polymerization of 1,5-Dioxepan-2-one with Lewis Acids in Bulk and Solution

Abstract 1,5-Dioxepane-2-one (DXO) was coordinatively ring-opening polymerized with different Lewis acids in bulk and solution. The reactivities of a series of initiators (SnCl4, FeCl3, AlCl3, BCl3, and BF3OEt2) at different temperatures and reaction times were analyzed. Polymerization of DXO in bulk with SnCl4, FeCl3, AlCl3, and BCl3 gave only oligomers or low molecular weight polymers irrespective of temperature and/or reaction time. Polymerization of DXO with BF3OEt2 at 70°C gave yields of nearly 100% and molecular weights up to M w = 10,000. The polymerization temperature was increased to 100°C and the reaction time prolonged, which resulted in nearly equal molecular weights as at 70°C but with lower yields, higher polydispersity, and generally not full conversion. In addition, side reactions, such as backbiting, transesterification and thermal degradation, occurred to a larger extent at higher reaction temperatures. Solution polymerization using the same initiators and THF, dioxane, or nitrobenzene as the solvent gave polymers of low molecular weights and of low yields, except with FeCl3 and BF3OEt2. The rates of polymerization were significantly higher in nitrobenzene than in dioxane and THF due to polarity and coordination of these solvents to the growing chain. Comparison of the initiators BF3OEt2 and SnCl4 in solution polymerization showed equal reactivity in nitrobenzene for both of them. The BF3OEt2-initiated systems give polymers with lower molecular weights than SnCl4-initiated systems, but with narrower polydispersity.