Preparation and characterization of cyclic poly(oxypropylene)

Poly(propylene glycol) α-hydro-ω-hydroxypoly(oxypropylene)] of number-average molar mass M?_n ≈ 2000 g · mol^?1 (PPG2000) was cyclised with high conversion (ca. 75%) by reaction with dichloromethane in the presence of powdered KOH. The cyclic product was separated from chain extended polymer by preparative GPC, giving an overall yield of polymer (M?_n ≈ 2000 g · mol^?1, narrow molar mass distribution) in excess of 50%. Characterisation by analytical GPC and ¹³C NMR spectroscopy confirmed cyclisation. DEPT and ¹H-coupled NMR spectra were used to show that the links in cyclic poly(oxypropylene) were 77% single acetal, 12% double acetal and 11% triple acetal (or higher). This complexity probably results from competitive reaction with water introduced with KOH.