The synthesis and polymerization of oxo‐crown ethers

A novel synthetic route to and a polymerization procedure for oxo‐crown ethers 2, 11‐dioxo‐18‐crown‐6 ( 1 ), 2‐oxo‐12‐crown‐4 ( 2 ) and 2‐oxo‐21‐crown‐7 ( 3 ) are described. Cyclization of the ω‐hydroxycarboxylic acid precursors of 1—3 has been achieved by heating these precursors in the presence of a Lewis acid catalyst (CoCl 2 ) and a template salt (MCl). Cyclization yields up to 82% were reached, using CsCl as template salt. Oxo‐crown ethers 1—3 have been polymerized using SnOct 2 as catalyst, giving polymers with molecular weights of approximately 5 kg/mol and dispersities of ca. 1.8 (measured with polyethylene oxide standards). The polymerization of 2 was monitored with 1 H‐NMR and SEC giving information about (a) the influence of monomer/catalyst ratio and temperature on polymerization rate and (b) the influence of temperature on molecular weight (distribution). The possibility of introducing endgroups into poly(2‐oxo‐12‐crown‐4) using SnOct 2 ‐catalyzed polymerization was also studied.