Synthesis of Macrocyclic Poly(ethylene oxide) and Polystyrene via Glaser Coupling Reaction

Abstract

Glaser coupling reaction of alkynyl groups was used as a new ring-closure technique to synthesize monocyclic poly(ethylene oxide) (PEO) and polystyrene (PS) successfully. The linear PEO with hydroxyl groups at both ends was prepared by ring-opening polymerization (ROP) of ethylene oxide (EO) using 2,2-dimethyl-1,3-propanediol and diphenylmethylpotassium (DPMK) as co-initiators, terminated by anhydrous methanol. The linear PS with hydroxyl groups at both ends was prepared by anionic polymerization using lithium naphthalenide as initiator and terminated by EO. The propargyl-telechelic precursors (l-PEO and l-PS) were then obtained by the reaction between hydroxyl-telechelic polymers (HO-PEO-OH and HO-PS-OH) and propargyl bromide in the presence of sodium hydride. The intramolecular cyclizations of the latter were carried out in the presence of Cu(I)Br/N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) under mild conditions with oxygen in the air as oxidant and the efficiency was as high as nearly 100%. The cyclic PEO and PS (c-PEO and c-PS) were characterized by GPC, 1H NMR, FTIR, and MALDI-TOF MS. G factors (ratio of the apparent peak molar masses of cyclic product to their linear precursor) derived from GPC profiles were in the range 0.63−0.80. The highly efficient Glaser coupling took place at ambient temperature and did not need oxygen removal procedures, so it was a convenient approach for nearly quantitative preparation of cyclic polymers.