Ring opening polymerization of styrene oxide initiated with potassium alkoxides and hydroxyalkoxides activated by 18-crown-6: determination of mechanism and preparation of new polyether-polyols

Abstract

It was stated that initiation in ring opening polymerization of styrene oxide depends on the kind of potassium alkoxide activated by 18-crown-6 used. In the presence of potassium methoxide the oxirane ring opening occurs exclusively in the β-position and not in the β or α position, i.e., contrary to the previous data. A similar result was obtained in the systems initiated with potassium t-butoxide, 2-methylpropoxide and 1-phenylethoxide. Unexpectedly, potassium i-propoxide and 1-methylpropoxide open the oxirane ring in the β or α position. In all polymerizations, deprotonation of methine group in the monomer takes place under the influence of the initiator and in chain transfer reaction to the monomer. It leads to the formation of macromolecules with unsaturated starting group. However, deprotonation of methylene group in the monomer does not occur. Applying of potassium hydroxyalkoxides, i.e., monopotassium salt of dipropylene glycol or tripotassium salt of 2,2,6,6-tetrakis(hydroxymethyl)cyclohexanol it was possible to synthesize PSO-diols and PSO-pentols without unsaturation. Molar masses of polymers (Mn = 1700–4800 Da) are much higher than reported in literature for other anionic systems. Dispersity of polymers is rather low (Mw/Mn = 1.07–1.15) indicating relatively high rate of initiation and cation exchange reaction.