Selectivity of PEO-block-PPO Diblock Copolymers in the Microwave-Accelerated, Anionic Ring-Opening Polymerization of Propylene Oxide with PEG as Initiator

Abstract

Diblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) were synthesized by the anionic ring-opening polymerization of propylene oxide (PO), with controlled microwave heating in sealed vessels. A detailed study was carried out to investigate the effects of different parameters on the formation of unwanted byproducts. Parameters that were considered include temperature; the concentration of NaH, monomer and hydroxy groups in the feed; and the polarity of the reaction medium. A continuous decrease of internal pressure during the sealed-vessel experiment reflected the consumption of PO monomer and the completion of the reaction was confirmed by a drop of the internal pressure to zero when reactions were performed in bulk. The products were characterized by using different chromatographic techniques. A comparison of the reaction times and composition of the polymers prepared by microwave and conductive heating is given.