Terminal Unsaturation in Polypropylene Glycol

Abstract

Both allyl and cis-propenyl end groups are present in polypropylene glycol synthesized by the base-catalyzed addition of propylene oxide to propylene glycol initiator. The cis-propenyl group is readily identifiable from the characteristic 5.98 and 13.83 μ absorption bands in the infrared spectrum. Evidence for allyl unsaturation is provided by the periodate scission of the double bond and recovery of the released formaldehyde. The presence of terminal unsaturation in polypropylene glycol can seriously limit the length of the polymer chain in the reaction with diisocyanates to form polyurethans. The amount of cis-propenyl unsaturation formed in the synthesis of polypropylene glycol increases with increasing reaction temperature, catalyst concentration and extent of certain metallic surfaces. There is no simple relationship between any of the known reaction variables and the amount of allyl unsaturation produced. © 1959, American Chemical Society. All rights reserved.