Ring-opening polymerization of monosubstituted oxiranes in the presence of potassium hydride : determination of initiation course and structure of macromolecules by MALDI-TOF mass spectrometry

Abstract

Several monosubstituted oxiranes were polymerized with suspension of potassium hydride (KH) in tetrahydrofuran (THF) at room temperature. This heterogeneous process resulted in polyethers with various starting groups depending on the kind of monomer. The macromolecules formed in ring-opening polymerization of monosubstituted oxiranes were analyzed by Matrix Assisted Laser Desorption/Ionization - Time of Flight Mass Spectrometry (MALDI-TOF MS). It was stated, that initiation of propylene oxide (PO) polymerization with KH proceeded via three ways, i.e. cleavage of oxirane ring in the β-position, monomer deprotonation and deoxygenation. Potassium isopropoxide, potassium allyloxide and potassium hydroxide were the real initiators. The main reactions, which occur in the initiation step, depend on the type of monomer used. In the case of allyl glycidyl ether (AGE) and phenyl glycidyl ether (PGE) deprotonation of the monomer did not occur. During initiation of glycidyl ethers oxirane ring was opened and also linear ether bond between glycidyl group and oxygen atom was cleaved under influence of KH. Interestingly, formation of new kinds of macromolecules was observed in the systems containing glycidyl ethers, which do not possess mers of the monomers used. Mechanisms of the studied processes were presented and discussed. Carbon-13 Nuclear Magnetic Resonance (13C NMR) was used as supporting technique for analysis of the obtained polymers. Number average molar masses of the polymers (Mn) determined by Size Exclusion Chromatography (SEC) were about two times higher than calculated ones. It indicated that half of used KH did not take part in the initiation step.