Monomer-activated Copolymerization of Ethylene Oxide and Epichlorohydrin: In Situ Kinetics Evidences Tapered Block Copolymer Formation
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The monomer-activated anionic ring-opening copolymerization (AROP) of ethylene oxide (EO) and epichlorohydrin (ECH) using tetraoctylammonium bromide as an initiator and triisobutylaluminum (i-Bu3Al) as an activator was studied. The properties of the copolymers as well as the microstructure have been analyzed in detail via an in situ NMR kinetics study. The statistical copolymers exhibited molecular weights ranging from 2350 gmol−1 to 38000 gmol−1 (measured by SEC, PEG-standards) and moderate dispersities of 1.27–1.44. The thermal property tests revealed both a glass transition and melting for all copolymers, supporting a block-like nature. Applying in situ NMR kinetic measurements, the reactivity ratios of EO and ECH were determined to be strongly disparate, i.e., rEO = 9.2 and rECH = 0.10. This shows that the simple one-pot statistical anionic copolymerization of EO and ECH via the monomer-activated AROP resulted in the formation of strongly tapered, block-like structures. Furthermore, post-polymerization functionalization of the reactive chloromethyl groups by nucleophilic displacement was investigated for the copolymers. Copolymerization of EO and ECH offers a broad platform for further functionalization and therefore the possibility to prepare a variety of multifunctional PEGs.
KeywordsEpichlorohydrin Polymerization Ring-opening Copolymerization Reactivity ratios Epoxide
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A. Danner is a recipient of a DFG-funded position through the Excellence Initiative by the Graduate School Materials Science in Mainz (GSC 266). The authors thank Dr. Johannes C. Liermann and Nadine Schenk for technical assistance during in situ NMR kinetics measurements as well as Maria Mueller and Monika Schmelzer for DSC and SEC measurements. Jan Blankenburg is acknowledged for help with the evaluation of in situ NMR data.
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