Fast Access to Dendrimer-like Poly(ethylene oxide)s through Anionic Ring-Opening Polymerization of Ethylene Oxide and Use of Nonprotected Glycidol as Branching Agent
Résumé
Dendrimer-like poly(ethylene oxide)s (PEOs) were synthesized through a semicontinuous process based on the anionic ring-opening polymerization (AROP) of ethylene oxide (EO), followed by AROP of a mixture of glycidol (G) and propylene oxide (PO). Glycidol was used as branching agent generating two hydroxyl groups after ring-opening, whereas propylene oxide served to prevent the aggregation of the generated terminal alkoxides. A three-armed PEO star was first prepared through AROP of EO from 1,1,1-tris(hydroxymethyl)ethane as trifunctional precursor using dimethyl sulfoxide (DMSO) as solvent. After completion of EO polymerization and without isolating the PEO star precursor, G and PO (molar ratio 1:3) were added in the same batch to be polymerized either sequentially or randomly. This led to a, three-armed PEO star with an average number of terminal hydroxyls per arm which depended on the number of G units inserted at PEO chain ends, as determined by H-1 NMR spectroscopy. Growth of the second and the third generation of PEO could be achieved upon reiterating the same steps of AROP of EO and subsequent AROP of G and PO (arborization step) in one pot, affording dendrimer-like PEOs of generation 3 with moderately distributed but expected molar masses. In a variant of this strategy, G was copolymerized in the presence of allyl glycidyl ether during the arborization step in order to introduce allylic double bonds at the branching points of the dendrimer-like PEOs.