Molecular weight distribution and endgroup functionality of poly(2-ethyl-2-oxazoline) prepolymers

Abstract

Control over molecular weight distribution and endgroup functionality is important for prepolymers that are to be further incorporated into block and graft copolymers. Monofunctional, telechelic and heterobifunctional poly(2-ethyl-2-oxazoline) (PEtOx) oligomers were prepared by cationic ring-opening polymerization with different classes of initiators including methyl triflate as the control, activated benzyl and xylyl halides, and non-activated alkyl iodides. Endgroup functionalities and molecular weight distributions were compared by SEC, 1H NMR and titrations. PEtOx oligomers initiated with methyl triflate had polydispersities (PDI's) near 1.1 while those initiated with activated benzyl or xylyl halides had PDI's of 1.30–1.45. The difference was attributed to slower initiation and to covalent species in the activated halide-initiated reactions that were present in addition to the more active cations. 1H NMR showed an approximately 1:1 endgroup functionality in these cases and titrations of the amine endgroups were in good agreement with the NMR endgroup data. Due to the control of functionality and relatively good control over molecular weights and dispersities, it was concluded that these polymers should be suitable as prepolymers for membrane, hydrogel and drug delivery applications. Non-activated alkyl iodides initiated these reactions quite slowly and there was a wider discrepancy between targeted and obtained molecular weights after isolation of the oligomers.