One of the most typical routes for obtaining poly(ethyleneimine) involves the ring opening polymerization of aziridine, however, the resulting polymer is highly branched with the presence of primary, secondary, and tertiary amino groups. In contrast, linear poly(ethyleneimine), LPEI, can be conveniently obtained by the hydrolysis of poly(2-alkyl-2-oxazoline) precursors. The poly(2-alkyl-2-oxazolines) are attractive starting materials due to their thermal stability, overall linear structure, low poly dispersity, and the ability to synthesize these over a wide range of molecular weights. LPEI synthesis is investigated from several routes including evaluating traditional methods used, and via non-traditional routes such as click-like reactions or transamidation of varying precursors. The most commonly used precursor from this class of polymers is poly(2-ethyl-2-oxazoline), Aquazol<sup>®</sup>, due to its commercial availability and high water solubility. The kinetics of this process are well-defined such that the degree of hydrolysis can be tailored for specific applications. The fully hydrolyzed product is crystalline and water-insoluble, whereas the partially hydrolyzed product is readily soluble in methanol. An example where partial hydrolysis is desired would be when LPEI is used for transfection into mammalian cells, where it is preferred that the polymer be left with 10-12% of the poly(2-ethyl-2-oxazoline) precursor. Despite the convenience of using commercial precursors, limitations exist in terms of the maximum molecular weights obtained after hydrolysis, due to known long-chain branching of Aquazol<sup>® </sup>at high M/I ratios. To combat this undesirable branching, poly(2-phenyl-2-oxazoline) can be used as an alternative precursor where long-chain branching is not apparent presumably due to the bulk and electron donating ability of the phenyl moiety, minimizing side reactions that promote branching.

Linear poly(ethylenimine) synthesis: Traditional and innovative approaches

251st National Meeting (2016)

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