Degradable Poly(2-oxazoline) Analogues from Partially Oxidized Poly(ethylene imine)

A series of degradable poly(2-n-alkyl-2-oxazoline-stat-glycine)s was synthesized in a modular manner via a straightforward postpolymerization synthesis route comprising consecutive hydrolysis of poly(2-ethyl-2-oxazoline) to yield linear poly(ethylene imine), partial oxidation of the backbone to yield statistically distributed glycine moieties, and reacylation of secondary amines to reintroduce N-acyl ethylene imine repeating units. The molecular structures were confirmed by analytical techniques such as infrared spectroscopy, size exclusion chromatography, amino group titration, and various nuclear magnetic resonance spectroscopy methods. Polymers with alkyl side chains up to six carbon atoms were amorphous with glass-transition temperatures decreasing with increasing number of side-chain carbon atoms (−71 °C ≤ Tg ≤ 105 °C). Longer n-alkyl substituents induced semicrystallinity. Melting temperatures increased with the length of the substituents (9 °C ≤ Tm ≤ 28 °C). Glycine repeating units enabled degradation of the polymer backbone under acidic conditions or proteinase K catalysis. The copolymers represent therefore degradable poly(2-n-alkyl-2-oxazoline) analogues.