A series of degradable poly(2-n-alkyl-2-oxazolinestat-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 ≤ T g ≤ 105 °C). Longer n-alkyl substituents induced semicrystallinity. Melting temperatures increased with the length of the substituents (9 °C ≤ T m ≤ 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.
We present the synthesis development of amphiphilic, degradable poly(2-ethyl-2-oxazoline) (PEtOx) analogue block copolymers in a modular fashion utilizing the strain-promoted azide–alkyne cycloaddition (SPAAC).
A 3-benzylmorpholine-2,5-dione monomer is synthesized from the natural amino acid l-phenylalanine and characterized by means of nuclear magnetic resonance and infrared spectroscopy, electrospray ionization mass spectrometry, and elemental analysis. Subsequent to preliminary polymerization studies, a well-defined poly(ester amide) homopolymer is synthesized via ring-opening polymerization using a binary catalyst system comprising 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and a 1-(3,5-bis(trifluoromethyl)phenyl)-3-cyclohexylthiourea (TU) cocatalyst with a feed ratio of M/I/DBU/TU = 100/1/1/10. Kinetic studies reveal high controllability of the dispersities and molar masses up to conversions of almost 80%. Analysis by mass spectrometry hints toward excellent end-group fidelity at these conditions. In consequence, utilization of hydroxyl-functionalized poly(ethylene glycol) and poly(2-ethyl-2-oxazoline) as macroinitiators results in amphiphilic block copolymers. Bulk miscibility of the building blocks is indicated by differential scanning calorimetry investigations. As more and more promising new drugs are based on hydrophobic molecules featuring aromatic moieties, the novel polyesteramides seem highly promising materials to be used as potential drug delivery vehicles.
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