Cryogels Based on Poly(2-oxazoline)s through Development of Bi- and Trifunctional Cross-Linkers Incorporating End Groups with Adjustable Stability

Nora Engel; Tim Hoffmann; Florian Behrendt; Phil Liebing; Christine Weber; Michael Gottschaldt; Ulrich S Schubert

doi:10.1021/acs.macromol.3c02030

Cryogels Based on Poly(2-oxazoline)s through Development of Bi- and Trifunctional Cross-Linkers Incorporating End Groups with Adjustable Stability

Macromolecules. 2024 Mar 12;57(6):2915-2927. doi: 10.1021/acs.macromol.3c02030. eCollection 2024 Mar 26.

Authors

Nora Engel^{1

2}, Tim Hoffmann^{1

2}, Florian Behrendt^{1

2}, Phil Liebing³, Christine Weber^{1

2}, Michael Gottschaldt^{1

2}, Ulrich S Schubert^{1

2}

Affiliations

¹ Laboratory of Organic Chemistry and Macromolecular Chemistry (IOMC), Friedrich Schiller University at Jena, Humboldtstraße 10, 07743 Jena, Germany.
² Jena Center for Soft Matter (JCSM), Friedrich Schiller University Jena, Philosophenweg 7, 07743 Jena, Germany.
³ Institute of Inorganic and Analytical Chemistry (IAAC), Friedrich Schiller University at Jena, Humboldtstraße 8, 07743 Jena, Germany.

Abstract

1,4-Bis(iodomethyl)benzene and 1,3,5-tris(iodomethyl)benzene were used as initiators for the cationic ring-opening polymerization (CROP) of 2-ethyl-2-oxazoline (EtOx) and its copolymerization with tert-butyl (3-(4,5-dihydrooxazol-2-yl)propyl)carbamate (BocOx) or methyl 3-(4,5-dihydrooxazol-2-yl)propanoate (MestOx). Kinetic studies confirmed the applicability of these initiators. Termination with suitable nucleophiles resulted in two- and three-armed cross-linkers featuring acrylate, methacrylate, piperazine-acrylamide, and piperazine-methacrylamide as polymerizable ω-end groups. Matrix-assisted laser desorption/ionization mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy confirmed the successful attachment of the respective ω-end groups at all initiation sites for every prepared cross-linkers. Except for acrylate, each ω-end group remained stable during deprotection of BocOx containing cross-linkers. The cryogels were prepared using EtOx-based cross-linkers, as confirmed by solid-state NMR spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Stability tests revealed a complete dissolution of the acrylate-containing gels at pH = 14, whereas the piperazine-acrylamide-based cryogels featured excellent hydrolytic stability.