2020, Daubian, Davy, Gaitzsch, Jens, Meier, Wolfgang

We report on the synthesis and self-assembly of poly(ethylene oxide)-block-poly(2-(3-ethylheptyl)-2-oxazoline) (PEO-b-PEHOx), a new amphiphilic diblock copolymer obtained via microwave-assisted polymerization of EHOx using a new nosylated PEO macroinitiator. The kinetics of the polymerization in different solvents was crucial to optimize the synthesis and revealed a controlled, yet fast polymerization of the AB diblock copolymer. Differential scanning calorimetry proved that PEO-b-PEHOx shows glass transition temperatures below room temperature, making it suitable for a wide range of self-assembly methods, especially under mild and solvent-free conditions. Self-assembly of PEO-b-PEHOx was then performed using film rehydration and solvent switch. In both cases, we were able to show the formation of various complex structures (multi-compartment micelles (MCMs), pseudo-vesicles and yolk/shell nanoparticles) by light scattering, TEM and Cryo-TEM. Our results show that PEO-b-PEHOx is a potent new AB diblock copolymer due to its fast synthesis and unique self-assembly behavior.

2020, Folini, Jenny, Murad, Wigdan, Mehner, Fabian, Meier, Wolfgang, Gaitzsch, Jens

Radical ring-opening polymerisation (RROP) of cyclic ketene acetals (CKAs) has gained momentum as it yields polyesters as biodegradable polymers from a radical polymerisation. In order to advance the polymerisation, some of its major limitations were addressed in the research presented, focussing on the four mainly used CKAs in modern research on RROP. Monomer synthesis has been updated towards a cobalt/TMSCl-based system that was performed reliably on several monomers at room temperature. Calculations using the density functional theory (DFT) revealed that the ring-opening step is energetically hampered in comparison to a ring-retaining reaction, which explained the challenges faced to promote the ring-opening reaction. Higher molecular weights up to four times the values reached by thermally initiated polymerisation were obtained by exploiting UV light and ultrasound as alternative methods to facilitate the polymerisation. The reaction procedure also influenced thermal properties of the polymers, which in turn affected the enzymatic degradation of nanoparticles based on those polymers. Altogether, the present study offers a holistic update to enhance the RROP of CKAs.

2020, Wehr, Riccardo, Gaitzsch, Jens, Daubian, Davy, Fodor, Csaba, Meier, Wolfgang

Aqueous self-assembly of amphiphilic block copolymers is studied extensively for biomedical applications like drug delivery and nanoreactors. The commonly used hydrophilic block poly(ethylene oxide) (PEO), however, suffers from several drawbacks. As a potent alternative, poly(glycidol) (PG) has gained increasing interest, benefiting from its easy synthesis, high biocompatibility and flexibility as well as enhanced functionality compared to PEO. In this study, we present a quick and well-controlled synthesis of poly(butylene oxide)-block-poly(glycidol) (PBO-b-PG) amphiphilic diblock copolymers together with a straight-forward self-assembly protocol. Depending on the hydrophilic mass fraction of the copolymer, nanoscopic micelles, worms and polymersomes were formed as well as microscopic giant unilamellar vesicles. The particles were analysed regarding their size and shape, using dynamic and static light scattering, TEM and Cryo-TEM imaging as well as confocal laser scanning microscopy. We have discovered a strong dependence of the formed morphology on the self-assembly method and show that only solvent exchange leads to the formation of homogenous phases. Thus, a variety of different structures can be obtained from a highly flexible copolymer, justifying a potential use in biomedical applications. This journal is © The Royal Society of Chemistry.