Poly(2-oxazoline)s (POx) are a unique class of polymers with an enormous potential for the preparation of functional materials. Besides POx, other poly(cyclic imino ether)s (PCIEs) such as poly(2-oxazine)s have gained attention in the past. Their synthesis via the cationic ring-opening polymerisation (CROP) of cyclic iminos ethers enables the design of tailored polymers with reactive sites at their α- or ω-end (telechelic PCIEs), or in the side chain. Due to their biocompatibility and low-fouling properties, hydrophilic PCIEs have shown promise as novel stealth polymers for applications in the biomedical area. However, they potential goes far beyond hydrophilic-hydrophobic interactions. This presentations aims at providing an overview about the synthesis and characteristics of stimuli-responsive PCIEs with tailored properties, further fostering the understanding of the CROP of CIEs and the unique properties of their derived polymers.

The development of new formulations for hydrophobic drugs is a key area of research in modern medicine, with the objective of improving bioavailability, biocompatibility and efficacy. This involves the conjugation of active pharmaceutical ingredients to drug delivery systems (DDS) and the solubilization of drugs in micellar systems. Excipients, such as the poly(ethylene glycol) (PEG)-modified Kolliphor EL, are frequently employed[1], but have been associated with severe side effects.[2] In context of circumventing these side effects, the exploration of a novel polymer class, exhibiting equivalent solubilization properties to PEG but reduced immunogenicity, is a primary focus.

Poly(2-oxazoline)s (POx) possess a pseudopeptide structure, resulting in diminished immune reactions in vivo compared to PEG.[3] Their chemical and physical properties can be tailored through the availability of numerous accessible monomers.
In addition to polymeric micelles introduced by DUNCAN[4], so-called molecular brushes (MB) overcome drawbacks over many DDS. They exhibit greater stability particularly in comparison to micellar DDS resulting in an increased blood retention time.[5]
We hereby present a novel synthesis of purely POx-based MB via grafting-to approach as well as the results from characterization of the respective MB.

Thermoresponsive polymers undergo a reversible phase transition in solution in response to temperature changes. For polymers exhibiting lower critical solution temperature (LCST) behavior, phase separation occurs above a specific critical temperature, known as the cloud point (Aseyev et al., 2011). In aqueous solutions, this transition is primarily driven by entropy loss associated with hydrogen bonding interactions between water and polymer repeating units. Among LCST type polymers, those with amide repeating units are the most extensively studied due to the strong hydrogen bonding capabilities of amides. Recently, we discovered an alternative way to tune LCST behavior of poly(2-oxazoline)s, polymers with tertiary amide repeating units, by replacing the amide oxygen atoms with sulfurs (Hacioglu et al., 2024). Thionation of poly(2-oxazoline)s reduced their hydrogen bonding ability, leading to lower cloud points as the degree of thionation increased.
In this study, we investigate the thionation of structurally isomeric amide-based polymers. Specifically, we synthesized poly(2-isopropyl-2-oxazoline) (PiPrOx), poly(N-isopropylacrylamide) (PNIPAM), and poly(N-vinylpyrrolidone) (PVP) with 10% thionation degree. The synthesized polymers were characterized using NMR and IR spectroscopy, elemental analysis, size exclusion chromatography, and differential scanning calorimetry. Solution behavior was studied by turbidity measurements, micro-DSC and dynamic light scattering measurements. Thionation resulted in increased rigidity, as evidenced by higher glass transition temperatures in thionated copolymers. Additionally, thionation reduced water solubility and resulted in lower cloud points.

Polyhydroxyurethanes (PHUs) are regarded as a promising alternative to conventional polyurethanes (PUs), primarily because they can be synthesized from less hazardous monomers [1]. However, two major challenges currently hinder their industrial adoption: (a) the low molecular weight and inferior mechanical properties of thermoplastic PHUs, and (b) their high moisture absorption, which causes a deterioration of mechanical performance [2].

In this study we introduced an approach utilizing the pendant hydroxyl groups in tailored thermoplastic PHUs and 1,4-phenylenediboronic acid to readily convert them into the robust and tough PHU vitrimers [3]. Using the proposed method, three family of PHU vitrimers were synthesized, incorporating non-stabilized dioxaborolane, non-stabilized, and nitrogen-stabilized dioxazaborocane moieties. A detailed comparative structure-property relationship study of these vitrimers confirmed that dioxazaborocanes stabilized with aliphatic nitrogen atoms exhibit a significant potential to improve the thermal and hydrolytic stability of PHU vitrimers. For the first time this difference was demonstrated through the direct observation of structural changes via solid-state NMR. It was found that while aromatic nitrogen atoms do not form stabilizing nitrogen-to-boron dative bonds, the aliphatic nitrogen atoms participate in stabilization. This reduces chain mobility, increasing Tg, massively enhancing mechanical performance (+65-170% tensile strength, +125-300% break strain, ~4-11× increase in tensile toughness), and allowing the resulting vitrimers to maintain their viscoelastic properties even at elevated humidity levels. Furthermore, the N-stabilized dioxazaborocane PHU vitrimers remain readily recyclable both mechanically (at least 3 times) and chemically (using ethanol / NaOHaq.) without any noticeable loss in mechanical properties.

Smart polymeric materials are revolutionizing advanced applications, from sensors and actuators to targeted drug delivery, driving cutting-edge research in functional materials. Mechanoresponsive polymer is a kind of smart polymer designed to undergo chemical or physical changes under mechanical force due to the presence of mechanically labile bonds, often resulting in detectable responses such as fluorescence or colour changes. These polymers are particularly valuable for real-time force detection, making them ideal for sensors, actuators, and self-healing systems.1 This work introduces a new approach to designing mechano-adaptive smart polymers based on Rhodamine 6G as well as anthracene-triazolinedione (TAD) adduct as mechanophore. In one approach, Rhodamine 6G was modified with glycidyl methacrylate (GMA) via an epoxy-amine reaction, forming a tri-arm macromonomer (Rh-GMA), which was then polymerized with butyl acrylate (BA) via free radical polymerization to create a crosslinked mechanophoric film. This film responded well to both mechanical force and UV light.2 The second approach employs Diels-Alder (DA) click chemistry to synthesize a mechanophoric polyurethane. A 3-arm star-polyurethane was functionalized with anthracene end groups and reacted with a bifunctional triazolinedione derivative (bis-TAD) via DA chemistry. The DA linkages disrupted anthracene’s conjugation, rendering the material non-fluorescent (turn-off). Upon applying mechanical force, a force-induced retro-Diels-Alder (r-DA) reaction restored fluorescence (turn-on). Additionally, this dynamic polymer exhibits self-healing properties, confirmed by fluorescence spectroscopy and optical microscopy. These mechano-adaptive systems open new possibilities in advanced polymer mechanochemistry for the applications in sensing, actuation, damage detection, and self-repairable high-tech materials.

Stimuli-responsive polymers, capable of altering their properties in response to environmental stimuli, are versatile materials with wide-ranging applications. Among these, temperature-responsive polymers are of particular interest due to their ability to undergo solubility transitions near critical temperatures. Poly(N-acryloyl glycinamide) (PNAGA) is a non-ionic temperature-responsive polymer that exhibits a sharp upper critical solution temperature (UCST) phase transition, making it suitable for diverse applications [1, 2, 3].
In this study, we focus on the Cu(0)-mediated reversible-deactivation radical polymerization of PNAGA, a hydrogen-bonding UCST polymer. This method, utilizing copper wire as the zerovalent catalyst, enables polymerization under mild, non-inert conditions with reduced metal content and simplified purification. Comparative studies of polymerization kinetics in DMSO and water demonstrate faster reaction rates and improved control under aqueous, ambient conditions. Remarkably, high conversions are achieved in non-degassed reactions within a short reaction time. Furthermore, the copper wire catalyst could be recycled multiple times without a significant loss of activity [4].
We also confirm that the UCST phase transition properties of PNAGA remain unaffected by the modified synthesis conditions, maintaining its sharp, reversible transition. The proposed method offers an efficient and potentially scalable synthetic route for the development of advanced temperature-responsive materials [4].