Here we report on a simple, generally applicable method for depositing metal nanoparticles on a wide variety of solid surfaces under all aqueous conditions. Noble-metal nanoparticles obtained by citrate reduction followed by coating with thermoresponsive polymers spontaneously form a monolayer-like structure on a wide variety of substrates in presence of sodium chloride whereas this phenomenon does not occur in salt-free medium. Interestingly, this phenomenon occurs below the cloud point temperature of the polymers and we hypothesize that salt ion-induced screening of electrostatic charges on the nanoparticle surface entropically favors hydrophobic association between the polymer-coated nanoparticles and a hydrophobic substrate.

Here we report on a simple, generally applicable method for depositing metal nanoparticles on a wide variety of solid surfaces under all aqueous conditions. Noble-metal nanoparticles obtained by citrate reduction followed by coating with thermoresponsive polymers spontaneously form a monolayer-like structure on a wide variety of substrates in presence of sodium chloride whereas this phenomenon does not occur in salt-free medium. Interestingly, this phenomenon occurs below the cloud point temperature of the polymers and we hypothesize that salt ion-induced screening of electrostatic charges on the nanoparticle surface entropically favors hydrophobic association between the polymer-coated nanoparticles and a hydrophobic substrate.

Poly(2-alkyl-2-oxazoline)s (PAOx) exhibit different crystallization behavior depending on the length of the alkyl side chain. PAOx having methyl, ethyl, or propyl side chains do not show any bulk crystallization. Crystallization in the heating cycle, that is, cold crystallization, is observed for PAOx with butyl and pentyl side chains. For PAOx with longer alkyl side chains crystallization occurs in the cooling cycle. The different crystallization behavior is attributed to the different polymer chain mobility in line with the glass transition temperature (T_g) dependency on alkyl side chain length. The decrease in chain mobility with decreasing alkyl side chain length hinders the relaxation of the polymer backbone to the thermodynamic equilibrium crystalline structure. Double melting behavior is observed for PButOx and PiPropOx which is explained by the melt-recrystallization mechanism. Isothermal crystallization experiments of PButOx between 60 and 90 °C and PiPropOx between 90 and 150 °C show that PAOx can crystallize in bulk when enough time is given. The decrease of T_g and the corresponding increase in chain mobility at T  >  T_g with increasing alkyl side chain length can be attributed to an increasing distance between the polymer backbones and thus decreasing average strength of amide dipole interactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 721–729

A straightforward end-capping strategy is applied to synthesize xanthate-functional poly(2-alkyl-2-oxazoline)s (PAOx) that enable gold nanoparticle functionalization by a direct “grafting to” approach with citrate-stabilized gold nanoparticles (AuNPs). Owing to the presence of remaining citrate groups, the obtained PAOx@AuNPs exhibit dual stabilization by repulsive electrostatic and steric interactions giving access to water soluble molecular AND logic gates, wherein environmental temperature and ionic strength constitute the input signals, and the solution color the output signal. The temperature input value could be tuned by variation of the PAOx polymer composition, from 22 °C for poly(2-ⁿpropyl-2-oxazoline)@AuNPs to 85 °C for poly(2-ethyl-2-oxazoline)@AuNPs. Besides, advancing the fascinating field of molecular logic gates, the present research offers a facile strategy for the synthesis of PAOx@AuNPs of interest in fields spanning nanotechnology and biomedical sciences. In addition, the functionalization of PAOx with xanthate offers straightforward access to thiol-functional PAOx of high interest in polymer science.

It is demonstrated how cellular uptake and protein corona of (co)polymer-coated gold nanoparticles can be altered by the hydrophilic-to-hydrophobic comonomer ratio. A novel, label-free flow cytometry strategy is developed to investigate particle uptake. These findings offer insight in the design and analysis of hybrid nanomaterials for interfacing with biological systems.

There is an increasing need for smart materials capable of removing multivalent ions from aqueous streams without the inconvenience of brine regeneration as in ion-exchange processes. Herein, we present a thermoresponsive micellar system consisting of polystyrene–poly(methoxy diethyleneglycol acrylate) block copolymer surfactants modified with carboxylic acid end groups (PS-PMDEGA-COOH) that can be used to switch between the adsorption and desorption of divalent calcium(II) cations by a mild temperature trigger, thus providing a new type of thermoregenerable ion-adsorbing materials. The switch of calcium(II)-binding capacity is demonstrated to result from a shift in the pK_a value of the carboxylic acid groups by the collapse and redissolution of the PMDEGA block and the associated change in local polarity.

There is an increasing need for smart materials capable of removing multivalent ions from aqueous streams without the inconvenience of brine regeneration as in ion-exchange processes. Herein, we present a thermoresponsive micellar system consisting of polystyrene–poly(methoxy diethyleneglycol acrylate) block copolymer surfactants modified with carboxylic acid end groups (PS-PMDEGA-COOH) that can be used to switch between the adsorption and desorption of divalent calcium(II) cations by a mild temperature trigger, thus providing a new type of thermoregenerable ion-adsorbing materials. The switch of calcium(II)-binding capacity is demonstrated to result from a shift in the pK_a value of the carboxylic acid groups by the collapse and redissolution of the PMDEGA block and the associated change in local polarity.

A poly[(2-ethyl-2-oxazoline)-ran-(2-nonyl-2-oxazoline)] copolymer in combination with hydroxypropylated cyclodextrins has been demonstrated to lead to a supramolecular self-assembly process that results in the formation of kinetically trapped thermoresponsive nanoparticles. Selection of the cyclodextrin type provides control over the nanoparticle phase-transition thermodynamics, thus affording optical temperature sensors with an unprecedented, long-term thermal memory function, which is reversible or irreversible. This research also sheds light onto kinetic and dynamic supramolecular assemblies, thus providing important insight because similar supramolecular processes are at the foundation of living matter.

Poly(2-oxazoline)s with methyl ester functionalized side chains are interesting as they can undergo a direct amidation reaction or can be hydrolyzed to the carboxylic acid, making them versatile functional polymers for conjugation. In this work, detailed studies on the homo- and copolymerization kinetics of two methyl ester functionalized 2-oxazoline monomers with 2-methyl-2-oxazoline, 2-ethyl-2-oxazoline, and 2-n-propyl-2-oxazoline are reported. The homopolymerization of the methyl ester functionalized monomers is found to be faster compared to the alkyl monomers, while copolymerization unexpectedly reveals that the methyl ester containing monomers significantly accelerate the polymerization. A computational study confirms that methyl ester groups increase the electrophilicity of the living chain end, even if they are not directly attached to the terminal residue. Moreover, the electrophilicity of the living chain end is found to be more important than the nucleophilicity of the monomer in determining the rate of propagation. However, the monomer nucleophilicity can be correlated with the different rates of incorporation when two monomers compete for the same chain end, that is, in copolymerizations. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2649–2661

In recent years, the layer-by-layer (LbL) assembly based on hydrogen bonding interactions is gaining popularity for the preparation of thin film coatings, especially for biomedical purposes, based on the use of neutral, non-toxic building blocks. The use of tannic acid (TA) as hydrogen bonding donor is especially interesting as it results in LbL films that are stable under physiological conditions. In this work, investigations on the LbL thin film preparation of TA with poly(2-oxazoline)s with varying hydrophilicity, namely poly(2-methyl-2-oxazoline) (PMeOx), poly(2-ethyl-2-oxazoline) (PEtOx) and poly(2-n-propyl-2-oxazoline) (PnPropOx), are reported. The LbL assembly process is investigated by quartz crystal microbalance and UV-vis spectroscopy revealing linear growth of the film thickness. Furthermore, isothermal titration calorimetry demonstrates the LbL assembly of TA, and PMeOx is found to be mostly enthalpy driven while the LbL assembly of TA with PEtOx and PnPropOx is mostly entropy driven. Finally, scanning electron microscopy and ellipsometry demonstrate the formation of smooth thin films for LbL assembly of TA with all three polymers. Such poly(2-oxazoline) coatings have high potential for use as anti-biofouling coatings.

A new class of polymeric thermometers with a memory function is reported that is based on the supramolecular host–guest interactions of poly(N-isopropylacrylamide) (PNIPAM) with side-chain naphthalene guest moieties and the tetracationic macrocycle cyclobis(paraquat-p-phenylene) (CBPQT⁴⁺) as the host. This supramolecular thermometer exhibits a memory function for the thermal history of the solution, which arises from the large hysteresis of the thermoresponsive LCST phase transition (LCST=lower critical solution temperature). This hysteresis is based on the formation of a metastable soluble state that consists of the PNIPAM–CBPQT⁴⁺ host–guest complex. When heated above the transition temperature, the polymer collapses, and the host–guest interactions are disrupted, making the polymer more hydrophobic and less soluble in water. Aside from providing fundamental insights into the kinetic control of supramolecular assemblies, the developed thermometer with a memory function might find use in applications spanning the physical and biological sciences.

Poly(2-propyl-oxazoline)s can be prepared by living cationic ring-opening polymerization of 2-oxazolines and represent an emerging class of biocompatible polymers exhibiting a lower critical solution temperature in aqueous solution close to body temperature. However, their usability is limited by the irreversibility of the transition due to isothermal crystallization in case of poly(2-isopropyl-2-oxazoline) and the rather low glass transition temperatures (T_g < 45 °C) of poly(2-n-propyl-2-oxazoline)-based polymers. The copolymerization of 2-cyclopropyl-2-oxazoline and 2-ethyl-2-oxazoline presented herein yields gradient copolymers whose cloud point temperatures can be accurately tuned over a broad temperature range by simple variation of the composition. Surprisingly, all copolymers reveal lower T_gs than the corresponding homopolymers ascribed to suppression of interchain interactions. However, it is noteworthy that the copolymers still have T_gs > 45 °C, enabling convenient storage in the fridge for future biomedical formulations. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3118–3122

A series of comb polymers consisting of a methacrylate backbone and poly(2-ethyl-2-oxazoline) (PEtOx) side chains was synthesized by a combination of cationic ring-opening polymerization and reversible addition–fragmentation chain transfer polymerization. Small-angle neutron scattering (SANS) studies revealed a transition from an ellipsoidal to a cylindrical conformation in D₂O around a backbone degree of polymerization of 30. Comb-shaped PEtOx has lowered T_g values but a similar elution behavior in liquid chromatography under critical conditions in comparison to its linear analog was observed. The lower critical solution temperature behavior of the polymers was investigated by turbidimetry, dynamic light scattering, transmission electron microscopy, and SANS revealing decreasing T_cp in aqueous solution with increasing molar mass, the presence of very few aggregated structures below T_cp, a contraction of the macromolecules at temperatures 5 °C above T_cp but no severe conformational change of the cylindrical structure. In addition, the phase diagram including cloud point and coexistence curve was developed showing an LCST of 75 °C of the binary mixture poly[oligo(2-ethyl-2-oxazoline)methacrylate]/water. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

The monomers 2-methyl-2-oxazine (MeOZI), 2-ethyl-2-oxazine (EtOZI), and 2-n-propyl-2-oxazine (nPropOZI) were synthesized and polymerized via the living cationic ring-opening polymerization (CROP) under microwave-assisted conditions. pEtOZI and pnPropOZI were found to be thermoresponsive, exhibiting LCST behavior in water and their cloud point temperatures (T_CP) are lower than for poly(2-oxazoline)s with similar side chains. However, comparison of poly(2-oxazine) and poly(2-oxazoline)s isomers reveals that poly(2-oxazine)s are more water soluble, indicating that the side chain has a stronger impact on polymer solubility than the main chain. In conclusion, variations of both the side chains and the main chains of the poly(cyclic imino ether)s resulted in a series of distinct homopolymers with tunable T_CP.

Here we evaluate poly(2-ethyl-2-oxazoline)s (PEtOx) as a matrix excipient for the production of oral solid dosage forms by hot melt extrusion (HME) followed by injection molding (IM). Using metoprolol tartrate as a good water-soluble model drug we demonstrate that drug release can be delayed by HME/IM, with the release rate controlled by the molecular weight of the PEtOx. Using fenofibrate as a lipophilic model drug we demonstrate that relative to the pure drug the dissolution rate is strongly enhanced by formulation in HME/IM tablets. For both drug molecules we find that solid solutions, i.e. molecularly dissolved drug in a polymeric matrix, are obtained by HME/IM.

Copoly(2-oxazoline)s, prepared by the cationic ring-opening polymerization of 2-(dec-9-enyl)-2-oxazoline with either 2-methyl-2-oxazoline or 2-ethyl-2-oxazoline, are crosslinked with small dithiol molecules under UV irradiation to form homogeneous networks. In situ monitoring of the crosslinking reaction by photo-rheology reveals the formation of soft gels within minutes. The degree of swelling in water is tunable based on the hydrophilicity of the starting macromers and the proportion of alkene side arms present. Furthermore, degradable hydrogels are prepared based on incorporation of a hydrolytically cleavable dithiol crosslinker. The rapid synthesis of the macromers and mild crosslinking conditions make these materials ideal for future biomaterial applications.

Poly(2-alkyl-2-oxazoline)s are biocompatible polymers with polypeptide-isomeric structures that are attracting increasing interest as biomaterials for drug, gene, protein, and radionuclide delivery. They are, however, still relatively new in comparison to other classes of hydrophilic water-soluble polymers already established for such use, including poly(ethylene oxide), polyvinylpyrrolidone, and polymethacrylamides such as poly[N-(2-hydroxypropyl)methacrylamide]. This feature article critically compares the synthetic aspects and physicochemical and biological properties of poly(2-alkyl-2-oxazoline)s and these commonly studied polymers in terms of their suitability for biomedical applications.

Olefin cross-metathesis is introduced as a versatile polymer side-chain modification technique. The reaction of a poly(2-oxazoline) featuring terminal double bonds in the side chains with a variety of functional acrylates has been successfully performed in the presence of Hoveyda–Grubbs second-generation catalyst. Self-metathesis, which would lead to polymer–polymer coupling, can be avoided by using an excess of the cross-metathesis partner and a catalyst loading of 5 mol%. The results suggest that bulky acrylates reduce chain–chain coupling due to self-metathesis. Moreover, different functional groups such as alkyl chains, hydroxyl, and allyl acetate groups, as well as an oligomeric poly(ethylene glycol) and a perfluorinated alkyl chain have been grafted with quantitative conversions.

The ability of merging the properties of poly(2-oxazoline)s and poly(ethylene imine) is of high interest for various biomedical applications, including gene delivery, biosensors, and switchable surfaces and nanoparticles. In the present research, a methodology for the controlled and selective hydrolysis of (co)poly(2-oxazoline)s is developed in an ethanol–water solvent mixture, opening the path toward a wide range of block poly(2-oxazoline-co-ethylene imine) (POx-PEI) copolymers with tunable properties. The unexpected influence of the selected ethanol–water binary solvent mixture on the hydrolysis kinetics and selectivity is highlighted in the pursue of well-defined POx-PEI block copolymers.

Poly(2-oxazoline)s are an interesting class of synthetic poly(amide)s that can be prepared by living cationic ring-opening polymerization. The properties of poly(2-oxazoline)s can be tuned by variation of the 2-substituent of the 2-oxazoline monomer. In this contribution the utilization of fatty acids as side chains for poly(2-oxazoline)s is highlighted. The incorporation of such long aliphatic side-chains results in hydrophobic crystalline poly(2-oxazoline)s that are often applied for the preparation of amphiphilic structures as well as for low surface energy and low adhesive coatings. The most popular fatty-acid based poly(2-oxazoline)s are the saturated poly(2-nonyl-2-oxazoline) and poly(2-undecyl-2-oxazoline) as well as the unsaturated poly(2-decenyl-2-oxazoline) and poly(2-“soy alkyl”-2-oxazoline).