Functional poly(2-oxazoline)s by direct amidation of methyl ester side chains

Poly(2-alkyl/aryl-2-oxazoline)s (PAOx) are biocompatible pseudopolypeptides that have received significant interest for biomedical applications in recent years. The growing popularity of PAOx in recent years is driven by its much higher chemical versatility compared with the gold standard in this field, poly(ethylene glycol) (PEG), while having similar beneficial properties, such as stealth behavior and biocompatibility. We further expand the PAOx chemical toolbox by demonstrating a novel straightforward and highly versatile postpolymerization modification platform for the introduction of side-chain functionalities. PAOx having side chain methyl ester functionalities is demonstrated to undergo facile uncatalyzed amidation reactions with a wide range of amines, yielding the corresponding PAOx with side-chain secondary amide groups containing short aliphatic linkers as well as a range of side-chain functionalities including acid, amine, alcohol, hydrazide, and propargyl groups. The PAOx with side-chain methyl ester groups can be prepared by either partial hydrolysis of a PAOx followed by the introduction of the methyl ester via modification of the secondary amine groups with methyl succinyl chloride or by the direct copolymerization of a nonfunctional 2-oxazoline monomer with a 2-methoxycarbonylethyl-2-oxazoline. Thus, this novel synthetic platform enables direct access to a wide range of side-chain functionalities from the same methyl-ester-functionalized poly(2-oxazoline) scaffold

Thermoresponsive poly(2-oxazoline)s, polypeptoids, and polypeptides

This review covers the recent advances in the emerging field of thermoresponsive polyamides or polymeric amides, i.e., poly(2-oxazoline)s, polypeptoids, and polypeptides, with a specific focus on structure-thermoresponsive property relationships, self-assembly, and applications

Self-healing metallo-supramolecular hydrogel based on specific Ni2+ coordination interactions of poly(ethylene glycol) with bistriazole pyridine ligands in the main chain

In this study, a supramolecular hydrogel formed by incorporating the 2,6-bis(1,2,3-triazol-4-yl)-pyridine (btp) ligand in the backbone of a polymer prepared by copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) "click" polyaddition reaction of 2,6-diethynylpyridine and diazido-poly(ethylene glycol) is reported. The hydrogelation is selectively triggered by the addition of Ni2+ ions to aqueous copolymer solutions. The gelation and rheological properties could be tuned by the change of metal to ligand ratio and polymer concentration. Interestingly, the hydrogel exhibits a fast (within 2 min) and excellent repeatable autonomic healing capacity without external stimuli. This self-healing behavior may find potential applications for the repairing of metal coatings, in the future

Bio-inspired hydrogels as multi-task anti-icing hydrogel coatings

In a recent report in Matter, Zhu, Wang, He and co-workers report a straightforward and effective strategy for the design of icephobic hydrogel coatings on the basis of polydimethylsiloxane (PDMS)-grafted polyelectrolyte hydrogels. These passive anti-icing and de-icing coatings were demonstrated to synergistically suppress ice nucleation, ice propagation, and ice adhesion

Structural diversification of pillar[n]arene macrocycles

Despite the fact that pillar[n]arenes receive major interest as building blocks for supramolecular chemistry and advanced materials, their functionalization is generally limited to the modification of the hydroxy or alkoxy units present on the rims. This limited structural freedom restricts further developments and has very recently been overcome. In this article, we highlight three very recent studies demonstrating further structural diversification of pillar[n]arenes by partial removal of the alkoxy substituents on the rims, which can be considered as the next generation of pillar[n]arenes

One-pot synthesis of charged amphiphilic diblock and triblock copolymers via high-throughput Cu(0)-mediated polymerization

Block copolymers containing functionalized monomers, for example those containing charged groups, can be used for many purposes, one of which is the design of polymeric supramolecular materials based on electrostatic interactions. In this paper the synthesis of diblock copolymers and ABA-triblock copolymers containing poly(n-butyl acrylate) as a first or middle block and poly(2-(dimethylamino) ethyl acrylate), poly(1-ethoxyethyl acrylate) and poly(1-ethoxyethyl-2-carboxyethyl acrylate) as second or outer blocks, resulting in block copolymers that can contain positive or negative charges, is reported. The polymerizations were performed and optimized via one-pot sequential monomer addition reactions via Cu(0)-mediated polymerization using an automated parallel synthesizer. Different initiators, monomer concentrations and polymerization times were tested. While a bromide-containing initiator led to the best results for most monomers, when polymerizing 2-(dimethylamino) ethyl acrylate the use of a chloride-containing initiator was necessary. Due to the slower polymerization using this initiator, a longer polymerization time was needed before addition of the second monomer. Using the optimized conditions, the diblock and triblock copolymers could be synthesized with good control over molecular weight and dispersities around 1.1 were obtained

Molecularly imprinted poly(2-oxazoline) based on cross-linking by direct amidation of methyl ester side chains

Molecularly imprinted polymers (MIPs) are tailor-made synthetic materials possessing memory of their molecular templates and have found numerous applications in separation science, drug delivery, and catalysis. Here, we report the development of an MIP based on poly(2-oxazoline)s. The cross-linked imprinted polymer was obtained by reacting a short-chain poly(2-oxazoline) with methyl ester side chains with diethylenetriamine in the presence of indometacin as template. The cross-linker diethylenetriamine simultaneously acted as cross-linker and interacted with the indometacin template. The influence of several parameters on indometacin adsorption such as initial concentration, contact time, and temperature, as well as reusability of the MIPs and kinetics of indometacin release, have been investigated. The maximum amount of indometacin bonded reached 293 mg g(-1) for the imprinted polymer versus 25 mg g(-1) for the nonimprinted polymer. This result clearly indicates that molecularly imprinted poly(2-oxazoline)s possess a large potential for developing new MIPs due to their high imprinting properties

Full and partial hydrolysis of poly(2-oxazoline)s and the subsequent post-polymerization modification of the resulting polyethylenimine (co)polymers

The synthesis of linear polyethylenimine (L-PEI) is mostly performed via the acidic or basic hydrolysis of poly(2-alkyl-2-oxazoline)s (PAOx). Besides full hydrolysis leading to L-PEI, the partial hydrolysis of the PAOx sidechains results in PAOx-PEI copolymers having secondary amine groups in the polymer backbone. The secondary amine groups of L-PEI and PAOx-PEI can act as charge carriers for the complexation of DNA for gene therapy. Furthermore, they are also excellent chemical moieties for post-polymerization modification reactions providing straightforward access to new PAOx (co)polymers based on a variety of PAOx, including the commercially available poly(2-ethyl-2-oxazoline) (PEtOx). Within this review, we will discuss the acidic and basic (partial) hydrolysis of PAOx as well as the corresponding mechanisms. In addition, an overview of the recent literature on the post-polymerization modification of the fully hydrolyzed L-PEI and the partially hydrolyzed PAOx-PEI is provided

Supramolecular control over self-assembly and double thermoresponsive behavior of an amphiphilic block copolymer

A poly(ethylene glycol)-b-poly[N, N-dimethylacrylamide-ran-2-acrylamidoethyl nonanoate] (PEG-b-P(DMA-AAEN)) block copolymer has been demonstrated to show double thermoresponsive behavior in aqueous solution in the presence of hydroxypropylated cyclodextrin (HPCD). The polymer itself is insoluble in water due to the presence of hydrophobic alkyl chain, however, with the presence of HPCD, fully dissolution of the polymer could be obtained indicating the formation of host-guest interaction between HPCD and the alkyl chain. The clear solution of HPCD/polymer complex showing a first thermoresponsiveness during heating and led to the formation of small micelles stabilized by PEG chains and DMA segments. Upon further heating of the aqueous solution, the small micelles aggregated and formed multimicellar aggregates. The reported double thermoresponsive behavior may provide a new strategy of designing smart polymeric systems, which can find broad applications in the fabrication of smart materials