Polymers without Petrochemicals: Sustainable Routes to Conventional Monomers

Access to a wide range of plastic materials has been rationalized by the increased demand from growing populations and the development of high-throughput production systems. Plastic materials at low costs with reliable properties have been utilized in many everyday products. Multibillion-dollar companies are established around these plastic materials, and each polymer takes years to optimize, secure intellectual property, comply with the regulatory bodies such as the Registration, Evaluation, Authorisation and Restriction of Chemicals and the Environmental Protection Agency and develop consumer confidence. Therefore, developing a fully sustainable new plastic material with even a slightly different chemical structure is a costly and long process. Hence, the production of the common plastic materials with exactly the same chemical structures that does not require any new registration processes better reflects the reality of how to address the critical future of sustainable plastics. In this review, we have highlighted the very recent examples on the synthesis of common monomers using chemicals from sustainable feedstocks that can be used as a like-for-like substitute to prepare conventional petrochemical-free thermoplastics.

N-Acyl Dibenzazepine Chemistry as Versatile Approach for Photoreversible Thiol-Ene Networks

It is herein reported that a facile application of N-acyl dibenzazepine (ADBA) photochemistry for preparing photoreversible ADBA based thiol-ene networks. Crosslinking of the ADBA thiol-ene networks is successfully achieved by UV induced dimerization of ADBA groups at wavelengths above 300 nm while a subsequent deep UV exposure (λ = 250 nm) results in a well-defined cleavage of the crosslinks. The photochemical bonding and cleavage of the process has been determined and studied in detail by spectroscopic measurements.

Recent advances and prospects in nano drug delivery systems using lipopolyoxazolines

Facing the growing demand in nano drug delivery systems (nDDS), hybrid excipients based on natural molecules and well-defined synthetic polymers are intensively investigated. Lipopolyoxazolines (LipoPOx) composed of a polyoxazoline block (POx) and a lipid or lipid-like derivative are detailed in this review. The nature of lipids used, the route to synthesize LipoPOx and their advantages for the formulation of drugs are reported. The place of POx family in nanomedicine is discussed compared to PEG, considered as the gold standard of hydrophilic polymers. LipoPOx nanoformulations including liposomes, mixed micelles, lipid nanocapsules are provided alongside discussion of the nDDS for intravenous or topical administration.

Thiol–ene coupling reaction achievement and monitoring by “in situ” UV irradiation NMR spectroscopy

In this study, the possibilities of a new “in situ” LED UV illumination NMR spectroscopic technique for performing an initiator-free thiol–ene “click” coupling reaction of an allyl-functionalized poly(allyl glycidyl ether) (PAGE) prepolymer with a number of mono- and di-oligo polyethylene glycol (PEG) thiols is demonstrated. The state-of-the-art setup constructed with LEDs as UV light sources that illuminate through optical fibers directly into an NMR testing tube at a fixed wavelength of 365 nm is appropriate for various polymeric materials and biologically active substances. The selected experimental protocol uses a series of periods of irradiation and dark periods, thus providing opportunities to conduct an effective thiol–ene “click” reaction and simultaneously study the kinetics of the photochemical reaction with the exposure time, as well as macromolecular association directly in a solution applying the whole types of NMR methods: from conventional ¹H or ¹³C NMR to diffusion NMR spectroscopy (DOSY). In addition, the molecular mass characteristics of the prepared copolymers were studied by gel-permeation chromatography (GPC). The observed differences in the reaction rates as well as in the size of species formed (the corresponding hydrodynamic radiuses R_h of aggregates) as a result of the coupling process of parent PAGE prepolymers and model PEG thiols were thoroughly discussed and the reaction pathway proposed.

An “In situ” LED UV illumination NMR setup for achievement of initiator-free coupling reactions of allyl-functionalized poly(allyl glycidyl ether) with polyethylene glycols thiols.

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

Recent advances in thermoresponsive poly(2-oxazoline)s, polypeptoids, and polypeptides, with a specific focus on structure–property relationships, self-assembly, and applications, are reviewed.

Multireactive Poly(2-oxazoline) Nanofibers through Electrospinning with Crosslinking on the Fly

Crosslinked hydrophilic poly(2-oxazoline)-based nanofibers amenable to facile multifunctionalization are fabricated using alkene-containing poly(2-alkyl-2-oxazoline)s (PAOx) via in situ photoinitiated radical thiol-ene crosslinking during electrospinning. The resulting crosslinked nanofibers are demonstrated to be multifunctionalizable using different chemistries as they contain two functional handles, being the alkene moieties from the parent copolymer and the residual thiol groups from the tetra-thiol-based crosslinker. While the thiol groups in these nanofibers could be passivated or conjugated to install functional molecules through thiol-maleimide conjugation, the alkene groups could sequentially be modified with thiol-containing molecules using photoinitiated radical thiol-ene reactions. Utilization of the photochemically induced conjugation of thiol-bearing molecules to the alkene groups on the nanofibers is used to obtain functionalization in a spatially controlled manner.

Modification Pathways for Copoly(2-oxazoline)s Enabling Their Application as Antireflective Coatings in Photolithography

Chromophore-functionalized copoly(2-oxazoline)s are successfully evaluated as bottom antireflective coatings (BARCs) in high-resolution photolithography. With respect to UV light sources used in photolithographic production routines, anthracene is chosen as a chromophore. For application as polymer in BARCs, the copolymer poly(2-ethyl-2-oxazolin)45 -stat-poly(2-dec-9'-enyl-2-oxazolin)20 -stat-poly(2-(3'-(1"-(anthracen-9-ylmethyl)-1",2",3"-triazol-4-yl)propyl)-2-oxazolin)35 can be synthesized by the Huisgen cycloaddition click reaction of the copolymer poly(2-ethyl-2-oxazolin)45 -stat-poly(2-dec-9'-enyl-2-oxazolin)20 -stat-poly(2-pent-4'-inyl-2-oxazolin)35 and the corresponding azide-functionalized anthracenes. These copolymers can be crosslinked by the thermally induced thiol-ene reaction involving the unsaturated C=C bonds of the poly(2-dec-9'-enyl-2-oxazoline) repetition units and a multifunctional thiol as crosslinker. Tests of this BARC in a clean room under production conditions reveal a significant decrease of the swing-curve of a chemically amplified positive photoresist by more than 50%, hence significantly increasing the resolution of the photoresist.

Microwave-assisted cationic ring-opening polymerization of 2-oxazolines

Unlike any other polymer class, the (co-)poly(2-oxazoline)s have tremendously benefited from the introduction of microwave reactors into chemical laboratories. This review focuses on the research activities in the area of (co-)poly(2-oxazoline)s prepared by microwave-assisted syntheses and, correspondingly, summarizes the current-state-of the-art of the microwave-assisted synthesis of 2-oxazoline monomers and the microwave-assisted ring-opening (co-)polymerization of 2-oxazolines as well as prominent examples of post-polymerization modification of (co-)poly(2-oxazoline)s. Special attention is attributed to the kinetic analysis of the microwave-assisted polymerization of 2-oxazolines and the discussion of non-thermal microwave effects.

Multifunctional poly(methacrylate) polyplex libraries: A platform for gene delivery inspired by nature

Polymer-based gene delivery systems have enormous potential in biomedicine, but their efficiency is often limited by poor biocompatibility. Poly(methacrylate)s (PMAs) are an interesting class of polymers which allow to explore structure-activity relationships of polymer functionalities for polyplex formation in oligonucleotide delivery. Here, we synthesized and tested a library of PMA polymers, containing functional groups contributing to the different steps of gene delivery, from oligonucleotide complexation to cellular internalization and endosomal escape. By variation of the molar ratios of the individual building blocks, the physicochemical properties of the polymers and polyplexes were fine-tuned to reduce toxicity as well as to increase activity of the polyplexes. To further enhance transfection efficiency, a cell-penetrating peptide (CPP)-like functionality was introduced on the polymeric backbone. With the ability to synthesize large libraries of polymers in parallel we also developed a workflow for a mid-to-high throughput screening, focusing first on safety parameters that are accessible by high-throughput approaches such as blood compatibility and toxicity towards host cells and only at a later stage on more laborious tests for the ability to deliver oligonucleotides. To arrive at a better understanding of the molecular basis of activity, furthermore, the effect of the presence of heparan sulfates on the surface of host cells was assessed and the mechanism of cell entry and intracellular trafficking investigated for those polymers that showed a suitable pharmacological profile. Following endocytic uptake, rapid endosomal release occurred. Interestingly, the presence of heparan sulfates on the cell surface had a negative impact on the activity of those polyplexes that were sensitive to decomplexation by heparin in solution. In summary, the screening approach identified two polymers, which form polyplexes with high stability and transfection capacity exceeding the one of poly(ethylene imine) also in the presence of serum.

Covalently cross-linked poly(2-oxazoline) materials for biomedical applications – from hydrogels to self-assembled and templated structures

We discuss covalently cross-linked poly(2-oxazoline)s including gels, nanogels and capsules on the basis of their synthetic origin in a biomedical context.

Easy daylight fabricated hydrogel array for colorimetric DNA analysis

The fabrication of 3D hydrogel microarrays for DNA analytics that allow simple visual signal readout for on-site applications is described. A convenient one-step polymerization of the hydrogel including in situ capture oligonucleotide immobilization is accomplished by using N,N'-dimethylacrylamide/polyethylene glycol (PEG1900 )-bisacrylamide monomers. The implementation of an acylphosphine-oxide photoinitiator even allows polymerization at daylight, whereas other approaches require exposure with light in the UV-range. This minimizes the risk of UV-caused DNA damages within the capture DNA-strand that could adversely affect the subsequent hybridization step. The porous network of these gel segments allows DNA as well as protein penetration. Thus, the successful in-gel DNA hybridization is monitored by the deposition of silver nanoparticles. These metal particles allow naked eye signal readout.

Controlled RAFT synthesis of side-chain oleic acid containing polymers and their post-polymerization functionalization

We report the synthesis and characterization of well-defined polymers from oleic acid as the bio-renewable resource. Double bonds in oleate side-chains in the polymer are further modified by thiol-ene reaction, epoxidation, and cross-linking.

Zwitterionic poly(2-oxazoline)s as promising candidates for blood contacting applications

The hemocompatibility and cytotoxicity of zwitterionic poly(2-oxazoline)s are investigated.

Thiol–ene “click” reactions and recent applications in polymer and materials synthesis: a first update

This contribution serves as an update to a previous review (Polym. Chem.2010,1, 17–36) and highlights recent applications of thiol–ene ‘click’ chemistry as an efficient tool for both polymer/materials synthesis as well as modification.