Poly(allyl glycidyl ether)-A versatile and functional polyether platform

Synthesis of polyvinylethylene glycols (PVEGs) via polyetherification of vinylethylene carbonate by synergistic catalysis

An efficient and controllable polyetherification of vinylethylene carbonate (VEC) using diols as initiators is developed. By using a synergistic catalysis with palladium and boron reagents under mild conditions, the polymerization process enables the regioselective production of a series of polyvinylethylene glycols (PVEGs) bearing pendent vinyl groups in high yields with accurate molecular weight control and narrow molecular weight distribution. The utility of PVEGs is demonstrated by the production of functional polyurethanes and post-polymerization modification via thiol-ene photo-click chemistry.

Influence of hydrophilic block length on the aggregation properties of polyglycidol-polystyrene-polyglycidol copolymers

Amphiphilic triblock copolymers, polyglycidol-polystyrene-polyglycidol (PGL-PS-PGL), were synthesised via anionic polymerization starting from the synthesis of a polystyrene macroinitiator with 60 styrene units in the block terminated by ethylene oxide. Poly(ethoxyethyl glycidyl ether) blocks of different lengths were created on both sides of the macroinitiator. By removing the ethoxyethyl blocking groups, PGL-PS-PGL copolymers containing polyglycidol blocks with DP 11, 23, 44 and 63 were received. Their structures were determined by NMR and FTIR. The hydrophilicity of PLG-PS-PGL films was studied upon exposure to water vapour. To perform the copolymers' aggregation in water, the samples were dialysed from DMF into water. The critical concentration of their micellisation (CMC) was determined by measuring the absorbance of the 1,6-diphenylhexa-1,3,5-triene (DPH) probe and the intensity of light scattered by the copolymers' solution as a function of concentration. CMC values increased with increasing the number of hydrophilic glycidol units in the copolymer chain. The sizes of aggregates formed slightly above the critical concentration were measured by dynamic light scattering (DLS), and particles were imaged by cryo-TEM. Cryo-TEM pictures showed the presence of regular micelles in copolymer dispersions. For copolymers with shorter PGL chains aggregated partices were detected. Moreover, cryo-TEM demonstrated that the copolymers with a polyglycidol block of DP = 63 formed regular spherical micelles that formed 2D ordered organisation on the surface. X-ray measurements showed the formation of a partially crystallised PS core in the micelle's interior. The aggregates of all copolymers were stable. Their sizes did not change after one year of storage. The particles did not disassociate even after diluting their dispersions to a concentration 10 times lower than the critical concentration.

A guide to modern methods for poly(thio)ether synthesis using Earth-abundant metals

Polyethers and polythioethers have a long and storied history dating back to the start of polymer science as a distinct field. As such, these materials have been utilized in a wide range of commercial applications and fundamental studies. The breadth of their material properties and the contexts in which they are applied is ultimately owed to their diverse monomer pre-cursors, epoxides and thiiranes, respectively. The facile polymerization of these monomers, both historically and contemporaneously, across academia and industry, has occurred through the use of Earth-abundant metals as catalysts and/or initiators. Despite this, polymerization methods for these monomers are underutilized compared to other monomer classes like cyclic olefins, vinyls, and (meth)acrylates. We feel a focused review that clearly outlines the benefits and shortcomings of extant synthetic methods for poly(thio)ethers along with their proposed mechanisms and quirks will help facilitate the utilization of these methods and by extension the unique polymer materials they create. Therefore, this Feature Article briefly describes the applications of poly(thio)ethers before discussing the feature-set of each poly(thio)ether synthetic method and qualitatively scoring them on relevant metrics (e.g., ease-of-use, molecular weight control, etc.) to help would-be poly(thio)ether-makers find an appropriate synthetic approach. The article is concluded with a look ahead at the future of poly(thio)ether synthesis with Earth-abundant metals.

Synthesis of Poly(allyl glycidyl ether)-Derived Polyampholytes and Their Application to the Cryopreservation of Living Cells

Through the postpolymerization modification of poly(allyl glycidyl ether) (PAGE), a functionalizable polyether with a poly(ethylene oxide) backbone, we engineered a new class of highly tunable polyampholyte materials. These polyampholytes can be synthesized to have several useful properties, including low cytotoxicity and pH-responsive coacervate formation. In this study, we used PAGE-based polyampholytes (PAGE-PAs) for the cryopreservation of mammalian cell suspensions. Typically, dimethyl sulfoxide (DMSO) is the cryoprotectant used for preserving mammalian cells, but DMSO suffers from key drawbacks including toxicity and difficult post-thaw removal that motivates the development of new materials and methods. Toxicity and post-thaw survival were dependent on PAGE-PA composition with the highest immediate post-thaw survival for normal human dermal fibroblasts occurring for the least toxic PAGE-PA at a cation/anion ratio of 35:65. With low toxicity, the PAGE-PA concentration could be increased in order to increase immediate post-thaw survival of the immortalized mouse embryonic fibroblasts (NIH/3T3). While immediate post-thaw viability was achieved using only the PAGE-PAs, long-term cell survival was low, highlighting the challenges involved with the design of cryoprotective polyampholytes. An environment utilizing both PAGE-PAs and DMSO in a cryoprotective solution offered promising post-thaw viabilities exceeding 70%, with long-term metabolic activities comparable to unfrozen cells.

Decoupling Ion Transport and Matrix Dynamics to Make High Performance Solid Polymer Electrolytes

Transport of ions through solid polymeric electrolytes (SPEs) involves a complicated interplay of ion solvation, ion-ion interactions, ion-polymer interactions, and free volume. Nonetheless, prevailing viewpoints on the subject promote a significantly simplified picture, likening ion transport in a polymer to that in an unstructured fluid at low solute concentrations. Although this idealized liquid transport model has been successful in guiding the design of homogeneous electrolytes, structured electrolytes provide a promising alternate route to achieve high ionic conductivity and selectivity. In this perspective, we begin by describing the physical origins of the idealized liquid transport mechanism and then proceed to examine known cases of decoupling between the matrix dynamics and ionic transport in SPEs. Specifically we discuss conditions for "decoupled" mobility that include a highly polar electrolyte environment, a percolated path of free volume elements (either through structured or unstructured channels), high ion concentrations, and labile ion-electrolyte interactions. Finally, we proceed to reflect on the potential of these mechanisms to promote multivalent ion conductivity and the need for research into the interfacial properties of solid polymer electrolytes as well as their performance at elevated potentials.

Controlled Oxyanionic Polymerization of Propylene Oxide: Unlocking the Molecular-Weight Limitation by a Soft Nucleophilic Catalysis

The oxyanionic ring-opening polymerization of propylene oxide (PO) from an exogenous alcohol activated with benign (complexed) metal-alkali carboxylates is described. The equimolar mixture of potassium acetate (KOAc) and 18-crown-6 ether (18C6) is demonstrated to be the complex of choice for preparing poly(propylene oxide) (PPO) in a controlled manner. In the presence of 18C6/KOAc, hydrogen-bonded alcohols act as soft nucleophiles promoting the PO S_N 2 process at room temperature and in solvent-free conditions while drastically limiting the occurrence of parasitic hydrogen abstraction generally observed during the anionic ROP of PO. The resulting PPO displays predictable and unprecedented molar masses (up to 20 kg mol^-1 ) with low dispersities (Đ_M < 1.1), rendering the 18C6/KOAc complex the most performing activator for the oxyanionic polymerization of PO reported to date. Preliminary studies on the preparation of block and statistical copolyethers are also reported.

Design of Polymeric Zwitterionic Solid Electrolytes with Superionic Lithium Transport

Progress toward durable and energy-dense lithium-ion batteries has been hindered by instabilities at electrolyte-electrode interfaces, leading to poor cycling stability, and by safety concerns associated with energy-dense lithium metal anodes. Solid polymeric electrolytes (SPEs) can help mitigate these issues; however, the SPE conductivity is limited by sluggish polymer segmental dynamics. We overcome this limitation via zwitterionic SPEs that self-assemble into superionically conductive domains, permitting decoupling of ion motion and polymer segmental rearrangement. Although crystalline domains are conventionally detrimental to ion conduction in SPEs, we demonstrate that semicrystalline polymer electrolytes with labile ion-ion interactions and tailored ion sizes exhibit excellent lithium conductivity (1.6 mS/cm) and selectivity (t ₊ ≈ 0.6-0.8). This new design paradigm for SPEs allows for simultaneous optimization of previously orthogonal properties, including conductivity, Li selectivity, mechanics, and processability.

Polyelectrolyte Complex Coacervation across a Broad Range of Charge Densities

Polyelectrolyte complex coacervates of homologous (co)polyelectrolytes with a near-ideally random distribution of a charged and neutral ethylene oxide comonomer were synthesized. The unique platform provided by these building blocks enabled an investigation of the phase behavior across charge fractions 0.10 ≤ f ≤ 1.0. Experimental phase diagrams for f = 0.30-1.0 were obtained from thermogravimetric analysis of complex and supernatant phases and contrasted with molecular dynamics simulations and theoretical scaling laws. At intermediate to high f, a dependence of polymer weight fraction in the salt-free coacervate phase (w P,c) of w P,c ∼ f 0.37±0.01 was extracted; this trend was in good agreement with accompanying simulation predictions. Below f = 0.50, w P,c was found to decrease more dramatically, qualitatively in line with theory and simulations predicting an exponent of 2/3 at f ≤ 0.25. Preferential salt partitioning to either coacervate or supernatant was found to be dictated by the chemistry of the constituent (co)polyelectrolytes.

pH-tunable nanoparticles composed of copolymers of lactide and allyl-glycidyl ether with various functionalities for the efficient delivery of anti-cancer drugs

The designing of biocompatible nanocarriers for the efficient delivery of their cargos to the desired targets remains a challenge. In this regard, the most promising strategy relies on the construction of pH- or thermo-responsive nanoparticles (NPs). However, it is also important to preserve the balance between the responsiveness of the carrier and their stability in physiological conditions. Therefore, we described a new family of copolymers of lactide and allyl-glycidyl ether which were subsequently modified by thiol-ene reaction to functionalize the resulting copolymer with acetylcysteine (ACC) or thioglycolic acid (tGA) moieties. Subsequently, these copolymers were used to obtain blank and doxorubicin (DOX) loaded NPs with an average diameter of about 50-100 nm. Interestingly, the NPs were stable in different pH conditions, however, the presence of ACC or tGA units in the polymeric chain allows for the reduction of the undesired burst release due to the supramolecular interactions between polymeric pedant groups and DOX. The release tests of DOX from NPs showed that DOX release rate decrease depending on the pH values and the copolymer functionalization in order of non-modified NPs > ACC-modified NPs > tGA functionalized NPs. Most importantly, the MTT assay showed that all blank NPs are non-toxic against the normal L929 cell line. Subsequently, the antitumor efficiency of the obtained NPs was tested towards L929 (murine fibroblast cell line), HeLa (cervical cancer), and AGS (human gastric adenocarcinoma cancer) cells. The results demonstrated that DOX-loaded NPs efficiently induce the reduction in the viability of the HeLa and AGS cell, and this reduction in the viability was even below 20 % for the AGS cells. Together with their biocompatibility, the obtained NPs offer a novel route for the preparation of nanocarriers for the controlled and efficient delivery of anticancer drugs.

Tailored self-assembled photocatalytic nanofibres for visible-light-driven hydrogen production

The creation of efficient artificial systems that mimic natural photosynthesis represents a key current challenge. Here, we describe a high-performance recyclable photocatalytic core-shell nanofibre system that integrates a cobalt catalyst and a photosensitizer in close proximity for hydrogen production from water using visible light. The composition, microstructure and dimensions-and thereby the catalytic activity-of the nanofibres were controlled through living crystallization-driven self-assembly. In this seeded growth strategy, block copolymers with crystallizable core-forming blocks and functional coronal segments were coassembled into low-dispersity, one-dimensional architectures. Under optimized conditions, the nanofibres promote the photocatalytic production of hydrogen from water with an overall quantum yield for solar energy conversion to hydrogen gas of ~4.0% (with a turnover number of >7,000 over 5 h, a frequency of >1,400 h^-1 and a H₂ production rate of >0.327 μmol h^-1 with 1.34 μg of catalytic polymer (that is, >244,300 μmol h^-1 g^-1 of catalytic polymer)).

Ion Pairing and the Structure of Gel Coacervates

A scaling model for the structure of coacervates is presented for mixtures of oppositely-charged polyelectrolytes of both symmetric and asymmetric charge-densities for different degrees of electrostatic strength and levels of added salt. At low electrostatic strengths, weak coacervates, with the energy of electrostatic interactions between charges less than the thermal energy, k B T, are liquid. At higher electrostatic strengths, strong coacervates are gels with crosslinks formed by ion pairs of opposite charges bound to each other with energy higher than k B T. Charge-symmetric coacervates are formed for mixtures of oppositely-charged polyelectrolytes with equal and opposite charge-densities. While charge-symmetric weak coacervates form a semidilute polymer solution with a correlation length equal to the electrostatic blob size, charge-symmetric strong coacervates form reversible gels with a correlation length on the order of the distance between bound ion pairs. Charge-asymmetric coacervates are formed from mixtures of oppositely-charged polyelectrolytes with different charge-densities. While charge-asymmetric weak coacervates form double solutions with two correlation lengths and qualitatively different chain conformations of polycations and polyanions, charge-asymmetric strong coacervates form bottlebrush and star-like gels. Unlike liquid coacervates, for which an increase in the concentration of added salt screens electrostatic interactions, causing structural rearrangement and eventually leads to their dissolution, the salt does not affect the structure of strong coacervates until ion pairs dissociate and the gel disperses.

Photoinduced Proton-Transfer Polymerization: A Practical Synthetic Tool for Soft Lithography Applications

Proton-transfer photopolymerization through the thiol-epoxy "click" reaction is shown to be a versatile new method for the fabrication of micro- and nanosized polymeric patterns. In this approach, complexation of a guanidine base, diazabicycloundecene (DBU), with benzoylphenylpropionic acid (ketoprofen) generates a photolabile salt. Under illumination at a wavelength of 365 nm, the salt undergoes a photodecarboxylation reaction to release DBU as a base. The base-catalyzed ring opening reaction then creates cross-linked poly(β-hydroxyl thio-ether) patterns. The surface chemistry of these patterns can be altered through alkylation of the thio-ether linkages. For example, a reaction with bromoacetic acid produces a hitherto unknown sulfonium/carboxylate-based zwitterionic motif that endows antibiofouling capacity to the micropatterns.

Lithium and magnesium polymeric electrolytes prepared using poly(glycidyl ether)-based polymers with short grafted chains

A simple and effective strategy to synthesize a new class of PAGE-based polymer electrolytes containing lithium and magnesium salts.

A Modular and Practical Synthesis of Zwitterionic Hydrogels through Sequential Amine-Epoxy "Click" Chemistry and N-Alkylation Reaction

In this work, the amine-epoxy "click" reaction is shown to be a valuable general tool in the synthesis of reactive hydrogels. The practicality of this reaction arises due to its catalyst-free nature, its operation in water, and commercial availability of a large variety of amine and epoxide molecules that can serve as hydrophilic network precursors. Therefore, hydrogels can be prepared in a modular fashion through a simple mixing of the precursors in water and used as produced (without requiring any post-synthesis purification step). The gelation behavior and final hydrogel properties depend upon the molecular weight of the precursors and can be changed as per the requirement. A post-synthesis modification through alkylation at the nitrogen atom of the newly formed β-hydroxyl amine linkages allows for functionalizing the hydrogels. For example, ring-opening reaction of cyclic sulfonic ester gives rise to surfaces with a zwitterionic character. Finally, the established gelation chemistry can be combined with soft lithography techniques such as micromolding in capillaries (MIMIC) to obtain hydrogel microstructures.

Glycidyl Tosylate: Polymerization of a "Non-Polymerizable" Monomer permits Universal Post-Functionalization of Polyethers

Glycidyl tosylate appears to be a non-polymerizable epoxide when nucleophilic initiators are used because of the excellent leaving group properties of the tosylate. However, using the monomer-activated mechanism, this unusual monomer can be copolymerized with ethylene oxide (EO) and propylene oxide (PO), respectively, yielding copolymers with 7-25 % incorporated tosylate-moieties. The microstructure of the copolymers was investigated via in situ 1 H NMR spectroscopy, and the reactivity ratios of the copolymerizations have been determined. Quantitative nucleophilic substitution of the tosylate-moiety is demonstrated for several examples. This new structure provides access to a library of functionalized polyethers that cannot be synthesized by conventional oxyanionic polymerization.

Effect of Ionic Group on the Complex Coacervate Core Micelle Structure

Pairs of ionic group dependence of the structure of a complex coacervate core micelle (C3M) in an aqueous solution was investigated using DLS, cryo-TEM, and SANS with a contrast matching technique and a detailed model analysis. Block copolyelectrolytes were prepared by introducing an ionic group (i.e., ammonium, guanidinium, carboxylate, and sulfonate) to poly(ethylene oxide-b-allyl glycidyl ether) (NPEO = 227 and NPAGE = 52), and C3Ms were formed by simple mixing of two oppositely-charged block copolyelectrolyte solutions with the exactly same degree of polymerization. All four C3Ms are spherical with narrow distribution of micelle dimension, and the cores are significantly swollen by water, resulting in relatively low brush density of PEO chains on the core surface. With the pair of strong polyelectrolytes, core radius and aggregation number increases, which reflects that the formation of complex coacervates are significantly sensitive to the pairs of ionic groups rather than simple charge pairing.

Recent progress of glycopolymer synthesis for biomedical applications

Glycopolymers are an important class of biomaterials which include carbohydrate moieties in their polymer structure.

Utilization of catecholic functionality in natural safrole and eugenol to synthesize mussel-inspired polymers

Naturally occurring safrole I upon epoxidation gave safrole oxide II, which underwent ring opening polymerization using a Lewis acid initiator/catalyst comprising of triphenylmethylphosphonium bromide/triisobutylaluminum to afford new polyether III in excellent yields. Epoxy monomer II and allyl glycidyl ether IV in various proportions have been randomly copolymerized to obtain copolymer V. A mechanism has been proposed for the polymerization reaction involving chain transfer to the monomers. A strategy has been developed for the deprotection of the methylene acetal of V using Pb(OAc)₄ whereby one of the methylene protons is replaced with a labile OAc group to give VI. The pendant allyl groups in VI have been elaborated via a thiol–ene reaction using cysteamine hydrochloride and thioglycolic acid to obtain cationic VII and anionic VIII polymers, both containing a mussel-inspired Dopa-based catechol moiety. During aqueous work up, the protecting group containing OAc was deprotected under mild conditions. Cationic VII and anionic VIII were also obtained via an alternate route using epoxide IX derived from 3,4-bis[tert-butyldimethylsilyloxy]allylbenzene. Monomer IX was homo- as well as copolymerized with IV using Lewis acid initiator/catalyst system to obtain homopolymer X and copolymer X1. Copolymer XI was then elaborated using a thiol–ene reaction followed by F⁻ catalysed silyl deprotection to obtain mussel inspired polymers VII and VIII, which by virtue of having charges of opposite algebraic signs were used to form their coacervate.

Naturally occurring safrole I upon epoxidation gave safrole oxide II, which underwent polymerization using a Lewis acid initiator/catalyst of triphenylmethylphosphonium bromide/triisobutylaluminum to afford new polyether III in excellent yields.

Poly(alkyl glycidyl ether) hydrogels for harnessing the bioactivity of engineered microbes

Herein, we describe a method to produce yeast-laden hydrogel inks for the direct-write 3D printing of cuboidal lattices for immobilized whole-cell catalysis.

Tailoring Polyethers for Post-polymerization Functionalization by Cross Metathesis

Olefin cross metathesis is reported for the first time to attach small molecules to a range of novel polyethers with a poly(ethylene glycol) backbone and pendent alkene groups, allowing for a loading of up to one compound per monomer unit. These polymers are tailored to prevent the occurrence of self metathesis (reaction of the polymer with itself) by varying the substitution on the pendent alkenes, thus steering their reactivity toward olefin cross metathesis. Efficient functionalization has been observed for a range of coupling partners as a proof of concept for the use of olefin metathesis to graft small and larger molecules to polyethers for drug delivery. This approach also paves the way for the use of olefin cross metathesis as an efficient method to functionalize a wide variety of polymers with pendent olefin groups.

Core-crosslinked diblock terpolymer micelles – taking a closer look on crosslinking efficiency

We present an in-depth study on the crosslinking of diblock terpolymer micellar cores.

Cross-linkable multi-stimuli responsive hydrogel inks for direct-write 3D printing

Triple-stimuli responsive hydrogel can be 3D printed and cross-linked in the presence of a photoradical generator and 365 nm UV light.

Synthesis and sequence-controlled self-assembly of amphiphilic triblock copolymers based on functional poly(ethylene glycol)

Given the increasing prosperity of multifunctional poly(ethylene glycol) (mf-PEG), an amphiphilic triblock copolymer, poly(ethylene glycol)-block-poly(ε-caprolactone)-block-poly(allyl glycidyl ether) (mPEG-PCL-PAGE), was synthesized by a combination of living ring-opening polymerization (ROP) and click chemistry.

pH-Tunable Thermoresponsive PEO-Based Functional Polymers with Pendant Amine Groups

Thermoresponsive polymers exhibiting lower critical solution temperatures (LCSTs) in aqueous solution have garnered considerable attention for the development of smart materials. Herein, we report the synthesis and properties of pH-tunable thermoresponsive poly(ethylene oxide) (PEO)-based functional polymers bearing pendant amine groups with varying cloud points. Well-defined poly(ethylene oxide-co-allyl glycidyl ether) (P(EO-co-AGE)) copolymers were prepared via controlled anionic ring-opening copolymerization of ethylene oxide (EO) with 10 mol % of a functional allyl glycidyl ether (AGE) comonomer. Facile, modular thiol-ene click chemistry was then employed to introduce a library of different aminothiols as side chains to the initial P(EO-co-AGE) copolymer. Depending on the nature of the pendant amine groups (primary amine, dimethylamine, and diethylamine) and the hydrophobicity of the side chains (ethyl, propyl, and hexyl), the cloud points could be tuned from 44-100 °C under different pH conditions. This is the first systematic investigation into the effect of PEO copolymer side chains on cloud point, which opens up the opportunity to make new thermoresponsive polymers for a variety of smart material applications.

Nanoparticle "switch-on" by tetrazine triggering

Small-molecule mediated release of drugs from self-assembled nanoparticles through the mediatory of a Diels–Alder reaction.

This work describes how a small-molecule chemical trigger, reacting through the mediatory of an inverse electron demand Diels–Alder reaction, results in enhanced cellular uptake and selective nanoparticle disintegration and cargo liberation, via gross polymeric morphological alterations. The power of these responsive nanoparticles is demonstrated through encapsulation of the anti-cancer agent doxorubicin and its triggered release, allowing controlled cell death in response to a small-molecule chemical trigger.