Mehmet Isik

Ionic Liquids and Cellulose: Dissolution, Chemical Modification and Preparation of New Cellulosic Materials

Due to its abundance and a wide range of beneficial physical and chemical properties, cellulose has become very popular in order to produce materials for various applications. This review summarizes the recent advances in the development of new cellulose materials and technologies using ionic liquids. Dissolution of cellulose in ionic liquids has been used to develop new processing technologies, cellulose functionalization methods and new cellulose materials including blends, composites, fibers and ion gels.

Room temperature synthesis of non-isocyanate polyurethanes (NIPUs) using highly reactive N-substituted 8-membered cyclic carbonates

There is a growing interest to develop green synthetic pathways towards industrially relevant polymers such as polyurethanes without the use of toxic and dangerous isocyanate monomers. The most promising route towards non-isocyanate polyurethanes (NIPUs) is the aminolysis of dicyclic carbonates derived from renewable resources. Although, cyclic carbonates of 5- and 6-members have been successfully proposed, aminolysis of these compounds requires the use of high temperatures to obtain high conversions and subsequently high molecular weight NIPUs. Indeed, these cyclic carbonates do not allow the achievement of high molecular weight NIPUs using low reactive diamines analogous to two of the most industrially relevant aliphatic diisocyanates. Herein, we report a (bis) N-substituted 8-membered cyclic carbonate that could be prepared from naturally abundant epoxides, diamines and dimethyl carbonate using sustainable chemical routes. This N-substituted 8 membered cyclic carbonate appeared to be much more reactive than the smaller 5- and 6-membered cyclic carbonates. Due to this increased reactivity, we obtained high molecular weight NIPUs using a variety of diamines, including industrially relevant hindered aliphatic diamines, such as 5-amino-1,3,3-trimethylcyclohexanemethylamine (IPDA) and 4,4′-methylenebis(cyclohexylamine). The synthesis of NIPUs was demonstrated at room temperature without the need for any additional catalyst. Altogether, this paper shows that (bis) N-substituted 8-membered cyclic carbonates are ideal starting materials for the synthesis of sustainable non-isocyanate polyurethanes (NIPUs).

Preparation of poly(ionic liquid) nanoparticles and their novel application as flocculants for water purification

New methods for preparing polymeric nanoparticles are actively being investigated such as self-assembly of amphiphilic block copolymers, self-crosslinking of single-chain macromolecules, nanoprecipitation or emulsion–miniemulsion polymerizations. However, most methods require multi-step synthesis, controlled polymerization mechanisms and tedious purification processes. In this work, amphiphilic poly(ionic liquid) random copolymers that self-assemble into polymeric nanoparticles were prepared in water through a simple partial anion exchange process. This method was demonstrated for different cationic polyelectrolytes such as poly(1-vinyl-3-ethyl imidazolium bromide), poly(diallyldimethylammonium chloride) and poly(allylamine hydrochloride). Their partial anion exchange was conducted by the addition of lithium bis(trifluoromethanesulphonyl)imide to the aqueous solution of the polymer. It was found out that the amphiphilic poly(ionic liquid)s containing small amounts (1–10%) of bis(trifluoromethanesulfonimide) anion self-assemble into spherical nanoparticles as revealed by dynamic light scattering and transmission electron microscopy. The nanoparticle size ranged from 100 nm to 600 nm depending on the extent of partial anion exchange and the nature of the polyelectrolyte. As an application, the poly(ionic liquid) nanoparticles were used as flocculants for water purification. The use of amphiphilic poly(ionic liquid)s as flocculants enhanced the evolution rate of the sediment considerably in comparison with the parent polyelectrolytes.

Cholinium-based ion gels as solid electrolytes for long-term cutaneous electrophysiology

Cholinium-based bio-ion gels were prepared by photopolymerization of poly(cholinium lactate methacrylate) network within cholinium lactate ionic liquid. The rheological and thermal properties as well as ionic conductivity of ion gels of different compositions were measured. As indicated by rheological measurements, the ion gels show the properties of gel materials which become soft by increasing the amount of free ionic liquid. Cholinium ion gels with various composition of free ionic liquid vs. methacrylic network show glass transitions between −40° and −70 °C and thermal stability up to 200 °C. The ionic conductivity of these gels increases from 10−8 to 10−3 S cm−1 at 20 °C by varying the amount of free ionic liquid between 0 and 60 wt%, respectively. Low glass transition temperature and enhanced ionic conductivity make the cholinium-based ion gels good candidates to be used as a solid electrolytic interface between the skin and an electrode. The ion gels decrease the impedance with the human skin to levels that are similar to commercial Ag/AgCl electrodes. Accurate physiologic signals such as electrocardiography (ECG) were recorded with ion gels assisted electrodes for a long period of time (up to 72 h) with a remarkable stability. The low toxicity and superior ambient stability of cholinium ionic liquids and ion gels make these materials highly attractive for long-term cutaneous electrophysiology and other biomedical applications.

Tuning the Selectivity of Biodegradable Antimicrobial Cationic Polycarbonates by Exchanging the Counter-Anion.

There is a growing interest in modern healthcare to develop systems able to fight antibiotic resistant bacteria. Antimicrobial cationic biodegradable polymers able to mimic antimicrobial peptides have shown to be effective against both Gram-positive and Gram-negative bacteria. In these systems, the hydrophilic-hydrophobic ratio and the cationic charge density play a pivotal role in defining the killing efficiency. Nevertheless, many of these antimicrobial polymers show relatively low selectivity as defined by the relative toxicity to mammalian cells or hemolysis relative to pathogens. In this study, a series of polycarbonates containing pendant quaternary ammoniums are used to understand the role of different counter-anions including chloride, citrate, malonate, benzoate, acetate, lactate and trifluoroacetate, and the antibiotic penicillin on antimicrobial efficacy and selectivity. Interestingly, it is found that in spite of the strong antimicrobial activity of trifluoroacetate and benzoate anions, they prove to be much less hemolytic than chloride anion. It is believed that the proper selection of the anion could enhance the potential of antimicrobial polymers to fight against clinically relevant pathogenic infections, while concurrently mitigating harmful side effects.

Redox-active poly(ionic liquid)s as active materials for energy storage applications

New polymeric materials such as polymer electrolytes or redox polymers are actively being searched for in order to increase the performance and security of electrochemical energy storage devices such as batteries. Poly(ionic liquid)s are very popular materials in energy nowadays finding applications as ion conducting polymer electrolytes and electrode binders for batteries and supercapacitors. In this work, the incorporation of redox-active counter anions (anthraquinone and nitroxide molecules) into poly(ionic liquid)s has broadened the scope of applications as redox-active materials in different energy storage technologies. Polymers having those known redox-active molecules usually involve challenging synthetic routes and yield insoluble materials very difficult to handle. In this paper, we show that the synthesis of the redox-active poly(ionic liquid)s can be achieved through a straightforward and simple anion exchange reaction. We also show that this new family of redox-active poly(ionic liquid)s can be applied in several electrochemical energy storage technologies such as lithium batteries, as electrocatalysts in fuel cells and metal–air batteries or as electrolytes in organic redox flow batteries.

Innovative Poly(Ionic Liquid)s by the Polymerization of Deep Eutectic Monomers

The incorporation of ionic liquid (IL) chemistry into functional polymers has extended the properties and applications of polyelectrolytes. However, ILs are expensive due to the presence of fluorinated anions or complicated synthetic steps which limit their technological viability. Here, we show a new family of poly(ionic liquid)s (PILs) which are based in cheap and renewable chemicals and involves facile synthetic approaches. Thus, deep eutectic monomers (DEMs) are prepared for the first time by using quaternary ammonium compounds and various hydrogen bond donors such as citric acid, terephthalic acid or an amidoxime. The deep eutectic formation is made through a simple mixing of the ingredients. Differential scanning calorimetry, nuclear magnetic resonance (NMR) and computational studies reveal the formation of the DEMs due to the ionic interactions. The resulting DEMs are liquid which facilitates their polymerization using mild photopolymerization or polycondensation strategies. Spectroscopic characterizations reveal the successful formation of the polymers. By this way, a new family of PILs can be synthesized which can be used for different applications. As an example, the polymers show promising performance as solid CO2 sorbents. Altogether the deep eutectic monomer route can lead to non-toxic, cheap and easy-to-prepare alternatives to current PILs for different applications.

New amphiphilic block copolymers from lactic acid and cholinium building units

New polylactide-block-poly(2-cholinium lactate methacrylate) amphiphilic block copolymers were synthesized and characterized. These new block copolymers are composed of chemicals from renewable sources such as lactic acid and cholinium. First a polylactide macro chain transfer agent was synthesized and used to conduct block copolymerization of 2-cholinium lactate methacrylate ionic liquid monomer to form an amphiphilic block copolymer. The polymerizations were successfully conducted through ring-opening polymerization and controlled radical RAFT techniques and confirmed by 1H NMR and GPC experiments. DLS experiments revealed the formation of self assembled micelles in water and TEM studies confirmed the presence of spherical nanostructures in a dry state having sizes down to 17 nm. To the best of our knowledge this is the first example of an amphiphilic block copolymer having lactic acid units in both copolymer blocks of potential interest in nanomedicine.

Expanding the Applicability of Poly(Ionic Liquids) in Solid Phase Microextraction: Pyrrolidinium Coatings

Crosslinked pyrrolidinium-based poly(ionic liquids) (Pyrr-PILs) were synthesized through a fast, simple, and solventless photopolymerization scheme, and tested as solid phase microextraction (SPME) sorbents. A series of Pyrr-PILs bearing three different alkyl side chain lengths with two, eight, and fourteen carbons was prepared, characterized, and homogeneously coated on a steel wire by using a very simple procedure. The resulting coatings showed a high thermal stability, with decomposition temperatures above 350 °C, excellent film stability, and lifetime of over 100 injections. The performance of these PIL-based SPME fibers was evaluated using a mixture of eleven organic compounds with different molar volumes and chemical functionalities (alcohols, ketones, and monoterpenes). The Pyrr-PIL fibers were obtained as dense film coatings, with 67 μm thickness, with an overall sorption increase of 90% and 55% as compared to commercial fibers of Polyacrylate (85 μm) (PA85) and Polydimethylsiloxane (7 μm) (PDMS7) coatings, respectively. A urine sample doped with the sample mixture was used to study the matrix effect and establish relative recoveries, which ranged from 60.2% to 104.1%.

Proton Conducting Membranes Based on Poly(Ionic Liquids) Having Phosphonium Counter-Cations

Proton conducting polymeric membranes are highly searched in many different technologies ranging from energy to biosensing. Protic ionic liquids and their polymeric version represent a new family of proton conducting molecules with relatively facile synthesis and excellent properties. In this work, protic poly(ionic liquids) having the most popular phosphonium counter-cations are presented for the first time. The synthesis is carried out through proton transfer reactions or through ion exchange reactions by using commercially available tertiary phosphines. Tributyl-, trioctyl-, and tricyclohexyl-phosphine are selected to form the desired cations. Polystyrene sulfonic acid, poly(2-acrylamido-2-methyl-1-propanesulfonic acid), and lithium poly[(4-styrenesulfonyl) (trifluoromethanesulfonyl)imide] polymers are used to form the polymeric anions. The chemical structure of the protic poly(ionic liquids) is confirmed by spectroscopic characterizations such as Fourier transform infrared and nuclear magnetic resonance spectroscopies. Thermal properties of the polymer are characterized by means of differential scanning calorimetry and thermogravimetric analysis. Polymers exhibit good membrane forming ability as well as high ionic conductivities in the range of 10-8 to 10-3 S cm-1 from 30 to 90 °C.