Halogen bonding in polymer science: towards new smart materials

The halogen bond is a special non-covalent interaction, which can represent a powerful tool in supramolecular chemistry. Although the halogen bond offers several advantages compared to the related hydrogen bond, it is currently still underrepresented in polymer science. The structural related hydrogen bonding assumes a leading position in polymer materials containing supramolecular interactions, clearly indicating the high potential of using halogen bonding for the design of polymeric materials. The current developments regarding halogen bonding containing polymers include self-assembly, photo-responsive materials, self-healing materials and others. These aspects are highlighted in the present perspective. Furthermore, a perspective on the future of this rising young research field is provided.

The incorporation of halogen bonding into polymer architectures is a new approach for the design of functional materials. This perspective emphasizes the current development in the field of halogen bonding featuring polymer materials.     

Nucleophilic addition to acetylenes in superbasic catalytic systems: XV. Vinylation of 2-hydroxymethylfuran

2-Hydroxymethylfuran reacted with acetylene in superbasic catalytic systems MOH-DMSO (M = Na, K) under mild temperature conditions (75–85°C, 1–2 h), yielding 80% of 2-vinyloxymethylfuran. The product, as well as acetaldehyde acetals derived therefrom, turned out to be promising as modifiers for electrolyte in lithium-sulfur rechargeable batteries.     

Nucleophilic addition to acetylenes in superbasic catalytic systems. 12. Vinylation of lupinine

The addition of a natural alkaloid lupinine to acetylene in the presence of superbasic catalytic systems (KOH—DMSO, KOBu^t—DMSO, KOH—dioxane) under elevated or atmospheric pressure affords O-vinyllupinine (in up to 88% yield), a promising optically active monomer and intermediate for the preparation of new quinolizidine alkaloids. The same vinyl ether was obtained (in 60% yield) by the reaction of lupinine with vinyl acetate in the presence of Hg(OAc)₂.     

The catalytic oxidation of biomass to new materials focusing on starch,cellulose and lignin

Biomass is a renewable class of materials of growing interest amongst researchers aiming to achieve global sustainability. This review focuses on the homogeneous catalysis of the oxidation of biomass, in particular starch, cellulose and lignin. Often such catalytic reactions lead to depolymerisation of the material as happens in Nature with for example brown rot fungi. This depolymerisation can be desirable or not, and control in industrial applications is thus important to obtain the desired outcome. The two main oxidants in use are O₂ and H₂O₂ and their use is described as appropriate. Industrial oxidation catalysis is highly significant in the bleaching of cellulose-containing materials due to its high volume application in the paper, pulp and laundry industries. Here, the presence of a ligand on the oxidising metal ion has a significant effect on the catalyst selectivity and stability. In addition to the bleaching of cellulose-containing materials, the oxidation of cellulose, starch, lignin and lignin model compounds are discussed with a focus on generating even more hydrophilic materials which have important applications or materials which may be further modified. Finally developing applications of biomass are described such as new support materials for catalysts, as supports for sensors and nanomaterials for microbial culture.     

Microfibrillated cellulose and new nanocomposite materials: a review

Due to their abundance, high strength and stiffness, low weight and biodegradability, nano-scale cellulose fiber materials (e.g., microfibrillated cellulose and bacterial cellulose) serve as promising candidates for bio-nanocomposite production. Such new high-value materials are the subject of continuing research and are commercially interesting in terms of new products from the pulp and paper industry and the agricultural sector. Cellulose nanofibers can be extracted from various plant sources and, although the mechanical separation of plant fibers into smaller elementary constituents has typically required high energy input, chemical and/or enzymatic fiber pre-treatments have been developed to overcome this problem. A challenge associated with using nanocellulose in composites is the lack of compatibility with hydrophobic polymers and various chemical modification methods have been explored in order to address this hurdle. This review summarizes progress in nanocellulose preparation with a particular focus on microfibrillated cellulose and also discusses recent developments in bio-nanocomposite fabrication based on nanocellulose.     

Nucleophilic addition to acetylenes in superbasic catalytic systems: XVI. Vinylation of alcohols of the furan series under atmospheric pressure

2-Hydroxymethylfuran and 2-hydroxymethyltetrahydrofuran reacted with acetylene in the superbasic catalytic system KOH-DMSO at 75-85°C under atmospheric pressure to give in 1.5–3 h the corresponding 2-vinyloxymethyl derivatives in 88 and 91% yield, respectively.     

Design of coordination polymer as stable catalytic systems

Here we report the first example of catalytic metallogels, which are formed irreversibly in dimethylsulfoxide via the creation of cross-linked, three-dimensional coordination polymer networks by using transition-metal ions with multiple sites available for coordination and multidentate ligands. Conformational flexibility of the ligands and slow formation of the coordination polymers apparently favor the gelation. These metallogels are stable in water and most organic solvents and can catalyze the oxidation of benzyl alcohol to benzaldehyde by using their PdII moieties as the catalytic centers. The best catalytic turnover of the metallogel is twice that of [Pd(OAc)2] under similar reaction conditions.     

Nanocoating of natural cellulose fibers with conjugated polymer: hierarchical polypyrrole composite materials

Astonishingly uniform polypyrrole nanocoating on morphologically complex cellulosic substances was achieved without disrupting the hierarchical network structures of individual cellulose fibers by means of polymerization-induced adsorption.     

Synthesis of new chitosan derivatives and combination with biodegradable polymer

New chitosan derivatives are synthesized by the reductive N‐alkylation reaction of chitosan with various aldehydes, such as 2,4‐dihydroxybenzaldehyde, cholesteryl 4‐formylbenzoate, and N‐dehydroabietyl‐4‐formylbenzamide. The palladium‐adsorption ability of the newly synthesized derivatives is found to be as good as that of chitosan. A blend of chitosan and other biodegradable polymers is also found to exhibit palladium‐adsorption ability. In comparison to the starting chitosan, the chitosan derivative having dehydroabietyl‐type side chains exhibited an improved solubility in methanol. The chitosan derivatives are successfully applied as plastic coating materials for electroless plating. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthetic approaches towards new polymer systems by the combination of living carbocationic and anionic polymerizations

This study summarizes recent efforts to obtain by combination of living carbocationic and anionic polymerizations block copolymers which are potential precursors for building new well-defined polymeric architectures with microphase separated morphology. Living carbocationic polymerization (LCCP) yields telechelic polyisobutylene (PIB) chains with a variety of useful endgroups, such as tert-chlorine, isopropenyl, primary hydroxyl, tolyl etc. When tolyl-ended PIB was used as precursor for macroinitiator of living anionic polymerization of 2-(tert-butyldimethylsilyloxy)ethyl methacrylate (tBuMe₂SiOEMA), mixtures of homopolymers and block copolymers were formed due to incomplete lithiation of this chain end. In another approach a new functionalization method was developed by end-quenching living PIB chains with 1,1-diphenylethylene (DPE). In the presence of BCl₃ a new telechelic PIB with 2,2-diphenylvinyl (DPV) endgroups was formed. A corresponding DPV model compound was synthesized from 2-chloro-2,4,4-trimethylpentane (TMPCl). Because of steric hindrance less than quantitative lithiation of this material occurred. Controlled deprotection of PtBuMe₂SiOEMA obtained by living anionic polymerization (LAP) was utilized to prepare a precursor network composed of partially deprotected PtBuM₂SiOEMA and hydroxyl-telechelic PIB by using a diisocyanate crosslinker. After network formation deprotection with HCl was completed and a new amphiphilic network (APN) containing PIB and poly(2-hydroxyethyl) methacrylate) (PHEMA) segments crosslinked by urethane linkages was obtained.     

Green polymer chemistry: new methods of polymer synthesis using renewable starting materials

The present article reviews the recent results reported mainly from our group on “green polymer chemistry”. Characteristic important aspects of green polymer chemistry include herein, typically (1) using renewable resources as starting materials for polymer production, and (2) employing green method for the polymer synthesis. As renewable starting materials, the following materials were employed; lactic acid, itaconic anhydride, renewable plant oils, and cardanol. Polymer production using these materials contributes to mitigate the carbon dioxide emission because of their “carbon neutral” nature. As green method, lipase enzyme was mainly used for polymerization catalyst, since lipase is a natural benign catalyst, showing a specific catalysis as well as recyclable character. Polymer synthesis from these materials and the catalyst provided various value-added functional polymers, demonstrating good examples of green polymer chemistry.

     

A new method for the evaluation of biodegradable plastic using coated cellulose paper

A highly sensitive analytical method for evaluation of poly(L-lactide) (PLA), poly(epsilon-caprolactone) (PCL), poly(beta-hydroxybutyrate) (PHB), and poly(butylene succinate) (PBS) degradability was developed using coated cellulose paper, prepared by penetration and adhesion of these plastics into/onto the cellulose paper. Enzymatic degradability of the obtained plastic coated papers was evaluated using various commercial proteases and lipases. PLA coated paper was highly susceptible to subtilisin and mammalian enzymes, alpha-chymotrypsin, elastase and trypsin. To our knowledge, this is the first report on the degradation of PLA coated paper using subtilisin and mammalian enzymes. Almost all lipase preparations degraded PCL and PHB coated papers but not PBS coated paper. The biodegradability of plastic coated paper was greater than that of plastic powder. The penetration of plastic into cellulose paper by coating improved the plastic degradability, and can be regulated easily.     

Multi-component self-assembled molecular-electronic films: towards new high-performance thermoelectric systems

The thermoelectric properties of parallel arrays of organic molecules on a surface offer the potential for large-area, flexible, solution processed, energy harvesting thin-films, whose room-temperature transport properties are controlled by quantum interference (QI). Recently, it has been demonstrated that constructive QI (CQI) can be translated from single molecules to self-assembled monolayers (SAMs), boosting both electrical conductivities and Seebeck coefficients. However, these CQI-enhanced systems are limited by rigid coupling of the component molecules to metallic electrodes, preventing the introduction of additional layers which would be advantageous for their further development. These rigid couplings also limit our ability to suppress the transport of phonons through these systems, which could act to boost their thermoelectric output, without comprising on their impressive electronic features. Here, through a combined experimental and theoretical study, we show that cross-plane thermoelectricity in SAMs can be enhanced by incorporating extra molecular layers. We utilize a bottom-up approach to assemble multi-component thin-films that combine a rigid, highly conductive ‘sticky’-linker, formed from alkynyl-functionalised anthracenes, and a ‘slippery’-linker consisting of a functionalized metalloporphyrin. Starting from an anthracene-based SAM, we demonstrate that subsequent addition of either a porphyrin layer or a graphene layer increases the Seebeck coefficient, and addition of both porphyrin and graphene leads to a further boost in their Seebeck coefficients. This demonstration of Seebeck-enhanced multi-component SAMs is the first of its kind and presents a new strategy towards the design of thin-film thermoelectric materials.

Through an experimental and theoretical study, cross-plane thermoelectricity in Self-Assembled Monolayers (SAMs) was enhanced by adding extra molecular layers, presenting a new strategy towards the design of high thermoelectric materials.     

A new biodegradable polydepsipeptide microsphere for application in drug delivery systems

A sequential polydepsipeptide containing a tripeptide sequence L-alanyl-Lalanyl-ethyl L-glutamyl and an-hydroxy acid L-lactic acid, poly(Ala-Ala-Glu(OEt)-Lac), was synthesized to prepare the microspherical particles by the solvent evaporation process. In this case, the solvents play the most important role for the preparation of polydepsipeptide microspheres and, as an example, when 200 mg of the polydepsipeptide dissolved in 10 ml of 98/2% chloroform/dichloroacetic acid mixture was stirred at 400 rpm and 30 C, the microspherical particles with mean diameter of 58m were formed after pouring into 200 ml of 1% (w/v) poly(vinyl alcohol) solution. 17-Estradiol was incorporated into the particles, and the resulting particles were found to contain 5 mg of drug per 25 mg of the particle. The in vivo release of drug from the microspherical formulation was evaluated by measuring the pharmacological influence on rat prostate. It was found that the sufficient amount of drug, keeping the effective pharmacological influence, is supplied during the first 12-week period, followed by an incomplete supplying of drug intil the implant is perfectly degraded in vivo in the 25th week from the start of implantation.     

Quantification of cellulose forms in complex cellulose materials: a chemometric model

In this paper, we present a chemometric model for quantifying the cellulose forms with different states of order found within cellulose I fibrils. The relative amounts of the different cellulose forms, that is crystalline cellulose I, para-crystalline cellulose and cellulose at accessible and inaccessible cellulose surfaces, were determined by non-linear least squares fitting of the C4-region in CP/MAS ¹³C-NMR (Cross-Polarisation Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance) spectra. By correlating these results from the C4-region with the full spectral data we obtained a model which is able to provide an assessment of the relative amounts of the different cellulose forms directly from NMR-spectra of complex lignocellulosic samples. Furthermore, this model enabled new assignments to be made in the C1-region for signals from cellulose at accessible fibril surfaces.     

Dendronized polystyrene supports for new catalytic systems

New catalytic systems based on tris(dimethylvinyl)methyl substituted polystyrene were prepared. Dendronized polystyrenes were obtained by modification of poly(styrene-co-chloromethylstyrene) precursors with LiC(SiMe₂CHCH₂)₃. Platinum was attached to the polymers via coordination to vinyl groups located on carbosilane moieties. Such the catalytic system makes an interesting alternative for heterogenous platinum catalysts (Pt/charcoal, Pt/C_act and Pt/Al₂O₃) and also to Karstedt’s catalyst, when used in hydrosilylation of vinylsilanes.     

Tetrathiafulvalene-acetylene scaffolding: new pi-electron systems for advanced materials

Novel extended tetrathiafulvalenes (TTFs) with hexa-2,4-diyne-1,6-diylidene spacers between the two 1,3-dithiole rings and laterally appended alkynyl moieties for one- and two-dimensional scaffolding were synthesised and investigated for their electronic properties.