Volume 86, Issue 11

The paper summarizes the history of the drug/gene delivery domain, pointing on polymers as a solution to specific challenges, and outlines the current situation in the field – focusing on the newest strategies intended to improve systems effectiveness and responsiveness (design keys, preparative approaches). Some recent results of the authors are briefly presented.

An approach to prepare some biobased flame retardant (FR) compounds is presented. The adopted strategy consists in functionalizing an aromatic biobased phenolic compound, the phloroglucinol, with different phosphate groups in order to promote a charring effect. Different chlorophosphates were grafted onto phloroglucinol hydroxy groups and the functionalization of the hydroxy groups was quantitative. The synthesized biobased FR were incorporated into an epoxy matrix as additive to estimate their flame retardant properties. The influence of different parameters was studied such as the phosphorus content of the thermoset or the nature of the R group of the used phosphate P-O-R. MEB/EDX observations proved the influence of this R group on the compatibility between the FR and the matrix and its importance to obtain homogeneous thermoset. Thermogravimetric analyses of the phosphorus-containing thermosets showed a small decrease in thermal stability accompanied by a char yield almost tripled for a 3 % w P-containing thermoset compared to that of the thermoset without any FR. Pyrolysis combustion flow calorimetry was also used to evaluate the flammability of the modified epoxy thermoset. A significant decrease in peak of heat release rate and total heat released was observed compared to thermoset without FR. These results demonstrate the good flame retardant properties of these biobased phosphates in an epoxy matrix. In addition these results show the potential of the biobased phenolic compounds as raw material for flame retardants syntheses.

Many of the most widely used reactions in organic synthesis suffer from drawbacks that can hamper their use. For example, the Mitsunobu, Wittig and Appel reactions all result in the formation of a full equivalent of triphenylphosphine oxide, which can be similar in polarity to the desired product, and thus be difficult to remove. Other reactions such as the Suzuki-Miyaura and Mizoroki-Heck reactions require the addition of numerous reagents, ligands and catalysts that can be laborious to separate from the targeted cross-coupled product. This review summarizes our recent work to address these issues by developing polymeric tools designed to simplify product isolation from these transformations.

Numerous publications report the existence of intracellular “Si” storage pools in diatoms representing intracellular concentrations of ca. 19–340 mM depending on the species. “Si” storage pools in diatom cells, if present, are supposed to accumulate “Si” for the production of new valves. The accumulated “Si” is then transported into the silicon deposition vesicle (SDV) where the new cell wall is synthesized. Interestingly, the reported concentrations of intracellular “Si” within the storage pool sometimes strongly exceed the solubility of monosilicic acid (ca. 2 mM pH <9). Various types of “Si” storage pools are discussed in the literature. It is usually assumed that “Si” species are stabilized by the association with some kind of organic material such as special proteins, thus forming a soluble silicic acid pools inside the cells. In an effort to mimic the above phenomenon, we have used a variety of neutral or cationic polymers that stabilize two soluble forms of “Si,” silicic and disilicic acids. These polymers include amine-terminated dendrimers, amine-containing linear polymers (with primary, secondary or tertiary amines), organic ammonium polymers, polyethylene glycol (PEG) neutral polymers, co-polymers (containing neutral and cationic parts) and phosphonium end-grafted PEG polymers. All the aforementioned polymeric entities affect the rate of silicic acid polycondensation and also the silica particle growth. Synergistic combinations of cationic and anionic polymers create in situ supramolecular assemblies that can also affect the condensation of silicic acid. Possible mechanisms for their effect on the condensation reaction are presented, with an eye towards their relevance to the “Si pools,” from a bioinspired/biomimetic point of view.

Polyphosphoesters gained importance especially due to their use as flame retardants and as biocompatible and biodegradable materials for medicine and in the pharmaceutical industry. This paper presents the results obtained by our research group in the synthesis of polyphosphoesters by interfacial polycondensation. This reaction is rapid and irreversible polymerization at the interface between a phase containing one difunctional intermediate and another phase containing a complementary difunctional reactant. Different methods like liquid–liquid, vapor–liquid or solid<uni-2013;liquid were used in the synthesis of polyphosphates of polyphosphonates using aliphatic/aromatic phosphoric/phosphonic dichlorides and different diols. Aqueous NaOH, or tripotasium phosphate were used as bases. In almost all cases a catalyst is not needed.

Polymers exhibiting cyclic topology have attracted great interest over the past 30 years. Macrocycles or cyclopolymers with more than 20 repeating monomer units are considered exceptional candidates for thermoplastic engineering application due to unique properties in comparison to their linear analogues including large hydrodynamic radii and functional group density, heat resistance, good insulating ability and low intrinsic viscosity. Cyclic polymers are thus expected to exhibit improved physical and mechanical properties for certain applications due to the absence of end groups. Although synthetic challenges have historically limited research on cyclic polymers, recent developments in ruthenium catalyzed ring-expansion metathesis polymerization (REMP) have enabled the synthesis and the preliminary investigation of structure-property relationships of high molecular weight macrocycles. In REMP reactions the polymer formation is proposed to proceed through a transient macrocyclic complex in which both ends of the growing polymer chain remain attached to the Ru center. This article summarizes the recent discoveries on the field of REMP assisted cyclopolymer based material development.

Polysaccharides are a natural and renewable feed stock for synthesizing high performance macromolecular materials. However, their structure does not allow reaching all properties required for specific applications and chemical modifications are necessary to reach such objectives. Despite the use of natural polymers, the chemistry and processes employed are not environment-friendly due to the nature of chemicals, solvents or because the conventional chemical process are energy-consuming. On the other hand, microwave assisted processes were developed in organic chemistry since the 1980s and more recently for polymer chemistry (polymer formation and modification). Within the chemistry of natural polymers, the use of microwave irradiation has been exploited in the past two decades to alleviate limitations in the synthesis of graft modified polysaccharide materials. Microwave heating is described as more homogeneous, selective and efficient as compared to conventional heating resulting in faster reactions with fewer or no side products as example. Different results reported within the recent literature will be discussed considering the role of microwave irradiation and its consequence on the reaction parameters and properties of final materials. Grafting of polysaccharides, specific modification of polysaccharides or fibers particularly for preparing smart textiles or medical products as well as reactions of polysaccharides to valuable bio-platform molecule will be discussed.

Interpenetrating polymer network (IPN) hydrogels brought distinct benefits compared to single network hydrogels like more widely controllable physical properties, and (frequently) more efficient drug loading/release. However, IPN strategy is not sufficient to design hydrogels with enhanced mechanical properties required for regenerative medicine like replacement of natural cartilage or artificial cornea. Some of the novel techniques promoted last decade for the preparation of IPN hydrogels which fulfill these requirements are discussed in the review. Among them, “double network” strategy had a strong contribution in the development of a large variety of hydrogels with spectacular mechanical properties at water content up to 90 %. Using cryogelation in tandem with IPN strategy led to composite cryogels with high mechanical properties and high performances in separation processes of ionic species. Highly stretchable and extremely tough hydrogels have been obtained by combining a covalently cross-linked synthetic network with an ionically cross-linked alginate network. IPN hydrogels with tailored mesh size have been also reported.

A study on the microwave-assisted alcoholysis of diethyl phosphite with ethylene glycol revealed that after optimization of the conditions (molar ratio, temperature and time), the target “monomer,” (HOCH 2 CH 2 O) 2 P(O)H was formed in a proportion of 59 %, but with an incomplete conversion. The formation of the (HOCH 2 CH 2 O)(EtO)P(O)H and H(EtO)(O)POCH 2 CH 2 OP(O)(OEt)H by-products was, in most cases, inevitable. The alcoholysis with ethanolamine was more efficient and took place in a conversion of 100 % to afford H 2 NCH 2 CH 2 O) 2 P(O)H in a proportion of 85 %. An alkyl substituent on the N -atom prevented the alcoholysis.

In the present work a polymer with phosphonium pendant groups impregnated with crown ether (dibenzo-18-crown-6) and loaded with iron ions was investigated for arsenic removal through adsorption from aqueous solutions. The impregnated polymer was loaded with iron ions due to the high affinity of arsenic to it. The characterization of the surface modification of the obtained new adsorbent material was performed on the basis of energy dispersive X-ray analysis; scanning electron microscopy and Fourier transform infrared spectroscopy. The arsenic adsorption was investigated, including effect of pH, arsenic initial concentration, the shaking time and temperature. The effect of the pH was examined over the range 2–11. The adsorption of As(V) increases with pH increasing reaching a maximum at pH higher than 8. Equilibrium, kinetic and thermodynamic studies were carried out to study the adsorption performance of the obtained material in the removal process of arsenic from aqueous solutions. For the studied materials the equilibrium data closely fitted Langmuir model and was achieved a maximum adsorption capacity of 32.6 μg As(V)/g of material. The pseudo-second order kinetic model is suitable for describing the adsorption system. The obtained results show that the studied adsorbent can be used with efficiency in the arsenic removal from underground water even from low influent arsenic concentration solutions.

This work reports the adsorption of thallium and strontium from aqueous solutions onto styrene-divinylbenzene grafted with aminoethylaminomethyl groups which was impregnated with various ionic liquids [trihexyltetradecylphosphonium chloride ionic liquid – (Cyphos IL-101); 1-octyl-3-methylimidazolium tetrafluoroborate – (OmimBF 4 ) and 1-butyl-3-methylimidazolium hexafluorophosphate – (BmimPF 6 )]. The impregnation of the solid support with the studied ionic liquids was realized through ultrasonication method. The obtained impregnated materials have been subjected to Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX). Their adsorption performance in the removal process of thallium and strontium from aqueous solutions was studied as a function of the initial concentration of metal ions. Adsorption isotherms like Langmuir, Freundlich, Dubinin–Radushkevich (D–R) and Temkin were used to analyze the equilibrium data at different concentrations. The studied materials showed a better adsorption performance in the removal process of strontium ions compared to the adsorption performance obtained in case of thallium ions removal process. From the studied ionic liquids, (OmimBF4) presented the most efficient performance for the removal of the studied metal ions.

The objective of the study was to investigate sorption of simazine, atrazine, propazine and terbuthylazine on specific polymeric adsorbent and thereby evaluate the possibility of triazine-based herbicide removal from the aqueous solution. In order to obtain polymer adsorbent for triazines removal, the poly(divinylbenzene) was synthesized in radical polymerization using bead polymerization, and modified with maleic anhydride in Diels–Alder reaction with subsequent base hydrolysis. The porous material containing carboxyl groups was obtained. Experiments have been performed in single and multi-component mixtures of herbicide in the ppm concentration range. Introduction of carboxyl groups into polymer structure resulted in obtaining specific interactions, such as hydrogen bonds between modified poly(divinylbenzene) and triazines, therefore intensification of adsorption was observed. Calculated distribution coefficients of triazines ( K = 2600–35 100) testify to their effective removal from aqueous solutions on the studied adsorbent. Selective sorption of triazines is observed and explained in relation to the binding mechanism which involve hydrophobic interactions and hydrogen bonding. The effect of the adsorbate structure on the ability to form specific interactions with the tested adsorbent was investigated. The kinetic of sorption and the parameters of Langmuir and Freundlich isotherms for the studied systems were determined.

In the recent years, the adsorption capacities of synthetic polymeric adsorbents have been intensively studied due to their diversity in surface and porosity, physicochemical stability and the regeneration potentiality. In this study four synthetic polymers have been used as alternative adsorbent for the removal of two azo dyes from aqueous solutions. The effects of dye concentration, adsorbent nature, temperature, and pH of the solution onto the kinetics of the adsorption process were in detail investigated. With the increase in the initial concentration from 5 . 10 –5 to 1 . 10 –3 mol/L the amount of dye adsorbed increased, while the removal percentage decreased. The increase of the temperature (298–338 K) induced a positive effect on the adsorption indicating that the process is endothermic, and the increase of pH induced a decrease in removal percentage. The maximum dye removal percentage obtained was found to be up to 99 %. The experimental data were well correlated by the Sips adsorption model, and the results were applied for obtaining the equilibrium parameters.

Enzymatic incorporation of carbohydrate-derived monomer units into hydrophobic polyester backbones represents a promising alternative to obtain new biodegradable oligomers and polymers. Immobilized lipases are efficient biocatalysts for copolymerization of β-butyrolactone and δ-gluconolactone, but only a systematic optimization study was able to highlight the influence of the main reaction parameters on the polymerization degree and on the relative copolymer content of the product. Therefore, experimental design was employed for determination of the optimal ring-opening copolymerization conditions in solventless reaction systems, at temperatures up to 80 °C. The obtained products, cyclic and linear polyesters, have been characterized by FT-IR, MALDI-TOF MS, NMR, and TG analysis, demonstrating the incorporation of gluconolactone unit(s) into the hydrophobic backbone of the polyester and the formation of new bio-based products.

Two enzymes, laccase and peroxidase, were immobilized on chloromethylated styrene-divinylbenzene copolymers supports functionalized with phosphonates ((RO) 2 PO) or mixed ammonium and phosphonium groups (N + R 3 Cl – , P + Ph 3 Cl – ). Phosphonates groups and quaternary ammonium salts were grafted on the “gel-type” copolymer by Michaelis–Becker polymer analogue reaction. Mixed polymer-supported ammonium and phosphonium salts were obtained by transquaternization of the ammonium groups to phosphonium group. The degrees of functionalization for obtained polymers were relatively high ensuring a sufficient concentration of active centers per unit mass of the copolymer. The obtained materials were characterized by thermal analysis, FTIR spectroscopy and SEM microscopy. The effects of OR1 and R2 radicals from phosphonate and respectively ammonium groups, as well as those of glutaraldehyde utilization on the immobilization yield and the catalytic properties of the supported enzymes were indicated. The activity of enzymes increased after immobilization and high immobilization yield was obtained for all the samples. The higher interaction of enzymes with support was indicated for mixed ammonium and phosphonium functions. A higher catalytic activity was obtained for peroxidase in oxidation of phenol and laccase in oxidation of anisole. The low effect of glutaraldehyde on enzyme activity reveals the strong interaction of enzyme with the polymer support, respectively with the functional groups.

Immobilization of well-defined catalytic units onto insoluble support promises significant benefits, but frequently results in a reduced activity and selectivity of the heterogenized catalysts. Recently, we showed that introduction of a dendritic spacer between the support and the units could remedy the compromised activity and/or selectivity of heterogenized catalysts and, in particular, of the systems based on N-alkylated imidazoles. These catalysts exhibit an outstanding multivalency effect on the activity in the Baylis-Hillman reaction, while preserving very high chemoselectivity. In order to better understand this remarkable effect, we decided to synthesize and examine soluble analogues of the supported systems. These soluble catalysts display poor chemoselectivity, although it improves with the increase of the dendritic generation. Though the consumption of the limiting aldehyde reactant (conversion) displays the opposite trend, experiments demonstrated that the chemoselectivity is generation-dependent rather than conversion-dependent. A hydrophobic “pocket” effect was implicated as responsible for the differences between the polystyrene-bound and the soluble catalysts. An MS analysis of the crude reaction mixture revealed that the formation of multiple adducts, which incorporate several enone and several nitrobenzaldehyde fragments into a single molecular structure (as opposed to one-to-one stoichiometry of the Baylis-Hillman reaction), is responsible for the decline in the chemoselectivity.

The synthesis of two new inherently chiral calix[4]arenes (ICCs, 1 and 2 ), endowed with electron-rich concave surfaces, has been achieved through the desymmetrization of a lower rim distal-bridged oxacyclophane (OCP) macrocycle. The new highly emissive ICCs were resolved by chiral HPLC, and the enantiomeric nature of the isolated antipodes proved by electronic circular dichroism (CD). Using time-dependent density functional calculations of CD spectra, their absolute configurations were established. NMR studies with ( S )-Pirkle’s alcohol unequivocally showed that the host-guest interactions occur in the chiral pocket comprehending the calix-OCP exo cavities and the carbazole moieties.

Alpha-morpholine substituted poly(vinyl methyl ketone) (PVMK) was determined to undergo rapid self-crosslinking by short-term vacuuming (i.e., 30–60 min) or curing at 70–100 °C. The chemical transformations involved were monitored by TGA, DSC, FT-IR, 1 HNMR and solid-state 13 C NMR techniques. These experiments revealed an “unzipping-like” mechanism yielding multi conjugated enone structure via consecutive deamination by β-hydrogen elimination and simultaneous Diels–Alder cyclization resulting in crosslinking. This chemistry was exploited for generating Michael acceptor thin film coatings on silica nanoparticles, in which the silica was impregnated with morpholine substituted poly(vinyl methyl ketone) and simply heated at 100 °C. The dense polyene functional films so formed were demonstrated to add amines and thiols at room temperature. The resulting silica nanoparticles were employed to form homogenous composite films using poly(butyl acrylate- stat -methylmethacrylate) as carrier matrix. Morpholine substituted poly(vinyl methyl ketone) (MSP) seems to be generally applicable for surface modification of different inorganic surfaces with organics.

The reactions of 2-cyano-3-ferrocenylacrylonitrile with malononitrile in a EtOH/H 2 O or MeOH/H 2 O medium in the presence of Na 2 CO 3 afforded 6-alkoxy-2-amino-4-ferrocenylpyridine-3,5-dicarbonitriles 3a , b (multi-component condensation), 6-alkoxy-2-amino-4-ferrocenyl-3-ferrocenylmethyl-3,4-dihydropyridine-3,5-dicarbonitriles 4a , b (multi-component cyclodimerization) and Na + polymeric complexes: {[Na + (2-ferrocenyl(tetracyano)propenyl) – L] ∞ 5a,b and [Na + (2-amino-3,5-dicyano-4-ferrocenyl-6-pyridyl-dicyanomethyl) – L] ∞ 6a,b , where L = ethanol, methanol. Complexes with L = acetonitrile, dimethylformamide, acetone, ethyl acetate were prepared by recrystallization. The structures of the compounds 3b , 4b and Na + polymeric complexes were established by the spectroscopic data and X-ray diffraction analysis. Two compounds 3a and 4a were tested in vitro against six human tumor cell lines U-251, PC-3, K-562, HCT-15, MCF-7 and SKLU-1 to assess their in vitro antitumor activity. The results suggest biological specificity towards PC-3, K-562 and HCT-15 cells for compound 3a , and towards PC-3 cell for compound 4a at doses of 50 μM, which are lower than cis -platin.

Improved ionic conductivity of solid polymer electrolytes (SPE) was achieved by adding polyaniline (PANI) in membrane formulation. SPE composite membranes contain: tris(4-hidroxybutylacrylate)-phosphate, polyphosphoester, lithium salts and small amount of PANI. The conductivity of membranes increases with PANI content and above a certain amount it decreases. The variation of the conductivity vs temperature is linear, characteristic for a thermally activated process. The activation energy for polymer matrix without PANI is 0.30 eV and 0.26 eV for polymer matrix with PANI. Conductivity enhancement in the composite polymer matrix is caused by the presence of PANI due to the increase in the concentration of free ions. PANI decreases the salt aggregation and as a consequence, the concentration of free ions was increased by improving dispersion of the lithium salt in membranes.

Two styrene-6.7 % divinylbenzene copolymers functionalized with aminophosphonate groups and phosphonic acid groups by means of “one-pot” reactions were evaluated for gaseous mercury removal. The results were compared with those obtained using a commercial activated carbon. These materials exhibit a significant capacity for mercury oxidation (13–25 %) with low mercury capture (9–30 μg g –1 ). The mercury retention capacity was observed to decrease when acid gases are present in the gas atmosphere. The highest retention capacity corresponded to the highest oxidation ratio and was obtained using the AMINOPHOS sample. These results suggest a mercury oxidation and a subsequent chemical adsorption mechanism in which the amino groups play a role in mercury capture.

Hydrodynamic properties developed in a series of mixtures, obtained from quaternized polysulfone and cellulose acetate phthalate or polyvinyl alcohol in N-methyl-2-pyrrolidone, were evaluated by viscometric investigations. Theoretical and experimental aspects concerning the viscometric data for binary polymer/solvent and ternary polymer/polymer/solvent mixtures have been discussed by the new Wolf model, as a function of the charge density of polyion, structural peculiarity of polymers, and polymer mixture composition. Intrinsic viscosity and also the hydrodynamic parameters obtained by the Wolf method offer new information on the competition between different types of interactions manifested in ternary polymer/polymer/solvent systems. The complex dependence of viscosity on polymer composition is influenced by conformational changes of constituent polymers from the mixture, as well as by cumulative effects of electrostatic interactions, hydrogen bonding or association phenomena. Additionally, the above-mentioned interactions indicate the compatibility of these polymers over a large composition domain. This study investigates the hydrodynamic functions from the perspective of some newly-issued theories and analyzes the choice of optimal polymer mixtures compositions for specific applications in biomedical domains.