Synthesis and characterization of highly functionalized polymers based on N,N,N′,N′-tetraalkyl-4,4′-diaminostilbene and maleic anhydride

Novel, highly functionalized rod-like copolymers have been synthesized by alternating copolymerization of N,N,N′,N′-tetraalkyl-4,4′-diaminostilbenes (TDASs) with maleic anhydride. These unique copolymers have been characterized by SEC, DSC and TGA. The solubility of these copolymers in organic solvents is strongly dependent on the length of the alkyl chains on the amino groups and the solubility in aqueous media is pH dependent. Light scattering studies indicate that the conformation of the polymer backbone does not change upon increasing temperature or introducing charges to the amino groups. High chain rigidity is further corroborated by the high T_g of the polymers. There is no observed glass transition below 280 °C. The light scattering and thermal results are indicative of a rod-like backbone structure.     

Electrochemically and electrochromically stable polyimides bearing tert-butyl-blocked N,N,N′,N′-tetraphenyl-1,4-phenylenediamine units

A new class of electrochemically active polyimides with di-tert-butyl-substituted N,N,N′,N′-tetraphenyl-1,4-phenylenediamine units was prepared from N,N-bis(4-aminophenyl)-N′,N′-bis(4-tert-butylphenyl)-1,4-phenylenediamine and various aromatic tetracarboxylic dianhydrides via a conventional two-step procedure that included a ring-opening polyaddition to give poly(amic acid)s, followed by chemical or thermal cyclodehydration. Most of the polyimides are readily soluble in many organic solvents and can be solution-cast into tough and amorphous films. They had useful levels of thermal stability, with relatively high glass-transition temperatures (276-334 °C), 10% weight-loss temperatures in excess of 500 °C, and char yields at 800 °C in nitrogen higher than 60%. Cyclic voltammograms of the polyimide films cast on the indium-tin oxide (ITO)-coated glass substrate exhibited two reversible oxidation redox couples at 0.70-0.74 V and 1.05-1.08 V vs. Ag/AgCl in acetonitrile solution. The polyimide films revealed excellent stability of electrochromic characteristics, with a color change from colorless or pale yellowish neutral form to green and blue oxidized forms at applied potentials ranging from 0.0 to 1.3 V. These anodically coloring polymeric materials exhibited high optical contrast of percentage transmittance change (Δ%T) up to 44% at 413 nm and 43% at 890 nm for the green coloration, and 98% at 681 nm for the blue coloration. After over 50 cyclic switches, the polymer films still exhibited good redox and electrochromic stability.     

Phase behavior, nucleation and optical properties of the binary system isotactic polypropylene/N,N′,N″-tris-isopentyl-1,3,5-benzene-tricarboxamide

The phase behavior of the binary system consisting of isotactic polypropylene (i-PP) and N,N′,N″-tris-isopentyl-1,3,5-benzene-tricarboxamide (1)—a selected member of a class of novel, versatile ‘designer’ nucleating/clarifying agents—was investigated over the entire additive concentration range by means of differential scanning calorimetry (DSC) and optical microscopy. Experimental phase diagrams were constructed from data obtained in melting and crystallization studies, and a simple monotectic is advanced, very similar to the previously studied binary system i-PP/1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS). In contrast to the latter, the crystallization temperature in the present system i-PP/1 was found to increase to ∼120 °C already at the lowest additive concentration employed and remained constant at further increasing additive concentration. Liquid-liquid phase separation was observed at elevated temperatures for i-PP/1 mixtures comprising more than ∼2 wt% of 1. A study on the optical properties of the i-PP/1 system revealed that the values for haze and clarity of injection-molded plaques progressively decreased and increased, respectively, in the concentration range up to 0.15 wt%. An intermediate region of fairly concentration-independent optical properties was found between 0.15 and 1 wt%, followed by a rapid increase in haze at concentrations exceeding 2 wt%.     

Large macro-dipoles generated in a supramolecular polymer of N,N′,N″-tris(3,7-dimethyloctyl)benzene-1,3,5-tricarboxamide in n-decane

A supramolecular polymer formed by N,N′,N″-tris(3,7-dimethyloctyl)benzene-1,3,5-tricarboxamide (DO₃B) in n-decane (C₁₀) possesses large macro-dipoles naturally generated by three-fold inter-molecular hydrogen bonding aligned along its helical columnar structure connected by defective portions, which are DO₃B molecules containing failure in the hydrogen bond formation, in the order of head to tail arrangement without dipole inversion like type-A polymers.     

Synthesis and characterisation of stimuli-responsive poly(N,N′-diethylacrylamide) hydrogels

Stimuli-responsive poly(N,N′-diethylacrylamide) gels were prepared by free radical polymerisation in aqueous solution, using N,N-methylenebisacrylamide as crosslinking agent. The gels were compared with the corresponding poly(N-isopropylacrylamide)-based gels. In particular, the swelling ratio of both gel types including the effect of the crosslinker content, their swelling and deswelling kinetics, their permeability and finally their drug (insulin) storage and controlled release ability were compared. In spite of the similarity in the monomer/crosslinker ratio, the deswelling kinetics and the critical temperatures (ca. 30-32 °C in pure water), some differences could be observed. Compared to poly(N-isopropylacrylamide)-based gels, poly(N,N′-diethylacrylamide)-based gels show a broader phase transition temperature interval, a more pronounced dependency of the swelling ratio on the crosslinker content, slower reswelling kinetics, a higher ingress percentage for dextran standards ranging from 5 to 70 kD, but lower ingress percentages for proteins (BSA, insulin) and much faster drug (insulin) release kinetics. While a non-linear release kinetic was observed in the case of the poly(N-isopropylacraylamide)-based gels both in water and in PBS (phosphate buffered saline), this was not the case for the poly(N,N′-diethylacrylamide)-based gels.     

A new cationic surfactant N,N′-dimethyl-N-acryloyloxyundecyl piperazinium bromide and its pH-sensitive gels by microemulsion polymerisation

A piperazine-based cationic surfactant, N,N′-dimethyl-N-acryloyloxyundecyl piperazinium bromide (DAOUPB) was synthesised by a two-step procedure. The monomer was polymerised in two new microemulsion systems: (i) DAOUPB/water/methyl methacrylate (MMA):hydroxyethylmethacrylate (HEMA) and (ii) DAOUPB/water/acrylonitrile with ethyleneglycol dimethacrylate (EGDMA) as the crosslinking agent. Transparent solid polymeric materials were obtained by photo-initiated polymerisation of some of these microemulsion compositions. Most of the bicontinuous microemulsions investigated gelled within 10 min resulting in transparent solid polymers. The electron micrographs of the polymers obtained from microemulsion compositions containing MMA:HEMA did not show any micropores, while those obtained using acrylonitrile revealed the existence of open-cell type micropores and also of the bicontinuous nature of the system. The width of the bicontinuous structure (micropores) was about 33 nm in the dry state, with long and winding channels of random distribution. The swelling of the gels was highly sensitive to pH.     

Esterification of ethylene-vinyl alcohol copolymers in homogeneous phase using N,N′-dimethylpropyleneurea as solvent

Ethylene-vinyl alcohol copolymers (EVAL) were esterified with 3,5-dinitrobenzoyl chloride using the cycled urea N,N′-dimethylpropyleneurea (1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone) (DMPU) as the solvent. Ethylene-vinyl alcohol-vinyl-3,5-dinitrobenzoate terpolymers (EVALVDNB) and ethylene-vinyl-3,5-dinitrobenzoate copolymers (EVDNB) were obtained. Both EVAL copolymers (6-73 mol% VAL) and esterified polymers, EVDNB, and EVALVDNB dissolve in DMPU. The substitution may become total under the experimental conditions. The degree of transformation was determined by ¹H NMR. EVDNB copolymers were characterised by IR spectroscopy and ¹H and ¹³C NMR. Thermal properties were studied by DSC. The glass transition temperature of the EVDNB copolymers having a low VDNB content (up to 14 mol%) is roughly constant, whereas above 50 mol% increases. Melting temperature decreases as the VDNB content is increased, owing to the fact that the VDNB groups are excluded from the polyethylene crystal lattice.     

Synthesis and photolytic properties of 1,5-di-N,N′-dialkylaminoanthraquinones containing acryloyl groups

Several l,5-di-N,N′-dialkyaminoanthraquinones containing acryloyl groups were synthesized and characterized by Fourier transform infrared (FTIR) and ¹H NMR spectroscopy. The photophysical and photoinduction properties of these anthraquinone derivatives were examined in solution, in combination with free radical producing agents such as hexa-aryl-bis-imidazoles (HABI). When UV–vis absorption and fluorescence spectroscopy were employed to investigate the photophysical process, results showed that the photobleaching rate of N-alkylaminoanthraquinones containing an acrylate group and HABI was much faster than the acrylate group-free N-alkylaminoanthraquinone/HABI combination. N-alkylaminoanthraquinone induced polymerization of 2-phenoxyethyl acrylate (POEA)/N-vinyl carbazole (NVC)/cellulose acetate butyrate (CAB) mixtures was studied using real-time infrared spectroscopy (RTIR). It was found that the rate of polymerization was faster if the acryloyl groups were connected to the N,N′-dialkylaminoanthraquinone structure and that 1,5-di-N,N′-dialkylaminoanthraquinone containing acryloyl groups was more sensitive to visible light system.     

A new stilbazolium salt with perfectly aligned chromophores for second-order nonlinear optics: 4-N,N-Dimethylamino-4′-N′-methyl-stilbazolium 3-carboxy-4-hydroxybenzenesulfonate

A new organic nonlinear optical crystal 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium 3-carboxy-4-hydroxybenzenesulfonate (DSCHS) has been developed with very promising properties for quadratic nonlinear optical applications. DSCHS single crystals with non-centrosymmetric structure have been obtained from aqueous methanol solution. X-ray crystallographic analysis revealed that the crystal structure of DSCHS is triclinic P1 with the chromophores aligned perfectly parallel, leading to the maximum possible order parameter <cos³θ> = 1 in the crystalline state, which is optimal for electro-optics, THz-wave generation and field detection applications. Kurtz powder test has shown that DSCHS exhibits a very large second-order optical nonlinearity, with a 30 percent higher second-harmonic signal than the well-known organic nonlinear optical crystal 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST).     

Adsorption of N,N′-dimethylthiourea at a mercury/aqueous solution of NaClO4 interface; dependence on the supporting electrolyte concentration

Adsorption of N,N′-dimethylthiourea (DMTU) on mercury electrode from 0.1, 1 and 5 M NaClO₄ was studied as the function of electrode charge density and adsorbate bulk concentration. In the study, the experimental data obtained from the measurements of differential capacity of double layer were used, the measurements of zero charge potential and surface tension at the zero charge potential. In each system studied the values of the relative surface excess increase with an increase of the concentration of N,N′-dimethylthiourea and NaClO₄. The adsorption parameters were obtained from the Frumkin, virial and modified Flory-Huggins isotherms. It was found that the values of free adsorption energy, interactions constants and integral capacity depends on the supporting electrolyte concentration. The strength of the surface bond formed between N,N′-dimethylthiourea and the electrode surface and the influence of water present on the electrode surface in the obtained results of calculations were discussed.     

Redox and catalytic properties of new polypyrrole modified electrodes functionalized by [Ru(bpea)(bpy)H2O] complexes; bpea=N,N′-bis(2-pyridylmethyl)ethylamine, bpy=2,2′-bipyridine

New ruthenium(II) complexes containing one or two pyrrole-functionalized polypyridylic ligands have been prepared in order to study their electrochemical behaviour in heterogeneous phase, after anodic polymerization from CH₂Cl₂ solution on an electrode surface. Complexes containing one pyrrole unit have general formula [Ru(bpea-pyr)(bpy)(L)]²⁺ (bpea-pyr=N-[3-bis(2-pyridylmethyl)aminopropyl]pyrrole, bpy=2,2′-bipyridine, L=Cl, complex 3, or L=H₂O, complex 1), whereas compounds having two pyrrole units correspond to [Ru(bpea-pyr)(bpy-pyr)(L)]²⁺ (bpy-pyr=4-methyl-4′-pyrrolylbutyl-2,2′-bipyridine, L=Cl, complex 4, or L=H₂O, complex 2). Upon oxidative polymerization, all complexes form highly stable polypyrrolic films on a graphite disk electrode surface. An electrode modified with complex 2 polypyrrole coating film, C/poly-2, has been tested as heterogeneous catalyst for the oxidation of benzyl alcohol, showing a remarkably high efficiency and notably improving the results obtained with analogous complexes in homogeneous phase.     

One-step synthesis of pegylated cationic nanogels of poly(N,N′-dimethylaminoethyl methacrylate) in aqueous solution via self-stabilizing micelles using an amphiphilic macroRAFT agent

Cationic nanogels of Pegylated poly(N,N′-Dimethylaminoethyl methacrylate) (PEG-PDAEMA) have been synthesized in aqueous solution by a one-step surfactant-free reversible addition-fragmentation transfer (RAFT) process. A Pegylated amphiphilic macroRAFT agent (mPEG₅₅₀-TTC) with a hydrophobic dodecyl chain was utilized to stabilize the micelles and control the polymerization and crosslinking of DMAEMA in aqueous solution. ¹H NMR, GPC, Elemental analysis, Dynamic light scattering (DLS), Zeta potential and Atomic force microscopy (AFM) measurements confirmed the formation of the cationic nanogels in size of about 20 nm with a narrow distribution. It also revealed that the concentration of monomer and the kinds of crosslinker are the key factors to control the formation of nanogel. This cationic nanogel has potential application in gene delivery.     

Fine tuning of frontier orbital energy levels in dithieno[3,2-b:2′,3′-d]silole-based copolymers based on the substituent effect of phenyl pendants

A series of dithieno[3,2-b:2′,3′-d]silole-based π-conjugated copolymers containing thieno[3,4-c]pyrrole-4,6-dione or thieno[3,4-b]thiophene units bearing 4-substituted phenyl pendants were synthesized and their thermal stability, optical properties and frontier orbital energy levels were systematically investigated. The introduction of electron-withdrawing substituents on the phenyl rings lowered their frontier orbital energy levels without deteriorating their thermal and optical properties. By replacing an electron-donating methoxy group with an electron-withdrawing trifluoromethyl group, both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital energy levels of the polymers were deepened by more than 0.3 eV. A relatively linear relationship was observed between the HOMO energy levels and the Hammett substituent constants.     

Adsorption and electrooxidation of ethylene glycol and its C2 oxidation products on a carbon-supported Pt catalyst: A quantitative DEMS study

Aiming at a better understanding of ethylene glycol oxidation, the adsorption and oxidation of ethylene glycol and its incomplete C₂ oxidation products glycol aldehyde, glyoxal, glycolic acid, glyoxylic acid and oxalic acid on carbon supported Pt catalysts were investigated by on-line differential electrochemical mass spectrometry (DEMS) under continuous electrolyte flow. This includes adsorption transients at different, constant potentials, oxidative removal (‘stripping’) of the resulting adsorbates, and potentiodynamic bulk oxidation/reduction of the respective molecules. The data show a pronounced influence of the different functional groups on the adsorption and oxidation characteristics, with hydroxyl and carboxylic functions resulting in lower adsorption rates and pronounced potential effects, while aldehyde functions lead to high adsorption rates at all potentials. The potential effects in the adsorption rate are mainly ascribed to surface blocking by H_upd species. For aldehydes and acids, CO₂ formation occurs already at potentials below the onset of OH_ad formation, which is ascribed to the decomposition of the carboxylic group or of the diol groups of hydrated aldehydes. The contributions of different reaction pathways, including: (i) ‘direct’ oxidation to CO₂, (ii) indirect oxidation to CO₂ via formation and further oxidation of CO_ad, and (iii) incomplete oxidation to more highly oxidized C₂ species, with the possibility of their further reaction via re-adsorption and reaction along (i)–(iii), are discussed.     

Thermo- and pH-sensitive dendrimer derivatives with a shell of poly(N,N-dimethylaminoethyl methacrylate) and study of their controlled drug release behavior

Novel dendrimer derivatives combining the temperature- and pH-sensitivities are synthesized. At first, polyamidoamine (PAMAM) dendrimers with generations 1-5 are synthesized by the reaction of ethylenediamine with methyl acrylate, and then the dendrimers are acylated by chloroacetyl chloride to obtain PAMAM-Cl, which can act as a macroinitiator for further synthesizing functional dendrimers. For fulfilling this goal, the polymers consisting of a dendritic PAMAM core and poly(N,N-dimethylaminoethyl methacrylate) (PDMA) shell are synthesized by atom transfer radical polymerization (ATRP). Their macromolecular structures are characterized by FTIR, ¹H NMR, DSC and particle size analyses, and their aqueous solutions are inspected by UV spectroscopy for understanding their thermo- and pH-sensitivities. The results show that novel dendrimer derivatives exhibit clearly thermo- and pH-respondings in accordance with the change of the environment. Using chlorambucil (CLB) as a model drug, the behaviors of the controlled drug release from polymers with different average graft length of PDMA are studied. The results indicate that the rate of the drug release can be effectively controlled by the pH value.     

Cellulose in lithium chloride/N,N-dimethylacetamide, optimisation of a dissolution method using paper substrates and stability of the solutions

Activation and dissolution in lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) of cellulose from paper substrates are studied. The importance of the multiple parameters involved such as salt concentration, sample source and preparation is shown in a literature review. The experiments are carried out in order to perfect the method of activation and dissolution of paper containing different kinds of additives, typically found in historic papers. The suitability and efficiency obtained in the different trials are evaluated. The final procedure involves the activation by solvent exchange, with a water/methanol/DMAc sequence, followed by dissolution in 8% LiCl/DMAc at 4 °C. A study of the stability of the cellulose solutions in the experimental conditions showed that no degradation nor aggregation occurred during the solvation process and even after several months and confirmed the non-aggressiveness of LiCl/DMAc.     

Hydrolytic processes and condensation reactions in the cellulose solvent system N,N-dimethylacetamide/lithium chloride. Part 2: degradation of cellulose

Certain cellulose samples, especially those of higher molecular weight, are initially insoluble in N,N-dimethylacetamide (DMAc, 1)/lithium chloride, which is a very common solvent system for cellulosic materials. According to a common protocol, heating or refluxing these samples in DMAc, or in DMAc containing dissolved LiCl, represents one of several so-called ‘activation’ procedures, which are aimed at facilitating subsequent dissolution. In the present work, it is shown that the improved solubility achieved by this method is not only caused by a better activation or improved accessibility of the pulp, but also by a progressing degradation of the cellulosic material (DP loss).The degradation of cellulose in DMAc or DMAc/LiCl is due to two separate chemical processes. The first one, involving N,N-dimethylacetoacetamide (2) which is the primary condensation product of DMAc, causes a slow degradation by thermal endwise peeling. The glucose units peeled off the reducing end are released as furan structures (3). The mechanism appears to be a thermal cleavage of the glycosidic bond, which becomes quite selective towards the proximal anhydroglucose unit by a neighbor group-assisted effect according to quantum-chemical calculations. Due to its stepwise and thus slow mechanism, this pathway contributes only insignificantly to the overall cellulose degradation.The second degradation mechanism causes random chain cleavage and thus pronounced and rather fast changes in the molecular weight distribution. It involves N,N-dimethylketeniminium ions (5), whose presence in DMAc/LiCl at temperatures above 80 °C—the coalescence temperature of DMAc as determined by dynamic NMR—was unambiguously demonstrated by specific trapping in a thermal [2+2]-cycloaddition with lipophilic olefins. The keteniminium ion is an extremely reactive electrophile, which is able to directly cleave glycosidic bonds. The detrimental effect of this intermediate on the integrity of cellulosic pulps was confirmed by addition of an external degrading agent of the keteniminium type. Also the precursor compound, a ketene aminal, was confirmed to be present in heated DMAc or DMAc/LiCl by trapping with allyl alcohol in a spontaneous Claisen-type rearrangement.     

The reaction between Pt- and Pd-cis di-chloro complexes and 4,4′-diethynylbiphenyl: synthesis and characterisation of a ‘zigzag’ metal/poly-yne polymer

The synthesis of poly-yne polymers containing transition metals inserted in the main chain has been attempted by reacting a dialkyne molecule, 4,4′-diethynylbiphenyl (or DEBP), with [PtCl₂(dppe)] and [PdCl₂(dppe)], the platinum- and palladium-cis square-planar di-chlorine complexes containing diphenylphosphine ethane (dppe) as bidentate ligand. The aim of this work was to obtain organometallic polymers ([Pt(dppe)DEBP]_n and [Pd(dppe)DEBP]_n, respectively) having an all-cis ‘zigzag’ structure, by formation of a σ-acetylide bond between the transition metal complexes and the dialkyne molecule. When [PtCl₂(dppe)] was reacted with DEBP, the formation of a chlorine-terminated [Pt(dppe)DEBP]_n oligomer was evidenced; in the reaction involving the Pd(II) complex, on the other hand, [PdCl₂(dppe)] seems to catalyse the polymerisation of DEBP via opening of the triple bond, producing a poly-DEBP polymer containing Pd(II) atoms inserted in the main chain.     

Poly(N‐vinylpyrrolidone‐co‐2‐acrylamido‐2‐methylpropanesulfonate sodium): Synthesis,characterization, and its potential application for the removal of metal ions from aqueous solution

In the current study, poly(N‐vinylpyrrolidone‐co‐2‐acrylamido‐2‐methylpropanesulfonate sodium), poly(VP‐co‐AMPS), was prepared and used for the removal of Cu²⁺, Cd²⁺, and Ni²⁺ ions via a polymer‐enhanced ultrafiltration (PEUF) technique. The copolymer was synthesized by radical polymerization in an aqueous medium with a comonomer feed composition of 50:50 mol %. The molecular structure of the copolymer was elucidated by ATR‐FTIR and ¹H NMR spectroscopy, and the average molecular weight was obtained by GPC. The copolymer composition was determined to be 0.42 for VP and 0.58 for AMPS by ¹H NMR spectroscopy. The copolymer and homopolymers exhibited different retention properties for the metal ions. PAMPS exhibited a high retention capacity for all of the metal ions at both pH values studied. PVP exhibited selectivity for nickel ions. Poly(VP‐co‐AMPS) exhibited a lower retention capacity compared to PAMPS. However, for poly(VP‐co‐AMPS), selectivity for nickel ions was observed, and the retention of copper and cadmium ions increased compared to PVP. The homopolymer mixture containing PAMPS and PVP was inefficient for the retention of the studied metal ions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41272.     

Synthesis and characterization of per-substituted spermine-bridged cyclophosphazene derivatives: the first example of syn/anti conformational polymorphism in a bridged cyclophosphazene

The synthesis and characterization of a series of per-substituted spermine-bridged cyclophosphazene derivatives are reported based on the known compound [N₃P₃X₄(NHCH₂CH₂CH₂N)CH₂CH₂]₂, (1a) (where X = Cl), to give a number of new compounds (1b–1h) in which X = OPh, [spiro-O(CH₂)₃O]_0.5, OCH₂CF₃, NHPh, NC₄H₈, Ph and NHBu^t, respectively. Two synthetic routes were utilized: (i) using the chloro-precursor 1a in nucleophilic substitution reactions with a variety of anionic and neutral nucleophiles to give compounds 1b–1f and (ii) reaction of spermine with the appropriate di-gem tetrasubstituted cyclophosphazene to give compounds 1g and 1h. Bridged compounds such as 1a–1h may exist as syn or anti conformers in the solid state and the first example of syn and anti conformational polymorphism is reported for a bridged cyclophosphazene, viz. for compound 1a.