Emil C. Buruiana

Synthesis and properties of some new polyazomethine-urethanes

Abstract Two new bisazomethine diols were prepared from terephthalaldehyde and aromatic or aliphatic aminoalcohols. The structure of the diols with bisazomethine moieties was confirmed by 1H-NMR, IR, UV spectroscopy and elemental analysis. Bisazomethine aliphatic diol exhibited a smectic phase that has been identified by means of polarizing microscopy and differential scanning calorimetry. By using these diols as partners in polyaddition reaction between poly(tetramethylene oxide)diol of 2000 average molecular weight, tolylene-2,4-diisocyanate (as 2,4- and 2,6-TDI, 80:20 v/v isomers mixture) and bisazomethine diol (1:3:2 molar ratio), two polyazomethine-urethanes were synthesized. Polyazomethine-urethanes with a higher concentration of poly-Schiffs base units were also obtained by reacting the above bisazomethine diols with the same diisocyanate (1:1 molar ratio). All polymers were characterized by viscometry, elemental analysis, IR, UV, 1H-NMR spectroscopy and TGA techniques.

Synthesis and characterization of some polyurethane cationomers with photochromic azoaromatic groups

Polyurethane cationomers based on polytetramethylene oxide, 4,4 0 -dibenzyldiisocyanate and N,N 0 -bis(b-hydroxyethyl)piperazine quaternized with methyl iodide were prepared. Using an ionic exchange reaction between this polycation and 3( p-oxyazobenzene)-propanesulfonic acid sodium salt, two azo-cationomers bearing chromophoric groups as counterions of ammonium quaternary structure were reported. The photochromic behavior of the above mentioned polycations in polymer solution as well as in thin films exposed to UV irradiation was discussed by comparison with other polycations having an azo dye (methyl orange) in the same hard segment. The increase of azo photochromic group concentration into polymer chains leads to a decrease in the isomerization rate. ” 2000 Elsevier Science Ltd. All rights reserved.

Synthesis of polyetherurethane cationomers with anthraquinone structure

Abstract An anthraquinone monomer, 1,4-bis-(β)-iodopropionyloxy)-9,10-anthraquinone was obtained by the condensation of 1,4-dihydroxy-9,10-anthraquinone with β-chloropropionyl-chloride, followed by an exchange reaction with potassium iodide in the presence of acetone. This derivative was used to synthesize polyetherurethane cationomers by two-step Menschutkin reaction. The resulting ionenes had ammonium quaternary groups content between 98.8 and 149.6 meq/100 g polymer and the quantity of anthraquinone units in polymeric chains was between 29.8 and 45.2 wt.% polymer, respectively. The tensile and thermal properties are similar to other elastomeric polyurethanes.These anthraquinone polyurethane colorants could be useful for coloring a wide variety of products such as fibers, films, coatings, paints or inks.

Novel Thermally-Reversible Epoxy-Urethane Networks

Thermally-reversible epoxy-urethane networks are prepared by the reaction of diamines and diepoxy monomers containing two Diels–Alder adducts. The diepoxy compounds are formed via a Diels–Alder reaction between two epoxy-containing furans and bismaleimides having urethane moieties. The urethanebismaleimides were obtained by the reaction of 4-maleimidophenylisocyanate with poly(tetrahydrofuran) diols with M n = 650, 1000 and 1450. The epoxy-urethane networks display two glass transition temperatures in the range of –70 and –50°C for the soft segment and 81–84°C for the hard segment. At temperatures exceeding 116°C the retro Diels–Alder reaction occurs, which leads to a significant loss in modulus.

Photopolymerization experiments and properties of some urethane/urea methacrylates tested in dental composites

Hydrophobic silyl-urea/urethane methacrylates (UHM-1, UHM-2) and a modified BisGMA derivative (BisGMA-UMA) were synthesized and used as photopolymerizable co-monomers in the preparation of dental composites, besides other urethane dimethacrylates containing oligoethylene oxide segments and carboxylic groups. The homo- and copolymerization behaviour of the synthesized monomers were investigated by FTIR spectroscopy using camphorquinone (CQ) and 4-(dimethylamino)-phenylacetic acid (DMPheAA) as a photoinitiating system, as well as by photo-DSC. The first hybrid monomethacrylate, N-(methacryloyloxyethyl-N’-diethoxymethylsilylpropyl)-urea showed the highest value for the maximum polymerization rate (0.117 s−1) followed by BisGMA analogue (0.085 s−1) and N-methacryloyloxyethyl-N’-bis(triethoxysilylpropylcarbamoyloxyethyl)-urea (0.069 s−1), whereas the degree of conversion decreased from 75.1% (UHM-2) to 41.6% (BisGMA-UMA). Polymerization shrinkage (PS) measured by picnometry for the mixture BisGMA-UMA/TEGDMA (4.78 vol.%) was lower than that exhibited of the control organic matrix BisGMA/TEGDMA (6.85 vol.%) at the same dilution. The addition of one of the obtained monomers into a mixture based on urethane oligomers led to a polymerization shrinkage varying between 8.33 and 6.97 vol.%. A number of properties of the composites formulated with our urethane methacrylates, a urethane dimethacrylate, BisGMA, and glass filler (Zr/Sr glass, quartz, and diatomite) were also determined including the surface damage caused by the Vickers indentation to establish their utility in dentistry.

Polycinnamates and Block Co-polymers Prepared by Atom Transfer Radical Polymerization and Microwave Irradiation

Homo-polymers of 2-cinnamoyloxyethyl methacrylate (PCEMA) and block co-polymers with methyl-methacrylate (MMA) synthesized via copper(I)bromide/pentamethyldiethylentriamine-mediated atom transfer polymerization (ATRP) and microwave irradiation, under homo(co)polymerization conditions, are reported. Method 1 led to homo-polymers with relatively low molecular weight (PCEMA-1: 5100; PCEMA-2: 25 000), while the second method offered polymer of 100 000 average molecular weight (PCEMA-3), the polymerization being completed within 60 min. Two di-block co-polymers, poly(2-cinnamoyloxyethyl methacrylate-block-poly(methyl methacrylate)) ((PCEMA-b-PMMA)-1, (PCEMA-b-PMMA)-2) with 0.33 and, respectively, 0.5 molar fraction of photo-cross-linkable PCEMA were also prepared and utilized for this study. Subsequent gel-permeation chromatography (GPC) measurements on block co-polymers have indicated molecular weights of 24 000 and 45 700, respectively. In addition, structural characteristics for all photo-polymers were determined by FT-IR, 1H-NMR, UV-Vis spectroscopy, AFM and SEM/ESEM measurements. Photochemistry in thin polymeric films suggested that UV irradiation is accompanied by an insolubilization of the film caused by the transformation of cinnamate moieties and the formation of intermolecular cross-links, with important effects on the morphology. As expected, it was found that by electrospinning the above photo-polymers produced electrospun fibers of small diameter.

Synthesis and characterization of novel polyurethane cationomers with dipeptide sequences and alkylammonium groups

A synthetic approach to polyurethane cationomers containing S-pyroglutamyl-S-glutamic acid dipeptide (S-PyGlu-S-Glu) and alkylammonium groups is presented. Two segmented polycations, based on polycaprolactone diol, isophorone diisocyanate and dipeptide together with N-methyldiethanolamine, subsequently quaternized with dodecylbromide, were synthesized and characterized by IR spectroscopy, GPC, DSC and reduced viscosity measurements. Such polycations exhibited excellent film forming properties and their soft elastomeric nature provides adequate physical properties. Optical rotation varying from +10 (monomer) to -15 (polycation) could be associated with a configuration pertubation through the asymmetric carbon atoms of glutamic residues. Susceptibility of the cationic surface to heparinization and then to blood-polymer interaction suggested an anticoagulant activity of the heparinized polymeric films.

Free-radical ring-opening polymerization of 2-(o-chlorophenyl)-4-methylene-1,3-dioxolane

Abstract2-(o-chlorophenyl)-4-methylene-1,3-dioxolane was synthesized and polymerized in presence of AIBN or by use of benzoin methyl ether as photosensitizer. Based on the analysis of the resulting polymers, a polymerization mechanism was proposed.

Polyurethane cationomers containing anthryl and nitroaromatic chromophores

Polyurethane cationomers bearing anthryl and o, p-nitroaromatic photoactive groups have been synthesized. Their photochemical behavior was studied by electronic absorption spectroscopy and viscosity measurements. It was found that the photosensitivity of the polyurethane cationomers is enhanced by incorporation of the nitroaromatic chromophore.

Elastomeric azo-polyurethanes containing fluorescent pyrene and their photo activity

Two bichromophoric polyetherurethanes with a small number of pyrene rings on the quaternary ammonium groups and photoisomerizable azobenzene chromophore attached to the soft (AzPUC-Py1) or hard segment (AzPUC-Py2) of the polymeric backbone were synthesized and characterized. The effect of polymer structure on the trans–cis and cis–trans photo(thermo)isomerization of azobenzene in thin films induced by UV light (λ = 365 nm) was investigated using UV spectroscopy, and in every case the quality of sensitizer of the pyrene was not evidenced. Moreover, a better photochromic response in the film containing azobenzene in the polyether component compared to that induced of the same chromophore in the hard segment was registered. Properties in the solution and thin films were then examined in relation with the fluorescence of pyrene molecule excited at λ exc = 335 nm. Results of the fluorescence study accompanied of a fluorescence quenching through N,N-diethylaniline (DEA) sustain that these polymers could be used for the detection of amines up to a concentration of 1.57 × 10−3 mol/l (AzPUC-Py1) and 3.14 × 10−3 mol/l (AzPUC-Py2), respectively, in DMF solution. Compared to the polymer solution, in the polymer film exposed to DEA-saturated vapors about 30% monomer fluorescence quenching was found after 90 min.