Polyacrylamide–graft–poly(ethylene oxide)

Water-soluble graft copolymers were synthesized by copolymerization of acrylamide with mono-methoxy-poly(ethylene oxide)-methacrylates (Me-PEO-MA). The Me-PEO-MA macromers were synthesized by a catalytic esterification of methacrylic acid with mono-methoxy-poly(ethylene glycol)s with different molecular weights. The graft copolymers obtained were characterized by ¹H-NMR spectroscopy, gel permeation chromatography (GPC) and Ubbelohde viscosimetry. The rheological behaviour of aqueous polymer solutions, which are expected to show hydrophobic association at elevated temperatures, was studied with a cone and plate-rheometer.     

[Bis(tetrahydrofuran–O)–bis(1,3–dialkyl–2–diphenylphosphanyl–1,3–diazaallyl)calcium] – Synthesis and Crystal Structures of Calcium Bis[phospha(III)guanidinates] and Investigations of Catalytic Activity

The reaction of [(thf)₄Ca(PPh₂)₂] ( 1 ) with diisopropyl– and dicyclohexylcarbodiimides yields the phospha(III)guanidinates [(thf)₂Ca{RNC(PPh₂)NR}₂] with R = isopropyl ( 2 ) and cyclohexyl ( 3 ). The metathesis reaction of K{RNC(PPh₂)NR} with anhydrous CaI₂ also allows the synthesis of these phospha(III)guanidinate complexes 2 and 3 . For 2 a cis arrangement is observed whereas 3 crystallizes as trans isomer. The phospha(III)guanidinates act as bidentate chelate bases with an average Ca–N distance of 242.5 pm. The C–P bond length between the PPh₂ fragment and the 1,3–diazaallyl unit is with values above 190 pm very large. The complexes 2 and 3 show a moderate catalytic activity in hydrophosphanylation reactions of dialkylcarbodiimides with diphenylphosphane.     

Crystallization of poly(ethylene terephthalate–co–isophthalate)

Melt crystallization behaviors of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate‐co‐isophthalate) (PETI) containing 2 and 12 mol % of noncrystallizable isophthalate components were investigated. Differential scanning calorimetry (DSC) isothermal results revealed that the introduction of 2 mol % isophthalate into PET caused a change of the crystal growth process from a two‐dimensional to a three‐dimensional spherulitic growth. The addition of more isophthalate up to 12 mol % into the PET structure induced a change in the crystal growth from a three‐dimensional to a two‐dimensional crystal growth. DSC heating scans after completion of isothermal crystallization at various T_c's showed three melting endotherms for PET and four melting endotherms for PETI‐2 and PETI‐12. The presence of an additional melting endotherm is attributed to the melting of copolyester crystallite composed of ethylene glycol, tere‐phthalate, and isophthalate (IPA) or the melting of molecular chains near IPA formed by melting the secondary crystallite T_m (I) and then recrystallizing during heating. Analyses of both Avrami and Lauritzen‐Hoffman equations revealed that PETI containing 2 mol % of isophthalate had the highest Avrami exponent n, growth rate constant G_o, and product of lateral and end surface free energies σσ_e. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2515–2524, 2000     

Vitrification/devitrification phenomena during isothermal and nonisothermal crystallization of poly(aryl–ether–ether–ketone) (PEEK) and PEEK/poly(ether–imide) blends

We have established time–temperature transformation and continuous-heating transformation diagrams for poly(ether–ether–ketone) (PEEK) and PEEK/poly(ether–imide) (PEI) blends, in order to analyze the effects of relaxation control on crystallization. Similar diagrams are widely used in the field of thermosetting resins. Upon crystallization, the glass transition temperature (T_g) of PEEK and PEEK/PEI blends is found to increase significantly. In the case of PEEK, the shift of the α-relaxation is due to the progressive constraining of amorphous regions by nearby crystals. This phenomenon results in the isothermal vitrification of PEEK during its latest crystallization stages for crystallization temperatures near the initial T_g of PEEK. However, vitrification/devitrification effects are found to be of minor importance for anisothermal crystallization, above 0.1°C/min heating rate. In the case of PEEK/PEI blends, amorphous regions are progressively enriched in PEI upon PEEK crystallization. This promotes a shift of the α-relaxation of these regions to higher temperatures, with a consequent vitrification of the material when crystallized below the T_g of PEI. The data obtained for the blends in anisothermal regimes allow one to detect a region in the (temperature/heating rate) plane where crystallization proceeds in the continuously close proximity of the glass transition (dynamic vitrification). These experimental findings are in agreement with simple simulations based on a modified Avrami model coupled with the Fox equation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 919–930, 1998     

Non–symmetrically p–nitrobenzyl–substituted N–heterocyclic carbene–silver(I) complexes as metallopharmaceutical agents

In the present work, a series of eight new imidazole, 4,5–dichloroimidazole, 4,5–diphenylimidazole and benzimidazole based nitro–functionalized mono–N –heterocyclic carbene (NHC)–silver(I) acetate ( 7a–d ) and bis–NHC–silver(I) hexafluorophosphate complexes ( 8a–d ) were synthesised by the reaction of the corresponding azolium hexafluorophosphate salts ( 6a–d ) with silver(I) acetate and silver(I) oxide in methanol and acetonitrile, respectively. All the synthesised compounds were fully characterized by various spectroscopic techniques and elemental analyses. Additionally, the structure of bis–(1–benzyl–3–(p –nitrobenzyl)–4,5–dichloroimidazole–2–ylidene)silver(I) hexafluorophosphate complex ( 8b ) was confirmed by single crystal X–ray diffraction analysis. Preliminary in vitro antibacterial evaluation was conducted for all the compounds ( 6a–d) , ( 7a–d) , and ( 8a–d) by Kirby–Bauer's disc diffusion method followed by the determination of Minimum Inhibitory Concentration (MIC) from broth macrodilution method against five standard bacteria; two Gram–positive bacterial strains (Staphylococcus aureus and Bacillus subtilis) and three Gram–negative bacterial strains ( Escherichia coli , Shigella sonnei, and Salmonella typhi). All the hexafluorophosphate salts ( 6a – d) were found inactive against the tested bacterial strains and their corresponding mono– and bis–NHC–silver(I) complexes ( 7a–d and 8a–d ) exhibited moderate to high antibacterial activity with MIC value in the range 8–128 μg/mL. In addition, preliminary in vitro anticancer potential of all the silver(I) complexes ( 7a–d and 8a–d ) was determined against the human derived breast adenocarcinoma cells (MCF 7) by MTT assay. All the mono– and bis–NHC–silver(I) complexes ( 7a–d and 8a–d ) orchestrated high anticancer potential with IC₅₀ values ranging from 10.39 to 59.56 nM. In comparison, mono– NHC–silver(I) complexes performed better than the bis–NHC–silver(I) complexes.