1999 рік

This paper gives further evidence of successful use of energy-filtering transmission elctron microscopy (EFTEM) for studying the polymer morphology of unstained samples. The method presents numerous advantages compared to traditional chemical staining methods using toxically staining agents such as osmium and ruthenium tetraoxide. For this purpose an EFTEM LEO912 equipped with an omega filter was used to produce conventional brightfield unscattered images and inelastic filtered images of high impact polystyrene ultramicrotomed samples. It was shown that morphology details observed in unstained samples are equivalent in quality contrast to those stained with osmium tetraoxide.

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An FT-i.r. method was used to investigate the thermal cyclization process in synthesis of polyesterimidazopyrrolones from diesterdianhydrides and 3,3 0 -diaminobenzidine. It was proved that the structure of diphenols in the diesterdianhydrides influences the cyclization which goes via an amino-imide to the imidazopyrrolone structure. The presence of an electron-donating group in the diphenol causes the beginning of cyclization at a lower temperature than in the case when in the diesterdianhydride there is a diphenol with electron-withdrawing group. The cyclization process was investigated by dynamic and isothermal heating.

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This paper describes the synthesis and characterization of 2-(methacryloyloxy) ethyl-l-lactate and 2-(methacryloyloxy)ethyl-di-l-lactate. These compounds were obtained by reaction of l-lactide and 2-hydroxyethyl methacrylate (HEMA) at a molar ratio of 1:2 using stannous octoate as catalyst. After a purification step using preparative HPLC, the obtained products were characterized by 1H-NMR, HPLC and mass spectrometry. 2-(Methacryloyloxy)ethyl-(di-)lactate as well as HEMA were grafted to dextran using 1,1 0 -carbonyldiimidazole as coupling agent resulting in dex–(lactate)1,2 –HEMA and dex–HEMA, respectively. Hydrogels were obtained by radical polymerization of aqueous solutions of the methacrylated dextrans. Due to the presence of hydrolytically sensitive groups in the crosslinks, these hydrogels degraded when exposed to an aqueous solution (pH 7.2, 37°C). For hydrogels with a fixed crosslink density, the degradation times were 30, 12 and 6 days for dex–HEMA, dex–lactate–HEMA and dex–(lactate)2 –HEMA hydrogels, respectively. This demonstrates that the degradation rate and time of dextran hydrogels can be tailored by the length of the spacer in the crosslink of the hydrogels.

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A critical volume fraction of the minor component within the major component can be distinguished above which the co-continuous morphology in a polymer blend remains stable during annealing of the blend. Below this volume fraction breakup leads to a transition of the co-continuous structure to a dispersed one. This critical composition can be understood by depicting the co-continuous structure as an assembly of fibres randomly oriented at their maximum packing density. These fibres have 'coalesced’ at their cross-over points. The length of the filament between two cross-over points decreases with increasing volume fraction of the minor phase. At a certain length the dominant wavelength of the sinusoidal disturbances is larger than the length between two cross-over points and the disturbances will not grow further. Consequently, the filament cannot break up. The critical volume fraction above which breakup of the co-continuous structure during annealing is not possible, is found to be around 30 vol% of the minor phase.

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A series of novel acidic and zwitterionic water-soluble diblock copolymers has been synthesized directly (i.e. without protecting group chemistry) via the TEMPO-mediated living free-radical polymerization of various hydrophilic styrenic monomers. In all syntheses TEMPOcapped poly(sodium 4-styrenesulfonate) was utilized as a well-defined macro-initiator. Chain extension of this macro-initiator with 2vinylpyridine proved very inefficient. Using 4-vinylbenzyltrimethylammonium chloride as comonomer led to an insoluble zwitterionic complex, whereas water-soluble zwitterionic block copolymers were obtained with 4-(dimethylamino)methylstyrene. Micellar solutions were obtained with the less hydrophilic 4-vinylbenzyl alcohol comonomer. A series of strong acid–weak acid block copolymers with varying sodium 4-styrene-sulfonate contents (20–80 mol%) were prepared via chain extension of the macro-initiator using sodium 4-styrenecarboxylate. These acidic block copolymers undergo reversible pH-induced aggregation in aqueous solution and 13C n.m.r. spectroscopy studies suggest that the carboxylic acid block forms the hydrophobic micellar core. Dynamic light scattering studies indicate intensity-average micelle diameters of 20–60 nm.

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Polymerization of vinyl chloride (VC) with tert-butyllithum (tert-BuLi) was investigated from the point of controlled polymerization. The polymerization of VC proceeded at ⫺30°C to give high polymers. The Mn of the polymers increased as a function of the reaction time and polymer yields, although the initiator efficiency was low. Linear dependence of the Mn of the polymer and polymer yields was observed, while Mw/Mn did not change significantly during the polymerization. The polydispersity (Mw/Mn) of the polymer was not narrow probably due to the heterogeneity of the reaction media.

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Polymerisation of acrylic acid has been initiated by the sodium metabisulphite/potassium bromate redox pair. The reaction occurred in aqueous drops dispersed in a paraffinic oil and stabilised by a non-ionic surfactant. Characterisation of drop/particle behaviour throughout the course of polymerisation, using a freeze-fracture technique with a scanning electron microscope, suggested a mechanism of drop polymerisation that included continuous and simultaneous drop coalescence and break-up. The important role of drop mixing in the polymerisation was investigated by conducting polymerisations with some varied experimental parameters. It has been found that the agitation speed, the composition of the reductant aqueous solution and the method of adding the aqueous reductant had significant effects on polymerisation rate, limiting monomer conversion, particle size and size distribution in the final latexes.

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A new method to prepare the graft copolymers that have an ethylene-propylene-diene terpolymer (EPDM) rubber backbone and poly(methyl methacrylate) (PMMA) branches was described. Firstly, the brominated EPDM (EPDM-Br) was produced by the reaction between the EPDM and N-bromosuccinimide(NBS), then the EPDM-g-PMMA was created by the ATRP of MMA initiated by EPDM-Br in the presence of CuBr/bpy at 90°C. The study shows that the free radical transfer grafting polymerization does not existed in the ATRP of MMA initiated by allyl bromide/CuBr/bpy in the presence of pure EPDM. The propagation of the PMMA graft chains are in situ initiated by EPDM radicals which is created through the reaction between the EPDM-Br and CuBr. Moreover, the reaction conditions, such as solvent, reaction time, molar ratio of EPDM-Br : CuBr : bpy, were examined. The maximum graft efficiency(93%) was obtained at 90°C for 20 h, when the ratio of EPDM-Br : CuBr : bpy was 1 : 0.8 : 2.4. The graft copolymers were characterized by solvent extraction, IR and H 1-NMR spectra technique.

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Structure and morphology of lamellar crystals of two polyamides derived from 2-methylpentamethylenediamine (MPMD) and dibasic acids with 4 or 8 methylenes have been studied by transmission electron microscopy, electron diffraction and X-ray diffraction. The crystallographic unit cell of MPMD-6 is triclinic with a ˆ 4.85, b ˆ 5.90, c (chain axis) ˆ 30.4 Å, a ˆ 115.40, b ˆ 99.9 and g ˆ 61.1°, the chain axis direction is not coincident with the c ⴱ reciprocal axis. These dimensions suggest a hydrogen-bonded sheet structure with a single hydrogen bond direction and a twist of 180° in the odd diamine unit. MPMD-10 shows two crystalline structures. The most abundant being a monoclinic unit cell with a ˆ 4.79, b ˆ 5.67, c (chain axis) ˆ 36.3 Å and g ˆ 61.8°. The less abundant structure was only observed in oriented fibers and was similar to the MPMD-6 crystalline structure. Single crystals of both MPMD-6 and MPMD-10 polyamides grow preferentially along their single hydrogen bond direction.

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The effects of precipitation temperature on the structures of the EVAL membranes formed in a wet phase inversion process were studied. As the temperature was changed, the phase behavior (liquid–liquid demixing and crystallization boundaries) of the membrane formation system changed accordingly. Therefore, a wide variety of morphologies of the EVAL membranes could be synthesized at different temperatures. At low temperatures (e.g., 25°C), the membrane solution precipitated into a particulate morphology that was governed by the polymer crystallization mechanism, whereas at elevated temperatures (e.g., 65°C) liquid–liquid demixing process dominated the precipitation process and the membrane became cellular in its morphology. In the intermediate cases, the membrane exhibited a structure containing features from both types of phase separations. For the current system, it was found that there existed a good correlation between the phase behavior and the morphology of the membranes.

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