1999 рік

Poly[(styrene)-rotaxa-(crown ether)]s were synthesized by free radical polymerizations of styrene in the presence of crown ethers using bulky 'blocking group’ initiators to ensure end-capping for prevention of dethreading. These statistical processes produced only low threading yields, but up to 26% cyclic by mass with large crown ethers. The poly[(styrene)-rotaxa-(crown ether)]s 'emulsified’ in protic solvents such as methanol and water. The dispersion polymerization of styrene in methanol or water using '42-crown-14’ ('42C14’) indicated that threading provided stability of the polyrotaxane micelles in such solvents through hydrophilic–hydrophobic phase separation. DSC investigations indicated that the threading prevents the crystallization of the crown ether and allows phase mixing to some extent, since two altered T g’s were observed.

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The effect of polyacrylate (PA) on wax-precipitation temperature in heptane was investigated using differential scanning calorimetry (DSC). A thermodynamic analysis for the dissolution of wax in the absence and presence of PA was conducted. Results suggested that the change in wax-precipitation temperature caused by the introduction of the additives may be regarded as an index for characterizing the interaction of polymer additives with wax.

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Molecular dynamics (MD) simulations were carried out to gain an understanding of the interfacial interactions and the phase separation process in a polymer dispersed liquid crystalline (PDLC) system. The most important components of the PDLC system of interest are: E7 (an eutectic mixture of cyanobiphenyl liquid crystals), a crosslinked polyacrylate, and octanoic acid (OA). The miscibility of the different components was investigated and the anchoring characteristics of 4-n-pentyl-4 0 -cyanobiphenyl (5CB) molecules on the penta-acrylate polymer surface were analyzed. The effects of introducing a surfactant on the miscibility and the anchoring strengths were also studied. Bilayers of polymer and liquid crystal (LC) of different alignments, show that an amorphous 5CB structure on the polymer surface was energetically most favorable, whereas homeotropic alignment had the next higher energy and planar alignment was the least favorable. Calculated solubility parameters indicate that prior to polymerization, the prepolymer and LC are miscible and OA is equally immiscible with both of them. Upon polymerization, the polymer is no longer miscible with the LC; phase separation occurs and OA acts as a surfactant forming a layer between the polymer and the LC. Anchoring energies calculated from the interfacial tensions indicate that the LC and polymer interface is strong. On addition of the surfactant, the anchoring energy at the interface of the LC and the surfactant becomes weaker. This decrease in anchoring strength may be one of the major factors responsible for a reduction in droplet size and also a lowering of critical field for switching, both of which are observed experimentally in volume holograms made of these PDLC materials.

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The aggregation of block copolymer dissolved in methyl ethyl ketone (MEK) as well as toluene was observed. The aggregation of molecules leads to micelles and clusters of micelles. Between micelles and clusters a dynamical equilibrium exists. Inside the micelles lyophobic chains of PEO are combined and the outer layer of micelles is formed by lyophilic chains of PMMA. This is observed particularly in samples with triblock or diblock structure and high portions of PEO. In these cases, there are great differences between molecular weights obtained by light scattering, SEC or vapour pressure osmometry (VPO). We introduce a factor A to study the relation of the PEO content in diblock or triblock structure, and the measured M w .

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The solution state of cellulose dissolved in N-methylmorpholine-N-oxide-monohydrate (NMMNO·MH) was investigated by static laserlight scattering. Special emphasis was placed on the potential influence of activation procedures. The light-scattering measurements were analysed in terms of Guinier–Zimm plots. Molecular masses of the order of several million g mol ⫺1 were observed. This indicates that cellulose aggregates exist and that the aggregates comprise several hundred cellulose chains. The radii of gyration of these aggregates exceed 160 nm. The overall scattering functions can be separated into two partial scattering contributions. This reflects a bimodal distribution of the particulate phase, consisting of large and small aggregates. Activation of cellulose prior to dissolution leads to particles consisting of significantly fewer cellulose molecules than without activation. However, the size of the aggregates does not change significantly.

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A mixture of (2S,3S) and (2S,3R)-3-methylaspartic acid, obtained by bioconversion of mesaconic acid in the presence of 3-methylaspartase as enzymatic catalyst, was transformed into the corresponding benzyl 3-methylmalolactonate stereoisomers using a multiple-step synthesis. A mixture of (3R,4R) and (3S,4R) (80/20 (mol/mol) ratio) benzyl-3-methylmalolactonate was transformed by anionic ring-opening polymerization to an optically active and stereoregular stereocopolymer constituted by 80 mol% of benzyl (3R,4S) 3-methylmalate repeating units and 20 mol% of benzyl (3S,4S) 3-methylmalate units, as determined by 1H NMR. The corresponding optically active poly(b -3methylmalic acid) was obtained by catalytic hydrogenolysis of the protecting benzyl ester groups, in N-methylpyrrolidone as solvent. This functionalized hydrosoluble polyester was degraded by simple hydrolysis in a phosphate buffer at pH 7, as shown by SEC measurements. It is worth noting that the kinetic profile was equivalent to the one of poly(b -malic acid). Moreover, at 378C, the hydrolysis was complete within six weeks, yielding to the corresponding optically active 3-methylmalic acid. In order to use this polymeric material for temporary therapeutic applications, polymers containing both diastereoisomers as repeating units as well as their ultimate products of degradation were evaluated based on harmlessness towards their environment. No toxicity was detected against a human cell line, HepG2.

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The polymerization of a mixture of cis (ca. 30%) and trans (ca. 70%) isomers of 7-tetradecene oxide (7-TDO) with methyl trifluoromethansulfonate (methyl triflate) as initiator has been investigated. The main reaction products afforded during the polymerization were a linear polyether, a cyclic dimer [2,3,5,6 tetra(n-hexyl)dioxane], and 7-tetradecanone. The ketone is formed both via pinacol rearrangement of the monomer and a transfer reaction when all the monomer is consumed, and is favoured by an increase of temperature. Kinetic studies on the ring opening polymerization of this system were performed by means of 1 H and 19 F NMR spectroscopies. Approximate rate constants of initiation (k i) for the cis and the trans isomers were determined at 298, 314 and 329 K in bulk, and at 298 K in C 6D 6. The reaction time of the cis isomer is faster than that of the trans isomer, with an initial molar reactivity ratio of about 11:1 at 298 K, and of about 7:1 at 329 K (in bulk). The activation energies of the initiation reaction for the cis and the trans isomers were calculated to be 59 and 73 kJ/mol, respectively. By means of 1 H-, 19 F- and 13 C-NMR the structure of the propagating species is reasonably well identified as an oxonium macroion rather than a linear triflic macroester.

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Effects of elongation on the electric resistance of graphite–EVA(ethylene-acetate copolymer) systems were studied. It was found that a linear relation holds between the logarithm of electric resistance and elongation. We have made a simulation with tunneling junction-model. Namely, we have assumed that the system consists of many tunneling junctions which form series and parallel circuits through the system and that widths of tunneling potentials proportionally increase with elongation. The result of the simulation agrees with experiment: a linear relation holds between the logarithm of electric resistance and elongation. This implies that tunneling conduction plays an important role in carbon–polymer systems. However this result raises a new problem on the mechanism of switching which was thought to have been solved already.

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A series of side chain liquid crystal polyurethanes (CnOMeP) with even-numbers of methylene units in the spacer was synthesised by the addition polymerisation of a -[bis(2-hydroxyethyl)amino]-v -(4-methoxyazobenzene-4 0 -oxy)alkanes (CnOMe-diol) with hexamethylene diisocyanate. The thermal and structural properties of CnOMeP were determined by means of polarising optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction. C2- and C4OMeP showed a completely amorphous nature, while C6– C12OMeP exhibited a bilayer smectic structure. Polyurethane backbones have a high tendency to crystallise. Crystallisation is closely related to hydrogen bonding between polyurethane groups. Short spacers favour an amorphous nature, while longer ones tend to lead to crystallisation. In order to obtain further information concerning backbone crystallisation, Fourier transform infrared spectroscopy (FT-IR) studies of CnOMeP polyurethanes were carried out at different temperatures focusing on the H-bonds between the N–H and CyO groups of the polyurethane backbone.

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A new class of polysiloxane-block-polyimides having silicate in the polysiloxane segments were successfully synthesized and the thermal and mechanical properties of their crosslinking investigated using cast films. The silicate-containing copolyimides were easily derived by hydrosilylation of polysiloxane-block-polyimides having vinyl groups in the polysiloxane segments prepared from 3,3⬘,4,4⬘-benzophenonetetracarboxylic dianhydride (BTDA), 2,2-bis[4-(3-aminophenoxy)phenyl]sulfone (BAPSM) and several kinds of copolyimides with vinyl functionalized diamino-(poly)siloxanes accompanied by solution imidization. During hydrosilylation a small excess of diethoxy(methyl)silane was reacted using hydrogen hexachloroplatinate (H 2PtCl 6·5H 2O) as the catalyst. The copolyimides finally obtained were soluble in various organic solvents and easily hydrolysed to form crosslinked copolyimides during solution casting of films for investigation. The resulting materials have various potential applications as organic–inorganic hybrid materials.

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