1999 рік

The multiple melting behaviour of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) and poly(butylene naphthalene-2,6-dicarboxylate) (PBN) as well as of eight random poly(ethylene-co-butylene naphthalene-2,6-dicarboxylate)s (PEBN) copolymers was studied using differential scanning calorimetry. The isothermally crystallized samples showed up to three melting peaks, depending on the crystallization temperature. Especially, the PEBN 70/30 copolymer showed a four-fold melting peak. Recrystallization exotherm is observed in some cases just before the ultimate melting peak of polymers. This multiple melting, as well as the effect of crystallization temperature on this behaviour, is discussed in detail in this work.

Детальніше...  

The atom-transfer radical polymerization of styrene was carried out in bulk at 110°C with a newly synthesized bromine-containing anthracene derivative, 9,10-bis( 1-bromoethylcarbalkoxymethyl)anthracene (ANTDBr), as a bifunctional initiator and a cuprous bromide complex Cu(I)Br/2dHbipy (dHbipy = 4,4’-di-n-heptyl-2,2’-bipyridine). g.p.c. and n.m.r. studies revealed that the initiation efficiency of ANTDBr is 100% and the polymerization proceeds in a controlled fashion, providing low-polydispersity polystyrenes with one anthracene chromophore in the middle of the main chain. This success opens up a new route to well-defined anthracene-labelled polymers including random and/or block copolymers, which will be useful as probe polymers to study, e.g., local chain dynamics by the fluorescence depolarization technique.

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2,2⬘-diethynylbenzidine and a series of copolyimides containing such a diamine moiety were synthesized. The crosslinking behaviors of these copolyimides were studied by differential scanning calorimetry and infrared measurements. Pervaporation (PV) properties of these copolyimide membranes to aromatic/non-aromatic hydrocarbon mixtures were investigated. The crosslinked membranes exhibited higher separation factors of benzene over cyclohexane than the corresponding uncrosslinked ones. The sorption results revealed that the increase in diffusivity selectivity was mainly responsible for the improvement in separation factor of PV. However, this improvement seemed still limited. In addition, tetracyanoethylene, an electron acceptor having high affinity for ethynyl-containing materials and aromatics, was homogeneously dispersed in one of these copolyimide matrices and such a membrane displayed high PV performance toward benzene/ cyclohexane and toluene/i-octane mixtures. For example, it had a specific permeation flux Ql of 0.44 kg mm m ¹ 2 h ¹ 1 and a separation factor a of 48 at the feed composition of 50% benzene in cyclohexane, and Ql ¼ 1.1 kg mm m ¹ 2 h ¹ 1 and a ¼ 330 at the feed composition of 45% toluene in i-octane at 70°C. Unlike the case of crosslinking, both the increases in solubility selectivity and diffusivity selectivity contributed to the improvement in separation factor of PV.

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In previous works, the processing of nanocomposites of cellulose whisker filled thermoplastics was presented as well as their mechanical behaviour in the glassy state, both in the linear and non-linear domains. The purpose of the present work is to evaluate the mechanical properties of these composites in the rubbery state. A simple modelling of the mechanical behaviour, using the classical entropy elasticity theory, is proposed and discussed. Particular attention was paid to damage phenomena, already observed with stretched composite in the glassy state. Damage is mainly explained as a debonding of the matrix at the whisker interface. Small-Angle Neutron Scattering experiments performed on stretched composites provide supplementary information on the matrix microstructure with and without whiskers, and on the evolution of this microstructure with the sample deformation. Results confirm the heterogeneous characteristic of the matrix. Void scattering is identified and interpreted.

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Dihydridocarbonyltrk (triphenylphosphine)ruthenium (Ru)-catalysed copolymerization of 4-benzoylpyridine and 1,3-divinyltetramethyldisiloxane leads to a mixture of 2,3-benzo-6,6,8,8-tetramethyl-7-oxa-l 1,12-m-pyridino-6,8-disilacyclododecan-l-one, cyclic co-monomer (I), and copoly (2’,3-[4-benzoylpyridinylene]/3,3,5,5-tetr~e~yl-4-oxa-3,5-disilahept~ylene). Similarly, Ru-catalysed reaction of benzophenone and 1,3-divinyltetramethyldisiloxane leads to a mixture of 5,6,8,9-dibenzo-2,2,12,12-tetramethyl-l-oxa-2,12-disilacyclododeca-7one, cyclic co-monomer (III) and copoly (2,2’-benzophenonylene alt. 2,6-benzophenonylene/3,3,5,5-tetramethyl-4-oxa-3,5-disila-1,7heptanylene). The formation of these products apparently results from the fact that only two of the four ortha hydrogens of 4-benzoylpyridine or benzophenone are reactive under Ru catalysis. Further, preferential reaction of one ortho hydrogen on each aromatic ring of 4-benzoylpyridine or benzophenone takes place. Products have been characterized by 'H, 13C, 29Si n.m.r., i.r., u.v.-vis spectroscopy, as well as elemental analysis and/or high resolution peak matching. In addition, g.p.c., d.s.c., and t.g.a. of copolymers have been determined.

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A thin film of triphenylaminemethylacrylate was fabricated by physical vapor deposition onto an indium–tin oxide substrate over a temperature range from 230 to 290 K. This thin film was subsequently polymerized by UV irradiation in vacuum with the aim of fabricating electroluminescent devices. Polymerization of the thin film in vacuum was investigated by in-situ FT–IR reflection absorption spectroscopy. UV irradiation achieved a polymer conversion of around 100%. Though the polymerization time increased at the lower temperature of the substrate, the surface flatness of the thin film was improved. The polymerization mechanism was elucidated as a simple radical polymerization on the basis of the order of monomer consumption rate. The number-average molecular weight increased with decreasing UV intensity.

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Dynamic mechanical analysis (DMA) is used to study the dynamic mechanical properties of injection-moulded discs of polypropylene, talc-filled polypropylene composites and silane-treated talc-filled polypropylene composites. Silane addition in a very low proportion improves the adhesion between the filler and the polymer and enables composites to be used where otherwise they could not. Therefore, on the one hand, the composites have different properties due to the filler and the coupling agent, and on the other hand the injection processing induces a structure, resulting in inhomogeneity and anisotropy for the moulded discs. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) techniques are used to help state the microscopic structure and justify the macroscopic properties measured with DMA.

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A series of end-capped oligomers 17, 21, 25 and 28 related to nylon 4 6, and 39,43, 47 and 50 related to nylon 6 6 have been prepared starting from adipic acid monoetbyl ester 6, the a,w-di-secondary diamines 8 and 29 and their mono end-protected derivatives 7 and 30, respectively, using the reactions of polypeptide chemistry. The formation of N-protected secondary amide bonds bearing the N-p-methoxybenzyl group ensured the solubility of all intermediates in common organic solvents and enabled purification by chromatography; boiling trifluoroacetic acid removed the protecting group in the final stage of the synthesis.

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An amine-functional styrene–acrylonitrile (SAN–amine) polymer is proposed as a reactive compatibilizer for bisphenol-A-polycarbonate/acrylonitrile –butadiene–styrene (PC/ABS) blends. This polymer should be miscible with the styrene/acrylonitrile (SAN) copolymer matrix of ABS materials, and the pendant secondary amine groups should react with PC at the carbonate linkage to form a SAN-g-PC copolymer. The graft copolymer molecules should reside at the PC/ABS interface and provide improved morphological stability at elevated temperatures by suppressing phase coalescence. This paper describes the synthesis of this reactive compatibilizer and its reaction with carbonate moieties. Characterization of this reaction was done by nuclear magnetic resonance spectroscopy and gel permeation chromatography using model secondary amine and carbonate-containing compounds to facilitate the investigation. The morphology of compatibilized and uncompatibilized PC/SAN blends was examined by transmission electron microscopy.

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Physical ageing in poly(ethylene terephthalate) (PET) was studied by differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) and thermally stimulated polarization currents (TSPC) as a function of the material crystallinity degree. Calorimetric measurements confirm the presence of two separated glass transitions in partially crystallized samples (xc ˆ 27%), associated with the presence of two different amorphous regions: the interspherulitic region and the interlamellar region within the spherulites. The a peak obtained by TSDC shows the progressive decrease of the chain segments mobility in the amorphous fraction as ageing progresses. The increase in the crystallinity degree of the material also produces a decrease of the mobility in the amorphous fraction. In this case the decrease observed is associated with the interlamellar conformation of these regions. However, TSDC measurements do not show evidences of a double glass transition. TSPC measurements on aged samples show a current peak, which is directly related to the polarization of the amorphous regions when mobility is recovered above the glass transition. The study of these peaks in aged partially crystallized samples shows evidences of a double glass transition associated with theinterspherulitic and interlamellar amorphous regions.

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