1994 рік

The photodegradation of heterophasic ethylene-propylene copolymers and their homopolymers has been investigated by the study of hydroperoxide formation, and by electron spin resonance (e.s.r.) and infra-red spectroscopy. On irradiation of polymer films in air at 60°C with a light of wavelength longer than 300 nm, polymer hydroperoxides are formed. The behaviour of peroxyl radicals generated in the samples on irradiation of polymer hydroperoxides with ultraviolet light at - 50°C in vacuum has been identified and compared with a combination of e.s.r, and derivatization reactions. From Fourier transform infra-red spectroscopy the structure of peroxyl radicals formed is identified.

Детальніше...  

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)s (P(3HB-co-4HB)s) with a wide range of 4HB contents were biosynthesized, and their crystalline states were studied by differential scanning calorimetry (d.s.c.) and compared with those of the cold-stretched copolyesters of poly(3HB-co-3-hydroxyvalerate) (P(3HB-co- 3HV)). A structural study was also carried out by the use of molecular mechanics calculations. It was demonstrated that P(3HB-co-4HB) cannot form isomorphic crystals because of the extent of the structural difference between the 3HB and 4HB comonomer components.

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Two series of block copolymers composed of poly(ether ether ketone) (PEEK) and poly(ether sulfone) (PES) components were prepared from the corresponding oligomers via a nucleophilic aromatic substitution reaction. In the first series of block copolymers, the )~n of the PEEK segment was fixed at 10000, while the A4,s of the PES segments ranged from 250 to 9330. (The PES contents of the copolymers varied from 2.2 to 46.2"/0.) For the other series of block copolymers, the compositions were kept almost constant (PES content ~36%), while the segment lengths were changed. Various properties of the copolymers were investigated by differential scanning calorimetry (d.s.c.), wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (t.g.a.), and dynamic mechanical analysis (d.m.a.). The results showed that the copolymers exhibited no phase separation and the relationship between the glass transition temperature and the compositions of the copolymers approximately followed the formula, Tg= Tg 1W 1 -~ Tg2W 2. The crystallization behaviour, thermal properties and dynamic mechanical behaviour of the copolymers were investigated and it was found that both the PES content and the segment length of the copolymers had a significant influence on their crystallization behaviour.

Детальніше...  

A new thermally reactive monomer has been designed and synthesized that brings novel crosslinking chemistry to high-performance polymers. This monomer (XTA) is a derivative of terephthalic acid and was based on the thermal chemistry of benzocyclobutene. Various model compounds have been synthesized to investigate substituent effects on benzocyclobutene reactivity. Irreversible reaction exotherms around 350°C were observed in these model compounds using differential scanning calorimetry. Based on these studies, polyaramid and poly(aryl ether ketone) XTA copolymers were synthesized. The formation of an insoluble network resulted after heat treatment of these polymers

Детальніше...  

The morphology of binary blends of a maleated triblock copolymer (with an ethylene/butene midblock and styrene endblocks, SEBS-g-MA) with a series of nylon materials (nylon 4,6, nylon 6,9, nylon 6,10, nylon 6,12, nylon 11, nylon 12 and nylon 12,12) was investigated and the results compared with previous work for nylon 6 and nylon 6,6. The nylon x materials (nylon I1 and nylon 12) yielded small, regular particles similar to that observed in nylon 6. These nylons have one amine endgroup per molecule and are only capable of end-grafting. The nylon x,y materials, on the other hand, led to much larger and more complex-shaped particles; their size decreased as the aliphatic content of the nylon increased. These polyamides contain a certain fraction of molecules with two amine endgroups and are capable of forming loops or crosslinks which dramatically affect the morphology generation in a single-screw extruder. The results further revealed that the large particles are formed because of the failure of the single-screw extruder to break them into smaller ones rather than by increased coalescence. There is evidence that thickness of the interface influences both the particle size and the extent of reaction in these blends as described.

Детальніше...  

Substituted poly(benzobisoxazole)s and poly(biphenylbisoxazole)s were synthesized by polycondensation of silylated diaminohydroquinone or 3,3'-dihydroxybenzidine with substituted terephthaloyl chlorides. Hexadecylthio-, 2,5-bis(hexadecylthio)- and 2,5-bis(hexadecyloxy)terephthaloyl chloride were used as reaction partners. A reaction temperature of 300°C was required for the final cyclization step of the reaction sequence. At this high temperature partial crosslinking occurred in most cases. The poly(biphenylbisoxazole)s melt in the temperature range of 310-350°C, but the characterization of the melt was affected by rapid thermal degradation. By means of wide-angle X-ray scattering powder patterns and 13 C nuclear magnetic resonance cross-polarization/magic-angle spinning spectroscopy, two kinds of sanidic layer structures were found for the solid state. The hexadecyl side chains form reversibly melting quasicrystalline paraffin domains between the layers of the main chain. The molar fraction of these ordered paraffin domains is significantly higher for bis(hexadecylthio)-substituted chains than for bis(hexadecyloxy)-substituted ones.

Детальніше...  

A partially esterified derivative of sodium alginate was substituted by various long-chain alkylamines. The resulting amphiphilic polymers exhibit intermolecular hydrophobic associations in semidilute aqueous solution, evidenced by rheological measurements and fluorescence spectroscopy experiments.

Детальніше...  

A novel '3F' fluorinated diamine monomer based on trifluoroacetophenone was synthesized via a straightforward, high yielding two-step procedure. Trifluoroacetophenone was reacted with 4-nitrophenyl phenyl ether to yield the 3F-dinitro compound, which was subsequently reduced to afford the fluorinated diamine, 1,1-bis[4-(4-aminophenoxy)phenyl]-l-phenyl-2,2,2-trifluoroethane (3FEDAM). New amorphous and semicrystalline polyimides based on 3FEDAM were prepared and characterized by differential scanning calorimetry, thermogravimetric analysis and wide-angle X-ray scattering (WAXS). In particular, the 3FEDAM-pyromellitic anhydride-phthalic anhydride material exhibited a glass transition temperature of 308°C and a melting temperature of 476°C, which are quite similar to the values reported for '6F'-based systems. The semicrystalline nature was confirmed by WAXS analysis, and is consistent with the excellent solvent resistance observed for these polyimides.

Детальніше...  

The mechanical properties of a series of polyamide materials (nylon 6,12, nylon 11, nylon 12 and nylon 12,12) were investigated using triblock copolymers of the type styrene-(ethylene-co-butene)-styrene (SEBS) and a maleic anhydride (MA) functionalized version (SEBS-9-MA). The results have been compared with the behaviour reported for nylon 6 and nylon 6,6 in our previous work. A much lower concentration of the maleated elastomer (SEBS-9-MA) was required for effective toughening of these polyamides with higher CHjNHCO ratios. This is believed to be a consequence of the inherently more ductile polyamide matrix as the methylene content of the nylon material increases. Further evidence of this was given by the trends in the ductile-brittle transition temperature of the various binary blends of these polyamides with SEBS-g-MA. Transmission electron microscopy techniques used for investigating the morphology generated in these blends showed that ternary blends of nylon x (monofunctional) materials (nylon 11 and nylon 12) yielded regular, spherical rubber particles with a continuously varying particle size as the proportion of SEBS and SEBS-g-MA in the rubber phase was changed, while ternary blends of nylon x,y (difunctional) materials (nylon 6,12 and nylon 12,12) yielded rubber particles with varying levels of complexity and size depending on the SEBS-9-MA/SEBS ratio. Such differences in the blend morphology between nylon x and nylon x,y materials have been attributed to differences in the basic chemical structure of these polyamides. The existence of critical limits on the rubber particle size for toughening these blends was also explored.

Детальніше...  

The chiral recognition property of poly[(1 ~ 6)-2,5-anhydro-3,4-di-O-methyl-D-glucitoll (2b) towards racemic RCH(CO2CHa)NH~"X- (3"HX) has been studied using a transport system involving an aqueous source and receiving phases separated by a chloroform phase containing 2b. For HPF6, HCIO4 and HC1 salts of 3a (R=Ph), the amount of 3a transported into the receiving phase decreased in the order of PF 6 > CIO£ > CI-, but the optical purities changed only slightly from 9.3 to 10.9%. The transport rates for aromatic guests, 3a and 3b (R = CH2Ph), were faster than those for aliphatic ones, 3e (R = CH(CH3)2) and 3d (CH2CH(CH3)2), using PF6 as the counterion. The optical purity was 10.9% for 3a as a maximum value and decreased in the order of 3a > 3e > 3b and 3d. The formation of a complex between 2b and 3a. HX was confirmed by IH and 13C n.m.r, spectral measurements.

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