1992 рік

This paper describes the synthesis and characterization of high char yield forming nadimide resins. Ten nadimide end-capped oligomeric resins were prepared by reacting endo-5-norbornene-2,3-dicarboxylic acid anhydride (nadic anhydride), 1,3-bis(3-aminobenzamide)/9,9-bis(p-aminophenyl)fluorene-3,3',4,4'- benzophenone tetracarboxylic acid dianhydride/pyromellitic dianhydride/2,2-bis(3,4-dicarboxylphenyl)- hexafluoropropane dianhydride. Structural characterization of resins was performed by elemental analysis, FTi.r. and I H n.m.r. Thermogravimetric studies revealed a multistep decomposition. Cured resins exhibited very high char yields in the range 63 to 77%.

Детальніше...  

The crystallization and melting behaviour of bacterially produced poly (3-hydroxybutyrate) homopolymer and poly(3-hydroxybutyrate/3-hydroxyvalerate) copolymer were investigated by means of optical microscopy, wide-angle X-ray scattering and calorimetric measurements. The spherulitic growth rate and X-ray diffraction patterns were measured at various temperatures, in order to understand the temperature dependence of crystallization kinetics and the changes in the degree of crystallinity which take place on heating. Structural reorganization during heating was investigated further by means of differential thermal analysis measurements at various heating rates

Детальніше...  

Halogenated phenoxyphosphazenes have been prepared by solution polymerization and characterized by g.p.c., d.s.c., Fourier transform i.r. spectroscopy, optical microscopy, solution and solid state n.m.r., dilatometry and diffraction techniques (WAXS and electron diffraction). Phase transitional behaviour was monitored above the thermotropic transition IT(l)] for each polymer and a general transformation scenario was established depending upon side group chemistry. It has been determined that side group size and substitution affects the glass transition temperature (Ts), T(1 ) and the melting temperature (Tin) in a way that can be scaled linearly with T(1 )~Tin providing a useful guide to polyphosphazene behaviour. Through measuring properties as a function of temperature, a unifying perspective of the transitional characteristics of PB (4-H) PP and PB ( 3 -H ) PP polymers below as well as above T ( 1 ) has been established. A smectic mesophase where the chain backbone is extended and packed (accommodated) into pseudohexagonal arrays is primarily responsible for the properties of polyphosphazene above T(1 ). This arrangement also facilitates the ability of the thermotropic state to organize and solidify into an orthorhombic three-dimensional phase upon cooling from the two-dimensional thermotropic state. The polymers as crystallized from solution are of relatively low crystallinity in the monoclinic form, the level depends upon the nature and size of the side group and the conditions of precipitation.

Детальніше...  

A new t-BOC protected monomer, N-(tert-butyloxycarbonyl)maleimide (t-BOCMI) 3 was synthesized by thermolysis in a high yield and a new kind of t-BOC protected polymer was prepared by radical copolymerization, t-BOCMI and styrene derivatives (X-St) were readily copolymerized to obtain alternating copolymers of P(t-BOCMI/X-St) 5 in high conversions. The t-BOCMI units of the t-BOC protected copolymers were converted to the maleimide (MI) units by heating at about 150°C or above, releasing 2-methylpropene and carbon dioxide. The facile deprotection of the side-chain t-BOC groups from the protected copolymers was attained to bring about a large polarity change. The deprotected copolymers P(MI/Y-St) 6 have very high glass transition temperatures (T~s) of about 250°C and good solubility in aqueous base solutions, whereas the t-BOC polymers P(t-BOCMI/X-St) are only soluble in organic solvents. The t-BOC protected maleimide polymers were found to have specific properties for application as chemically amplified resist materials such as alkaline solubility, high Tg and facile deprotection.

Детальніше...  

The orientation of the crystalline regions in the vinylidene fluoride/trifluoroethylene (VDF/TrFE) copolymer with molecular ratio 70:30 has been studied by wide-angle X-ray diffraction. This copolymer crystallizes in the fl-phase or form I upon compression moulding. Dumb-bells 90 mm wide by 50 mm long were drawn at 0.25 mm min-1 and 80-85°C to the natural draw ratio of 7; the oriented sheets were void-free, and the crystal phase remained form I. Some samples were then poled at 200 MV m- 1. Strips 0.5 mm wide of both unpoled and poled samples were examined in a two-circle X-ray diffractometer, and all equatorial co scans corrected for absorption of the X-ray beam. Both (200/1 10) and (3 1 0/020) composite reflections then showed six distinct intensity maxima round the draw direction, separated by 60 ° from each other, indicating a high degree of uniplanar-axial orientation within the drawn sheets. Calculation of the structure factors from two crystal models and comparison with the measured intensity ratios round the draw direction by curve-fitting methods showed that most of the polar b axes of the unpoled material are in the sheet plane (bc sheets), and that poling increases the number of these axes taking on positions 60 ° from this plane, in line with similar results in the poly(vinylidene fluoride) homopolymer

Детальніше...  

Experimental cloud-point curves of unsaturated polyester (UP) prepolymers with styrene have been determined in this work. The UP prepolymers are copolymers based on maleic anhydride and two types of glycols: diethylene glycol (DEG) and neopentyl glycol (NPG). For UP prepolymers with the same number-average molecular weight ()0"n) and the same hydroxyl functionality (fon), the miscibility with styrene increases when the NPG content increases. For the different chemical structures, the calculated solubility (6) and interaction (g) parameters of the prepolymers decrease when the NPG content increases. A linear correlation between the theoretical critical temperatures (T?) and the interaction parameters (g) is observed.

Детальніше...  

Polyaniline dispersions can be prepared by the oxidative polymerization of aniline in the presence of the steric stabilizer, poly(vinyl alcohol). Dispersion particles are spherical and relatively uniform. Dynamic light scattering was used to determine their hydrodynamic radius and static light scattering to estimate mass-average particle mass. From a series of experiments, a typical example of the preparation and characterization of polyaniline dispersion is described

Детальніше...  

The effects of electrodialysis on the structures of ionic clusters in a perfluorocarboxylic membrane were studied by means of small-angle X-ray scattering (SAXS). Specially made cells for the electrodialysis were used for measuring SAXS profiles in situ and in real time during the electrodialysis. It was found that the electric field did not reshape the structure of ionic clusters during the electrodialysis within our experimental conditions.

Детальніше...  

Measurements of sound velocity and solution density of hydroxyalkyl cellulose have been carried out at temperatures of 15, 25 and 35°C. The partial molar volume and partial molar adiabatic compressibility of hydroxyalkyl cellulose have been evaluated from these data as a function of molar substitution. The partial molar volume of hydroxyethyl and hydroxypropyl cellulose increased with the molar substitution, but they were independent of temperature. The partial molar adiabatic compressibility of hydroxyalkyl celluloses depends strongly on the structure of the substituted group and the molar substitution. The compressibility data indicate that hydroxypropyl cellulose shows a strong hydrophobic character but hydroxyethyl cellulose a weak hydrophilic one.

Детальніше...  

The spin-trapping technique and electron spin resonance (e.s.r.) spectroscopy were employed to study radicals produced by milling ethylene-propylene (EPM) and ethylene-propylene-diene (EPDM) polymers. Mastication of EPDM polymers on a laboratory micromill at room temperature under nitrogen, and in the presence of 2,4,6-tri-tert-butylnitrosobenzene (TBNB), gave a spin adduct which was identified as an anilino type radical where the trapped radical is tertiary in structure. On the other hand, the milling of EPM copolymers in the presence of TBNB did not give spin-trapped radicals.

Детальніше...