摘要:

The introduction of 2,9,16,23-tetracarboxy-Fe(III)phthalocyanine [Fe(III)tcPc] units onto fractions of poly(N-vinylcarbazole) (PVK) by Friedel-Crafts reaction leads to amorphous PVK-based grafted compounds that show major interchain distances by the wide-angle x-ray scattering (WAXS) technique. Glass transition temperatures of the products are lower than the main glass transition temperature of PVK and are attributed to local movements of the voluminous added groups. Dynamic thermogravimetric experiments show decarboxylation processes within the 250°C-500°C range and little weight loss. The large remaining residue, up to 70% of the sample at 800°C, is suggested to be the consequence of successive cross-linking reactions. The Fourier transform infrared (FTIR) spectrum of the residue is similar to that of the grafted sample before degradation.

ISSN:0022-2348    

DOI:10.1080/00222349808212404

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The results of crystallization and melting studies of polyphenylene sulfide (PPS) in presence of a low molecular weight (LMW) compound ate reported. The crystallization is studied using differential scanning calorimetry (DSC) and optical microscopy. It is observed that the addition of the LMW compound resulted in a decrease in melting point and crystallization temperature, suggesting significant changes in crystalline morphology and crystallization behavior, respectively. The spherulitic morphology was also found to become altered in terms of size and texture, confirming incorporation of the compound in the structure. The changes observed were more significant for melt-blended samples than those observed for dry blends.

ISSN:0022-2348    

DOI:10.1080/00222349808212405

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In this work, using water as an inert penetrant, it was possible to obtain transport parameters without changing die original polymer structure, making possible a comparative analysis of how the methodologies of preparation and film thickness can influence the structural organization of the original polymer. A simultaneous analysis of transport and physical properties is very useful for this purpose.

ISSN:0022-2348    

DOI:10.1080/00222349808212406

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Synthesis of the liquid crystalline (LC) diol 6,6′-[ethylenebis(l,4-phenylene-oxy)]-dihexanol (I) is described. The structure of polyurethanes prepared from diol I and 4,4′-methylenedi(phenyl isocyanate) (MDI), 4,4′-methylenedi(cyclohexyl isocyanate) (HMDI), or 2(4)-methyl-l,3-phenylene diisocyanate (TDI) at 1:1 molar ratios of isocyanate and hydroxy groups is studied by dynamic mechanical spectroscopy, differential scanning calorimetry (DSC), polarizing microscopy, and x-ray scattering. The polymer prepared from HMDI and the diol (I/HMDI) shows, on cooling, thermal behavior typical of amorphous polymers. A frequency-temperature superposition could be applied to the mechanical data, and the horizontal shift factor satisfied the Williams-Landel-Ferry (WLF) equation. A more-complex thermal behavior was found for I/HMDI polymer during subsequent heating; above 70°C, the formation of an ordered structure takes place, and this structure melts at about 120°C. Complex thermal behavior is exhibited by I/TDI polymer. On cooling its melt, the polymer forms a nematic phase at about 80°C, which freezes into the LC glassy state. On heating, the mesophase melts, and. subsequently, a better-ordered smectic phase is formed at 95°C, which melts at 120°C. This structure buildup is accompanied by a rapid increase in storage modulusG′, and the sample shows thermorheologically complex mechanical behavior. The polymer formed from the diol and MDI (I/MDI) exhibits a most-complex thermal behavior. On cooling and heating, four transitions can be detected in its thermal mechanical behavior, and the structure of the polymer is strongly dependent on its thermal history.

ISSN:0022-2348    

DOI:10.1080/00222349808212407

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Time-resolved simultaneous small- and wide-angle x-ray scattering (SAXS and WAXS, respectively) of poly(aryl ether ether ketone) (PEEK) during isothermal crystallization, melting, and subsequent cooling were conducted using synchrotron radiation. Unit cell parameters were determined using WAXS measurements, and the dimensions of lamellar-level moieties were extracted from SAXS profiles. It was found that the changes in unit cell parameters were reversible on heating and cooling, and there were remarkable differences in the thermal expansion coefficients in different lattice directions. The long periodL, the lamellar thicknesslc, and the thickness of amorphous layerslawere calculated from the correlation function, and the changes of these dimensions during the processes mentioned above were traced. Sharp decreases inLandlcin the initial stage of isothermal crystallization and cooling from melt were observed, and a corresponding continuous distributed model is proposed. When cooling from the melt, the invariantQexhibited a maximum. The maximum is attributed to a change in the difference of the densities of crystalline and amorphous phases (ρc- ρa) with decreasing temperature.

ISSN:0022-2348    

DOI:10.1080/00222349808212408

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Phonon dispersion studies fortrans-l,4-polybutadiene (TPBD) are reported. The change in profile of the dispersion curves as a function of the ═CH─CH2─ dihedral angle φ has been obtained in order to find the geometry of the polymer that gives the best interpretation of the spectra. It is found for φ = 71°. The regions of high density of states obtained from the dispersion curves for an isolated chain have been used to explain the features of the spectra. Some of these, which were earlier attributed to interchain interactions, in fact arise due to intrachain interactions. Prominent features of the dispersion curves are discussed and heat capacity, derived therefrom, is reported. Calculations have also been performed for unsaturated C-deuterated and fully deuterated TPBD samples to check the validity of the force field and assignments.

ISSN:0022-2348    

DOI:10.1080/00222349808212409

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The toughening effect of the shell content of a core-shell latex polymer poly(butyl acrylate) (PBA)-cs-poly(methyl methacrylate) (PMMA) on its blends with polycarbonate (PC) was studied. The changes of mechanical properties, morphology, and compatibility of the blends of PC/PB A-cs-PMMA with the change of the shell thickness of PBA-cs-PMMA were investigated. It is interesting to notice that mechanical properties of the blends are very sensitive to the shell thickness (i.e., shell content), and that there is a possibility to adjust the impact and tensile properties of the blend by selecting a PBA-cs-PMMA with a proper core/shell ratio. Hence, a modified PC material with balanced mechanical properties may be prepared.

ISSN:0022-2348    

DOI:10.1080/00222349808212410

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Physical aging in amorphous poly(ethylene terephthalate) (PET) was studied by means of modulated differential scanning calorimetry (MDSC). Two different thermal histories were used: (1) quenching from above theTgto 0°C; (2) slow cooling at l°C/4 min from above theTgto just below theTg. The enthalpy relaxation of the amorphous PET is affected by thermal histories induced by annealing below Tg. The data showed that all the parameters describing the relaxation process (ΔH Tmax, andTons) were strongly dependent on the thermal histories of the sample before annealing. The magnitude and position of the endothermal peak are enhanced in the order slow cooling quenching.

ISSN:0022-2348    

DOI:10.1080/00222349808212411

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A blend of polyethersulfone (PES) and polycarbonate (PC) with a ratio of 40/ 60 was studied by scanning electron microscopy (SEM), dynamic mechanical analysis, and transmission electron microscopy (TEM). It was found that the PES-PC blend is a partially miscible, two-phase system, and an interfacial layer exists between the phases of PES and PC. Specific interaction resulting from the n-complex between PES and PC provides the driving force for formation of the interfacial layer. In addition, phase inversion behavior was also observed for the 40/60 composition.

ISSN:0022-2348    

DOI:10.1080/00222349808212412

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor