摘要:

A series of epitaxial polymerizations of poly(p-oxybenzoate) (POBA) on substrates of single-crystal mica, potassium bromide (KBr), and uniaxially aligned poly(tetrafluoroethylene) (PTFE) was performed at temperatures from 200°C to 270°C. As the temperature rose, not only did the POBA domain dimension in the polymer chain direction and the thickness of the epitaxial layer increase, but also the domain morphology changed correspondingly. The POBA domains tended to grow more three dimensionally at low temperatures, accompanied by a decreased epitaxial order. Thus, a high temperature favored epitaxial crystallization of POBA onto crystalline substrates. The POBA film grown on KBr substrate at 220°C revealed a low density layer consisting of lamellaelike plates. Subsequent annealing at 320°C produced a fibrous morphology in which the POBA fibrils were aligned, forming a 90°C cross-hatched network. More interestingly, a POBA film on KBr substrate, prepared by melt condensation reaction at 180°C for 24 h followed by annealing at 280°C for 1 h and then at 320°C for 2 h, produced laminae with both square and rectangular patterns with domain boundaries that aligned with KBr crystal axes. The electron diffraction (ED) pattern showed a phase 1 crystal pattern with the POBA polymer chains perpendicular to the substrate surface with very high crystallinity.

ISSN:0022-2348    

DOI:10.1080/00222349808220451

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Thermal crystallization from the glassy state was investigated for isotactic polystyrene (iPS) at three temperatures (140°C, 170°C, and 200°C) for different times. The crystallized samples were analyzed by x-ray diffraction, differential scanning calorimetry (DSC), and transport properties of dichlo- romethane vapor. X-rays and DSC give very similar values of crystallinity. At variance, sorption measurements indicate a fraction of amorphous phase much lower than the previous. The presence of a mesophase, impermeable to the vapors at low activity, was hypothesized. Its value is constant for annealing at 140°C, whereas it decreases with time at 170°C and 200°C, in correspondence with an increase of the crystalline fraction.

ISSN:0022-2348    

DOI:10.1080/00222349808220452

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The heat capacity of poly-p-dioxanone (PPDX), (CH2‒CH2‒O‒CH2‒COO‒)x, was determined using both differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC) from 200 K to 430 K. Based on the new data and literature data, the heat capacity of the solid state was analyzed using an approximate group vibrational spectrum and skeletal vibrations. The 10 skeletal vibrational modes are well represented by a Tarasov function with theta temperatures of1= 478.7 K and3= 50.4 K. The heat capacity of the liquid was fitted to a linear function,Cliquid= 0.1484T+ 144.3 in units of J K−1mol−1, which is close to the sum of equations developed earlier for the liquids of poly(oxyethylene) and polyglycolide. The change in heat capacity of amorphous PPDX at the glass transition temperature (264 K) is 69.9 J K−1mol−1, and the heat of fusion for perfect crystals at the melting temperature (≈400 K) is 14.4 kJ mol−1. The integral thermodynamic functions were derived, and the residual entropy of the glass at 0 K, determined from these functions, is extrapolated as 13.4 J K1mol−1(or 2.7 J K−1mol−1per chain atom).

ISSN:0022-2348    

DOI:10.1080/00222349808220453

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Maleic anhydride-stearyl methacrylate copolymer was synthesized by radical polymerization. The copolymer was fractionated and characterized by dynamic and static light scattering (DLS and SLS) experiments in different concentration regimes. Seven fractions of low polydispersity index (<1.18) were studied. A typical behavior corresponding to good and theta () solvents, according to the classical theories for polymers in solution, was found in the dilute regime. The results indicate in a semiquantitative way that this copolymer shows a normal behavior in the dilute regime. The rigidity parameters σ and C∞ show flexibility of the polymer chain, due to the incorporation of the maleic anhydride (MA) units, when the copolymer is compared with those corresponding to other poly(methacrylates) previously reported. In the semidilute regime and depending on the solvent nature, aggregation of the copolymer was detected. The aggregation was analyzed in terms of the values of the autocorrelation function determined by dynamic light scattering.

ISSN:0022-2348    

DOI:10.1080/00222349808220454

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The thermal behavior, morphology of the melt-grown crystals, and polymorphism of poly(ketone sulfide) (PKS) were studied and compared with those of poly(ether ketone) (PEK), using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and wide-angle x-ray dif- fractometry (WAXD). The following results were obtained: (1) The melting temperature of PKS is somewhat lower than that of PEK, suggesting that the sulfide linkage (‒S‒) has a relatively shallower rotational conformational energy than that of the ether linkage (‒O‒). (2) The spherulites of PKS and PEK are composed of long, narrow lamellar crystals. It has been confirmed by electron diffraction (ED) studies that the longitudinal, transverse, and thickness directions of the long lamellar crystals correspond to theb, a, and c-axes, respectively. (3) The melt-grown and the melt- quenched and subsequently heat-treated PKS and PEK have a similar two- chain orthorhombic unit cell. The orthorhombic unit cell parameters of PKS area= 0.767 nm,b= 0.620 nm, andc= 1.044 nm. On the other hand, drawn or rolled PKS films have a two-chain monoclinic unit cell with parameters ofa= 0.836 nm,b= 0.606 nm,c= 1.044 nm, and γ = 68.5°. These results indicate that a crystal (orthorhombic)-crystal (mono- clinic) transition occurs during the deformation of PKS. The crystal structure of PEK does not change at all during deformation.

ISSN:0022-2348    

DOI:10.1080/00222349808220455

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The temperature dependence of the electrical conductivity and the Seebeck coefficient for some chelate-modified polysulfones (PSF-Cs) derived from chloro-terminated polysulfones and bis (2,4-dihydroxybenzaldehyde) Cu2+were studied. The measurements were performed using the thin films deposited from solution. The investigated polymers have semiconducting properties. The correlations between these properties and the molecular structure of the respective polymers are discussed.

ISSN:0022-2348    

DOI:10.1080/00222349808220456

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The structure/property relationships in a series of melt-spun poly(ethylene terephthalate) (PET) fibers processed under different conditions have been investigated. The structure of the fibers was characterized using a variety of techniques, including gel permeation chromatography (GPC), differential scanning calorimetry (DSC), optical birefringence, and wide-angle x-ray scattering (WAXS). The mechanical properties of the PET fibers were also investigated, and the fibers showed different stress-strain and modulus- strain curves as a result of the different processing conditions employed. Raman spectroscopy was used to study molecular deformation processes in the PET fibers. It was found that most of the PET Raman bands shifted to a lower wavenumber when the fibers were subjected to axial tension, and the shift of the 1616 cm−1band was examined in detail. It was found that there was a linear relationship between the position of the center of gravity of the band and stress and that the stress-induced band shift factor of −4].0 cm−1/GPa was identical for all PET fibers studied. Band broadening was also found under stress, and the Raman bandwidth (full width at half maximum, FWHM) provided information about the spread of molecular stresses resulting from the application of macroscopic tensile stress to the fibers. The molecular deformation processes in the PET fibers have been interpreted in terms of a modified series aggregate model in which the molecules are subjected to a constant average level of stress.

ISSN:0022-2348    

DOI:10.1080/00222349808220457

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Molecular chain orientation characterized by an order parameter in fibers about 102μm n in diameter of poly(phenyl-p-phenylene terephthalate) and related copolyesters was investigated by means of infrared attenuated total reflectance (IR ATR) spectroscopy. Samples had a tensile strength of about 1 GPa, which could be increased to 2–3 GPa by a heat treatment under appropriate conditions. It has been found that the chain orientation is parallel to the fiber axis in the surface layer. At a distance of about 10–15 μm from the surface, the orientation decreases, with the most oriented surface layer being easily detachable from the weakly oriented fiber core. The great difference between the molecular orientation in the surface layer and in the fiber bulk was supported by wide-angle x-ray scattering (WAXS) data.

ISSN:0022-2348    

DOI:10.1080/00222349808220458

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Fu et al. [1] have reported an interesting set of experimental results on ultra- high molecular weight (UHMW) polymer fibers. The characterization techniques used in their study are primarily x-ray diffraction,13C solid-state nuclear magnetic resonance (NMR), and differential scanning calorimetry (DSC). We do not comment on the specific results reported using these techniques, but make some comments regarding statements on other techniques not employed by these authors (i.e., Raman spectroscopy and theoretical simulations), as well as several more general comments.

ISSN:0022-2348    

DOI:10.1080/00222349808220459

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor