摘要:

AbstractWe have developed a flash radiometry technique for the determination of the thermal diffusivity of polymer films that consists of flashing a laser pulse on the front surface of the sample and monitoring the thermal radiation from the rear surface as a function of time using an infrared detector. This method is applicable to polymer films of thickness 14–250 μm in the wide temperature range between 150 and 500 K. We have performed measurements on four polymers, including polycarbonate, polyimide, polyvinylidene fluoride, and polyethylene terephthalate. The temperature dependence of the thermal conductivity of polycarbonate can be understood by considering the phonon mean free path, and the crystallinity and orientation dependence of the thermal conductivity of polyethylene terephthalate can be explained in terms of the two‐phase model proposed by Choy and Y

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250901

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractFractions of two cellulose tricarbanilate samples were characterized by light‐scattering (weight‐average molecular weight, second virial coefficient, mean‐square radius of gyration), gel permeation chromatography (polydispersity index), and viscometry (intrinsic viscosity) in tetrahydrofuran and acetone. The intrinsic viscosity data were analyzed in terms of the theory developed for the continuous wormlike cylinder model, and the chain parameters (Kuhn statistical segment length λ−1, chain diameterd, and shift factorML) were evaluated. The molecular‐weight dependence of the mean‐square radius of gyration in tetrahydrofuran was calculated for the Kratky—Porod chain model and compared with the experimental results. Data on the intrinsic viscosity and radii of gyration for other solvents at temperatures from 0 to 100°C were analyzed in the same way, and the effects of solvent and temperature on the statistical segment length were evaluated. Polymer—solvent interaction parameters were estimated from the second vi

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250902

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractMechanisms for low‐temperature relaxations of three spiro‐ring‐type epoxide resin systems with and without methoxy branches were investigated by comparison with those of a bisphenol A‐type resin system. In the spiro‐ring‐type epoxide resin systems, two well‐defined relaxation peaks, denoted as the β and β′ relaxations, and a shoulder peak were observed at about −70, +60, and 0°C, respectively. The magnitude of the β relaxation was decreased by the introduction of methoxy branches on the phenylene group. This phenomenon could be interpreted as a result of the formation of hydrogen bonds between the hydroxy‐ether group and methoxy branch. Moreover, it was concluded that the β′ relaxation and the shoulder peak are due to the motion of thep‐phenylene group adjacent to the spiro‐ring and of the hydroxy‐ether group blocked by

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250903

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractWide‐angle X‐ray scattering from presumed block copolymers of polypropylene (PP) and ethylene‐propylene copolymer (EPR), i.e., PP‐EPR and PP‐EPR‐PP, synthesized by sequential polymerization with δ‐TiCl3Et2AlCl, was examined and compared with WAXS of mechanical blends and chain‐transfer mixtures of PP and EPR with comparable compositions. The peak at 2θ = 20° for both the copolymers and the mixtures was attributed to the γ modification of PP in EPR. A strong variation in the ratio of diffraction intensitiesI040/I110of PP in block copolymers and mixtures was explained in terms of crystallite growth in different directions. Analysis of the patterns and calculation of crystallinity, crystallite size, and lattice parameters led to the conclusion that block structure existed in th

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250904

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe dynamics of a single copolymer chain in a solution containing identical chains is studied. The intermediate scattering function is calculated, and two different modes are identified and analyzed as a function of wave vectorq. The first mode is characteristic of the copolymer system and leads to a peculiar constant relaxation frequency asqgoes to zero. The second mode represents the diffusion of the chain in the solution.

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250905

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe dynamic mechanical behavior of 10 and 20% poly(vinyl methyl ether)‐polystyrene blends has been studied in the frequency range 10−5Hz to 5 Hz and temperature range 100–450 K. Isochronal plots of modulusG′ and loss factor, tan ϕ, show the presence of one relaxation process at temperatures below the transition zone. A second relaxation process at intermediate temperatures but belowTgmay be inferred from the breadth of theG″ frequency curves in the transition zone of both blends. This process, at 280

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250906

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractOptical and calorimetric studies of the kinetics of mesophase formation and crystallization in poly(diethylsiloxane) have been conducted. The mesomorphic phase is found to grow from the isotropic melt in the form of lamellar domains about 2 μm thick in the temperature range 293–307 K. According to birefringence data, macromolecules in the mesomorphic lamellae are perpendicular to the end faces. The kinetics of mesophase formation obey the Avrami equation with the morphological parameternclose to 2 (it is equal to 1.75 ± 0.05), which corresponds to the two‐dimensional growth of the mesomorphic phase from athermal nuclei. The limiting conversion of the isotropic melt was shown to be temperature‐dependent. This is likely to be connected with a change in the number of nuclei with temperature. The crystallization of polymer from the mesomorphic state occurs with retention of the optical texture of the sample. The process proceeds not as a sporadic crystallization of individual mesomorphic lamellae but as a growth of the nucleated crystalline regions via a consecutive incorporation of adjacent crystallizing l

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250907

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractFurther thermoluminescence data are presented supporting our earlier suggestion that the electron traps associated with the three peaks in the thermoluminescence glow curve of a low‐density polyethylene sample from which absorbed air has been removed are formed by the polymer chains themselves in the chain‐fold regions of the samples. These traps are shown to be sensitive to heating of the sample to temperature around its melting point; in particular, the lowest temperature peak disappears if the sample is held at 90°C in vacuum for 5 min. If the sample is maintained in vacuum at room temperature after such treatment, its modified glow curve remains unchanged for a period of at least 7 days; however, if the sample is exposed to air, nitrogen, or argon after such treatment, its gas‐free glow curve begins to change within 3 days, evolving toward a three‐peak form with the same peak temperatures but with relative intensities different from those observed before heating began. This suggests that the gas molecules “lubricate” the polymer chains, which then begin to move toward new equilibrium configurations. Immersion inn‐hexane at room temperature has little effect on the luminescence centers but disables the electron traps. Immersion in fuming nitric acid at room temperature for 2 days appears to destroy the electron traps permanently, as would be expected if the chain folds are digested by the acid; its effect on the luminescence centers is still to

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250908

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractElectron spin resonance (ESR) of γ‐irradiated poly(vinyl alcohol) (PVA) at room temperature has been used to identify the radiation damage products. The ESR spectrum is analyzed by using least‐squares fits between observed and calculated spectra, assuming various free radical species. The best theoretical fit, together with UV absorption data, enabled the assignment of the observed ESR spectrum. The existence of carbonyl macrofree radicals, probably with aldehyde functional groups, is proposed in irradiated

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250909

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe permittivity and loss of poly(methyl methacrylate) (PMMA) network crosslinked with trimethylol‐1,1,1 propane and its interpenetrating network polymers with 10, 34, and 50% (by weight) poly(urethane) have been measured from 100 to 400 K over a frequency range of 12 to 1 × 105Hz. Two relaxation processes, γ and β, are observed in the PMMA network, and a third process, αpu, in the 10% poly(urethane) IPN. At higher concentrations of poly(urethane), the γ process is removed from the temperature‐frequency range of our study. Crosslinking in pure PMMA slows the segmental motions involved in the β process and raises its activation energy. Physical aging of the 10 wt% poly(urethane)‐PMMA causes its γ process to become indiscernible and the αpuprocess to become better resolved. A discussion of these results in terms of local regions of segmental motio

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250910

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY