摘要:

AbstractThe crystal structures of drawn copolyamides 6/6.6, 6/6.T, 6/6.1, 6/PXD.6, 6/MXD.6, and 6/MXD.I were examined by wide‐angle x‐ray diffraction. Copolyamide 6/6.6, which follows the inclusion model, shows only α‐characteristics at all the comonomer compositions examined (0–33.3 mol%). However, the other copolyamides, which follow either the partial‐inclusion or complete‐exclusion model, show γ‐characteristics more predominantly as the comonomer content increases. The interplanar spacing of the (200) planes, which corresponds to the hydrogen bond distance between antiparallel chains, remain constant, whereas the spacing of the (020) planes corresponding to the distance between hydrogen bonded sheets increases monotonically with increasing the comonomer content. It is also observed that both the crystal perfection index and the crystal thickness decrease as the comonomer co

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280501

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe gas barrier properties of a wide range of biaxially oriented polyethylene terephthalate films have been investigated. The permeability and diffusion coefficients for oxygen and water vapor transmissions were determined for films prepared by both simultaneous and sequential biaxial stretching. The effect of annealing was also studied and a comparison made with previous results for uniaxially oriented films. It was found that the permeability correlated well with the density of the sample, but that the dependence on thegauche/transconformer ratio shown for uniaxial material was not so clear. A good empirical correlation was also obtained between permeability and a proposed measure of molecular orientation obtained from refractive index measurements. A more detailed interpretation, based on infrared measurements of orientation, showed that there is a systematic reduction in permeability as the planes of the terephthalate residues become parallel to the film surface.

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280502

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractPolyurethanes (PU) based on poly(butylene adipate) [PU(PBA)] and poly(oxypropylene) [PU(PPG)]polyols have bean introduced into the diglycidyl ether of bisphenol A (epoxy) to form interpenetrating polymer networks (IPNs) with a PU‐grafted epoxy structure (graft‐IPNs).The tensile strength in both PU(PPG)/epoxy and PU(PBA)/epoxy systems increases with increasing PU content. Maximum values emerge at PU/epoxy ratios between 19/81 and 27/73. This is explained as a result of the presence of the graft structure, which leads to more intimate interpenetration between the PU and epoxy in the graft‐IPNs.Dynamic mechanical analysis (DMA) indicates that the PU introduced can be incorporated in either the α or β transition domain of the epoxy. The tensile strength of the resulting graft‐IPNs shows a significant improvement as the PU is incorporated in the α transition domain of the epoxy. It is also noted that suitable amounts of PU incorporated in both the α and β transition domains of epoxy can increase the tensile strength of the IPNs, while excessive amounts of PU introduced into both α or β transition domains tend to decrease the tensile strength of

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280503

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractHigh density polyethylene was biaxially oriented by high‐pressure forging and subsequently low‐pressure thermal forming. The permeability of O2, CO2, and CH4was reduced slightly by biaxial orientation, the diffusivity of the gases was found to increase with the degree of orientation. The solubility decreased markedly with orientation. Density measurements indicated that crystallinity increases with the extent of biaxial deformation. Based on the concept of particle flow in viscous media, the variation of gas diffusivity with orientation is viewed as a frictional resistance effect. The diffusivity is inversely proportional to a phenomenological friction coefficient; which can be related to orientation by a shape factors. The diffusivity for the oriented state,D, is then related to that of the nonoriented state,D0, asD=D0/(1 +sϕ). The variation of diffusivity selectivity with orientation is also formulated based on this consideration. Results on both biaxially and uniaxially oriented HDPE are examined in light of this m

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280504

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractCopolymerization of ethylene (E) with propylene (P) initiated with soluble (polystyrene)100‐butadiene3‐Li/TiCl4complexes leads to [St]‐b‐[E‐co‐P]diblock copolymers with a random [E‐P] block. GPC and13C‐NMR analyses of copolymers with various compositions and block lengths disclose well‐defined linear structures. From DSC measurements of such materials, three different endothermal transition regions are observed: two glass transition regions corresponding, respectively, to theTgof styrenic and olefinic blocks, and one [E‐P] block melting region in which propylene units play a primary role. Furthermore, an additional endotherm is observed, depending on the thermal hi

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280505

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractQuantitative thermal analysis of a family of semicrystalline polyimides containing from one to three ethylene glycol spacer units has been conducted. Special emphasis has been placed upon the changes in the thermodynamic properties resulting from the successive additions of ethylene glycol units. The solid and liquid heat capacities were measured in the temperature range 230–640 K. The solid heat capacities were also calculated from the vibration spectra of the polymers. An in‐depth description of the glass transitions, the heat capacity increases at the glass transition temperatures, and the widths of the glass transitions is provided. Three parts of the heat of fusion have been identified:Wc(H), that contributed from the high melting peak;wc(L), that contributed from the low melting peak; andwc(C), that developed during cooling after isothermal crystallization. The metastability, sequence of crystallization, and rate of reorganization of the low and high melting peaks have been investigated by stepwise crystallization and by analysis using different heating rates after isothermal crystallization. A rigid amorphous fraction is needed to explain the failure of the two‐phase (crystallinity)

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280506

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe dielectric permittivity ε′ and loss ε″ of anhydrous poly(2‐hydroxyethyl methacrylate) and its 38.6 w/w% hydrogel have been measured in the frequency range from 12 Hz to 200 kHz and the temperature range from 77 to 273 K. The former has a sub‐Tgrelaxation with a half‐width of 4.5 decades for the loss spectra, whose strength increases with temperature, and an activation energy of 62.5 kJ/mol. The dielectric relaxation time of the α process of supercooled water in the hydrogel is 53 s at its calorimetricTgof 135 K. The half‐width of the relaxation spectrum is 2.85 decades and, in the narrow temperature range, its apparent activation energy is 60.8 kJ/mol. Heating of the hydrogel causes crystallization of water which begins at about 207 K and becomes readily detectable as a second dielectric loss peak at about 230 K. For each temperature between 207 and 267 K, supercooled water in the hydrogel coexists with its crystallized form, with the amount of the crystallized solid increasing with increasing temperature. These results are discussed in terms of “bound” and “free” states of

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280507

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe goal of this study is to elucidate the relationship between the mechanism of bond formation, resulting structure, and the viscosity during the step polymerization of a thermoset. The system chosen for this work consists of a bifunctional epoxy, diglycidyl ether of bisphenol A, cured with a tetrafunctional amine, diaminodiphenyl sulfone. Steady shear and dynamic viscosity are measured as a function of extent of reaction throughout the epoxy‐amine cure. Branching theory is used to relate the extent of reaction (i.e., conversion of epoxy groups) to certain structural parameters, including the weight‐average molecular weight. The combination of the viscosity‐conversion data with the branching theory enables the correlation between changes in rheological properties and network structure during polymerization. The steady shear viscosity rise is modeled as the product of a structure‐dependent friction factor and weight‐average molecular weight. The structural significance of the point in cure when the dynamic storage and loss modulus are equal (i.e., tan δ = 1) is als

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280508

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractLaser light scattering, with the aid of Mie's scattering theory, was used to investigate bubble nucleation in concentrated polymer solutions. Solutions with 40, 50 and 60 wt % polystyrene in toluene were used. A test solution in a high‐pressure optical cell made of strain‐free quartz was heated to a predetermined temperature under pressure. Upon release of the pressure in the cell, both scattered and transmitted light fluxes were measured with photomultipliers, and the variation of system pressure with time was measured using a piezoelectric pressure transducer. The measurement of the light scattering flux and control of the experiment were performed by means of a microcomputer with a general‐purpose data acquisition interface. Data reduction was done using the same microcomputer. The critical bubble size was determined by obtaining a one‐to‐one correspondence between the extrema of the experimental and theoretical scattering curves. While the Mie scattering theory is for monodisperse particles, the experimental scattering curves indicated that the bubbles had a distribution of sizes. Therefore, the log‐normal distribution function was used to represent the size distribution; and theoretical scattering curves were computed by varying the breadth parameter in the log‐normal distribution function, until we had a one‐to‐one correspondence between the extrema of the experimental and theoretical scattering curves. In this way, we were able to determine (a) the size distribution of bubbles in the optical cell, (b) the critical bubble size, (c) the total number of bubbles nucleated, and (d) the critical pressure for bubble nucleation, as functions of temperature, the initial equilibrium pressure in the optical cell, and the concentration of the

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280509

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractA theory based on classical nucleation theory is developed for bubble nucleation in polymer solutions. The theory requires information on solubility, diffusivity, concentration, surface tension, temperature, and degree of supersaturation. The effects of supersaturation and of the presence of large molecules in a liquid mixture on the free energy of bubble formation are included in the theoretical development. A semiempirical equation for the determination of bubble nucleation rate is developed, with the aid of experimental results reported in part I of this series. Using the experimental data, computer simulations of bubble nucleation in polymer solutions are performed. The consumptions of the volatile component in a liquid mixture, due to bubble nucleation and subsequent growth, and the variation of bubble nucleation rate during the expansion process are included in the simulation of the bubble nucleation process.

ISSN:0887-6266    

DOI:10.1002/polb.1990.090280510

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY