摘要:

AbstractA new technique is described for dilatometry under high pressure. The technique is based on optical interferometry and is analogous to measuring the thickness of thin, nonabsorbing films and coatings. The procedure is demonstrated for the well‐characterized system ofn‐pentane sorption by polyisobutylene, and then results for the dilation of polycarbonate by the sorption of carbon dioxide are presented. The dilation of polycarbonate by CO2is nearly linear with concentration; the partial molar volume of CO2decreases slightly with increasing pressure. This result indicates that all sorbed CO2molecules contribute equally to the dilation of the polymer matrix and that none reside in microvoids or in preexisting free‐volume elements which do not contribute to volume expansion of the po

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240501

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractWe have used an optical interference technique to measure the dilation of polystyrene films in the presence of carbon dioxide or helium at pressures up to 20 atm. Dilation isotherms (plots of dilation versus gas pressure at constant temperature) were obtained for three samples of polystyrene which had widely differing molecular weights. The dilation isotherms have the same general shape as sorption isotherms, which means that all of the sorbed gas molecules contribute to volume dilation and non can be thought of as occupying molecular‐sized voids in the polymer. Using sorption results from the literature we show that the partial molar volume of CO2at 35°C is about 39 cm3mol−1and appears to be independent of polystyrene molecular weight. For a polystyrene sample withMn= 3600, the partial molar volume of sorbed CO2increases to 44 and 50 cm3mol−1at 45 and 55°C, respectively. The sorption of CO2in polystyrene is shown to depress the glass transition temperature of the mixture, consistent with theoretical predictions. The shape of the dilation and sorption isotherms are consistent with the depression of the glass transition temp

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240502

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe emulsifying activity of block copolymers is investigated in blends of incompatible engineering polymers such as polyvinyldene fluoride (PVF2) and Noryl (high impact polystyrene‐poly‐2,6‐dimethyl‐1,4‐phenylene oxide mixture). When the blends are modified by a poly(styrene‐b‐methyl methacrylate) copolymer, (PS‐PMMA) each block of which being selectively miscible with Noryl and PVF2respectively, Phase dispersion, interfacial adhesion and ultimate mechanical properties are significantly improved; major effect is observed upon addition of 12 percent copolymer, resulting in intermingled and firmly adherent phases and a rough additivity of both tensile strength and elongation at break. All these features clearly demonstrate the important emulsifying effect of PS‐PMMA in these very attractive

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240503

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractBlock copolymers of two crystallizable compounds, poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), were developed with PET as the major component and the amount of PBT varying from 1.0 to 20.0 wt %. These block copolymers were prepared by end‐group coupling of preformed oligomers. All polymers prepared were of equivalent molecular weight as determined by the intrinsic viscosity method. Thermal properties were determined by differential thermal analysis (DTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). With increasing PBT content, the block copolymers showed a general decrease in the values of glass transition temperature, melting temperature, initial decomposition temperature, and maximum decomposition temperature. The heat of fusion and heat of crystallization first increased and then decreased slightly. Rates of crystallization were determined by measuring density as a function of time of isothermal crystallization carried out at 95°C. It was found that small amounts of PBT increased the crystallization rate considerably over that of PET. Random copolymers did not show this phenomenon and behaved more like pure PET. The crystallization behavior of block copolymers was analyzed by the Avrami equation and Avrami exponents were determined. Results were explained on the basis that the faster‐crystallizing PBT blocks crystallized first and provided built‐in nucleation sites for the subsequent crystallization of PET, thus resulting in a relatively fast‐crystallizing cop

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240504

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractSmall‐angle light‐scattering (SALS) studies were carried out on block copolymers of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), the synthesis and characterization of which have been reported in an earlier paper. Samples were crystallized isothermally from the melt at 95°C for predetermined crystallization times in order to follow the formation and growth of crystalline superstructure. During the early stages of crystallization, the block copolymers showed unusualHvpatterns with the four lobes along the polarizer directions, while at later stages they showed the usualHvpatterns with the four lobes at 45° to the polarizer directions. The unusual patterns are characteristic of PBT superstructure, while the usual patterns are characteristic of PET superstructure. These results show that PBT, which is the faster‐crystallizing component, crystallizes first and provides nucleation sites for the crystallization of PET, which crystallizes later. Similar behavior was not observed in PET homopolymer and random copolymers of equivalent compositions. In each case the spherulite size increased with the time of crystallization. The ultimate spherulite size decreased with increasing PBT content in the block copolymer, thus showing an increase in nucleation density. It was demonstrated that light scattering is a useful tool to characterize block copolymers of two crystalline components which have different types of superst

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240505

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractQuenched films of isotactic polypropylene were drawn at 110°C up to draw ratio λ = 18. The axial elastic modulus was measured as function of λ up to the highest achieved λ. The sorption and diffusion of CH2Cl2at 25°C in the undrawn and drawn samples were studied. Exclusively transparent samples were used for the measurement of the density and transport properties. This reduces the maximum usable draw ratio to 15. The drawing process is inhomogeneous with neck propagation. In the neck the draw ratio increases by about 6. As a consequence of the increasing fraction of taut tie molecules the axial elastic modulus increases faster than the draw ratio. The transport parametersD,S, and λ indicate that the original lamellar morphology is completely transformed into the microfibrillar stru

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240506

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractIonic interactions in blends of poly(styrene‐co‐styrene–sulfonic acid) and poly(ethyl acrylate‐co‐4‐vinylpyridine) result in greatly extended rubbery regions. Measurements of dynamic shear moduli as a function of frequency at various temperatures above the glass transition indicate that time–temperature superposition is applicable in almost all cases. Relative to a blend of pure polystyrene with pure poly(ethyl acrylate), the copolymeric blends strongly resemble one another regardless of either compatibility or ion content. Higher ion content appears to enhance the extension of the rubbery plateau. True flow is not achieved even at temperatures as high as 220°C (0.1 rad/s). Flow is clearly evident in the nonionic blend at 170°C (0.1–1.0 rad/s). It is postulated that the ionic interactions are such that bond breaking and reforming are more rapid than the rate

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240507

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractPolyethylene films were stressed in uniaxial tension at room temperature while the infrared (FTIR) or Raman spectra were simultaneously measured. The purpose of these experiments was to gain an understanding of the molecular origins of the stress‐induced vibrational frequency shifts Δν and determine the mechanisms of molecular deformation and fracture of PE molecules with stress σ. The PE samples consisted of ultradrawn, high‐density, ultrahigh‐molecular‐weight, solid‐state‐extruded films and the stress was applied parallel to the nearly perfectly oriented orthorhombic crystalc‐axis direction. The experimental frequency shifting coefficients α = (∂ν/∂σ)σ→0were compared with calculated α values determined from a vibrational analysis of an isolated PE chain using conformational energy minimization methods in which both harmonic and anharmonic (Morse) potential energy functions were used for the CC stretching modes in the valence force field. The following α values were obtained and are compared with theory (anharmonic case in parentheses, in cm−1/GPa): CC symmetric stretch, α(1127) = −5.9 (−5.3); CC asymmetric stretch, α(1059) = −11.2 to −5.7 (−5.8); CH2rock, α(730/720) = −2.0 to −3.0 (−2.2); CH2scissors, α(1472/1462) = −1.0 to −1.2 (−1.1); CH2twist, α(1295) ≃ 0(0.8); CH2wag, α(1370) undetermined owing to weak bands (−4.6); CH2stretch α(3000) ≈ 0. The largest negative frequency shifts were observed for the CC stretching modes, in agreement with the calculations using the Morse potential. The harmonic potential for CC stretching resulted in small positive α values for both the CC stretching and CH2wagging modes, while the other modes were unaffected by this choice of potential. The relative contribution of CC bond stretching and CĈC valence angle bending to thec‐axis strain was about 1:1, in agreement with exp

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240508

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractIn the production of ultrahigh‐modulus (45–60 GPa) polyoxymethylene (POM) by microwave heating drawing, ultradrawing to draw ratios over 20 causes formation of numerous voids and radicals. The volume fraction of the internal voids is proportional to the drawing‐induced radical concentration. On the basis of the idea that the rupture of taut tie‐molecules (TTM) is responsible for void and radical formation, the relationship between the fraction of tiemolecules that are taut and the fraction that are ruptured is discussed by assuming both a Takayanagi structure model and the normal distribution of the tie‐molecule lengths. The results indicate that longer tie‐molecules are successively converted to TTM's followed by ruptures of shorter TTM's in the ultradrawing process; a small variance in the tie‐molecule length distribution is effective for increasing TTM's without void formation. The maximum value of the volume fraction of taut tie‐molecules for highly oriented POM tubes is estimated

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240509

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe crystallization behavior, via annealing, of PEEK was investigated using FTIR spectroscopy. It was found that predominantly amorphous PEEK (e.g., quenched polymer) follows two distinct mechanisms when it is annealed. One is a lower energy relaxation process that involves the partial rotation of the ether linkages, allowing the molecular chains in the disordered phase to become better packed, and occurs from 50 to 140°C (slightly belowTg). This relaxation process is also observed by dynamic mechanical analyses. The other process is a crystallization that takes place above the glass transition, with its onset characterized by the rotation of the benzophenone linkages nearTg. Isothermal crystallization kinetics data on PEEK can be described by an Avrami equation with an Avrami constantnof about 1

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240510

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY