摘要:

AbstractThe volatile‐component evaporation mechanism proposed by Chen et al. to explain molecular‐weight‐dependent endothermic peaks found at temperatures aboveTgin anionically prepared polystyrenes (PSs) on first heating in open DSC pans is inconsistent with several bodies of literature data which were overlooked, including similar data with closed DSC pans. Moreover, this mechanism appears deficient in explaining details of the dependence of the endothermic peak temperature on M̄nboth below and above the entanglement molecular weightMc, with a sharp increase in slope atMc. The original fusion–flow mechanism of Stadnicki et al. is compatible with all other known literature data including results on thermal PS and PMMA fractions. Hot‐stage microscope examination of powdered anionic PSs supports the Stadnicki mechanism from M̄n= 1900 to at least M̄n= 350,000. Addition of small amounts (ca. 1 wt %) of benzene or ethylbenzene to PS results in open‐pan DSC traces without endothermic peaks but with an endothermic slope change indicating gradual loss of diluent at decreasing rate as the temperature is increased from belowTgup throug

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230101

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractIt is proposed here that readily observable viscous deformation is the common underlying phenomenon which is reflected in several kinds of evidence advanced for the existence of a liquid–liquid transitionTLL. These include flow temperatureTfmeasurements, microscope hotstage coalescence, and differential scanning calorimetry (DSC) measurements. A DSC peak observed atTgin high‐molecular‐weight bulk‐polymerized poly(methyl methacrylate) is discussed in terms of the presence of conformations of low

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230102

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractA formal definition ofTLLas a function of M̄nfor polystyrene was prepared with literatureTLLvalues from torsional braid analysis (TBA), differential scanning calorimetry (DSC), and zero‐shear melt viscosity η0. Data from six authors using anionically prepared PS and blends thereof were involved. The resultant linear least‐squares regression line,TLL(°C) = 148.5 − 11.487 × 104M̄ n −1[standard error inTLL(calculated) 4.056 K, correlation coefficientR2= 0.9534] is considered valid from M̄n= 2000 to the entanglement molecular weightMc= 35,000. The “best”TLLvalues reported by Orbon and Plazek from double Arrhenius plots are well below this line for M̄v= 47,000, 16,400, 3400, and above it for M̄v= 1100. These bestTLLvalues are artifacts arising from no or insufficient data points above or belowTLLand/or too many data points nearTg. The associated high enthalpies of activation which they report confirm this diagnosis. The fact that these artificialTLLvalues tend to disappear when checked by the three‐parameter Vogel equation, logη = logA+Bexp[(T−T∞)−1], has no relevance to the controversy concerning the existence and meaning ofTLL. The claim by Orbon and Plazek thatTLLvalues obtained by TBA, DSC, and melt viscosity are all artifacts of the individual methods by which they were obtained is inconsistent with the excellent master plot which they generate. Alternative plotting devices which revealTLL>Tgfrom η0vs.T−1data, as developed by van Krevelen and Hoftyzer and by Utracki and Simha (not previously considered by either party), are reviewed. A statistical examination of the nature of the Vogel–Fulcher–Tammann–Hesse equation, based on synthetic data, is presented. Evidence forTLLin atactic polypropylene is offered based on published data by Plazek and Plazek.TLLis considered to possess both relaxational and q

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230103

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractData on the temperature dependence of viscosity obtained on three different polystyrenes with narrow molecular weight distributions are fitted to the Vogel, Fulcher, Tamman, and Hesse (VTFH) equation as well as to two intersecting Arrhenius lines. Both fits are optimized by means of computer programs. The data were chosen to fit the requirements stated by Boyer. The results of the analyses support the earlier conclusions that temperature‐dependent viscosity data do not indicate the presence of any liquid‐liquid transitionTLLabove the glass temperatureTg. In addition, evidence is presented which indicates that the viscosity atTgof high‐molecular‐weight polystyrenes is proportional to the 3.4 power of the molecular weight. HenceTgis not an isoviscous temp

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230104

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractPolyesteramide 6NT6–polytetramethylene ether glycol (PTMEG) copolymers, precipitated from dilute solution, have been studied by small‐angle x‐ray scattering (SAXS) and wide‐angle x‐ray scattering (WAXS) with variation of the PTMEG content. A comparison of the structural characteristics of these materials has been made with those of the 6NT6 homopolymer. Chain folding is assumed as the crystallization mechanism for the low‐PTMEG‐content copolymers, with possible inclusion of polyether segments within the 6NT6 crystal lattice. WAXS data support the view of a weakening of the 6NT6 crystalline packing in the equatorial planes as the reason for broadening of the diffraction peaks, for changes in their relative intensities, and for the increase in the equatorial interplanar distances in the high‐PTMEG‐content samples. The annealing behavior has also

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230105

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractProton spin–spin relaxation times and the Weibull coefficient have been measured as functions of temperature for poly(ethylene terephthalate) (PET) drawn at 50°C in both the amorphous and the semicrystalline (50%) states. Two relaxation timesT2a(long) andT2c(short) are observed for all samples. They are ascribed, respectively, to the relaxation of the amorphous and of the crystalline components including highly strained noncrystalline segments. Effects of initial morphology are found for chain mobility in the noncrystalline regions and for the crystal perfection, evaluated fromT2aand the Weibull coefficient μcof theT2c‐component, respectively. For all draw ratios,T2afor extrudates prepared from the semicrystalline polymer (C‐50) is short compared to that for preparations from the amorphous (A‐50) polymer. In the A‐50 samples, the perfection of stress‐induced crystals increase with increasing draw ratio. In the C‐50 samples, the crystal orientation increases, whereas the perfection decreases with increasing draw ratio. To improve the crystal perfection, annealing at higher temperature or longer time is required for C‐50 as compared with A‐50. The value of μccorrelates well with the change in crystal perfection during defor

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230106

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe translational diffusion coefficientD, needed in treatments of flow‐induced polymer migration phenomena, is studied. Explicit results are reported for bead–spring model macromolecules with two, three, and four beads, respectively. If the number of beads is large, an integral formulation is used. The results obtained show thatDdepends upon the hydrodynamic interaction parametersh*andh*N1/2. Nondraining behavior ofDis predicted irrespective ofhifh*is close to 0.2357. Approximations forDare obtained and the error involved is estima

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230107

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe cross‐stream migration velocityv⊥is that part of the velocity of a particle which has no component in the direction of the undistrubed flow. In order to obtainv⊥for bead–spring model macromolecules, it is necessary to compute the trace of the matrix product\documentclass{article}\pagestyle{empty}\begin{document}$ \underline \ell \cdot \underline {{\rm \hat C}} $\end{document}, where\documentclass{article}\pagestyle{empty}\begin{document}$ \underline \ell $\end{document}denotes the migration matrix and\documentclass{article}\pagestyle{empty}\begin{document}$ \underline {{\rm \hat C}} $\end{document}is the modified Kramer's matrix. In this paper this is done via an eigenvalue calculation, where the eigenvalues are estimated by using the Rouse eigenfunctions. The results are then checked against the few known exact results and excellent agreement is found. It turns out thatv⊥depends on the third power of the molecular weight for free‐draining polymers. The dependence upon molecular weight becomes weaker with increasing hydrodynamic interaction until, in the nondraining limit,v⊥∝M2.5. A simple yet accurate formula forv⊥is proposed. In conjunction with the results forD(of Part I), purely rotational flow fields are shown to be characterized by a single parameter, the particle Peclet number Pe. Up to a constant of order one (actually a function of the hydrodynamic interaction parametersh*andh, which can vary only between 0.8 and 2.057), Pe depends only uponD, the mean‐square equilibrium extensionR 02, andq0, the magnitude of the maximum sh

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230108

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractIsotactic polypropylene of various degrees of crosslinking was prepared using high concentrations of dicumyl peroxide as the crosslinking agent. Free radicals were generated by γ irradiation of crosslinked iso‐PP with a dose of 2.4 Mrad. It was found that the rate constant for free‐radical decay is independent of crosslinking in the temperature range from −30 to +20°C. The result is discussed from the point of view of degradation processes taking place simultaneously with crosslinking of

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230109

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractAudio‐frequency dielectric relaxation measurements and differential scanning calorimetry studies have been performed on poly(ethylene oxide) (PEO) complexed with calcium and barium thiocyanate. The measurements were performed over the temperature range 5.5‐300 K. The relaxation spectrum for the complexed material consists of two peaks. The activation enthalpy for the peak corresponding to the γ relaxation of pure PEO depends upon the size of the dopant cation. The activation enthalpy for the second peak is independent of the nature of the dopant cation and is very similar to that observed for the αcrelaxation observed in pure PEO. Furthermore, the room‐temperature electrical conductivity of the complexed materials is much smaller than that for pure PEO and hence very much less than for PEO‐complexed with alkali‐metal salts. However, aboveTgthe conductivity rises rapidly and is larger for the barium‐thiocyanate‐complexed PEO than for the calcium‐complexed material. Finally, the DSC studies show that one effect of the ions is to shift the glass transition to hi

ISSN:0098-1273    

DOI:10.1002/pol.1985.180230110

出版商:John Wiley&Sons, Inc.    

年代:1985

数据来源: WILEY