摘要:

AbstractThe mechanical anisotropy in shear of oriented from I poly(vinylidene fluoride) sheet has been studied, completing the measurement of all nine independent compliances for this material. The morphology is parallel‐crystallite; however, the crystalline regions are not lamellar in shape, but take the form of blocks with a bricklike shape oriented along the draw direction. The results have been analyzed in terms of a three‐dimensional generalization of the Takayanagi model. First, modelling of the three principal extensional compliances based on previous measurements indicates that the gaps between the crystalline units are smaller in the transverse directions than in the draw direction. A voided sample shows a marked increase in the transverse compliances of the amorphous regions and considerable anisotropy owing to the voids. Secondly, a novel development of the Takayanagi model has been made to analyze the shear behavior. This has enabled the calculation of the shear compliances of the amorphous regions and indicates that the larger magnitude of the shear compliance in the plane normal to the draw direction is due to the large magnitude of the corresponding amorphous shear compliance, and that this is not affected by increased draw ratio or by the vo

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270701

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe complementary application of the NMR inversion recovery measurements and the computer fitting of the overlapping spectral region is found to be a useful method for structural analysis of vulcanized natural rubber in the solid state. Since the linewidths in13C‐NMR spectra of solids are relatively broad compared with the differences between chemical shifts, some weak signals are completely obscured in the resulting spectra. If the resonances have sufficiently different relaxation times, such as methyl and methylene carbons, it is possible to detect neighboring heavily overlapped signals by using the inversion recovery delay τ value at which the interfering strong resonance has null intensity. The 20 resonances observed in the spectra of crosslinked rubbers are tentatively assigned to the structural units formed during the vulcanization process. It is found that vulcanizates containing smaller amounts of sulfur (1 and 3%) show insignificant changes in the NMR spectra for curing times of 30 and 90 min. Structural modifications in rubbers cured with 10% sulfur continuously increase with the increasing curing time up to 120 min, indicating a significant loss in double bonds in the later stages of the reacti

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270702

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe molecular weight dependence of the glass transition temperatures of polystyrene, polyα‐methyl styrene, polyisopropylα‐methyl styrene, polymethylmethacrylate, polyvinylchloride, poly‐isobutylene, polyisoprene, and poly‐N‐octadecylmaleimide is described by an equation developed from the Principle of Corresponding States. A statistical analysis is used to test the adequacy of the equation, and it is shown that from a statistical point of view the three molecular parameters,Se/Sm, ε ee*/ε mm*, andCe/Cm, characterizing, respectively, the ratios of contact area, lattice energy, and segmental mobility of end groups relative to repeating segments along the chain, will adequately describe the data. It is also shown that in one limit the equation reduces to the well‐known Ueberreiter‐Kanig result, which for most cases is a good first approximation to the data. The molecular weight‐TGdata were used to estimate the depression of the glass transition temperature of polystyrene and polymethylmethacrylate by a series of plasticizers. It was concluded that in the absence of important changes in the molecular structure within a homologous series of polymers, the Principle of Corresponding States can be employed to describe the molecular weight dependence of glass transition temperature over the entire

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270703

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270704

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractDynamic mechanical relaxation spectra were obtained for solution‐grown crystals oftrans‐1,4‐polyisoprene (TPI) in the α and β form. For single crystal mats three relaxations were observed. The highest temperature relaxation peak was characterized as due to the crystalline regions, whereas the intermediate peak was assigned to the primary amorphous relaxation which originates from the fold regions. The nature of the amorphous regions was elucidated by examining the effect of epoxidation on the lamellar fold surface. For an epoxidized single crystal mat, the intermediate relaxation maximum shifted to a higher temperature which corresponds to the glass transition of the almost completely epoxidized TPI. These results are discussed in terms of the fold structure of the TPI single c

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270705

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractPentacontane, hexacontane, 15‐ketohentriacontane (palmitone), and solid solutions of the twon‐paraffins were deposited from the vapor phase onto surfaces of potassium hydrogen phthalate (PHP) crystals and cleavage faces of potassium chloride (KCl) crystals in vacuo. Epitaxial growth, with molecular chains parallel to the substrates, occurs within a temperature range (e.g., 25–50°C for palmitone), and the epitaxial relationship between molecules and substrates was broken at higher temperatures. The electron diffraction patterns, similar to that of polyethylene, were obtained from all samples prepared at room temperature. The [100] or [130]directions of palmitone crystals are parallel to the substrate surface of PHP, and the [110] direction is parallel to that of KCl; the crystals in both cases are the orthorhombic form with lattice parametersa= 7.56 Å,b= 4.93 Å,c= 82.8 Å and a space group of Pna21. The (100) planes ofn‐paraffin crystals are parallel to the surface of PHP, and the crystals are again orthorhombic. Also, solid solutions ofn‐paraffins can be formed from the vapor phase, with the nucleation process on the two substrates being the same as for p

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270706

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractIsothermal enthalpy relaxation in polystyrene was measured as a function of temperature and molecular weight on a differential scanning calorimeter. Relaxation spectra were derived from the data and expressed as a distribution of relaxation times. For a given molecular weight the relaxation spectra at different temperatures could not be superimposed by a shift in time. The relaxation curves of samples of different molecular weights could be superimposed only when the difference between the temperature at which the relaxation was monitored (Ta) and their respectiveTgwas the same. The relaxation spectrum at any temperature for a given molecular weight was also expressed as a distribution of energies. The average energy represented by this distribution was associated with an activation energy required for the motion of a chemical repeat unit. The activation energy extracted from the temperature shift in the relaxation spectra corresponded to the motion of a statistical unit (Kuhn's segment) in polystyrene.

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270707

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractWide‐angle and small‐angle X‐ray diffraction patterns of polypivalolactone single crystals were recorded as a function of temperature while heating at a constant rate. Long periods were found to increase abruptly at a certain temperature, while the degree of crystallinity decreased up to that temperature and then recovered on further heating, to an extent depending on the rate of heating. Multiple endotherms were observed in DSC measurements. The temperature at which the first endotherm peak was observed corresponded exactly to the temperature of the long period jump mentioned above. From these data, it is concluded that the original lamellar crystals melt at each peak temperature in the DSC thermogram and new lamellae are produced by subsequent crystallization. Multiple endotherms in the DSC thermogram are thus considered to represent repeated melt‐recrystallization pr

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270708

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractFibers were spun from isotropic and biphasic solutions of regenerated cellulose (DP = 290) inN, N‐dimethylacetamide +7.8% LiCl using water as a coagulant. There is an increase in mechanical properties through the isotropic → anisotropic transition with moduli reaching 22 GPa. The problem with this system is that crystallization encroaches on the biphasic region, and a pure mesophase is never observed. However, owing to the slow nucleation rate of the crystals, a biphasic solution is stable for a long time and can be spun to yield high modulus and orientation. The best approach is to use small flow gradients (extrusion rate and pick‐up ratio) and to allow long times for homogenization and nucleation of the meso

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270709

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractPolyamic acid films interact as ion‐exchange substrates for dilute aqueous cation solutions. Three conditions were evaluated: basic solutions which form soluble amic acid salts and dissolve the film, weakly acidic solutions which encourage classical weak acid cation exchange, and strongly acidic solutions which discourage exchange. Thermal treatment of the generated cationamate salts generally causes degradation of the polymer backbone. Furthermore, lead and copper react directly with the polyamic acid to yield surface‐bound salts, but tin and aluminum seem unreact

ISSN:0887-6266    

DOI:10.1002/polb.1989.090270710

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY