摘要:

AbstractEnergy levels and molecular orbital wave functions of π‐electrons in a carbazole ring are calculated by the ω‐method. The result agrees well with observed optical absorption spectra of carbazole and poly(N‐vinylcarbazole) (PVCA). Molecular orbital wave functions are obtained for a PVCA chain in a 3/1 helix. The overlap integral between adjacent carbazole rings is evaluated for each molecular orbital of the ring. The result affords evidence for hole conduction in PVCA and explains the photoconductivity spectrum under high d

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131001

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe mechanical properties (Young's modulus, ultimate tensile strength, deformation processes) of extended‐chain polydiacetylene crystals are investigated. The properties observed are similar to those of metal and ceramic whiskers. The elastic modulus is strain‐dependent and the ultimate tensile strength increases with decreasing crystal size. The maximum tensile strength observed was 1700 Nmm−2. The ultimate tensile strength seems to be controlled by the presence of a small number of defects near the surface at which fracture nucleates. Irreversible deformation of the crystals was observed to occur by crack propagation normal and parallel to the direction of the macromolecules. The observed mechanical behavior corresponds to exceptionally high per‐chain properties. The per‐chain modulus obtained for these crystals is nearly as high as that of diamond. A chain‐aligned polyethylene fiber with the same per‐chain mechanical properties would have an ultimate strength as high as 0

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131002

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractA terpolymer of butadiene–styrene–vinylpyridine has been crosslinked by addition of iron chloride. Differential enthalpic analysis gives evidence of a two‐phase system. Electron microscope studies at 0.1 and 1 MeV show the existence of precipitates. The majority of these ironrich aggregates have diameters less than 100 Å. Their form is polyhedral but very nearly spherical. No crystallinity has been detected inside the clusters. Thus the existence of strong interactions as in crystals of FeCl3hydrates is ex

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131003

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe effects of temperature and pressure on the shift factor and the dielectric increment of the β relaxation process were measured for vulcanized chlorinated polyethylene. The isobaric and isochoric activation enthalpies,H*PandH*V, the activation volumeV*, the pressure dependence of the glass–glass transition temperature,Tgβ/dP, and the apparent extinction temperatureT0βwere obtained. The pressure dependences of bothV*and the dielectric increment would reach very small values near the liquid–glass transition temperatureTg, and the β process seems to be affected by the transition nearTg. The value ofH*v/H*pfor the β process is larger than that for the α process, and it is suggested that the molecular motions pertaining to the β process are more strongly restricted than those pertaining to the α process. The ratioT0β/T0, whereT0is the characteristic temperature in the Vogel–Fulcher–Tammann–Hesse equation for the α process, follows the empirical relation of Matsuoka and Ishida,Tgβ/Tg∼0.75. The value ofdTgβ/dPestimated fromTgandT0β/T0is consistent wit

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131004

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractFracture energies have been measured for two types of polybutadiene elastomer, crosslinked to various extents and torn under various conditions. Threshold values, ranging from 40 to 80 jm−2, were observed for samples torn at extremely low rates of tearing, at high temperatures, and in the swollen state. These values were found to be independent of temperature and rate of tearing, and also of the degree of swelling and the nature of the swelling liquid, provided a correction is made for the reduced areal concentration of molecular chains. They decreased somewhat with increased crosslinking, in good agreement with theoretical predictions of Lake and Thomas.6The results for the two elastomers were substantially the same.These observations are strikingly different from those made at normal temperatures and rates of tearing, when large differences in fracture energy were observed between the elastomers, and between samples crosslinked to different extents, due to energy losses from nonequilibrium deformation processes in addition to the energy required for fractur

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131005

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractContraction experiments were performed on hot‐stretched polystyrene during isothermal annealing and tempering. Activation energy spectra were obtained from the experimental data using the Primak theory. In the case of isothermal annealing the theory of Kimmel et al. with shift factors was used. There is an appreciable difference between this spectrum and that obtained from the tempering experiment by the original theory without shift factors. These two spectra should be the same according to the theory. In order to resolve the conflict, we have included a correlation between activation processes in the fundamental equation of the Primak theory. A new formula for calculating the activation energy spectra was obtained. For isothermal annealing, it can be written the same as that of Kimmel et al. The shift factor is also included in the formula for tempering. The activation energy spectra obtained by the new formula gives good agreement between the two method

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131006

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractPolymerization ofp‐xylylene was carried out from the gas phase with monomer produced by the pyrolysis of [2,2]‐p‐cyclophane. The crystalline form and preferred orientation of as‐polymerized polymer deposited at various temperatures (−196 to 80°C) were investigated by x‐ray diffraction methods. The melting behavior and other thermal transitions were studied by DSC. At 80°C the polymer film deposit is a mixture of the α and β forms, while between 60 and 0°C the deposit is of the α form. At lower temperature the polymer deposit is mainly of the β form, which shows diffuse reflections. At liquid nitrogen temperature it is of the β form with sharp reflections, contaminated with a small amount of oligomer. It was also found that at low temperatures, fibrillar crystals grow from the substrate in a direction 45° against the gas flow, and at even lower temperature, well‐oriented filmlike crystals grow perpendicular to

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131007

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractObservations by transmission electron microscopy suggest that surface‐controlled recrystallization of polyethylene occurs by the solid state nucleation and growth of new crystals with (110) or (110) planes parallel to the free surface. The nucleation site of these crystals is the free surface. The growth process involves the migration of [002] tilt boundaries suggesting that these boundaries have high mobilities. The migration process may occur by the lateral rearrangement of the macromolecules in the [002]tilt boundar

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131008

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractIt has been presumed in studies of the orientation of low‐density polyethylene and its time dependence that the degree of crystallinity remained constant with elongation and did not vary with time following elongation. This paper represents a test of this hypothesis by several methods. The change in crystallinity accompanying stretching has been followed by a modification of an x‐ray method for uniaxial orientation proposed by Ruland in which diffraction peaks are resolved into crystalline and amorphous components and their respective areas are determined by two‐dimensional integration over both the Bragg angle and the azimuthal angle of diffraction. The weight‐fraction crystallinity is then determined from the ratio of the weighted crystalline area to the total area. There appears to be no significant variation in crystallinity up to 50% sample elongation for both slowly and rapidly stretched samples at room temperature. The dynamic crystallinity change accompanying small amplitude vibration has also been determined by the dynamic x‐ray diffraction technique and found to be negligible over a wide range of frequency. The degree of crystallinity has also been evaluated from the absolute infrared absorbance of crystallinity‐sensitive bands and has also been found to be independent of elongation at room temperature up to 80% elongation. Changes have also been observed by this method during relaxation at constant length following rapid extension and have also been found to be negligible. These results also indicate negligible changes in rotational isomer population. Consequently, we conclude that changes observed during relaxation and vibration arise from orientational changes rather than changes in the degree of cr

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131009

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractIsochronal measurements of dielectric constant and loss are made for poly(isobutyl methacrylate) (PiBMA), poly(n‐butyl methacrylate) (PnBMA), poly(isopropyl methacrylate) (PiBMA), and poly(4‐methylpentene‐1) (P4MP1) at temperatures ranging from 4°K to 250°K. Loss peaks are found around 120°K (10–100 Hz) for PiBMA, PnBMA, and P4MP1. By comparing the activation energy with the calculated potential barrier for the internal rotation of alkyl group in the side chain, the motion responsible for the 120°K peak is concluded to be essentially the rotation of the isopropyl group as a whole for PiBMA and P4MP1 but, for PnBMA, the rotation ofn‐propyl group accompanied by the rotation of the end ethyl group. Multiple paths of internal rotation are involved with the 120°K peaks of PiBMA and, in particular, PnBMA, which explain differences between PiBMA and PnBMA in the broadness and the temperature location of the 120°K peak. The 120°K peak is in general assigned to a side chain including a sequenceOCCC or CCCC. PiPMA without this sequence in the side chain does not show the 120°K peak, but it exhibits the 50°K peak (1 kHz) like poly(ethyl methacrylate). The 50°K peak is assigned to the rotation of ethyl or isopropyl group attached to COO group. Poly‐L‐valine in which the isopropyl group is directly attached to carbon does not have the 50°K peak. An additional loss peak at 20°K (1 kHz) for P4MP1 is also discussed

ISSN:0098-1273    

DOI:10.1002/pol.1975.180131010

出版商:John Wiley&Sons, Inc.    

年代:1975

数据来源: WILEY