摘要:

Nuclear magnetic resonance absorption in oriented polytetrafluoroethylene fibers has been investigated in the temperature range 170°–380°K. The sample, in the form of a parallel bundle of fibers, showed a marked dependence of line shape on the direction of the applied magnetic field over the temperature range studied, although the observed anisotropy was much greater above 285°K than below. Changes occurring in the linewidth and second moment at around 285°K indicate a rotational disorder transition in the crystalline regions of the polymer, and serve to illustrate the advantages of using oriented fibers in the NMR investigation of semicrystalline polymers.

ISSN:0021-8979    

DOI:10.1063/1.1735462

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A simple Brownian motion model is used to discuss thermal diffusion in dilute polymer solutions. The thermal diffusion coefficient is found to be independent of polymer at sufficiently large molecular weights and to be given byDT= − (DsEs) /RT2whereDsis the self‐diffusion of the solvent andEsis the activation energy for this diffusion. This suggests that the thermal diffusion ratio &agr;=TDT/ D0should show a marked temperature dependence, a molecular weight dependence proportional toM½, and a concentration dependence governed for the most part by that ofD0. The results are shown to agree with published data in most respects and are contrasted to the results of other theoretical models. The results indicate that thermal diffusion is not a particularly promising method of fractionating various molecular weight molecules.

ISSN:0021-8979    

DOI:10.1063/1.1735463

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Ham [J. Appl. Phys.31, 1853 (1960) (preceding paper)] has derived a simplified theory for thermal diffusion in dilute solutions of high polymers. It is of interest to apply this theory to two different types of polymer solutions: (a) dilute solutions in a good solvent, and (b) dilute solutions in a poor solvent. By studies of the concentration, temperature, and molecular weight dependence of the thermal diffusion ratio in these two different types of polymer solutions, it has been possible to obtain a detailed test of the theory.

ISSN:0021-8979    

DOI:10.1063/1.1735464

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Nuclear magnetic resonance measurements have been made of the development of chain motion in linear polyethylene and polymethylene crystallized from solution. It is shown that segmental mobility is produced at room temperature when the compounds are heated below the melting point. The changes are rapid and irreversible, and are independent of crystallization temperature and concentration, except at high concentration. The effects are ascribed to the development of defects in the crystalline structure.

ISSN:0021-8979    

DOI:10.1063/1.1735465

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A series of uniaxially oriented polyethylene terephthalate fibers irradiated in a nuclear reactor have been investigated. On the basis of tensile studies the ultimate tensile strength is found to decrease as the dose of reactor irradiation increases. However, the ultimate tensile strength is found to increase when the degree of molecular orientation increases. But after the samples have received a relatively high dose of irradiation the tensile strength approaches practically zero. The x‐ray diffraction scans of the nonirradiated samples with low degrees of orientation indicate very little crystallinity, whereas the very definite diffraction peaks associated with the irradiated and oriented samples indicate a definite trend toward crystallinity.

ISSN:0021-8979    

DOI:10.1063/1.1735466

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Samples of biaxially oriented polyethylene terephthalate irradiated in a nuclear reactor have been investigated at five temperature levels ranging from − 150°F to 350°F. In general, from tensile studies, the ultimate tensile strength was found to decrease markedly to a relatively low magnitude upon receiving a reactor irradiation dose having a thermal neutron bombardment component of 1018nvt and over. The modulus of elasticity for both the irradiated and nonirradiated samples was found to increase with the decrease of the temperature.The fracture surfaces of the biaxially oriented polyethylene terephthalate samples obtained at − 15°F are also recorded for reference.

ISSN:0021-8979    

DOI:10.1063/1.1735467

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The photographic light scattering technique permits a measurement of the size, anisotropy, radial periodicity, packing, and internal structure of polymer spherulites. The theory of some of these effects is described, and experiments are presented showing changes occurring in the melting and growth of spherulites.

ISSN:0021-8979    

DOI:10.1063/1.1735468

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Stress relaxation measurements on SBR were carried out at temperatures from −5 to +60°C and at initial strains of up to 550%. The effects of strain and time were found to be factorable, so that the isochronal stress‐strain curve may be written as a modified Hooke's law with a time dependent modulus:S = E(t)ef(&agr;), wheref(&agr;) is an appropriate function of the strain. By defining a strain‐reduced stressS*=S/f(&agr;), i.e., a strain‐reduced modulusE*(t) =E(t)f(&agr;), it can be shown that Ferry's method of reduced variables may be extended to large deformations. An appropriate strain function was obtained from the empirical Martin‐Roth‐Stiehler equation [Trans. Inst. Rubber Ind.32, 189 (1956)] asf(&agr;) = &agr;−2expA(&agr;−&agr;−1) withA=0.40. Although it cannot yet be certain thatAis truly a constant and the same for all elastomers, this equation has the advantage of being valid right out to the breaking strain.

ISSN:0021-8979    

DOI:10.1063/1.1735469

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The ultimate properties of amorphous rubbers at temperatures aboveTgare considered in terms of stress‐strain curves to rupture measured at different strain rates and temperatures. The consideration indicates that a specimen held at a fixed elongation should break eventually, provided the elongation exceeds a critical value. This expected behavior was found by studying an SBR rubber. For samples maintained at different elongations for up to seven days, both the time to break and the stress at break were measured at eight temperatures from 1.7° to 60°C. For comparison, the ultimate properties were also measured at different strain rates and temperatures. The comparison indicates that for a given ultimate elongation and stress at break, the time to break under conditions of constant elongation is less than under conditions of constant strain rate.

ISSN:0021-8979    

DOI:10.1063/1.1735470

出版商:AIP    

年代:1960

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1735471

出版商:AIP    

年代:1960

数据来源: AIP