摘要:

An apparatus has been developed to determine the components of the complex shear modulus of viscoelastic liquids and dilute gels over a continuous frequency range from 0.01 to 5 cps by amplitude‐phase shift measurements and from 2.5 to 400 cps by single coil transducer impedance measurements. The temperature range is from −40° to 150°C. The sample is deformed in very small strains with annular pumping geometry, as in the earlier apparatus of Smith, Ferry, and Schremp. Preliminary results on 2.29 and 3.00% solutions of polyvinyl chloride in di‐2‐ethyl hexyl phthalate provide the dynamic storage and loss moduli and the relaxation spectrum as they change during the process of gelation. The moduli of the ungelled solutions, at an early stage of the aggregation process, follow the Zimm theory rather closely, and the local effective viscosity derived therefrom lies between the solvent viscosity and the solution viscosity. The loss compliance of the aged gels is approximately represented by the Bueche theory for cross‐linked networks. However, it is evident that the gels contain a large proportion of sol fraction (polymer species unattached to the network).

ISSN:0021-8979    

DOI:10.1063/1.1777064

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Isothermal crystallization in bulk has been compared dilatometrically with linear polyethylene samples which have been molded in different ways, including melt orientation and sintering of precipitated powders from dilute solutions. These experiments show significant differences in the crystallization kinetics, which in some cases cannot be removed even by prolonged heating of the melt prior to crystallization. The data have been analyzed by an empirical expression in terms of nucleation and growth processes, according to the theoretical approach of Avrami. The results suggest that, in general, the melted polyethylene is not in a true thermodynamic equilibrium and includes some ``quasi‐indestructible'' clusters, which act as heterogeneous nuclei in the crystallization process. The nature and the amount of these nuclei depend on the molding, melting, and mechanical history of the sample, so that the semicrystalline material may have a wide variety of structure.

ISSN:0021-8979    

DOI:10.1063/1.1777065

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The origins of characteristic bands in the infrared spectrum of isotactic polystyrene have been studied with the aid of the spectrum of isotactic poly (ring‐d5styrene). It is found that these bands can be classified into three types according to their experimental behavior upon crystallization of the specimen. Assignments show that the bands in any one group are associated with a specific kind of normal vibration, either of the chain or of the benzene ring. Analysis of one of these band types indicates that rotational disordering of the benzene rings may occur, and that crystallization of the polymer is probably correlated with the growth of regions which maintain statistical variability at the local chain level.

ISSN:0021-8979    

DOI:10.1063/1.1777066

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The rheology of concentrated and bulk polymer systems has been investigated. Studies have been made on a low molecular weight series of several polymers using capillaries and a high shear concentric cylinder viscometer. The compositional and shear conditions for non‐Newtonian flow have been closely defined. Limiting high and low shear viscosities and the path of non‐Newtonian flow may be consistently correlated for concentrated systems of linear, flexible polymers. The minimum molecular weight for non‐Newtonian flow is related to the transition at low shear in log viscosity vs log molecular weight correlations. For non‐Newtonian systems, changes in apparent activation heat for viscous flow are reported as a function of shear. The conditions for laminar flow shear degradation of polymers are also given.

ISSN:0021-8979    

DOI:10.1063/1.1777067

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Platelet crystals of linear polyethylene recrystallize extremely rapidly when immersed in a bath of a hot liquid such as ethylene glycol, glycerine, or Woods metal. This recrystallization rate is much faster and to greater extent than when the heating medium is air. For example, heating in the liquids at 127°C causes the length of the chains between folds to increase 50% in 1 sec; the ultimate increase of 200% occurs in about 10 sec. No definite explanation is presently apparent for this much faster rate and greater extent in liquids. No evidence is found for reversibility when annealed crystals are reheated at a lower temperature.

ISSN:0021-8979    

DOI:10.1063/1.1777068

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The expressionV=xVc+(1−x)Va, for the specific volume of a semicrystalline polymer, is a highly successful approximation; herexis the degree of crystallinity,Vcis the specific volume for the crystalline regions, andVais the specific volume for the amorphous regions. In specimens for whichxis near unity, however, this equation demands values for the parameters which are inconsistent with other experimental evaluations. We suggest that the discrepancy arises because of the presence of voids. Thus in addition to crystalline and noncrystalline regions we propose regions of zero density. The average volume of such voids is not known, but their existence can be inferred from the significant, permanent density enhancement which can be brought about by pressure‐induced crystallization.

ISSN:0021-8979    

DOI:10.1063/1.1777069

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The Eyring‐Ree theory of non‐Newtonian flow is extended to the case of a continuous distribution of flow units. This results in an integral equation of the formF(s˙)=0∞G(t)arc sinh(s˙t)dt.This equation can be solved by integral transform methods to yield the unknown distribution functionG(t) when the flow curveF(s˙) is known as an analytic function. For the case of limited empirical data, approximation methods can be used to obtainG(t). Experimental data are shown for polyethylene at two temperatures and the distribution functions calculated.

ISSN:0021-8979    

DOI:10.1063/1.1777070

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Proton magnetic resonance studies have been made to compare the molecular motions ascribable to the disordered regions of solution‐grown and melt‐grown specimens of solid polyethylene. Studies have been made of both the spin‐lattice and spin‐spin relaxations. Restricted motion attributable to defect regions develops in solution‐grown crystals as the temperature is raised, but the number of protons in motion changes reversibly with heating and cooling, provided the maximum temperature is below ∼100°C. With higher temperatures the motion is greater in abundance and broader in frequency distribution. The increase is permanent despite annealing. Segmental motion attributed to molecules within the crystal is seen in solution‐grown crystals in the interval 50–100°C, but occurs to a much smaller degree in melt‐grown and heat‐treated samples. A model for the observed behavior is proposed.

ISSN:0021-8979    

DOI:10.1063/1.1777071

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Low‐angle light‐scattering patterns are obtained for stretched polyethylene films which are annealed both with and without the constraint of constant length. The effects of stretching temperature, annealing temperature, temperature of measurement, and degree of elongation are studied. Morphological changes in superstructure are found which parallel changes in crystal orientation.

ISSN:0021-8979    

DOI:10.1063/1.1777072

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The dielectric behavior of samples of nylon 6–6 and nylon 6–10 has been studied in the temperature region from −160° to 60°C at frequencies of 0.1 to 100 kc/sec. The effects of thermal history, electron irradiation, and post irradiation annealing on the two dielectric loss peaks found in this frequency‐temperature range have been explored. Electron irradiation of nylon 6–6 and 6–10 and thermal quenching of nylon 6–6 lowers the &ggr; peak (−70°C at 1 kc/sec for 66 nylon) and raises the &bgr; peak (+15°C for 66 nylon at 1 kc/sec). Post irradiation annealing of nylon 6–6 or 6–10 irradiated to low doses (25 to 100 mrad) removes the effect of the irradiation on the dielectric behavior, but on irradiation to high dosages (900–1000 mrad) the dielectric loss values in the region of the &bgr; maximum at 0.1 and 1.0 kc/sec are greatly reduced. The frequency shifts of the dielectric loss maxima for all samples give activation energies in kcal/mole which fall in the 8–15 range for the &bgr; maximum and 9–19 for the &ggr; maximum. These absorption peaks and the effect of various variables on them are discussed in terms of the molecular structure and possible molecular motions responsible for their occurrence.

ISSN:0021-8979    

DOI:10.1063/1.1777073

出版商:AIP    

年代:1961

数据来源: AIP