摘要:

AbstractThe Fujita equation relating molecular weight distribution to concentration of solution subjected to centrifugal forces in equilibrium proved to be an improperly posed problem in the Hadamard sense. Application of Tikhonov's regularizing functions leads to a good approximate solution of Fujita's equation. Such functions have been applied to a monomodal and a bimodal molecular weight distribution, and approximate results have been computed.

ISSN:0449-2978    

DOI:10.1002/pol.1970.160081201

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractThe NMR relaxation timesT1andT2have been measured for fractionated samples of polydimethylsiloxane with different molecular weights in the amorphous state and in tetrachloroethylene solutions. The results are interpreted on the basis of the anisotropic reorientation model proposed by Woessner for small molecules. A correlation time characteristic of the diffusional rotation of chain segments is calculated and shown to be proportional to the square root of the bulk viscosity.

ISSN:0449-2978    

DOI:10.1002/pol.1970.160081202

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractAn elastic‐fluid theory of die‐swell for long dies is presented. The theory predicts a swelling ratioDe/dasymptotically proportional, for large values of swelling, to the cube root of the recoverable shear evaluated at the die wall. Here the recoverable shear is defined to be half the ratio (first normal stress difference/shear stress). Excellent agreement is shown between predictedDe/dand measuredDe/dfor experiments on melts and solutions for which adequate data are availa

ISSN:0449-2978    

DOI:10.1002/pol.1970.160081203

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractThe unit‐cell dimensions and density, at room temperature, of bulk‐ and solution‐crystallized linear polyethylene have been determined. The macroscopic measured densities for the bulk‐crystallized samples ranged from 0.917 to 0.993 g/cc, and the lattice parameters were found to be independent of the sample density. In contrast, for solution‐formed crystals, despite the limited range in macroscopic densities that can be attained, there is a systematic variation in theaandbdimensions with the measured density and the crystallite thickness. The implication of these results for the calculation of the degree of crystallinity and the interpretation of certain infrared bands are

ISSN:0449-2978    

DOI:10.1002/pol.1970.160081204

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractData on dilute solutions of a pyrrone “prepolymer” are presented and the tendency of this polymer to aggregate in certain solvents commonly used in dilute solution studies is discussed. It is concluded that reliable molecular weights can be determined if solvents that interact with the prepolymer through hydrogen bonding are u

ISSN:0449-2978    

DOI:10.1002/pol.1970.160081205

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractElectron‐microscopic texture and physical properties of a styrene–butadiene–styrene (SBS) block copolymer obtained by casting from toluene, carbon tetrachloride, ethyl acetate, and methyl ethyl ketone are discussed. Two peaks are observed in the mechanical loss (tan delta;) curve at −70 and 100°C which are attributed to segmental motion of polybutadiene and polystyrene, respectively. The polybutadiene peak heights are in the order of solubility in the solvent used; the polystyrene peak heights are in converse order. In addition to these peaks, a third peak is observed at 10°C for specimens cast from ethyl acetate or methyl ethyl ketone. A transition corresponding to this peak is also noticed in thermal analysis. It is proposed that aggregation of styrene blocks is relatively incomplete in specimens cast from solution in poor

ISSN:0449-2978    

DOI:10.1002/pol.1970.160081206

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractA relatively novel method of calculating molecular weight changes and broadening during a polymerization is proposed. It differs from others in that the distribution is considered implicitly rather than explicitly. This allows direct use of kinetic rate equations in the derivation of weight‐average and number‐average degree of polymerization etc.; the mathematics simplifies to simple integration rather than sums of complicated series. The method is illustrated by applying it to several cases. These range from various models where only monomer concentration changes, to where both monomer and initiator or monomer and chain transfer agent are changing. Cases previously unsolvable can now be hand

ISSN:0449-2978    

DOI:10.1002/pol.1970.160081207

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractThe calculation of the scattering from a sheaflike sector of a two‐dimensional spherulite has been carried out as a function of the apex angle of the sector. It is found that while for a complete spherulite theHvscattered intensity is zero at zero scattering angle, there is an increasing intensity of scattering at 0° as the sector angle narrows. For very small values of the sector angle, the scattering becomes similar to that of a rod, with the exception that a scattering maximum is still seen at an angle close to that at which the spherulite scattering maximum occurs. The predictions of the model compare favorably with the scattering patterns observed for polymers in early stages of spherulitic grow

ISSN:0449-2978    

DOI:10.1002/pol.1970.160081208

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractPrevious theoretical calculations of the scattering from spherulites are for isolated complete spheres, whereas most spherulitic polymer samples contain truncated spherulites as a result of impingement by other spherulites. The effect of such truncations on the scattering patterns for two‐dimensional spherulites is explored as a function of the size, number and location of the truncations. The scattering of severely truncated spherulites is modified, particularly with regard to the enhancement of theHVscattering at small angles. However, reasonable amounts of truncation corresponding to experimentally observed structures do not produce appreciable modification of the pattern so that the neglect of truncation will not lead to appreciable error in the estimated spherulite size from light scatterin

ISSN:0449-2978    

DOI:10.1002/pol.1970.160081209

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractLow molecular weight poly(ethylene terephthalate) samples were crystallized isothermally at 120–245°C from both the amorphous state and the melt. Isothermal annealing of these polymers at 215°C provided polymers which exhibited multiple melting peaks in thermal analysis, referred to as form I and form II, as assigned by Bell and Dumbleton. In these samples the peak temperature of the form II melting endotherm and the average crystallite size are dependent on the temperature of initial crystallization. This result requires a mechanism for retaining some structural feature during the conversion from morphological form I to form II. DSC thermograms obtained at varying heating rates on samples showing only form II endotherms support the assignment of superheating as the cause of the shift to higher peak temperatures with increasing heating r

ISSN:0449-2978    

DOI:10.1002/pol.1970.160081210

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY