摘要:

AbstractThe orientation of crystallites grown isothermally in several drawntrans‐polychloroprene networks is studied as a function of crystallization temperaturetx, degree of crystallinity ω, and elongation ratio α. The orientation distribution is particularly simple for this polymer since the crystallographiccaxis (chain axis) orients preferentially along the stretching direction, whileaandbare randomly arranged aboutc. Hence the parameter cos2χcadequately characterizes the distribution, where χcis the angle between thecaxis and the fiber axis, and the average is taken over all crystallites. A treatment due to Krigbaum and Roe is utilized to obtain values ofv(the number of statistical segments comprising the crystallization nucleus of critical size) through comparison of the average orientation of crystallites and amorphous statistical segments. The behavior observed falls into two categories. First, if the initial amorphous network is well oriented, 〈cos2χc〉 is independent of crystallinity during both crystallization and melting, andvvaries withtz(or the degree of supercooling) as predicted by nucleation theory. If different networks are to have the same crystallite orientation distribution, they must not only be crystallized at the same supercooling, but must also have the same distribution of amorphous segment orientations. Both the relative elongation and the network crosslink density affect the latter distribution. Next, we consider the second category. If the initial amorphous orientation is poor, 〈cos2χc〉 decreases linearly during crystallization and increases along approximately the same path during melting. Further, 〈cos2χc〉 for a giventzyieldsvvalues which are too large. These two behaviors can be explained if, in the former case, nucleation involves the best oriented statistical segments of all network chains, while in the latter there is a selection according to the chain displacement vector orientation. Thus, if the amorphous orientation is poor, both the orientation and thermodynamic stability of the crystallites decreases with further crystallization. If this decreased stability is reflected in shorter fold lengths, the reversible variation of long period spacing with temperature reported earlier for an oriented polychloroprene network can also be explained as a preferen

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070201

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractThe effect of birefringence of a polymer film upon its photographic light‐scattering pattern is considered for the case of a single, anisotropic, two‐dimensional spherulite imbedded in a birefringent matrix. It is shown that for the case of a polarizer and analyzer crossed at +45° and −45° to the analyzer, the scattering pattern is modified in a manner agreeing with experimental obse

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070202

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractThe effect of birefringence on light scattering is considered, using classical theory. It is shown that in conjunction with polarized light scattering, the use of birefringence can aid in the reduction of experimental errors; also how new checks on theory can be made. The treatment is applied to scattering from simple gaseous molecules and thin polymeric films.

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070203

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractOsmotic‐pressure, viscosity, and light‐scattering measurements have been carried out on dilute solutions of poly‐N‐vinylcarbazole fractions (4<10‐4M<230) in toluene, dioxane, and benzene. The theta temperature for poly‐N‐vinylcarbazole in toluene solutions has been found to be 37 ± 1°C. The intrinsic viscosity of poly‐N‐vinylcarbazole in toluene at 37°C is represented by [η]θ = 76.2 × 10−3M̄n0.50. Values of the characteristic ratios (〈L2〉0/M)1/2and σ = (〈L2〉0/〈L2〉0f)1/2have been obtained as 633 × 10−11and 2.85, respectively. It appears that the large σ value is due to the

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070204

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractThe molecular weight distributions of three polydimethylsiloxanes (PDMS) have been determined by gel‐permeation chromatography (GPC), by gas–liquid chromatography (GLC), and by precipitation fractionation. The GPC data are greatly improved by correction for band spreading. For a high molecular weight polymer the corrected distribution agrees closely with the theoretical molecular weight distribution calculated from polymerization kinet

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070205

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractThe Huggins and Kraemer equations generally used to determine intrinsic viscosity frequently do not yield identical results, and their constants often do not add up to 1/2 as is mathematically required. To overcome these difficulties an equation has been deduced which through linear plots gives unambiguous intrinsic viscosities, constants which meet the 1/2 condition, as well as two other flow constants. Extensive tests of the equation with precise data on solutions of poly(methyl methacrylates) and polystyrenes in benzene and toluene confirm the validity of the new equation in every respect. It is further shown that the four constants involved are interrelated, and that it is possible to express the values of three of these in terms of the fourth.

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070206

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractThe mechanical anisotropy of regenerated cellulose films is investigated, first, on the basis of the theory of infinitesimal elasticity. Fairly good agreement of calculated with observed results is obtained on the basis of orthogonal anisotropy with respect to the machine direction and the transverse and thickness directions of the films. The shear modulusG23along the film plane and the Poisson ratiov32are 1.5 times; 102kg/mm2and about 0.4, respectively, in the standard dry state. Second, the mechanical anisotropy in three different dry states is analyzed in terms of the degree of biaxial orientation of two kinds of structural units, cellulose II crystallites and noncrystalline chain segments, and their mechanical anisotropy. The calculation for averaging the mechanical anisotropies of these structural units on the basis of the homogeneous strain hypothesis gives results much higher than the experimental data, whereas the calculation on the basis on the homogeneous stress hypothesis gives results rather lower than experiment. As a modification of the two extreme calculations, a different averaging gives considerably better agreement between the calculated and observed results. The mechanical anisotropy in the wet state is further analyzed primarily in terms of the degree of biaxial orientation of noncrystalline chains by a modification of Krigbaum treatment, based on application of the kinetic theory of entropy elasticity for semicrystalline polymers, to anisotropic systems. The calculation gives results, however, much lower than those obtained experimentally, unless the ratio of the end‐to‐end distance of the noncrystalline chain to its fully stretched length is taken as unusually large. This may be due to underestimation of the contribution of the crystalline phase to terms of the same type as appear in the Krigbaum treatm

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070207

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractThe assumed analogy between polymer solutions and polymer‐network gels as regards the thermodynamics of swelling—a fundamental assumption implicit in all previous analyses of swelling measurements on gels, aimed at checking the statistical theories of rubber elasticity—is shown in fact to be rather limited. In particular, excluded volume effects, which play a dominant role in both solutions and gels, are quite different in the two types of systems. A new thermodynamic description of swelling equilibria, taking account of differences in excluded volume effects, is given, and analogies and differences between gels and solutions are pointe

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070208

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractThe design of a differential thermal analysis apparatus for use at elevated pressure is described. Experiments on melting and crystallization of folded‐chain crystals of polyethylene and poly(ethylene–butene‐1) copolymer, and melting of extended‐chain polyethylene crystals have been conducted at pressures up to 4200 bars. The precision in transition temperature measurement was ±1°C. The Clausius‐Clapeyron equation predicts the melting point increase with pressure at atmospheric pressure to be 32.0°C/kb. The melting point depression due to copolymerization remained constant over the complete pressure range analyzed on the poly(ethylene–butene‐1) used in this study. Crystallization of polyethylene is retarded at elevated pressures, and a 50% larger degree of supercooling is necessary at 5000 bars to give a crystallization rate equal to that observed at atmospheric pressure. The difference in melting point between folded‐chain and extended‐chain polyethylene increases from 8.4°C at 1 bar t

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070209

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractMechanical relaxation data as a function of temperature (ca. 1 Hz) have been obtained for several samples of isotactic polypropylene crystallized from the melt, which exhibit both α and β forms as well as varying degrees of lamella orientation. The samples ranged in morphology from an unoriented sample showing only the α form to one highly oriented having approximately 90 per cent the β form. Results for the logarithmic decrement Δ and loss modulusG″ are that the low temperature (ca. −75°C) and glass temperature (ca. 0°C) relaxations show little or no sensitivity to orientation in the α form, but that the intensity of the two processes is different in the α form than in the β form for samples of nearly equal overall per cent crystallinity. In both Δ andG″, the low‐temperature peak decreased and the glass temperature peak increased in intensity as the fraction of β form crystallinity present increased. Data for the high‐temperature relaxation (ca. 80°C) indicate a dependence upon orientation and/or crystal form in addition to a dependence upon

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070210

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY