摘要:

AbstractIn order to verify precisely the applicability and reasonableness of the time–humidity superposition method to hydrophilic crystalline polymers, stress relaxation measurements were carried out with films of polyvinyl alcohol and nylon 6 by means of a table model Instron Tensile Tester equipped with a special glass cell to control temperature and humidity. In the case of PVA, only the time–humidity superposition is applicable at humidities higher than that at which the transition begins. For nylon 6, on the other hand, time–temperature and time–humidity superposition apply very well in the transition region and fairly well at higher temperatures and humidities. The results obtained by both the superpositions coincide very well, showing the time–humidity superposition is as reasonable as the time–temperature one. The superposed results were also compared with other existing data, and the reasonableness of the time–humidity superposition

ISSN:0022-3832    

DOI:10.1002/pol.1962.1205816601

出版商:Interscience Publishers, Inc.    

年代:1962

数据来源: WILEY

摘要:

AbstractThe internal friction and the dynamic modulus of isotactic polypropylene samples subject to varying degrees of pile irradiation have been studied at low audio frequencies and over the temperature range from 100°K. to over 400°K. The radiation dosages used varied from 5.4 × 1017to 14 × 1018nvt. For irradiation doses up to about 3 × 1018nvt, one observed change is a decrease in the temperature at which the final upswing in damping and drop in modulus occurs, presumably as a result of defects produced in the crystallites by the irradiation. As the irradiation dose increases above 3 × 1018nvt, all evidence of crystallinity is lost, and the internal friction peak which occurs in the neighborhood of 300°K. and which is associated with the glass transition of the amorphous regions moves to higher temperatures as a result of the increasing chainstiffening effect due to crosslinking. The secondary loss peak at 250°K. attributed to the motion of a small number of segments in the amorphous regions is found to increase in magnitude with increasing dose. The results of density determinations made before and after irradiation and also after subsequent exposure of the irradiated samples to melting temperatures and of solvent extraction studies of the irradiated samples confirm the simultaneous occurrence of crosslinking and of crystalline degradation upon pile irradiation of polypropylene

ISSN:0022-3832    

DOI:10.1002/pol.1962.1205816602

出版商:Interscience Publishers, Inc.    

年代:1962

数据来源: WILEY

摘要:

AbstractThe relationship at 190°C. between Newtonian melt viscosity η0and the weight‐average molecular weight,M̄wfor polyethylenes has been developed by use of melt viscosities obtained from capillary viscometry and molecular weights from intrinsic viscosity and bulk flow measurements in addition to the usual light‐scattering determinations. The same η0vs.M̄wrelationship is obeyed by whole and fractionated linear polyethylenes and also by ethylene–butene and ethylene–propylene copolymers. The Newtonian viscosity therefore seems virtually independent of molecular weight distribution and the influence of short (ethyl, methyl) chain branches. Low density polyethylenes have consistently lower Newtonian melt viscosities at givenM̄wthan their linear counterparts. At constantM̄wand temperature, therefore, η0depends primarily on long‐chain branching. A viscosity index of long‐chain branching (v.b.i.) is defined by the ratio of Newtonian viscosities of a linear and a branched polyethylene of the sameM̄w. The v.b.i. correlates well with an intrinsic viscosity branching index provided long branch incidence is high. The correlation breaks down otherwise, because the intrinsic viscosity is also sensitive to molecular weight distribution and the presence of short‐chain branches. The v.b.i. is therefore more useful as a long branching index. It is a comparative index, however, and not an absolute evaluation of the number of long branches per molecule. The η0vs.M̄wrelationship of linear polyethylenes does not obey the often reported 3.5 power law for linear polymers, but is well fitted by a 4.2 power factor. The present work indicates the necessity of using polyethylenes which have been stabilized against the effects of thermally induced changes if meaningful values of Newtonian visc

ISSN:0022-3832    

DOI:10.1002/pol.1962.1205816603

出版商:Interscience Publishers, Inc.    

年代:1962

数据来源: WILEY

摘要:

AbstractThe effects of molecular weight distribution and branching on the viscosity of polyethylene melts were studied by making mixtures of paraffin wax with 0 to 100% of various types of high and low density polyethylenes of known weight‐average molecular weights,M̄wand measuring their Newtonian melt viscosity at 150°C. The range of molecular weights from about 400 to 106gave about a billionfold range in the viscosities (10−2to 10+7poises). The results showed that the melt viscosity did not vary withM̄w3.4, since samples with the sameM̄wmight differ by up to 100,000‐fold in viscosity. An analysis of the flow process in melts suggested that the viscosity‐average molecular weightM̄vmight be more significant than theM̄w. Within the accuracy of our knowledge of the initial molecular weight, the viscosities of all mixtures having viscosities above about 10 poises fit the equation\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {\log \eta = - 12.3 + 3.45\log (w_1 M_1^\alpha + w_2 M_2^\alpha)^{1/\alpha}} \\ {= - 12.3 + 3.45\log \bar M_v} \\\end{array} $$\end{document}wherew1andw2are the weight fractions, andM1andM2are the molecular weights of the paraffin and polyethylene, respectively, andM̄vis a viscosity‐average molecular weight of the mixture. Theory and experiment show that the value of α may be obtained without any knowledge of the initial molecular weight, from the slope of the curve for log η0versus log concentration at small concentrations of wax. Polyethylenes with large amounts of long‐chain branching had low values of α (down to about 0.25), while polymers with relatively little long‐chain branching had values of α up to about 0.8. Where the comparisons could be made, the value of α determined from a polymer melt was surprisingly close (∼ +0.15) to the value of α in the intrinsic viscosity equation for the same polyethyle

ISSN:0022-3832    

DOI:10.1002/pol.1962.1205816604

出版商:Interscience Publishers, Inc.    

年代:1962

数据来源: WILEY

摘要:

AbstractThree impact testing devices for different test purposes are described and the measuring, amplifying, and indicating equipment for the plotting of stress–strain curves is shown in diagrammatic form. The problem of evaluating the impact strength of high polymers for specified applications is discussed for the case of diverse semifinished and finished parts. In the case of safety belts for motor vehicles, the difference between plastic and elastic deformation energy for various belt materials is shown. With films, a distinction is made between the amount of energy used in deformation until the first tear and the total impact energy. For sheet specimens subject to tensile stress, the stress‐strain curves for slow and shock stresses are contrasted. Further experiments must show whether, with the help of the new testing equipment, the usability of high polymers for specified applications may also be forecast quantitativ

ISSN:0022-3832    

DOI:10.1002/pol.1962.1205816605

出版商:Interscience Publishers, Inc.    

年代:1962

数据来源: WILEY

摘要:

AbstractThe rate of polymerization of aqueous methyl methacrylate under nitrogen at 32°C. is proportional to the first power of catalyst (MnO4−) concentration (0.633 to 15.83 × 10−5mole/l.) at fixed concentrations of the activator (0.8 × 10−2mole/l.) and monomer (6.204 × 10−2mole/l.), independent of activator concentration over a wide range (0.50 to 0.0625 × 10−2mole/l.), and proportional to the first power of monomer concentration within the range (0.94 to 7.52 × 10−2mole/l.) at fixed concentrations of the catalyst (3.16 × 10−6mole/l.) and the activator (0.8 × 10−2mole/l.). The initial rate of polymerization attains a maximum value at 45°C., but falls with further rise in temperature. The rate of polymerisation is depressed by agitation after initiation, salts and organic solvents, and is accelerated by MnSO4and complexing agent like NaF (only at low monomer concentration), and in presence of peptizers like sodium cetyl sulfate or cetyltrimethylammonium bromide. The separating phase in the absence of peptizers is a course coagulum, and possibly a steady state with respect to radicals is not attained at high catalyst concentration. Injection of catalyst late in a run increases both the rate of polymerization and yield in unpeptized systems and does the reverse in peptized systems. The molecular weight of the polymers increases in the course of a run and is also affected by change of catalyst concentration but not by activator concentration in the range where the rate of polymerization is independent of

ISSN:0022-3832    

DOI:10.1002/pol.1962.1205816606

出版商:Interscience Publishers, Inc.    

年代:1962

数据来源: WILEY

摘要:

AbstractThe polymerization of acrylonitrile in aqueous solution initiated by ammonium persulfate in the presence of cupric salts was studied by a dilatometric method. The presence of cupric sulfate, nitrate, or acetate has a pronounced effect on polymerization, leading to an increase in the rate, and both cupric chloride and bromide retard or inhibit polymerization beyond certain salt concentrations. The increased rate is explainable by the following reactions:The polymerization of acrylonitrile can be initiated by an oxidizing agent such as cupric sulfate, ferric sulfate, stannic chloride, nitric acid, or periodic acid. The decreased rate can be explained by assuming that the complexes of Cu+ion with a halide ion X−such as CuX2−, CuX3=, CuX4≡, or Cu2X3−shows lower reactivity in the reaction with S2O8=. The cupric‐terminated reaction depends on the coexisting anion. The effect of sulfate, nitrate, acetate, phosphate, chlorate, or fluoride anions is negligible, while that of the chloride is marked, and that of the bromide is overwhelming. The CuX+(X = Cl, Br) ion appears to terminate polymer chains more efficiently than does Cuaq++. Apparent transfer constants of cupric sulfate in the presence of sodium chloride or bromide and the transfer constant of CuCl+are given. It is suggested that the possibility of the termination reactions by halogen atom transfer is large under conditions of high halide ion concent

ISSN:0022-3832    

DOI:10.1002/pol.1962.1205816607

出版商:Interscience Publishers, Inc.    

年代:1962

数据来源: WILEY

摘要:

AbstractThe reciprocal of the viscosity‐average degree of polymerization (P̄v−1) vs. rate of polymerization (V) relation is expressed as:where [η] =K′P̄vα, β =ktd/kt,k= rate of primary radical formation out of cages/concentration of initiator,\documentclass{article}\pagestyle{empty}\begin{document}$ \sum {_i k'} _{pi} [R_i \cdot][{\rm M}]= {\rm rate of initiation of polymerization} $\end{document},\documentclass{article}\pagestyle{empty}\begin{document}$ \sum {_i k'} _{ti} [R_i \cdot][{\rm M} \cdot]$\end{document}= rate of termination of growing chains M· by reaction with primary radicals Ri·. From this equation, several, important constants can be determined. In the polymerization of styrene at 60°C. with 2,2′‐azobisisobutyronitrile, the results obtained are as follows:kp2/kt= 5.52 × 10−4(or 5.86 × 10−4) l.‐mole.−1‐sec.−1.ktrM/kp= 6 × 10−5,ktrS/kp1.1 × 10−2(carbon tetrachloride as solvent),k= 1.57 × 10−5(or 1.48 × 10−5) sec.−1,\documentclass{article}\pagestyle{empty}\begin{document}$ \sum {_i k'} _{pi} [R_i \cdot]/\sum {_i k'} _{ti} [R_i \cdot]= 1.20 \times 10^{- 7} $\end{document}. These values agree well with those obtained by the other authors. The rate of initiation\documentclass{article}\pagestyle{empty}\begin{document}$ \sum {_i k'} _{pi} [R_i \cdot]{\rm -}[{\rm M}]$\end{document}and the rate of termination\documentclass{article}\pagestyle{empty}\begin{document}$ \sum {_i k'} _{ti} [R_i \cdot][{\rm M} \cdot]$\end{document}between the growing chains and primary radicals are calculated, respectively, from the equations:The rate of disappearance of the primary radicals through the reaction among themselves is negligible in comparison with the other termination rates in the usual conditions. The ratio of concentrations of the primary radicals R· and growing chains M· is expressed under an ordinary condition as:whereVRis the rate of primary radical

ISSN:0022-3832    

DOI:10.1002/pol.1962.1205816608

出版商:Interscience Publishers, Inc.    

年代:1962

数据来源: WILEY

摘要:

AbstractThe influences of surface charges on polysilicic acid on light‐scattering, electrokinetic, viscosity, and emf measurements were examined. It was substantiated that the potential‐determining ions are hydrogen and hydroxyl, which control the dissociation of the acidic silanol groups, SiOH → SiO−+ H+. The zeta potentials are also influenced by the ionic strength of the solutions. The effect of cations on the surface charges increase with valence: Na

ISSN:0022-3832    

DOI:10.1002/pol.1962.1205816609

出版商:Interscience Publishers, Inc.    

年代:1962

数据来源: WILEY

摘要:

AbstractThe effect of different thermal treatments on the degree and type of orientation produced by cold drawing three polyolefin films: polyethylene, polypropylene, and polybutene‐1, was studied by two complementary techniques: x‐ray diffraction for the measurement of crystal orientation and birefringence for the measurement of the total film orientation. Variations in the texture of these polymer films were characterized by these techniques as well as by density, tensile stress measurements and photomicrographs. The birefringence–strain data showed a decrease in birefringence values at a given strain as the polymer side group size increased. This decrease appears to be associated with a more symmetrical polarizability ellipsoid and hence a decrease in crystal birefringence. The birefringence–strain curves for the same polymer system showed a decrease in birefringence value at a constant strain with increased annealing. X‐ray diffraction data indicate that theaandbaxes in both polyethylene and polybutene‐1 film orient by different amounts at a given strain. Polypropylene, on the other hand, shows equal amounts orientation of theaandbaxes. The different orientation behavior for these polymer systems is discussed in terms of variation in the ease with which polymer crystals may

ISSN:0022-3832    

DOI:10.1002/pol.1962.1205816610

出版商:Interscience Publishers, Inc.    

年代:1962

数据来源: WILEY