摘要:

AbstractIn this article a conception of the mechanism of crystallization is given, on the basis of which, it is suggested the origin of spherulites might be explained. A tentative explanation of several related phenomena is based on the new concept. Crystallites are conceived to be small collections of strongly oriented polymer which, on fusing, exhibit marked shrinking in the direction of orientation. Particles of amorphous material therefore stretch out in a certain direction during crystallization, as the result of which there is substantial contraction in the other directions. This is termed “auto‐orientation.” As the growing crystallite has to be fed from surrounding material, an orienation is initiated in the latter at right angles to the first crystallite. As a result of this orientation, crystallites are formed there which are orientedPerpendicularto the first crystallite. In their turn, these crystallites induce orientation in the surroundings and in this way crystallization becomes autocatalytic in character. Spherulites owe their origin to the fact that the various sectors in a symmetrical spherical order mutually cancel out their stretching and shrinking tendencies. In highly crystalline polymers with rapid nuclear formation there first comes into existence numerous radomly oriented nuclei which proliferate to small crystallites. Wherever these small crystallites come to be arranged in a suitable position, their relative tensions will be cancelled out and they will grow into a spherulite. Simultaneously small crystallites which are in an unfavorable position will be consumed by the growing spherulite, or else oriented in the correct direction and incorporated. As spherulites commonly measure from 10 to 50 microns, compensation between the tensions of the various sectors has to take place at long distance. At higher temperatures, compensation is as a rule found at short distances,i.e., crystallites which are at right angles to each other are in close proximity. Therefore “spherulites” varying individually come into existence as the crystallites are subject to other influences in addition to auto‐orientation. At very low temperatures the primary small crystallites are too stable to develop into spherulites. The mechanism of crystallization as thus conceived implies that the melting point of a polymer depends not only upon the dimensions and perfection of the crystallites, but also upon the specific arrangement of the crystallites,i. e., the degree in which they stabilize each other by a mutual compensation of tensions. It also helps to explain the following facts which have been noted in experiments performed with natural rubber: (1) The typical S‐shape of the crystallization curve and the constancy of the product of induction period and maximum rate of crystallization. (2) The fact that natural rubber always crystallizes under nonequilibrium conditions. (3) The failure of rubber in latex to crystallize and the fact that the rate of crystallization in films produced from latex is poorly

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110501

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

摘要:

AbstractThe chain transfer constants of twelve solvents have been determined for the peroxide catalyzed polymerization of styrene and are compared, where possible, with those for methyl methacrylate. The values found are discussed in relation to structure and activity.

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110502

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

摘要:

Abstract(1) The electrostatic free energy of randomly kinked, ionized, macromolecules was calculated for polyelectrolyte solutions of finite ionic strenght. A detailed analysis of the charging process and the reference state of the free energy is given. The mutual electrostatic repulsion of the fixed charges on the macromolecule is the main part of the electrostatic free energy. Its calculation is based on two main assumptions: the validity of Kuhn's statistics and of Debye's approximation. (2) The electrostatic contribution per macromolecule to the free energy of the solution is found to beFe= (v2ϵ2/Dh)ln {1 + (6h/κh 02)}, wherevis the number of charged groups per polymolecule, ϵ the unit of charge,Dthe dielectric constant, κ Debye's inverse radius, based on the number of free ions in solution,hthe end‐to‐end distance of the charged molecule, andh0the corresponding end‐to‐end distance in and uncharged reference state. (3) Activity coefficients of free ions in polyelectrolyte solutions have been derived from the theory. The calculated values compare favorably with the activity coefficients from measurements on Donnan distrib

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110503

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110504

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

摘要:

AbstractBy means of a mathematical treatment the distributions of the tensile strength of natural rubber and GR‐S were studied. As a result of this study it is shown that the distributions are of the so‐called doubly exponential t

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110505

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

摘要:

AbstractThe small angle scattering of ramie and of 25 highly oriented rayon samples of widely different prehistory has been examined in both the air‐dry and the water‐swollen condition with monochromatic radiation in a vacuum camera. All intensity curves are given. For some rayons the curves show distinct maxima or inflection points in either the swollen or the dry condition which seem to be indicative of the existence of a maximum of relatively low intensity superimposed on a normally descending small angle intensity curve. The Bragg spacing corresponding to these maxima lies close to 80 A. for the swollen and to 50 A. for the dry fibers. Other specimens either do not show these superimposed maxima or show only faint indications of their occurrence. The existence of maxima (particularly pronounced in Fortisan, Fiber G, Super Cordura, and Celanese K 36) seems to demonstrate that in some rayons a part of the fiber substance has a micellar structure of unexpectedly high regularity and with average interparticle distances given by the Bragg spacings indicated. The intensity curves of those swollen specimens which did not exhibit a maximum, when evaluated by the Guinier method for dilute systems, assuming parallel cylinders as the basic structure, yield figures between 35–55 A. for the diameter of the cylinders. Evaluation of the intensity curves according to an approximation suggested by Kratky (based on the picture of closely packed lamellae) points to the existence of a preferred spacing of the same order of magnitude (∼40 A.) for the dry and of ∼60 A. for the swollen fibers. No clear correlation between small angle scattering features and other known properties of the rayons has been

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110506

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

摘要:

AbstractA simple and inexpensive instrument for measuring the osmotic pressure of polymer solutions has been designed. It consists of two 1‐mm. I. D. Pyrex capillary tubes sealed into a flanged Pyrex sleeve, which is ground to fit snugly into a 19 × 60 mm. roundbased Alundum Thimble of medium porosity. A regenerated cellulose membrane is cast over the Alundum thimble, and the entire assembly is sealed in a test tube containing the polymer solution to be examined. This osmometer offers several unique advantages over others in current use. Its low cost and compact size permit inexpensive simultaneous measurement of many polymer solutions.A 1:3 copolymer of vinyltoluene and styrene monomers was separated into 24 cuts by fractional precipitation. On the basis of viscosity data these cuts were combined into 14 fractions. They were in the order of decreasing molecular weight, and infrared analysis indicated a uniform distribution of the ring methyl groups among the fractions. These two observations demonstrate that introduction of methyl groups into the benzene rings of a polystyrene molecule does not influence the polymer solubility appreciably.Osmotic molecular weights obtained with the Alundum thimble instruments and experimental limiting viscosity numbers gave values of 2.69 × 10−4and 0.622 forKand α respectively in the Flory‐Staudinger relation [η] =KMα. These results compare favorably with reported values for polystyrene samples prepared under similar

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110507

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

摘要:

AbstractAn exploratory investigation of the kinetics of the polymerization of chlorotrifluoroethylene (I) has been made. Experiments were conducted in bulk, in solution in several solvents, and in the presence of several comonomers. Acetyl peroxide (II) was found to be the most effective of common initiators and was used in most of the experiments. The sealed empoule technique was employed. The bulk polymerization of I is zero order to 60–80% conversion; the rate varies as the 0.7 to 0.8 power of the acetyl peroxide concentration, and the over‐all activation energy is 17 kcal./mole. The solution polymerization in benzene appears to be first order in monomer; in other solvents the order was not ascertained. The rate and activation energy in solution are solvent dependent and there appears to be an inverse relationship between the rate of polymerization of I in a solvent and the rate of decomposition of II in that solvent. The rate of decomposition of II was measured in a number of solvents and found to vary widely and to parallel, roughly, the rate of decomposition of benzoyl peroxide. The polymerization rate of I in solution is alsoc.0.7 order in acetyl peroxide, but was 0.5 order in Porofor N in limited experiments. From copolymerization experiments with styrene, vinyl acetate and methyl methacrylate values ofQof 0.025, 0.025, and 0.016, and ofeof 1.4, 2.0, 1.4, respectively, were inferred, in theQ–escheme of Alfrey and Price. These results above are discussed in the light of polymerization t

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110508

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110509

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY

摘要:

AbstractIn the dextrose‐free recipe at 41°F. for the copolymerization of butadiene and styrene, using 6 × 10−4mole of initiator per one hundred grams of monomers, methyl oleate peroxide (MOP) and methyl linoleate peroxide (MLP) gave higher polymerization rates and conversions than cumene hydroperoxide (CHP), and they gave as high rates of conversion asp‐menthane hydroperoxide (PMHP). In the peroxide‐dextrose recipe at 122°F., at both low and high dextrose levels, only about one‐half as much MOP (1.5 × 10−4mole) as CHP or PMHP was employed on a molar basis to achieve the same conversion and polymerization rate. In the low dextrose‐redox recipe at 41°F., using 6 × 10−4mole of initiator per one hundred grams of monomers, MLP gave slightly higher conversions than CHP or PMHP, but in the amine recipe at 41°F., MLP

ISSN:0022-3832    

DOI:10.1002/pol.1953.120110510

出版商:Interscience Publishers, Inc.    

年代:1953

数据来源: WILEY