ISSN:0022-3832    

DOI:10.1002/pol.1959.1203813301

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractThe polymerizations of butadiene and of styrene by various organosodium reagents combined with sodium isopropoxide (or methylphenyl carboxide) and sodium chloride have been compared. In general a reagent which is a good promoter of 1,4‐polymerization of butadiene is a poor agent for isotactic polymerization of styrene and vice versa. Also, rapid polymerization of styrene seems unrelated to stereospecific polymerization of styrene.m‐Xylylsodium, combined with sodium isopropoxide and sodium chloride, was a preferred agent for isotactic polymerization of styrene but did not induce enough 1,4‐polymerization of butadiene to qualify as an alfin catalyst. Catalysts of this type might be called “albyl” systems in order to differentiate them from alfin catalysts. A definite relationship exists between the structure of the reagent and the polymer it produces. Therefore, adsorption of the monomer on the surface of the catalyst is probably the controlling and most important factor in polymerization induced by these

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203813302

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractThe product from the metalation of methylcyclohexene can be used in an alfin catalyst combination provided the proportions of the components are suitable, but the sodium compound from the metalation of cyclohexene cannot be used irrespective of the proportions. The metalation product from methylcyclopentene appears to form an alfin catalyst, but that from cyclopentene does not. These facts have an important bearing upon any opinion about the structure of the catalyst and the nature of a surface which affect profoundly the polymerization of butadiene, indeed, control polymer growth.

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203813303

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractPhysical changes which accompany the crystallization of isotactic polypropylenes have been observed by dilatometry and optical microscopy at temperatures between 120 and 160°C. Samples were fused at 220°C. and then held at a predetermined crystallization temperature for times ranging up to many hours. Rate constants for the crystallization were calculated from volume changes and from measurements of radial growth of spherulites. Polypropylenes from different sources exhibited quite different concentrations of spherulites and growth rates. Crystallization appears to proceed, at least at the higher temperatures, by spherical growth from a fixed number of nuclei, apparently arising from foreign matter in the polymer. With decreasing temperature, the number of nuclei (hence also the number of spherulites) increases, since apparently the conditions for nucleation become less critical. The crystallization follows the kinetics of a nucleation‐controlled process according to an Avrami equation, ‐log (1 ‐ ΔV/ ΔV∞) =kt3. Deviations from the third power of time at the lower temperatures may be the result of a secondary ordering process, slower than the primary crys

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203813304

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractButadiene‐(1,3) reacts with certain Ziegler‐catalysts almost exclusively according to the principle of the 1,4‐addition to form cyclododecatriene‐(1,5,9). In contrast to that, 2,3‐dimethylbutadiene‐(1,3) follows a new linking mechanism of hydrogen‐transfer to form an open‐chained trimer. Isoprene and piperylene react according to

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203813305

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractMost of the reported polymerizations of ethylene at atmospheric pressures utilize heterogeneous catalysts. This paper summarizes some studies of the polymerization of ethylene at atmospheric pressure with nonprecipitate titanium+4catalyst systems. The nature of the alkyl metal used to make the catalyst influences the occurrence of reduction of titanium which produces the usual heterogeneous state. The highly active alkyl metals must be modified to decrease their reducing power. Electrophilic materials which are normally produced during the reduction step in the Ziegler catalysts must be present to obtain optimum activity of the nonprecipitate catalyst. The homogeneous titanium+4catalysts described here are more active than the usual heterogeneous Ziegler catalyst. The catalyst formation is explained as due to the formation of complexes.

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203813306

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractCrystalline poly(tert‐butyl acrylate) was prepared with lithium dispersions,n‐butyllithium, and lithium plusn‐butyllithium as catalysts. Methyl acrylate,n‐, see‐, andiso‐butyl acrylate gave only amorphous polymer under the conditions that produced crystalline poly(iert‐butyl acrylate). Very pure monomer was necessary for the preparation of crystalline poly(tert‐butyl acrylate) with lithium dispersions. That the poly(tert‐butyl acrylate) was crystalline was shown by x‐ray diffraction, observation with the polarizing microscope (preparation of birefringent spherulites) and the electron microscope, study of infrared absorption, softening point, and density, and finally by preparation of crystalline polymethyl acrylate from crystalline poly(tert‐butyl acrylate) by ester interchange. The nuclear magnetic resonance spectrum of the crystalline poly(tert‐butyl acrylate) showed no evidence of band splitting and the viscosity‐slope constant,k′, was the same for crystallizable an

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203813307

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractMany polymers in solution exhibit well‐resolved NSR spectra, in contrast to the broad peaks observed for the solid state. The peaks for polystyrene dissolved in carbon tetrachloride are not very much broader than those of cumene and other small organic molecules. When segmental motion is restricted or prevented, polymer peaks may become very broad even in solution. This is observed for poly‐γ‐benzyl‐L‐glutamate in trichloroethylene, in which it probably exists as large aggregates of α‐helices. It is shown that the α‐helical conformation itself is not responsible for this broadening. Many proteins also show poorly resolved spectra in the native state, but well‐resolved peaks in the unfolded state. Large “anomalous” shifts observed in the positions of the proton peaks in the NSR spectra of polystyrene and substituted polystyrenes are interpreted in terms of a π‐current model of the benzene ring. It is concluded that where sequences of 10 or more phenyl groups are present on a polymer chain, they tend to cluster together in a quas

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203813308

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractPreformed transition‐metal oxides on high‐surface supports and precipitated catalysts from transition‐metal salts and aluminum alkyls produce linear polyethylene and stereoregular polyolefins. An introductory study of the kinetics of ethylene polymerization with a specially prepared preformed solid catalyst was undertaken as an aid in understanding the catalytic action. At constant pressure, ethylene uptake is linear. The rate depends on amount of catalyst and on ethylene concentration at various temperatures and pressures. The molecular weight of the product is primarily a function of temperature. The observed rate and its dependence on ethylene concentration and temperature are consistent with bound‐ion‐radical polymerization in a chemisorbed ethylene layer. The equations are similar in form to those based on a coordinate‐anion Polymerization mechanism. Further study will be needed to distinguish between these mechanisms, because they differ essentially only in the electronic environment of the growing chain end and in the movement of the growing reaction center during pol

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203813309

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractCrystallization kinetics of Hercules polypropylenes were studied between 133 and 155°C. using dilatometers. The crystallization rates of these samples became too rapid below 133°C. for accurate dilatometric measurements. One sample (A) was a commercial sample containing stabilizer and 9% extractable polymer (with boilingn‐heptane). B was an experimental extracted sample containing no stabilizer. A portion of B was thermally degraded under vacuum at 350°C. for 7 hr. (C). The DPn′s of A, B, and C were 2300, 7300, and 1200, respectively. Their melting points were determined dilatometrically, under conditions approaching equilibrium, and were 175, 176, and 173°C., respectively. 95% of the crystallization can be described by an Avramitype equation with annvalue of 3, indicating a three‐dimensional growth with residual nucleation or a two‐dimensional growth with spontaneous nucleation. The heterogeneities may result from catalyst residues. The crystallization rate of A was lower than that of B or C at a given temperature, possibly due to the presence of atactic polymer. At a given temperature C crystallized faster than B, which may be an effect of the difference in molecular weight. Plotting the rate as a function of the degree of undercooling (ΔT) increases the difference bet

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203813310

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY