摘要:

AbstractThe viscosity surfaces of two samples of DNA as a function of rate of shear and concentration of polymer and of NaCl are described. The measurements were performed with a rotation viscometer with electrostatic resorting torque recently described, at rates of shear from 0.13 to 200 sec.−1. The limiting slopes of the viscosity against rate of shear curves are zero in agreement with hydrodynamic theory. The measurements are not amenable to interpretation by the rigid ellipsoid of rotation model but are better described by the Gaussian chain model with high internal viscosit

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202511001

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractAn improved model of a precision rotation viscometer with electrostatic restoring torque for the centipoise range is described. In this instrument torques from 0.1 to 500 dyne cm. are measured with an accuracy of 0.2%. Rates of shear range from 0.1 to 200 sec.−

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202511002

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractThe copolymerization ofn‐butyl acrylate with both 2 and 4 vinylpyridine was investigated. Spectrophotometric analysis was employed for determining copolymer compositions utilizing the vinylpyridine absorption at 263 mμ. Reactivity ratios for butyl acrylate/2‐vinylpyridine werer1= 2.50 ± 0.50 andr2= 0.10 ± 0.04. For butyl acrylate/4‐vinylpyridiner1= 5.51 ± 0.09 andr2= 0.46 ± 0.09. These values were compared with calculated estimates made from th

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202511003

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractCellulose nitrate was degraded ultrasonically at 0 to 85°C. in the alkyl acetates from methyl to heptyl. In each solvent there is a high and low limit temperature where cavitation and degradation both cease. The upper limits are at the temperatures where vapor pressure of the solvent is about one‐half atmosphere, and cavitation evidently ceases because the solvent vapor pressure becomes too great for rapid bubble collapse. The lower limits of pressure and temperature vary in a linear manner, but have not been explained. The results confirm the need for cavitation as an initiator of the degradation mechanism, and explain some effects previously ascribed to solvent viscosity and temperature. When radio frequency power was varied, the rate of degradation was found to be independent of power so long as cavitation was present. In other experiments, degradation was found to be approximately constant to concentrations much lower than previously tested, whereas some proposed mechanisms would require that it should be reduced by dilution. Addition of a nonsolvent reduced the intrinsic viscosity of the polymer solution but did not reduce the extent of degradation; thus degradation is a function of the chain's length but not of its solvation. Finally, comparison of a series of celluloses from diverse sources showed that all gave about the same minimum degradable chain length, of 800–1000 DP. It was concluded that there was no evidence for the existence of weak links in the celluloses at shorter inter

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202511004

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractThe tensile creep behavior of natural rubber, high and low temperature GRS, polybutadiene, and a syntheticcis‐polyisoprene have been investigated. By combining measurements over the temperature range −70 to +60°C., it has been possible to obtain a composite creep curve covering over 15 decades of time for each of these materials. In addition, similar curves have been obtained for most of these materials at several degrees of cure and containing various amounts of carbon black. All measurements were confined to elongations below about 5%. One can conclude from these data that the synthetic rubbers, except for thecis‐polyisoprene, do not vulcanize to give a mechanically stable network. That is to say, these materials never reach equilibrium elongation under an applied load. It is concluded that the number‐average molecular weights of GRS is so low that excessive degrees of crosslinking are needed in order to form a stable network. Natural rubber and certain syntheticcis‐polyisoprene, do not suffer from this defect. The excessive heat generation found in GRS upon flexure is attributed to the fact that an equilibrium extension is never achieved in these materials. A theoretical relation for the heat production in flexed rubbers is given. It is showed that the theory predicts the relative behavior of the various rubbers in respect to heat generation und

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202511005

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractThe kinetics of the degradation of polyisobutene in cetane solutions produced by mechanical shearing action in a capillary has been studied as a function of rate of shear energy application and of concentration. The initial rate constant,k, for the degradation was determined as the initial rate of bond cleavage per unit concentration by weight. Logkwas found to be a linear function of the reciprocal of the rate of shear energy application per unit volume,J. At all concentrations studied in the range 5–20 weight per cent, logkwas the same function of 1/J, but such a plot for 3% solutions had a much greater negative slope. This indicates a decreased efficiency for the concentration of mechanical energy by the polymer molecules in less concentrated solution

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202511006

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractA systematic investigation was undertaken of the kinetics of polymerization of styrene and methyl methacrylate in bulk as well as in solutions of benzene, toluene, methyl ethyl ketone and ethyl acetate and of methyl acrylate in ethyl acetate with methyl ethyl ketone peroxide (MEKP) as initiator at 65–80°C. The decomposition of MEKP in ethyl acetate at 70 and 80°C. was studied and the specific rate constants for spontaneous as well as induced decomposition have been evaluated. Transfer coefficients for the monomer, catalyst, and solvent with their respective activation energies have been determined. The rates of initiation have been evaluated by measuring rates and the degree of polymerization for the monomers under study. The catalyst efficiencies in the polymerization of the monomers have been evaluated from the rates of initiation and the rate of decomposition of the catalyst. It is found that the initiator MEKP is comparable to Bz2O2and azobisisobutyronitrile in its catalyst efficiency, while its capacity for chain transfer is found to be intermediate between the nontransferring initiators like azobisisobutyronitrile and the highly transferring initiators such as cumene hydroperoxide. That the effect of solvents on the various rate constants such as termination and initiation appears to be of no inconsiderable importance has been infer

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202511007

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202511008

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

摘要:

AbstractA simple and rapid method is described in which infrared spectroscopy is used to follow the decrease in the epoxy content of an epoxy resin as it is cured. A film of resin plus curing agent between two disks of potassium bromide is cured by heat and its infrared spectrum is measured as the cure proceeds. The technique is used to compare the activities of diamines as curing agents.

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202511009

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY

ISSN:0022-3832    

DOI:10.1002/pol.1957.1202511010

出版商:Interscience Publishers, Inc.    

年代:1957

数据来源: WILEY