ISSN:0022-3832    

DOI:10.1002/pol.1959.1203613001

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractA procedure and apparatus are described for the large scale (50‐gram) fractionation of high‐density polyethylene by Desreaux's fractional extraction technique. Two samples of Ziegler polyethylene were fractionated by this technique and the intrinsic viscosity in decalin at 135°C. and molecular weight by light scattering were measured on the fractions. The relationship [η] = 4.6 × 10−4M̄w0.73was found to hold for molecular weights between 25,000 and 640,000. The samples differed in polydispersity, one having a broad distribution and the other a rather narrow distribution. Evidence for the sharpness of the fractions obtained by the new technique was provided by refractionating of one fraction and the resolation of two fractions which were combined and refra

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203613002

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractWith three polymers widely different in polarity—polyethylene terephthalate, polyethylene, and nylon 610—the water vapor permeabilityPof unoriented films has been shown to increase as the amorphous fractionXais increased, following the relationP=PaXa2. For polyethylenes, adherence to this relation is exhibited only with structures having densities above 0.94, a range in which the number of short chain branches is low. Films with densities lower than 0.94 exhibit higher film permeabilities than those calculated on the basis of the permeability of the amorphous areasPaof “linear” polyethylene; this results from the increase in the number of short chain branches and hence, an increase inPaof the lower density polyethylenes. The above variation of water vapor permeability with the square of the amorphous fraction may be theoretically accounted for by a linear variation of the diffusion and solubility coefficients with the amorphous fraction. With polyethylene terephthalate and nylon 610, the solubility coefficients do exhibit this linear relation. The square permeability relation appears to be a limiting case for structures in which crystallization does not impose restraints on the segmental motions important in permeability. Where restraints do occur, as in oriented films, a higher order dependency on the amorphous fraction exists. This was exemplified with biaxially and uniaxially oriented polyethylene terephthalate films, with which it was shown that orientation in oriented crystalline films effects a decrease in permeability in addition to that ascribable to crystallinity. This is not true for such films as polystyrene or stretched rubber which has not crystallized. Only those oriented structures in which the orientation is “locked‐in,” as by crystallization, exhibit a decrease in water vapor permeability. The relations of permeability and solubility coefficients to crystallinity have an important utility in that the extent of crystallinity or crystal density may be estimated with the proper data. On the basis of literature water vapor permeability data of Szwarc et al. for two high density polyethylenes at three different vapor pressure differentials, the crystal density of polyethylene was estimated to be 0.995, 1.008, and 0.998 or an average of 1.00, in agreement with Bunn's value calculated on the basis of x‐ray diff

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203613003

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractA homopolymer of vinyl pinonate and copolymers of vinyl pinonate and vinyl chloride have been described. The copolymer containing 19.8% of vinyl pinonate seems to show the best all around properties as a rigid plastic. The presence of vinyl pinonate as a component of the copolymer does not give a plasticized film. The homopolymer of vinyl pinonate exhibits adhesive characteristics. The use of an external plasticizer, di‐2‐ethylhexyl phthalate, with these compositions is not very promis

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203613004

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractC14‐Labeled initiators, viz., di‐(ar‐C14)‐benzoyl peroxide, di‐(carboxyl‐C14)‐benzoyl peroxide, and C14‐azobisisobutyronitrile (AZBN), have been used to initiate the polymerization of methyl methaerylate at 60°C. in benzene. Determination of the rates of polymerization, and the molecular weights (M̄n) and C14‐contents of the resultant polymers permits the following conclusions to be made. (1) Rates of initiation by benzoyl peroxide and AZBN are given by the equations,Ri= 5.15 × 10−6[Bz2O2] mole l.−1sec.−1andRi= 1.17 × 10−5[AZBN] mole l.−1sec.−1, respectively. (2) The initiator efficiency,f, for AZBN is 0.50;ffor benzoyl peroxide cannot be evaluated in the absence of a reliablekdvalue for this compound in the present system. (3) Initiation is solely by addition of initiator radicals, R·, to the monomer; in the case of benzoyl peroxide, 43% of the radicals R· are phenyl and 57% are benzoyloxy under the reaction conditions used. (4) The average number of C14‐initiator fragments per polymer molecule,n, is 1.27, indicating that bimolecular termination of polymethyl methacrylate radicals is 57.5% by dispro

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203613005

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractPolymerization of methyl methacrylate at 60°C. by benzoyl peroxide in benzene solutions of polyisoprenes (e.g., natural rubber and gutta‐percha) yields polymethyl methacrylate and a graft interpolymer having polymethyl methacrylate side chains attached to the polyisoprene backbone. Use of azobisisobutyronitrile (AZBN) as initiator in comparable systems gives free polymethyl methacrylate, but no graft interpolymer. The cause of this specific initiator effect, and the mechanism of graft polymerization have been determined by using C14‐labeled initiators. Benzoyl peroxide initiates graft polymerization by prior reaction of the derived phenyl and benzoyloxy radicals with the polyisoprene by addition to the double bond, and by abstracting α‐methylenic hydrogen atoms to give polyisoprenic alkyl and alkenyl radicals, respectively, which act as loci for methyl methacrylate polymerization. In the system gutta‐percha‐methyl methacrylate, at 60°C., 35–45% of the grafted vinyl polymer side chains are initiated by hydrogen abstraction, and about 90% of the initiator radicals undergoing addition to the double bond are benzoyloxy. The modes of termination of the grafted and free polymethyl methacrylate radicals have been evaluated semiquantitatively, and it is found that, in the graft interpolymer, 13–27% of the polymethyl methacrylate chains have both ends attached to gutta‐percha chains (i.e., have an “I” structure), while 73–87% are attached at one end only to gutta‐percha chains (i.e., are “T” structures). The reliability of the separatory procedure previously devised8to resolve the bulk polymer obtained in the graft‐polymerization system has now been verified by use of the isotopedilution technique. The inability of AZBN to initiate graft polymerization is attributed to the markedly inferior capacity of the resonance‐stabilized Me2Ċ(CN) radicals, relative to C6H5· and C6H5COO·, to engage in double bond additi

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203613006

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractNatural rubber is converted by reaction with a small amount of a thiol acid into a modified rubber which crystallizes at low temperatures much more slowly than the original rubber. This change in rate of crystallization is probably due to the conversion of some of thecisdouble bonds in natural rubber into thetransconfiguration. The preparation of the modified rubber from latex and its physical properties are described in detail.

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203613007

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractRelationships, as reported in the literature, between intrinsic viscosity and weight‐average molecular weight for high‐density polyethylene are in poor agreement. Experimental work in this laboratory, aimed at resolving similarly conflicting data, suggests that likely causes for these discrepancies are: polydispersity, incorrect dissymmetry correction, and inadequate solution clarification. These factors are discussed in some detail, and results on both fractionated and unfractionated samples support these conclusions. It is apparent that fairly narrow fractions must be studied to obtain a valid intrinsic viscosity‐weight‐average molecular weight relat

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203613008

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractTheGvalue for crosslinking of polydimethylsiloxanes by high energy electrons has been redetermined using cryoscopc methods and checked by quantitative determinations of the amounts of gases evolved. The value found,G= 2.5 ± 0.4, is significantly different from that reported previously. The swelling of high polymers crosslinked by high energy electron has been measured using benzene and toluene. Thex1value calculated using equilibrium tension and swelling measurements are in good agreement with those obtained from the vapor pressure measurements of Newing. The equilibrium tension measurements indicate that 1 mole of crosslinks produces 1.3 ± 0.3 moles of effective chain between crosslinks in the Wall, Flory, Rehner scheme. This is in agreement with the predictions of Guth and Jame

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203613009

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY

摘要:

AbstractThe behavior of linear polyethylene in various solvents has been investigated by the light scattering, osmotic pressure and viscosity methods. It is shown that polyethylene associates in α‐chloronaphthalene solution. The degree of association increases with molecular weight, but, at low molecular weights, it essentially vanishes. A comparison of molecular weights obtained from light scattering and osmotic pressure studies of solutions of polyethylene fractions in tetralin and‐p‐xylene yields no evidence of association over a broad range of molecular weights. The unperturbed molecular dimensions are shown to be considerably greater than those of polystyrene at the same degree of polymerization. In terms of Flory's theory of chain stiffness, linear polyethylene becomes competitive in stiffness with some cellulose derivatives of comparable temperatures. At a sufficiently high degree of polymerization, the Fox‐Flory equation i

ISSN:0022-3832    

DOI:10.1002/pol.1959.1203613010

出版商:Interscience Publishers, Inc.    

年代:1959

数据来源: WILEY