摘要:

AbstractA technique is described for quantitatively examining the diffraction pattern of polydimethylsiloxane at and below room temperature with the x‐ray diffractometer. The crystalline fraction of the unstretched material is determined by the classical method developed for natural rubber. In the case of the stretched elastomer, a modified procedure is required which takes into account the extent of preferred orientation of the molecular chains. As the extension ratio is increased, the crystallization temperature rises and preferential orientation of the crystallites with respect to the extension axis increases. The crystallinity increases with decreasing temperature and appears to be independent of the extension ratio below −60°C. An over‐all crystalline fraction of 0.42 was measured for a silicone rubber specimen at −60°C. and an extension rat

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202711501

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractDensity data for a silica‐filled dimethylpolysiloxane rubber define incipient crystallization conditions and indicate the forms of crystalline growth for the unstressed rubber and for a sample at 200% elongation. Temperature—tension data for the same silicafilled rubber show incipient crystallinity temperatures as a function of extension. While stress relaxed filled silicone rubber samples show a tension decrease with falling temperatures, they are far from ideal rubbers. The change in polymer filler interaction links with temperature may account for this nonideality. Both the filled and unfilled rubbers show a thermoelastic inversion. The comparison with x‐ray data yields good evidence that crystallization is responsible for the tension rise at low temperatures. This rise may stem from the tendency of silicone rubber to crystallize without altering the orientation of chain segments. The ability to crystallize chain elements in all states of orientation may be founded upon a much greater chain segment mobility for silicone rubber than found with natural rubber. Normal stress—strain curves taken at low temperatures qualitatively show the effects of crystall

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202711502

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe copolymerization reaction of five vinyl esters of aliphatic acids with vinyl chloride, vinylidene chloride, acrylonitrile, butadiene, styrene, and methyl acrylate have been studied. The reactivity ratios have been determined and theQandevalues for the esters have been calculated. The results clearly show that the nature of the acyl residue in a vinyl ester has little influence on its reactivity ratio in a copolymerization reaction or on theQorevalue.

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202711503

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractGelatin solutions shrink as water evaporates from the gel. If the shrinkage is prevented, tensile stresses develop. A technique is described for measuring the tensile stress developing in the plane of edge‐clamped gelatin films during drying. It is based on measurement of the elastic deformation of the film when stressed normally to the plane of the film. A stress of 4000 pounds per square inch was observed in a dried gelatin film. The reality of the stress was confirmed in a completely independent manne

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202711504

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe proton spin resonance spectrum of polyethylene consists of two superimposed lines. The narrow line is attributed to the amorphous phase, and the broad line to the crystalline phase. The width of the narrow line was measured at various temperatures from 25−130°C. for Alathon 10, Alathon 14, DYNH, and Marlex 50 polyethylene and it was found to vary with temperature. The results have been interpreted using the theory of motional narrowing, which indicates that the product of temperature and line width is proportional to the viscosity. A plot of log of line width times temperatureversusreciprocal temperature is linear for Marlex 50 polyethylene, and is curved for the other three. The linearity is believed due to the simple structure of the material, and the slope yields an activation energy of 8200 cal./mole. The curvature of the other data is believed due to extensive branching which causes a change of composition of the amorphous phase upon cooling, and the apparent activation energy varies from 11,800 cal./mole at 130°C. to 4900 cal./mole at 2

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202711505

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe effect of time and temperature on the crystalline recovery of quenched Marlex 50 polyethylene has been investigated. Quenching thin films in ice water reduced the room temperature crystallinity from a normal value of 93 to 82%. These specimens were maintained at 25, 66.2, and 106.4°C., and the time variation of crystallinity was followed by nuclear spin resonance. The crystalline recovery appears to follow the empirical formula,X=A+Blogt, whereXis the percentage crystallinity andt, is the time in hours. The rate,X, increases with temperature. The temperature‐dependence ofBwas computed by assuming the rate to be controlled by diffusion in the amorphous phase. The temperature‐dependence of diffusion is determined by nuclear spin resonance line width measurements to be exp {−8700/RT}. The rate is thenX=C/texp {−8700/RT}, andC, evaluated at 25, 66.2, and 106.4°C., is 2.2 ± 1.9, 1.7 ± 0.5, and 2.1 ±0.2 × 105. This agreement is within the probable error, and justifies the assumption of diffusion as the rate‐controlling factor. The result isX= 2.04 × 105(1/t) exp { −8700/RT} andX=A+ 4.70 × 10

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202711506

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractAn equation is developed for calculating the fractures/chain link from the change in weight‐average molecular weight for the case of the photochemical degradation of a polymer with an initial random molecular weight distribution. From calculations made on the degradation of cellulose with 2537 A. light, it appears that the formation of aldehyde groups and the evolution of hydrogen are in part due to reactions not involving chain scissio

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202711507

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe scattering of both unpolarized and polarized light by a series of stretched polyethylene films has been studied. The radiation envelope of the scattered light loses its cylindrical symmetry upon stretching. The dissymmetry depends upon the orientation of the stretching direction of the film as does the intensity of scattered light. The results imply a scattering unit which is anisotropic both in shape and in polarizability. The largest dimension and highest polarizability lie in the stretching direction. The Debye‐Bueche theory has been generalized to describe oriented anisotropic systems. The single parameter,a, describing the size of the heterogeneity is replaced by two parameters,aandc. The mean‐square dielectric constant fluctuation η2depends upon the principal polarizabilities of the scattering unit and upon its orientation. The parameters are evaluated for the series of polyethylene samples. A model is proposed which accounts for the variation of the parameters as well as the changes occuring during melting and crystallizing the pol

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202711508

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe crosslink density in polybutadiene has been determined by measurement of the polymer molecular weight by osmometry and the primary chain molecular weight by modifier analysis involving radioactive materials. Since the number of polymer molecules is equal to the number of primary chains less the number of crosslinkages, the experimental measurements may be used to calculated the crosslink density. This method can be used to determine crosslink density at a combination of conversions, modifier loadings, and polymerization temperatures which could not be done by other methods. Branching and cyclic structure forming crosslinks are not measured by this method, the principal assumption of which is that one and only one modifier fragment is attached to each primary chain. Initiation and termination processes tend to reduce the validity of this assumption, but these have been minimized by reduction of the amounts of initiator and found insignificant by comparison of different systems. Modifiers which react with polymer in nonterminal positions also reduce the validity so that primary dodecyl mercaptan was not satisfactory as a modifier in this work, while tertiary alkyl mercaptans were. Also, diisopropyl xanthogen disulfide was not satisfactory because of secondary reactions. The crosslink density of polybutadiene prepared in emulsion decreases with decreasing polymerization temperature. At a given molecular weight, the crosslink density does not appear to be a function of conversion within the range studied. At a given polymerization temperature, increasing polymer number average molecular weight was accompanied by increasing crosslink density although the rate of such increase was smaller at subfreezing polymerization temperatures. These results agree with kinetic theory of crosslinking in emulsion polymerization, but actual values are higher than those obtained in comparable systems by the gel point method.

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202711509

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY

摘要:

AbstractThe dielectric dispersion of dilute solutions of ethyl cellulose in dioxane was studied using a “differential” bridge method for the range from 200 cycles to 300 kilocycles. The frequency where the dispersion was 0.50 was recorded as the “critical” frequency. The critical frequency is related to the intrinsic viscosity of the samples as log 100[η] = 2.97 − 0.59 (vc). Since the determination of critical frequency is very rapid this method apparently is satisfactory for molecular weight determinations in the syste

ISSN:0022-3832    

DOI:10.1002/pol.1958.1202711510

出版商:Interscience Publishers, Inc.    

年代:1958

数据来源: WILEY