摘要:

AbstractTensile deformation of poly(methyl methacrylate) carried out under hydrostatic pressures up to 4 kbar has shown that the pressure‐transmitting fluid (silicone oil) strongly affects the mechanical properties of this polymer. Unsealed specimens fractured in a brittle manner at almost the same strain of 5% in the whole pressure range examined, while specimens sealed with Teflon tape and rubber showed a brittle to ductile transition at only 0.25 kbar. At this pressure, the craze initiation and shear band initiation stresses were found to become equal. The pressure dependence of the shear band initiation stress could be expressed well with a “nonlinear” pressure‐dependent von Mises criterion and the onset of the shear banding was proved to relate to the enthalpy energy density stored in the specimen. The combination of the nonlinear pressure‐dependent von Mises criterion and the enthaply energy density concept enabled us to predict the pressure dependence of Young'

ISSN:0098-1273    

DOI:10.1002/pol.1976.180140411

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractThe tensile strength of poly(methyl methacrylate) (PMMA), polycarbonate (PC), polychlorotrifluoroethylene, and polysulfone was measured in liquid nitrogen over the strain rate range of 2 × 10−4to 660 min−1. These polymers deformed by crazing which was induced by the liquid nitrogen. The stress versus log strain rate curve was sigmoidal in that its slope increased and then decreased with strain rate. Above a critical strain rate of about 200 min−1, which varied somewhat with the polymer, crazing was not observed with the optical microscope; the behavior became brittle, and the tensile strength became constant. The nonlinear behavior of stress versus log strain rate at low strain rates was associated with a decrease in activation volume with increasing strain rate whereas the nonlinear behavior at high strain rates was associated with an increase in density and decrease in length of the crazes with strain rate. The strain rate effect was the basis for calculating the diffusion coefficient of nitrogen into the polymers at 77°K.The shear deformation mode of PC was measured under compression and under tension. The compressive strength versus log strain rate was linear throughout the entire range giving a compression shear activation volume of 360 Å3. The shear tensile strength of PC varied only slightly with strain rate when compared to the compressive strength. The brittle fracture stress of PMMA, in the absence of crazing, in compression and in tension, did not vary with str

ISSN:0098-1273    

DOI:10.1002/pol.1976.180140412

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractBrillouin scattering has been studied from amorphous bisphenol‐A polycarbonate in the temperature interval 60–240°C. Both longitudinal and transverse Brillouin peaks are observed over the entire range. The behavior of both types of Brillouin splittings, Δωland Δωt, in the region of the glass–rubber relaxation is typical of an amorphous polymer. Equilibrium values of Δωland Δωtwere obtained 20°C below the glass‐transition temperatureTgdetermined at cooling rates of 20°C/hr. Comparison of the present results with previous ultrasonic data reveals a considerable dispersion in the longitudinal phonon velocity belowTg. The origin of the large transverse Brillouin intensities is related to the structur

ISSN:0098-1273    

DOI:10.1002/pol.1976.180140413

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractStyrene–acrylonitrile (St–AN) copolymers of three compositions—27.4 mole‐% (SA1); 38.5 mole‐% (SA2); and 47.5 mole‐% (SA3) acrylonitrile—and styrene–methyl methacrylate (St–MMA) copolymer (SM) of 46.5 mole‐% methyl methacrylate were prepared by bulk polymerization at 60°C with benzoyl peroxide as the initiator, and were then fractionated. The molecular weights of unfractionated and fractionated samples were determined by light scattering in a number of solvents. The [η] versus M̄wrelations at 30°C were established for SA1, SA2, SM, and polystyrene (PSt) in ethyl acetate (EAc), dimethyl formamide (DMF), and γ‐butyrolactone (γ‐BL), and for SA3in methyl ethyl ketone (MEK), DMF, and γ‐BL. Second virial coefficientsA2and the Huggins constant were determined. From values ofA2and the exponent a of the Mark–Houwink relation it is seen that the solvent power for samples SA1, SA2, and PSt is in the order EAc<γ‐BL

ISSN:0098-1273    

DOI:10.1002/pol.1976.180140414

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractExperimental data on styrene–acrylonitrile (St–AN), and styrene–methyl methacrylate (St–MMA) copolymers reported in Part I of this series are tested by “two‐parameter” theoretical relations. The Fox–Flory (F–F) parameterKis estimated using the F–F, Stockmayer–Fixman (S–F), and Inagaki–Ptitsyn (I–P) equations. In general, theKvalues obtained by the F–F equation are low for the three St–AN copolymer samples in the systems studied while the values obtained from S–F and I–P equations agree within the limits of experimental error. Values ofKobtained from Kurata–Stockmayer (K–S) equation for sample SA1agree with values obtained by the S–F and I–P equations. The specific solvent effect on theKvalues is discussed. Values of the unperturbed dimension r̄02/M̄w, calculated from theKvalues estimated from the S–F equation and from the homopolymer data are compared. Except in one case, the calculated r̄02/M̄wvalues from homopolymer data are low in comparison with the values obtained from experimental data, which shows that the presence of the repulsive interactions between unlike monomer units brings about an expansion of copolymer molecule. The effect of composition on the steric factor σ values is discussed. The long‐range interaction parameterB, the excess interaction parameters ΔBAB, and χABare calculated. The effects of com

ISSN:0098-1273    

DOI:10.1002/pol.1976.180140415

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

ISSN:0098-1273    

DOI:10.1002/pol.1976.180140416

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY