摘要:

A predictive equation for the influence of chain ends on glass‐transition temperatures is derived from a thermodynamic theory for the compositional variation ofTg. This relation is found to give excellent agreement with results for the effect in polystyrene, and produces a convenient and accurate first approximation. Secondary approximations to the principal equation are formally identical to the Ueberreiter‐Kanig and Fox‐Flory equations for the variation ofTgwith molecular weight.

ISSN:0021-8979    

DOI:10.1063/1.325792

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

AbinitioH‐F SCF quantum‐mechanical calculations have been done to evaluate the energy of covalent bond deformation of a –CH2CH2– ethylene repeat unit at strains up to &egr;=0.6. The computational scheme involves subtracting energies of axially strained normal paraffins (n‐C3H8,n‐C5H12, andn‐C7H16) differing in length by one ethylene unit. At small strains it is found that the deformation is contributed to equally by C–C bond stretch and by CCC bond angle opening. At higher strains the majority of the deformation is accomplished by C–C stretch. The calculated elastic modulus is 405 GPa and the tensile strength of the polymer in the chain direction is 66 GPa. While both of these values are higher than previous estimates, it is believed that these quantities are the most reliable which have been calculated.

ISSN:0021-8979    

DOI:10.1063/1.325723

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Young’s modulus, yield (break) strength, and elongation to yield (break) have been measured for blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) with polystyrene (PS), poly(p‐chlorostyrene) (PpClS), and random copolymers of styrene andp‐chlorostyrene (pClS). The significant difference between blend compositions is the compatibility of PPO with each styrene polymer. Blends of PPO with PS or copolymers with 67.1 mole% or less pClS are compatible (i.e., oneTg) and show small synergistic maxima in modulus, strength, and elongation as a function of PPO composition. These maxima correspond to observed maxima in packing density as a result of specific interactions contributing to blend compatibility. A rule of mixtures for one‐phase systems with an adjustable compatibility parameter gives adequate fit to the observed composition dependence of the modulus. In a narrow composition range between 67.8 and 68.6 mole% pClS, copolymers exhibit partial miscibility with PPO. Two mixed composition phases are present. Moduli of these transitional blends follow the same form of synergistic dependence on blend composition as do the compatible blends but strength and elongation exhibit a sigmoidal relation to blend PPO content. At about 20% PPO, strength (and elongation) reaches a minimum as predicted by a simple composite model for a dispersed phase with good adhesion to the matrix. A maximum is reached at ∼80% PPO at which composition blend test specimens yield prior to failure. Blends of PPO with PpClS and with copolymers of ≳68.6 mole% pClS exhibit a broader minimum in strength (and elongation) but a similar maximum at 80% PPO. Unlike the compatible and transitional blends, moduli follow a nonsynergistic composition dependence adequately represented by the series model for two‐phase systems.

ISSN:0021-8979    

DOI:10.1063/1.325793

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Lattice vibrations are incorporated into the Gibbs‐DiMarzio configurational entropy theory of glasses. A comparison is made with data compiled by O’Reilly. The resulting theory predicts the specific‐heat discontinuity at the glass transition to within 20%. No adjustable parameters are involved; only the chemical structure need be known. The specific‐heat discontinuity has three parts. The formula in customary notation is &Dgr;cp=R(&Dgr;&egr;/kTg)2 f(1−f) +RTg&Dgr;&agr; (4−Tg&Dgr;&agr;/0.06) +0.5Tg&Dgr;&agr;cp(Tg−). The first part is a configurational term arising from shape changes of the molecules (?50% of total). The second part is a configurational term arising from volume expansion (?30% of total). Finally there is a vibrational contribution arising from the change of the force constants (or characteristics frequencies) with temperature (?20% of total).

ISSN:0021-8979    

DOI:10.1063/1.325794

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The optical mode structures of solvent cast films of different polymers have been measured with a single prism film coupler. The allowed modes define the index of refraction for light polarized in and perpendicular to the plane of the film. It is shown that the solvent coating process preferentially aligns the polymeric chain backbone in the plane of the film and that this biaxial orientation may produce birefringent films in optically anisotropic resins. The sign of this birefringence depends upon the orientation of the dominating polarizable group relative to the chain backbone in the plasticized melt. The magnitude of this effect reflects both the optical anisotropy of the group and the steric constraints to its free rotation.

ISSN:0021-8979    

DOI:10.1063/1.325795

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The glass transition temperature of nylon 6–inorganic salt mixtures has been investigated.Tgnot only increases monotonically with the salt content but the rate of increase depends on the type of salt. Infrared measurements indicate that metal ions form adducts with the amide group, and, as a result, the nylon chains are stiffened. This effect appears to be a major cause of theTgincrease. The adduct formation between the ions and the amide group is very similar to hydration of ions and the observed effect of ions on theTgof nylon 6 is similar to the effect of the same ions on hydration. The effect is also shown well correlated toQ/Rof the ion, the ratio of the oxidation number to ionic radius of the ion.

ISSN:0021-8979    

DOI:10.1063/1.325796

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

In a previous publication from this laboratory, the Rouse‐Bueche‐Zimm molecular theory of viscoelasticity has been extended by using a transient network model to apply to binary blends of monodisperse polymers with chain entanglements. The dynamics of the entanglements were modeled both by the enhanced frictional coefficients and by the additional elastic couplings. It was recognized that entanglements not only may form between chains of the same lengths (intracomponent entanglements) but also between those of different lengths (intercomponent entanglements). At a given intercomponent entanglement, the longer chain was assumed to have the frictional coefficient of the shorter chain. Similarly, for blends consisting of several monodisperse components with different molecular weights, such modifications are also required to predict their linear viscoelastic behavior. The frequency of these interactions is assumed to be proportional to the weight ratio of the respective component chains in the blend. Equations of motion are formulated for each component and solved numerically for the relaxation time spectra. Linear viscoelastic properties such as the dynamic mechanical moduli, stress relaxation moduli, and zero‐shear viscosity can then be computed for these systems by linear summation of those of the components. The reduced steady‐state shear compliance of the blends can also be computed from the component relaxation times. Results are found to be in good agreement with experimental data on polystyrene ternary blends.

ISSN:0021-8979    

DOI:10.1063/1.325797

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

An equation for the retardation time for enthalpy recovery has been tested for polystyrene as a function of heating rate, temperature, and initial displacement. The temperature dependence &Vthgr; and displacement dependence &xgr; of the retardation time are determined from the data assuming a single relaxation time. The fraction of the temperature dependence of the retardation time due to structure (1−X) and due purely to temperature (X) are calculated and compared with results for other polymers. Some factors which can affectXare discussed.

ISSN:0021-8979    

DOI:10.1063/1.325798

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Extended Hu¨ckel and MNDO programs developed for molecular systems have been modified without reparametrization to perform crystal orbital calculations. A comparison of the qualitative results of these methods with the extended tight binding results of Grant as applied to the band structure calculation oftrans‐polyacetylene is presented. It is demonstrated that the ETB, EHCO, and MNDO methods give results which show a similar trend with minor differences in detail. The usefulness of the crystal orbital method for the interpretation of experimental density of state curves of doped and undoped polymers is inferred from this study and previous studies on polyethylene.

ISSN:0021-8979    

DOI:10.1063/1.325776

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

&bgr;‐phase PVF2films having a ’’single‐crystal’’ orientation (single‐crystal analog) were prepared by a combination of drawing, rolling, and annealing, applied in sequence. X‐ray diffraction patterns revealed that the polar b axis was preferentially oriented normal to the surface of the film while the a and c axes were in the plane of the film, lying along two mutually orthogonal axes. Piezoelectric outputs (d13) of the films were compared with those of drawn‐only films under the same poling conditions (about 500 kV/cm) and found to be on average about 25% higher than the latter. X‐ray and dynamic mechanical data showed that the improvement depends primarily on the preferred alignment of the a and b axes in the plane normal to the draw and rolling direction.

ISSN:0021-8979    

DOI:10.1063/1.325777

出版商:AIP    

年代:1979

数据来源: AIP