Showing papers in "Macromolecules in 1968"

Elastically Effective Strand Density in Polymer Networks

Abstract: A new expression is derived which relates the density of elastically effective strands in a polymer network to the densities of random cross-links, main-chain scissions, and entanglements and to the molecular weight distribution of the initial linear polymer. Methods are recommended for characterizing the cross-link and scission densities from measurable sol fractions and for determining the entanglement density empirically. The strand density can be evaluated quite easily for the random and uniform initial molecular weight distributions. The new expression differs appreciably from that of Mullins and Bueche, owing principally to a new criterion for effectively trapping network entanglements. The statistical approach used to derive the strand density is also used in a new derivation of an existing implicit expression for the gel fraction.

Polarized Infrared Studies of Amorphous Orientation in Polyethylene and Some Ethylene Copolymers

Abstract: : Measurements were made of the dichroic ratios of a number of infrared bands for uniaxially deformed low-density polyethylene. In order to characterize the amorphous orientation in the polymer, orientation functions were derived from the results on the conformationally sensitive amorphous bands at 1368/cm, 1352/cm, 1303/cm and 1078/cm. In conjunction with x-ray data and infrared dichroism data on the crystalline 1894/cm band, amorphous orientation functions were also derived from the 2016/cm band which appears to contain a normal amorphous component. The results indicate that extended trans sequences in the amorphous phase orient to a larger extent than isolated trans bonds flanked by gauche bonds. Results on the bands at 720 and 730/cm appear to show discrepancies when compared with the data from the other bands, and possible reasons for this apparent inconsistency are suggested. Amorphous orientation functions have also been derived from the CN stretching band at 2250/cm in a copolymer of ethylene and (2 weight percent) acrylonitrile. The bands at 2016/cm and 1894/cm were also analyzed for this copolymer, in addition to a C = O stretching band at 1740/cm due, apparently to thermal oxidation. Infrared dichroism results are also discussed for a copolymer of ethylene and (4.1 mole percent) methacrylic acid in which 70% of the -COOH groups are neutralized with sodium hydroxide. (Author)

Thermodynamics of Mixing of n-Alkanes with Polyisobutylene

Abstract: The volume changes on mixing polyisobutylene (PIB) with n-pentane, n-hexane, n-heptane, n-octane, n-decane, and n-hexadecane have been determined by direct measurements at 45°, and for n-heptane at 0 and 50° as well. They are negative in every case; the magnitude of the excess volume decreases with chain length, and increases with temperature. These results on volume changes, which are beyond the scope of conventional theories of polymer solutions, are rationally taken into account by the recent statistical mechanical theory of solutions which relates properties of the mixture to characteristics of the pure liquids manifested in their equation-of-state parameters. The negative enthalpies of mixing found by Delmas, Patterson, and Somcynsky for all of these systems with the exception of PIB-n-hexadecane are similarly shown to arise from negative equation-of-state contributions to the enthalpy which reflect differences between the liquid characteristics of n-alkane and PIB. The energy contributed by...

Determination of the Equation of State of Polyisobutylene

Abstract: The density, thermal expansion coefficient, and thermal pressure coefficient for polyisobutylene of mol wt 40,000 have been accurately determined from 0 to 150°. Results are compared with the reduced equation of state employed in the theory of solutions. The characteristic parameters v*, T*, and p* required for the treatment of polyisobutylene solutions are obtained from the experimental results.