Dwain M. White

MUTUAL DIFFUSION IN THE MISCIBLE POLYMER BLEND: POLYSTYRENE:POLY (XYLENYL ETHER)

We have used forward recoil spectrometry to measure the mutual diffusion and tracer diffusion coefficients, D and D*, in the miscible polymer blend of deuterated polystyrene (d-PS):poly(xylenyl ether) (PXE). Using the “fast theory” of mutual diffusion, D is related to the D*, degree of polymerization N, and volume fraction φ of the individual blend components by, D = 2 φ (1-φ) [D* PS N PS + φD* PXE N PXE ](χ S -χ), where χ and χs are tne Flory interaction parameter of the blend and its value at the spinodal. From the measured values of the D*’s and D at a volume fraction φ=0.55 of d-PS, the interaction parameter χ=0.112-62/T was estimated as a function of temperature T(K). At low T, D was much larger than D*’s due to the large negative value of χ whereas at high T, D becomes less than the D*’s as χ becomes positive (thermodynamic slowing down). Similar measurements show that χ is not markedly composition-dependent in the d-PS:PXE blends.

Reptation in polymer blends

Forward recoil spectrometry (FRES) was used to measure the tracer diffusion coefficients D∗PS and D∗PXE of deuterated polystyrene (d-PS) and deuterated poly(xylenyl ether) (d-PXE) chains in high molecular weight protonated blends of these polymers. The D∗s were shown to be independent of matrix molecular weights and to decrease as M−2, where M is the tracer molecular weight, suggesting that the tracer diffusion of both species occurs by reptation. These D∗s were used to determine the monomeric friction coefficients ζ0,PS and ζ0,PXE of the individual PS and PXE macromolecules as a function of ф, the volume fraction of PS in the PS:PXE blend. Since ζ0,PS⪡ζ0,PXE at each ф, the rate at which a PS molecule reptates is much greater than that of a PXE molecule, even though both chains are diffusing in identical surroundings. Part of this difference may be due to the difficulty of backbone bond rotation of the PXE molecule. However, even when measured at a constant temperature increment above the glass transition temperature, ζ0,PS and ζ0,PXE were observed to be markedly composition dependent. In addition the ratio ζ0,PSζ0,PXE varied from a maximum of 4 × 10−2 near ф=0.85 to a minimum of 5 × 10−5 for ф=0.0. These results show that intramolecular barriers do not solely determine the ζ0s of the components in this blend. Clearly, the interactions between the diffusing chains and the matrix chains also influence ζ0.

13C fourier-transform NMR study of trimethyl(phenylethynyl)silane: Silicon-carbon bonding

Abstract A 13 C Fourier transform (FT) NMR study of trimethyl(phenylethynyl)silane gives new evidence for ( p → d ) π bonding or equivalent interaction between bonded carbon and silicon atoms. Pulsed FT operation allows detection of 29 Si 13 C spinspin coupling observed as 2.3 % 29 Si satellites in 13 C spectra. The one-bond 13 C 29 Si coupling constants for seven compounds were found to be roughly proportional to “ s ” character on carbon, ranging from 50.2 ( sp 3 ) to 83.6 Hz ( sp ).

Polybutadiene emulsion particles observed by scanning tunneling microscopy

Particles of polybutadiene were prepared by an emulsion polymerization process. We have been able to observe their size and shape in a scanning tunneling microscope. Critical to this success was the deposition of gold onto a mica substrate to give a smooth, conductive surface. A drop of methanol was then placed on this surface, and a very small amount of the polybutadiene latex (a stable emulsion of polymerized butadiene particles in water) was injected into the methanol drop. After the methanol evaporated, several areas showed isolated emulsion particles, while aggregates of particles were found in other areas. The surface of the particles was adequately conductive to get stable tunneling currents at a bias voltage of −0.1 V. The conductivity may be related to the layer of surfactant molecules on the surface. Isolated particles were typically oblate ellipsoids: 15 nm long, 10 nm wide, and 3 nm high. Individual particles of about the same size were visible in the aggregates. Because the glass transition t...

Poly(phenylene oxide)s

Poly(phenylene oxide)s [poly(oxyphenylene)s] are useful materials for engineering thermoplastic applications because of their thermal, oxidative and chemical stability. The polymers are readily prepared from phenols in good yields by a variety of oxidative coupling procedures and other types of step-growth polymerization reactions. Poly(2,6-dimethyl-1,4-phenylene oxide), PPO® resin, is the most important commercial poly(phenylene oxide) and is sold as a blend with polystyrene and other additives as Noryl® resin by the General Electric Co. The preparation of PPO and other poly(phenylene oxide)s is described in this chapter, with a major emphasis on PPO.