Copolymerization of styrene–m-divinylbenzene in the presence of poly(vinyl chloride)

The crosslinking copolymerization of styrene (St)-m-divinylbenzene (m-DVB) in the presence of poly(vinyl chloride) (PVC) was studied. The rate of the copolymerization decreased with the addition of PVC powder, because of the depressing of the diffusion of the monomers to the polymerizing center and the difficulty in the transfer of the polymer radicals in the swelled PVC powder. The exponential value of the benzoyl peroxide concentration and the activation energy of the copolymerization were obtained as 0.67 and 17.4 kcal/mol, respectively. The monomer reactivity ratios of St and m-DVB were determined as r₁ = 0.25 and r₂ = 1.42 (M₁: St, M₂: m-DVB). From the extraction of the resultant polymer composite with THF, both the grafting of the St-m-DVB copolymer onto PVC and the entanglement of PVC with St-m-DVB copolymer seems to occur in the St-m-DVB-PVC system.     

Computer analysis of random and channeled backscattering spectra

Three types of computer codes are described which simulate random and channeled backscattering spectra from: (1) multielemental, multilayered structures, (2) specimens with inhomogneously distributed impurities and (3) single crystals damaged by ion implantation. Both effects of energy fluctuation and isotopic shifts from each constituent element are taken into account in the simulation. The elemental compositions and layer thicknesses of multielemental, multilayered films and the damage distributions induced by ion implantation are determined by fitting the simulated spectrum to the corresponding experimental one. The effect of surface and interface roughness on the spectrum shape is also discussed.     

Dynamic mechanical properties and morphology of styrene-divinylbenzene copolymer/poly(vinyl chloride) systems. (II). Effect of polymerization temperature

Effect of polymerization temperature on the phase-separated structure of the composite materials [P(St-DVB)/PVC systems] prepared by copolymerization of styrene (St) and divinylbenzene (DVB) in the presence of fine poly(vinyl chloride) (PVC) powder was studied by electron microscopy and dynamic mechanical test. P(St-DVB)/PVC systems have the two-phase nature with a styrene-divinylbenzene copolymer as the continuous phase [P(St-DVB) phase) and a PSt/PVC composite as the dispersed phase (PSt-PVC phase), in which PSt penetrates into the PVC domain. The crosslinking density of the P(St-DVB) phase is larger than that estimated from the recipe in the feed, suggesting that there exists a difference of the diffusion constants of styrene and divinylbenzene into the PVC particles on the paste formation and the polymerization process. The changes of the phase-separated structure of P(St-DVB)/PVC systems polymerized at various temperatures are also explained on the basis of the difference between the diffusion behavior of styrene and that of divinylbenzene into fine PVC particles at these temperatures.     

On Markov Maintenance Problems

The applicability of Markov maintenance models is crucial. We need to fill the gap between theoretical and practical maintenance problems. A model is proposed for that purpose.     

Molecular characterization of hydroxyl-terminated polybutadienes

A comparative study has been made on the functionality distribution of two hydroxyl terminated polybutadiene products which are used largely as prepolymers for sealants, adhesives, and solid propellants. They are known to possess nearly the same molecular characteristics. To this end, each product was fractionated into 17 fractions with different molecular weights by the preparative GPC technique. Sample fractions thus obtained were subjected to “polarity-controlled adsorption” thin-layer chromatography (TLC) to determine the functionality distribution. From these experimental results it was concluded that a decisive difference between these products consists in the functionality distribution, within a molecular weight range higher than 7000.     

Room temperature aging effects of blistering and surface roughening after Ar+ ion bombardment on Mo single crystals

300 keV Ar⁺ ions are bombarded on the surface of Mo single crystals to doses of $\text{1 × 10}{}^{17}$, $\text{6.2 × 10}{}^{17}$, $\text{1 × 10}{}^{18}$ and $\text{2.8 × 10}{}^{18}$ ions/cm². After bombardment with $\text{6.2 × 10}{}^{17}$ ions/cm², blistering is observed after room-temperature aging of less than 100 days, in spite of the large sputtering yield. Disappearance of the formed blisters and concurrent surface roughening are observed with further aging. For higher dose bombardments, only surface roughening is observed without prior formation of blisters. Distribution of the injected ions associated with large sputtering yield is derived. From this distribution, the critical amount of injected ions required for blistering to occur is estimated to be equal to or less than $\text{3.4 × 10}{}^{17}$ ions/cm².