Preirradiation grafting of acrylic and methacrylic acid onto polyethylene films: Preparation and properties

The method of preirradiation grafting of acrylic acid and methacrylic acid onto polyethylene films was studied. The trapped radicals and hydroperoxides or diperoxides appeared to be able to induce graft polymerization. Mohr's salt was added to depress homopolymerization. The influences of crystallinity, dosage, and storage period on the grafting behavior were investigated from the viewpoint of practical application. At elevated temperature, the degree of grafting increased rapidly with reaction time initially, and then leveled off to the value of final percent grafting. Dosage and storage periods had greater extent of influence on the final percent grafting of LDPE than on that of HDPE. Electrical properties, transport properties, and mechanical properties were measured to compare the differences between acrylic-acid-and methacrylic-acid-grafted copolymer films. It was found that the properties of methacrylic-acid-grafted copolymer film was superior to those of acrylic-acid-grafted copolymer film, especially in electrical conductivity. The KOH diffusion test confirmed that grafting occurred not only on the surface but also in the interior of the polymer matrix, and the grafting is believed to proceed from the surface to the interior of the matrix.     

Guest-host ferroelectric side-chain liquid crystalline polymeric materials with improved electro-optical properties

A ferroelectric side-chain liquid crystalline polysiloxane (FLCP) containing azobenzene dyes as guest molecules for electro-optics has been investigated. The intensity and frequency of the Goldstone mode for the FLCP were increased remarkably after doping with azobenzene dyes. Larger fluctuation of the spontaneous polarization vector in each smectic layer under an applied electric field can be brought about with the addition of a strong dipole-moment guest molecule. This leads to a larger spontaneous polarization and shorter response time. It was found that the doping of a suitable amount of a strong dipole-moment azobenzene dye in the LC phase of the FLCP is helpful for the improvement of the electro-optical properties.     

New peracid-type polymeric initiator for radical polymerization

In this study, a radiation-induced copolymer, namely polyethylene-g-acrylic acid powder, was used, whose carboxyl groups can be oxidized to form a highly reactive polymer initiator. The activation energy for its decomposition is 22.4 kcal/mol. It was found that the peracid-type polymeric powder was effective as an initiator for radical polymerization. It had high reactivity toward 2-hydroxyethyl methacrylate (HEMA), which could be easily grafted onto the polymeric powder; also, the homopolymer could be obtained. The kinetic investigation indicated that this polymerization proceeded by a radial mechanism, and the overall activation energy of homopolymerization was 18.67 kcal/mol and the overall activation energy of bigraft polymerization was 17.35 kcal/mol. By using the peracid-type polymeric powder as initiator for the copolymerization of methyl methacrylate with styrene, it was confirmed that the polymerization initiated by the peracid-type polymeric powder was a radical reaction.     

Ag+ contained complex membrane for the separation of C4 olefin/paraffin mixture

The C₄ olefin/paraffin mixture was separated by means of the PE modified reversible complexing membrane, polyethylene-g-acrylic acid-Ag₊(PE-g-AA-Ag₊). The olefin could be transported to the other side of the membrane by silver facilitating phenomenon owing to the formation of (Ag-olefin)₊ complex. The SEM-EDX spectrum showed a homogeneous silver ion distribution across the dense complex membrane's cross-section at higher than about 60% grafting. The gas permeation properties measured by a gas chromatographic method implied a silver ions facilitating effect towards olefin. At 30°C and 111.7% grafting, the complex membrane exhibited a trans-2-butene/isobutane selectivity of 12.5 and a cis-2-butene/isobutane selectivity of 9.2. The permeation activation energy of the C₄ olefins became lower than that of C₄ paraffin as a result of the silver ions facilitated effect. The cis-2-butene has a significant higher complex equilibrium constant than that of the trans-2-butene in complexing with the complex membrane.     

Synthesis,thermal properties,and flame retardancy of phosphorus containing polyimides

Phosphorus containing polyimides were prepared via phosphorylation of organosoluble polyimides. This was achieved by phenoxaphosphine oxide ring formation reaction or esterification with diethylchlorophosphate. The phosphorylation was confirmed by infrared, ³¹P nuclear magnetic resonance, and elemental analysis for phosphorus. Polyimides containing phosphorus of 8.3 and 5.4% by weight were found. Thermal characteristics and decomposition behavior of the resulting polyimides were investigated by differential scanning calorimetry and thermogravimetric analysis. Introduction of phosphorus into polyimides slightly reduced their initial weight loss temperatures and led to high char yields at temperatures higher than 800°C. Limiting oxygen index values higher than 48 were found for the phosphorylated polyimides. Such properties make these polymers useful in flame retardant applications. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 875–882, 1997     

Synthesis,characterization, thermal and flame-retardant properties of silicon-based epoxy resins

A new silicon-containing oxirane triglycidyl phenyl silane oxide (TGPSO) and its corresponding silicon-containing epoxy resins are synthesized and characterized. The activation energies of TGPSO curing reaction with various curing agents, including 4,4-diaminodiphenylmethane, 4,4-diaminodiphenylsulfone, and dicyanodiaminde, are found to be 180, 196.5, and 154 kJ/mol. The curing reaction of TGPSO with diamines is determined to be a first-order reaction through means of Arrhenius plots. The introduction of the silicon-containing group results in higher curing reactivity. This silicon-containing resin possesses higher char yield as well as higher limiting oxygen index (LOI = 35) than the commercial epoxy resins, confirming the usefulness of these silicon-containing epoxy resins as flame retardants. Char yields and LOI measurements demonstrate that incorporating silicon into epoxy resins is able to improve their flame retardancy. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1231–1238, 1999     

Fatal acute pulmonary oedema after inhalation of fumes from polytetrafluoroethylene (PTFE)

The cases of three patients with acute pulmonary oedema caused by inhalation of fumes from heated polytetrafluoroethylene (PTFE) in a plastic factory are described. One patient died from profound hypoxaemia and shock shortly after admission, and the other two patients survived after medical treatment. This is the first report of fatal pulmonary oedema in a worker exposed to PTFE heated in a plastic extruding operation. From this observation, it appears that inhalation exposure to pyrolytic products from polytetrafluoroethylene can cause fatal respiratory complications. Special precautions are warranted in this kind of operation to prevent workers from being exposed to these substances.     

Stress relaxation and the domain structure of thermoplastic elastomer

The relationship between the stress relaxation phenomena and domain structure of thermoplastic elastomer (TPE) was studied. Two representative thermoplastic elastomers: styrenebutadiene-styrene block copolymer (SBS) and 1,2-syndiotactic polybutadiene (1,2-PB), representing the amorphous glassy domain and crystalline domain, respectively, were tested in different atmospheres and temperatures. Results show that the structure of the domain has a significant effect on the stress relaxation curve. It is found that the way the glassy domain is formed determines the failure of the domain and hence the stress relaxation rate. In the case of crystalline domain, the history of heat treatment determines the crystal structure and, in turn, the stress relaxation rate.     

Rheological and morphological properties of thermal-aged poly(phenylene sulfide) resin

This paper discusses the morphological properties of thermal-aged poly(phenylene sulfide) (PPS) resin by Fourier-transform infrared spectroscopy (FT-IR) and solid-state ¹³C-NMR. Also included is a method of applying the dynamic melt viscoelastic properties to determine the molecular weight distribution of the PPS resin. For virgin PPS resin, two resonance peaks were detected by NMR magic angle spinning (MAS) and cross polarization (CP) studies. However, four additional peaks can be seen for heat-treated PPS resin, indicating that the aromatic ring in PPS resin was attacked by sulfur-containing species or by the aryl ether group. The two most important reactions are crosslinking and chain extension. However, the chain extension is predominant when PPS is heated in nitrogen. The results coincide with the phenomenon observed in FT-IR studies. The molecular weight distribution of thermal-aged PPS resin was determined from dynamic melt viscoelasticity data. Results show that the longer the preheated time the broader the molecular weight distribution. It indicates that crosslinking and chain-extension reaction may have occurred when PPS resin was heated in air.