Preparation and characterization of petroleum‐pitch‐based carbon aerogels

Carbon aerogels were prepared by the sol–gel polymerization of petroleum pitches followed by ambient‐pressure drying and then carbonization. Furfural and sulfuric acid were found to be the best crosslinking agent and best catalyst for the reaction system, respectively. It was necessary to add acetic acid as a cosolvent, and the volume ratio of toluene to acetic acid played an important role in the mass densities of the samples. The average diameters of the nanonetwork particles of the typical carbon aerogels thus obtained were about 30–40 nm, and their surface areas were over 360 m²/g. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

CROSSLINKING OF HYDROXY-TERMINATED POLYBUTADIENE WITH 60Co-γ-RAYS

Crosslinking of hydroxy-terminated polybutadiene was carried out in the presence of functional reactive monomers like trimethylolpropane triacrylate and ditrimethylolpropane tetraacrylate, employing high-energy ⁶⁰Co-γ-rays. Specimens of the crosslinked material were then no longer soluble in organic compounds such as toluene, but swelled to an extent that inversely depended on the amount of radiation to which they have been exposed, that is on the degree of crosslinking. Not all molecules were, however, linked into the network, and appreciable amounts of soluble material could be removed, which allowed the gel fraction determination. The gel content and the swelling index were found to follow the progress of the reticulation reaction.     

Poly(hydroxyether of bisphenol A) ‐alt‐polydimethylsiloxane: a novel thermally crosslinkable alternating block copolymer

BACKGROUND: An important strategy for making polymer materials with combined properties is to prepare block copolymers consisting of well‐defined blocks via facile approaches. RESULTS: Poly(hydroxyether of bisphenol A)‐block‐polydimethylsiloxane alternating block copolymers (PH‐alt‐PDMS) were synthesized via Mannich polycondensation involving phenolic hydroxyl‐terminated poly(hydroxyether of bisphenol A), diaminopropyl‐terminated polydimethylsiloxane and formaldehyde. The polymerization was carried out via the formation of benzoxazine ring linkages between poly(hydroxyether of bisphenol A) and polydimethylsiloxane blocks. Differential scanning calorimetry and small‐angle X‐ray scattering show that the alternating block copolymers are microphase‐separated. Compared to poly(hydroxyether of bisphenol A), the copolymers displayed enhanced surface hydrophobicity (dewettability). In addition, subsequent crosslinking can occur upon heating the copolymers to elevated temperatures owing to the existence of benzoxazine linkages in the microdomains of hard segments. CONCLUSION: PH‐alt‐PDMS alternating block copolymers were successfully obtained. The subsequent self‐crosslinking of the PH‐alt‐PDMS alternating block copolymers could lead to these polymer materials having potential applications. Copyright © 2008 Society of Chemical Industry     

Drying biodegradable poly(hydroxybutyrate‐co‐3‐hydroxyvalerate) gels in the elongated state to improve their mechanical properties

Polyhydroxyalkanoates are a class of biodegradable polymers that may be used more as environmentally friendly materials if their mechanical properties can be improved. We approached this goal by modifying poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) with a well‐established processing technique involving crosslinking the polymer chains and then drying a swollen gel of the network under uniaxial strain. The mechanical properties of the resulting oriented films were determined in continuous extension as a function of the degree of crosslinking and the extent of strain during the drying process. Crosslinking invariably improved the toughness. Similarly, the subsequent orientation of the process generally increased the toughness as well, but in some cases, a reduction in the extensibility offset the increase in the ultimate stress at break and yielded reduced values of the toughness. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1519–1523, 2005     

Mechanism of dielectric‐barrier discharge initiated wet‐strength development

The fundamental mechanism of wet‐strength development for dielectric‐barrier discharge treated thermomechanical pulp fibers was explored. Electron spectroscopy for chemical analysis (ESCA), vapor phase fluorine surface derivatization followed by ESCA, and dynamic contact angle analysis were performed to assess the surface chemistry in terms of both chemical functionality and wettability. Effects of the intensity of dielectric‐barrier discharge treatment on the surface chemistry of lignocellulosic fibers and the corresponding impacts to fiber wet‐tensile properties are described. This study indicates that low treatment intensities result in increased wettability due to surface oxidation, which leads to a small reduction in wet‐tensile index. However, increased treatment intensity brings about diminished wettability due to covalent crosslinking, which leads to increases in wet‐tensile index. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2219–2225, 2005     

Crosslinking of low‐density polyethylene by diisocyanates for superior barrier properties

The chemical modification of low‐density polyethylene (LDPE) resins with hexamethylene diisocyanate and toluene diisocyanate was achieved. The reaction of LDPE with diisocyanate was monitored by Fourier transform infrared spectroscopy, wherein the appearance of new peaks at 3326, 1620, and 1572 cm^?1 corresponding to ? N? H stretching, ? (C?O)? NH₂ stretching, and ? N? H bending in an amide moiety, respectively, was observed. Modified films of excellent clarity and uniform thickness were obtained by the solution casting of crosslinked polyethylene. The oxygen transmission rate (OTR), water vapor transmission rate (WVTR), grease resistance, and thermal properties of the modified films were studied. The results clearly indicate that the OTR was improved by 35% and that grease resistance was improved by 90–125% in the crosslinked LDPE films with little change in their strengths. The heat seal characteristics, however, showed that relatively higher temperatures were needed to achieve efficient sealing in these films. Differential scanning calorimetry showed a decrease in the melting temperature from 104°C for LDPE to 101°C for both of the crosslinked LDPE films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1193–1199, 2005     

Evaluation of the diethylene glycol bis(allyl carbonate)/acrylic acid copolymer behavior by solid‐state 13C‐NMR

The dynamic behavior of diethylene glycol bis(allyl carbonate) (CR‐39)/acrylic acid (AA) copolymers was evaluated by ¹³C high‐resolution solid‐state nuclear magnetic resonance (NMR). The NMR data showed that the copolymerization of CR‐39 and AA generated copolymers with different molecular behaviors as a function of AA content, which promoted changes in the crosslinking of CR‐39 chains and in the intramolecular forces. The copolymerization process influenced the sequence distribution and domain formation of the monomers, which is a consequence of the dispersion of comonomers along the macromolecular chains. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 740–745, 2005     

Synthesis and properties of polyurethane networks derived from new soybean oil‐based polyol and a bulky blocked polyisocyanate

BACKGROUND: Developing vegetable oil‐based polyols for polyurethane manufacturing is becoming highly desirable for both economic and environmental reasons. Most vegetable oils do not bear hydroxyls naturally. The objective of this work was to prepare a new soybean oil‐based polyol with high functionality of hydroxyl groups and built‐in (preformed) urethane bonds. RESULTS: A facile and improved method was developed for the transformation of epoxidized soybean oil into carbonated soybean oil under ambient pressure of CO₂ gas, with tetrabutylammonium bromide/calcium chloride as catalyst/co‐catalyst couple. Ring‐opening reaction of the carbonated oil with ethanolamine led to the desired polyol. A one‐pack polyurethane system was prepared via combination of the polyol and a blocked polyisocyanate. The polyol and final polyurethanes were fully characterized, and their physical, mechanical, viscoelastic and electrical insulating properties were studied. CONCLUSION: The application of this newly developed soybean oil‐based polyol for preparation of electroinsulating casting polyurethanes was examined. The prepared soy‐based polyurethanes offered excellent thermal and electrical insulating properties. Also, tunable physical and chemical properties for the final polyurethanes were achieved by replacing part of the soybean oil‐based polyol with poly(propylene glycol) (M_n = 1000 g mol^?1). Copyright © 2008 Society of Chemical Industry     

离子交联乳聚丁苯橡胶的合成与性能

评述了提高乳聚丁苯橡胶生胶强度的技术路线，介绍了离交联乳丁苯橡胶胶的合方法、生胶物性和并用胶特性，从理论和实践上证明了离子交联键的热，剪切可逆行为。