Thermal Curing (thermal + curing)

Distribution by Scientific Domains

Selected Abstracts

Synthesis, characterization, and cure reaction of methacrylate-based multifunctional monomers for dental composites

Mousa Ghaemy
Abstract The synthesis of 2,2-bis[(4-(2-hydroxy-3-methacryloxyethoxy)phenyl]propane (BHEP) and (1-methacryloxy-3-ethoxymethacryloxy-2-hydroxy)propane (MEHP) for use as the monomer phase in dental composites are reported. The monomers were prepared by the reaction of 2-hydroxyethyl methacrylate (HEMA) with diglycidyl-ether of bisphenol A (DGEBA) and with glycidyl methacrylate (GMA), respectively. The progress of the reaction was followed by measuring the disappearance of the epoxide group peak using FTIR and the structure of the monomers was characterized by 1H-NMR. BHEP and MEHP have lower viscosity because of the presence of long aliphatic spacer on both sides of the aromatic ring in BHEP and the absence of aromatic rings and the presence of only one hydroxyl group in each molecule of MEHP. Thermal curing of the monomers was conducted in a DSC using benzoyl peroxide as an initiator. Photopolymerization of the monomers was also conducted with the visible light using camphorquinone and N,N -dimethylaminoethyl methacrylate as the photoinitiating system. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source]

Fabrication of Polyimide-Blend Thin Films Containing Uniformly Oriented Silver Nanorods and Their Use as Flexible, Linear Polarizers

S. Matsuda
Fully aromatic polyimide films containing uniformly oriented Ag nanorods (see Figure) have been prepared by a simple method consisting of thermal curing and uniaxial drawing of submicrometer-scale phase-separated polyimide-blend films containing dissolved AgNO3. The films exhibit outstanding optical dichroism, over 20,dB (see inset), in the near-IR region due to the high aspect ratio of the nanorods and the high transparency of the matrix. [source]

Synthesis and characterization of novel saponified guar-graft-poly(acrylonitrile)/silica nanocomposite materials

Vandana Singh
Abstract The combination of carbohydrates with silicon-based ceramic materials offers attractive means of production for high performance materials. Present article describes the synthesis of novel nanocomposites out of SiO2 and saponified guar-graft-poly(acrylonitrile) (SG). Tetraethoxysilane was used as the precursor for silica and growth of SiO2 phase was allowed concurrently in the presence of SG. The material so obtained was thermally treated at 80C, 160C, 500C, and 900C to study the effect of thermal curing on its properties. During the curing process, silanol surface groups of silica globules reacted to create the reinforced SiO2 -SG substance. It was observed that at 900C, the SiO2 phase crystallized out in tetragonal shape (similar to Cristobalite form of silica) in presence of SG. The chemical, structural and textural characteristics of the composites were determined by FTIR, XRD, TGA-DTA, SEM and BET studies. The materials were also evaluated as efficient Zn2+ metal binder. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 536,544, 2007 [source]

Synthesis and characterization of novel crosslinkable polymers with a nonlinear optical chromophore as a pendant group

Sung-Ho Jin
Abstract New crosslinkable polymers with a nonlinear optical (NLO) active chromophore as a pendant group were synthesized by condensation chain polymerization via palladium-catalyzed carbon,carbon coupling reactions. The polymerization yields were almost quantitative between the diiodobenzene (DIB) and diethyldipropargyl malonate (DEDPM) or 4-(dimethylamino)-4,-(6-dipropargylacetoxypropylsulfonyl)stilbene (DASS-6) monomers. To improve the molecular weight and mechanical properties of the NLO active polymer, we carried out the copolymerization with DIB and DASS-6 with various feed ratios of DEDPM. The resulting polymers were soluble in organic solvents and spun-cast onto indium tin oxide-coated glass substrates to make thin films. The molecular structures of the resulting polymers were characterized with various instrumental methods to confirm the carbon,carbon coupling reactions between the DIB and diacetylene monomers. The absorption of the ultraviolet,visible spectrum of the resulting polymers was drastically reduced after thermal curing at 160 C because of the crosslinking of the reactive acetylene group in the polymer backbone. The electrooptic coefficient (r33) measured at 1.3 ,m ranged from 7 to 15 pm/V. 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4025,4034, 2001 [source]

Synthesis and Characterization of Thermally Curable Benzoxazine-Functionalized Polystyrene Macromonomers,

Baris Kiskan
Abstract Summary: Thermally curable benzoxazine ring-containing polystyrene macromonomers were synthesized and characterized. 1,4-Dibromo-2,5-bis(bromomethyl)benzene and 1,4-dibromo-2-(bromomethyl)benzene were used as initiators in the atom transfer radical polymerization of styrene. The resulting polymers were used in combination with 3-aminophenylboronic acid hemisulfate, for a Suzuki coupling. The obtained polymers, with amino groups in the middle or end of the chains, were reacted with formaldehyde and phenol to yield benzoxazine ring-containing macromonomers. In addition to the glass transition temperature of the polystyrene segment observed at ca. 105,C, differential scanning calorimetry thermograms exhibit an exotherm at ca. 276,C corresponding to the oxazine thermal polymerization. Both macromonomers undergo thermal curing with the formation of thermosets having polystyrene segments. Structure of the benzoxazine-functionalized polystyrene. [source]

Microwave and conventional curing of thick-section thermoset composite laminates: Experiment and simulation

Erik T. Thostenson
In conventional processing, thermal gradients cause differential curing of thick laminates and undesirable outside-in solidification. To reduce thermal gradients, thick laminates are processed at lower cure temperatures and heated with slow heating rates, resulting in excessive cure times. Microwaves can transmit energy volumetrically and instantaneously through direct interaction of materials with applied electromagnetic fields. The more efficient energy transfer of microwaves can alleviate the problems associated with differential curing, and the preferred inside-out solidification can be obtained. In this work, both microwave curing and thermal curing of 24.5 mm (1 inch) thick-section glass/epoxy laminates are investigated through the development of a numerical process simulation and conducting experiments in processing thick laminates in a conventional autoclave and a microwave furnace. Outside-in curing of the autoclave-processed laminate resulted in visible matrix cracks, while cracks were not visible in the microwave-processed laminate. Both numerical and experimental results show that volumetric heating due to microwaves promotes an inside-out cure and can dramatically reduce the overall processing time. [source]

Curing of diglycidyl ether of bisphenol-A epoxy resin using a poly(aryl ether ketone) bearing pendant carboxyl groups as macromolecular curing agent

Fuhua Liu
Abstract BACKGROUND: Reactive thermoplastics have received increasing attention in the field of epoxy resin toughening. This paper presents the first report of using a novel polyaryletherketone bearing one pendant carboxyl group per repeat unit to cure the diglycidyl ether of bisphenol-A epoxy resin (DGEBA). The curing reactions of DGEBA/PEK-L mixtures of various molar ratios and with different catalysts were investigated by means of dynamic differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy methods. RESULTS: FTIR results for the DGEBA/PEK-L system before curing and after curing at 135 C for different times demonstrated that the carboxyl groups of PEK-L were indeed involved in the curing reaction to form a crosslinked network, as evidenced by the marked decreased peak intensities of the carboxyl group at 1705 cm,1 and the epoxy group at 915 cm,1 as well as the newly emerged strong absorptions of ester bonds at 1721 cm,1 and hydroxyl groups at 3447 cm,1. Curing kinetic analysis showed that the value of the activation energy (Ea) was the highest at the beginning of curing, followed by a decrease with increasing conversion (,), which was attributed to the autocatalytic effect of hydroxyls generated in the curing reaction. CONCLUSION: The pendant carboxyl groups in PEK-L can react with epoxy groups of DGEBA during thermal curing, and covalently participate in the crosslinking network. PEK-L is thus expected to significantly improve the fracture toughness of DGEBA epoxy resin. Copyright 2009 Society of Chemical Industry [source]

Siloxane/silane-crosslinked systems from supercritical carbon dioxide: II.

Pendant phenyl poly(carbosilane/siloxane)s
Abstract New silicone-containing polymers with crosslinkable units have been synthesized by hydrosilation polymerization in both toluene and supercritical carbon dioxide (70C, 3000,psi) catalyzed by platinum-divinyltetramethyldisiloxane (Pt-DVTMS). It was found that high molecular polymers were obtained in both toluene and supercritical carbon dioxide. The polymers were characterized by FTIR, NMR, GPC, TGA, and DSC. The molecular weights of these polymers ranged from 9000 to 39,000. With further hydrolysis and thermal curing, the molecular weight can be increased significantly. Comparison of the properties between reactions in toluene versus supercritical carbon dioxide indicated that the green solvent is a usable alternative for hydrosilation polymerization. The new polymers synthesized in either toluene or supercritical carbon dioxide are thermally stable, ranged from 350 to 488C. Copyright 2008 John Wiley & Sons, Ltd. [source]

Anisotropy in optical transmittance and molecular chain orientation of silver- dispersed uniaxially drawn polyimide films

Sho-ichi Matsuda
Abstract The anisotropy in optical transmittance in the visible and near-infrared region observed for uniaxially drawn and silver-dispersed polyimide (PI) films was investigated. The films were prepared in a one-step operation that consists of thermal curing and simultaneous uniaxial drawing of poly(amic acid) (PAA) films dissolving 5.7,,,20 mol% of silver nitrate. The PAA was converted to PI by heating, and the PI chains were orientated along the drawing direction during curing. Silver nanoparticles were precipitated in the films when they were cured in air and under nitrogen. In particular, silver nanoparticles aggregated along drawing direction and spheroidal nanoparticles (size of longer axis: 10,25,nm, aspect ratio: ca. 1.5) were observed in the films cured in air, and distinct anisotropy in optical transmittance was observed. The maximum optical anisotropy was obtained with a specific holding time at the final curing temperature (320,C). In addition, the anisotropy can be controlled by polymer chain orientation when films are cured with the optimal holding time. In optimized preparing conditions, anisotropies in transmittance larger than 500,:,1 were obtained at the wavelengths between 700 and 900,nm, and its optical properties were retained after annealing at 150,C for 1,hr. The PI films thus obtained can be used as thermally stable thin-film polarizers. Copyright 2003 John Wiley & Sons, Ltd. [source]