Glass-transition Temperature (glass-transition + temperature)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Glass-transition Temperature

  • high glass-transition temperature

  • Selected Abstracts

    Glass-Transition Temperature (Tg) of Free-Radically Prepared Polyacrylonitrile by Inverse Gas Chromatography, 1.

    A Study on Tg of Atactic Monodisperse Polystyrenes
    Abstract The glass-transition temperature (Tg) of several atactic monodisperse polystyrenes (PSt)s was studied by an inverse gas chromatographic (IGC) analysis, as a preliminary study for the detection of the Tg of polyacrylonitrile. The Tg of PSt with different molecular weights was clearly obtained by this method. The agreement in the Tg values obtained by IGC and by differential scanning calorimetry (DSC) was quite good within the molecular-weight range Mp,=,7,600,2,430,000 (where, Mp,=,(Mn,,Mw)1/2). This method has a wide universality for the detection of the Tg of polymers. Several essential factors were extracted for the establishment of the optimum conditions for IGC measurements, such as the concentration of polymer toward a clay matrix (10 wt.-%), and the type of lower probe, decane. The best probe was determined empirically from the most effective detection in the IGC measurements of PSt. Molecular-weight dependence of the Tg of PSt. Experimental data obtained here are indicated by an arrow. Other data was taken from ref.21 [source]

    Glass-Transition Temperature (Tg) of Free-Radically Prepared Polyacrylonitrile by Inverse Gas Chromatography, 2,.

    Molecular-Weight Dependence of Tg of Two Different Types of Aqueous Polymers
    Abstract The molecular-weight dependence of the glass-transition temperature (Tg) of a series of atactic polyacrylonitriles (PAN)s was studied by inverse gas chromatographic (IGC) analysis. PANs having different molecular weights were prepared by either; (i) the addition of isopropyl alcohol as a chain-transfer agent, or (ii) a scission reaction induced by the addition of alkali (NaOH) to a solution (N,N -dimethylformamide solution, at 25,C) of the resulting polymer. The intrinsic viscosity [,] was in the range of 10.9,0.1 (dl,,g,1), which corresponds to a viscosity-averaged molecular weight (Mv) of 1,590,000,3,000. As part of the results, a side reaction, which saw the conversion of the nitrile (CN) groups of PAN into amide (CONH2) and/or carboxylic acids (COOH) groups by alkali, was found to occur. The typical molecular-weight dependence of the Tg in free-radically prepared PAN was discussed in connection with a chain-transfer mechanism in an aqueous medium. Molecular-weight dependence of the Tg for PAN (WA). An error bar is given by a short vertical arrow. [source]

    Synthesis of Carrier-Transporting Dendrimers with Perylenebis(dicarboximide)s as a Luminescent Core

    Jianfeng Pan
    Abstract Well-defined, modular dendrimers enable processing techniques and electronic properties to be tuned independently. Moreover, the dendritic topology can isolate the core chromophore, thus reducing or eliminating strong intermolecular interactions. This paper presents the synthesis of three series of flexible, dendron-functionalized dendrimers as red-light-emitting materials by a convergent approach: (1) carbazole (CZ) or oxadiazole (OXZ) terminated imide-type dendrimers, (2) cascade energy-transferring imide-type dendrimers, and (3) CZ-terminated perylene bay-type dendrimers. They all consist of the luminescent core of perylenebis(dicarboximide)s with specific functional groups of CZ or OXZ at the periphery and are constructed from flexible Frchet-type poly(aryl ether) dendrons. The chemical structures of the dendrons and dendrimers were determined by standard spectroscopic techniques including 1H and 13C NMR spectroscopy and low/high-resolution mass spectrometry (ESI or MALDI-TOF). The dendrimers are designed on the basis of the following considerations: (1) dendron functionalization to incorporate CZ or OXZ units to realize the carrier-injection adjustment, (2) tuning or improving solubility, functionality, glass-transition temperature (Tg) with well-defined dendrons, and (3) avoiding luminescence quenching with the help of high site-isolation of dendrons to enhance core luminescence. DSC results indicate that the incorporation of Frchet-type poly(aryl ether) dendrons can improve the amorphous properties and increase Tg. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    High-Performance Organic Photovoltaic Devices Using a New Amorphous Molecular Material with High Hole Drift Mobility, Tris[4-(5-phenylthiophen-2-yl)phenyl]amine

    Hiroshi Kageyama
    Abstract A new amorphous molecular material, tris[4-(5-phenylthiophen-2-yl)phenyl]amine (TPTPA), is synthesized and characterized. TPTPA forms a stable amorphous glass with a glass-transition temperature of 83,C when the melt sample is cooled. It also forms amorphous thin films by a thermal deposition technique. TPTPA exhibits a hole drift mobility of 1.0,,10,2,cm2 V,1 s,1 at an electric field of 1.0,,105,V cm,1 and at 293,K, as determined by the time-of-flight method, which is of the highest level among those of amorphous molecular materials. pn-Heterojunction organic photovoltaic devices (OPVs) using TPTPA as an electron donor and C60 or C70 as an electron acceptor exhibit high performance with fill factors of 0.66,0.71 and power conversion efficiencies of 1.7,2.2% under air-mass (AM) 1.5G illumination at an intensity of 100,mW cm,2, which are of the highest level ever reported for OPVs using amorphous molecular materials. [source]

    Template Deformation-Tailored ZnO Nanorod/Nanowire Arrays: Full Growth Control and Optimization of Field-Emission

    Haibo Zeng
    Abstract Here, a facile and effective route toward full control of vertical ZnO nanorod (NR)/nanowire (NW) arrays in centimeter-scale areas and considerable improvement of field-emission (FE) performance is reported. Controlled deformation of colloidal crystal monolayer templates is introduced by heating near glass-transition temperature. The NR/NW density, uniformity, and tapering were all adjusted through selection of template size and deformation, and electrolyte composition. In line with the adjustments, the field-emission performance of the arrays is significantly improved. A low turn-on electric field of 1.8,V m,1, a field-enhancement factor of up to 5,750, and an emitting current density of up to 2.5,mA cm,2 were obtained. These improved parameters would benefit their potential application in cold-cathode-based electronics. [source]

    Spontaneous Formation of Complex Periodic Superstructures under High Interferential Illumination of Small-Molecule-Based Photochromic Materials

    Elna Ishow
    Abstract A series of push-pull azo compounds containing bulky substituents are synthesized, yielding fully amorphous materials with glass-transition temperatures above 200,C. Thin films are subjected to holographic illumination and show superior bulk photomigration in terms of speed and efficiency compared to materials exhibiting similar electronic and photochromic properties in the solid state. The reported results give evidence that a microscopic consideration of the free volume rather than macroscopic parameters like the glass-transition temperature should to be adopted to interpret the matrix stiffness and its deformation ability. Irradiation performed at higher laser intensity produces periodic superstructures whose height is five to six times as high as the initial film thickness. The surface tension and instability effects are put forward to interpret the growth of such superstructures. [source]

    Room-Temperature Self-Organizing Characteristics of Soluble Acene Field-Effect Transistors,

    Wi Hyoung Lee
    We report on the room-temperature self-organizing characteristics of thin films of the organic small-molecule semiconductor triethylsilylethynyl-anthradithiophene (TES-ADT) and its effect on the electrical properties of TES-ADT-based field-effect transistors (FETs). The morphology of TES-ADT films changed dramatically with time, and the field-effect mobility of FETs based on these films increased about 100-fold after seven days as a result of the change in molecular orientation from a tilted structure in the as-prepared film to a well-oriented structure in the final film. We found that the molecular movement is large enough to induce a conformational change to an energetically stable state in spin-coated TES-ADT films, because TES-ADT has a low glass-transition temperature (around room temperature). Our findings demonstrate that organic small-molecule semiconductors that exhibit a low crystallinity immediately after spin-coating can be changed into highly crystalline structures by spontaneous self-organization of the molecules at room temperature, which results in improved electrical properties of FETs based on these semiconductors. [source]

    UV-vis-Induced Vitrification of a Molecular Crystal,

    T. Naito
    Abstract A charge-transfer complex of 2,5-dimethyl- N,N,-dicyanoquinonediimine (DM) with silver (crystalline Ag(DM)2, defined as ,) is irreversibly transformed by UV-vis illumination. Depending on the illumination conditions, three new types of solids (defined as ,, ,, and ,) with different structural and physical properties are obtained and examined by a variety of analytical techniques, including solid-state, high-resolution, cross-polarization magic angle spinning (CP-MAS) 13C,NMR, elemental analysis (EA), mass spectrometry (MS), X-ray absorption fine structure (XAFS), and powder X-ray diffraction (XRD). The CP-MAS, EA, MS, and XAFS results indicate that compound , is a glass state of Ag(DM)2. The transformation from crystalline (,) to amorphous (,) solid Ag(DM)2 is an irreversible exothermic glass transition (glass-transition temperature 155.2,C; ,H,=,,126.8,kJ,mol,1), which implies that the glass form is thermodynamically more stable than the crystalline form. Compound , (Ag(DM)1.5) consists of silver nanoparticles (diameter (7,,2),nm ) dispersed in a glassy matrix of neutral DM molecules. The N,CN,Ag coordination bonds of the , form are not maintained in the , form. Decomposition of , by intense illumination results in a white solid (,), identified as being composed of silver nanoparticles (diameter (60,,10),nm). Physical and spectroscopic (XAFS) measurements, together with XRD analysis, indicate that the silver nanoparticles in both , and , are crystalline with lattice parameters similar to bulk silver; however, the magnetic susceptibilities differ from bulk silver. [source]

    Cover Picture: Structural Modifications to Polystyrene via Self-Assembling Molecules (Adv. Funct.

    Abstract The cover shows tensile failure of a sample of pure polystyrene (left), and a polystyrene sample with greater impact strength containing 1% by weight of dispersed nanoribbons (right), as reported in work by Stupp and co-workers on p.,487. The nanoribbons are formed by self-assembly of molecules known as dendron rodcoils (DRCs) in styrene monomer, resulting in the formation of a gel. This gel can then be polymerized thermally. We have previously reported that small quantities of self-assembling molecules known as dendron rodcoils (DRCs) can be used as supramolecular additives to modify the properties of polystyrene (PS). These molecules spontaneously assemble into supramolecular nanoribbons that can be incorporated into bulk PS in such a way that the orientation of the polymer is significantly enhanced when mechanically drawn above the glass-transition temperature. In the current study, we more closely evaluate the structural role of the DRC nanoribbons in PS by investigating the mechanical properties and deformation microstructures of polymers modified by self-assembly. In comparision to PS homopolymer, PS containing small amounts (,,1.0,wt.-%) of self-assembling DRC molecules exhibit greater Charpy impact strengths in double-notch four-point bending and significantly greater elongations to failure in uniaxial tension at 250,% prestrain. Although the DRC-modified polymer shows significantly smaller elongations to failure at 1000,% prestrain, both low- and high-prestrain specimens maintain tensile strengths that are comparable to those of the homopolymer. The improved toughness and ductility of DRC-modified PS appears to be related to the increased stress whitening and craze density that was observed near fracture surfaces. However, the mechanism by which the self-assembling DRC molecules toughen PS is different from that of conventional additives. These molecules assemble into supramolecular nanoribbons that enhance polymer orientation, which in turn modifies crazing patterns and improves impact strength and ductility. [source]

    Processing of Bulk Metallic Glass

    ADVANCED MATERIALS, Issue 14 2010
    Jan Schroers
    Abstract Bulk metallic glass (BMG) formers are multicomponent alloys that vitrify with remarkable ease during solidification. Technological interest in these materials has been generated by their unique properties, which often surpass those of conventional structural materials. The metastable nature of BMGs, however, has imposed a barrier to broad commercial adoption, particularly where the processing requirements of these alloys conflict with conventional metal processing methods. Research on the crystallization of BMG formers has uncovered novel thermoplastic forming (TPF)-based processing opportunities. Unique among metal processing methods, TPF utilizes the dramatic softening exhibited by a BMG as it approaches its glass-transition temperature and decouples the rapid cooling required to form a glass from the forming step. This article reviews crystallization processes in BMG former and summarizes and compares TPF-based processing methods. Finally, an assessment of scientific and technological advancements required for broader commercial utilization of BMGs will be made. [source]

    Low-Temperature Fusion of Polymeric Nanostructures Using Carbon Dioxide,

    ADVANCED MATERIALS, Issue 2 2007
    Y. Yang
    A low-temperature fusion method for preparing polymeric nanostructures based on low-pressure CO2 -enhanced chain mobility at the nanoscale is presented. Characterization of the structures reveals a pressure-tunable rubbery layer on the surface. The successful fusion of polymeric nanostructures (see figure) at temperatures below the bulk glass-transition temperature of the polymer is demonstrated. The technique has potential for the assembly of 3D micro/nanoscale polymeric devices for biomedical applications. [source]

    Synthesis and characterization of biodegradable crosslinked polymers from 5-hydroxylevulinic acid and ,,,-diols

    Yan Zhang
    Abstract Novel biodegradable chemically crosslinked polymers, poly(5-hydroxylevulinic acid- co -,,,-diol)s (PHLA-diols), were synthesized from 5-hydroxylevulinic acid and ,,,-diols and characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. The gel content, swelling ratio, tensile properties, and hydrolytic degradation behaviors were also measured and assessed. The glass-transition temperature of the PHLA-diols could be adjusted within a wide range (,50 to 30C) by the type and feed ratio of the diol. Because of the low glass-transition temperature and crosslink structure, they exhibited certain elastic properties. The tensile modulus, strength, and elongation at break measured at 37C were 1.4,6.3 MPa, 0.8,1.6 MPa, and 10,25%, respectively. These polymers could be hydrolytically degraded. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

    Glass transition and cold crystallization in carbon dioxide treated poly(ethylene terephthalate)

    Yeong-Tarng Shieh
    Abstract An amorphous poly(ethylene terephthalate) (aPET) and a semicrystalline poly(ethylene terephthalate) obtained through the annealing of aPET at 110C for 40 min (aPET-110-40) were treated in carbon dioxide (CO2) at 1500 psi and 35C for 1 h followed by treatment in a vacuum for various times to make samples containing various amount of CO2 residues in these two CO2 -treated samples. Glass transition and cold crystallization as a function of the amount of CO2 residues in these two CO2 -treated samples were investigated by temperature-modulated differential scanning calorimetry (TMDSC) and dynamic mechanical analysis (DMA). The CO2 residues were found to not only depress the glass-transition temperature (Tg) but also facilitate cold crystallization in both samples. The depressed Tg in both CO2 -treated poly(ethylene terephthalate) samples was roughly inversely proportional to amount of CO2 residues and was independent of the crystallinity of the poly(ethylene terephthalate) sample. The nonreversing curves of TMDSC data clearly indicated that both samples exhibited a big overshoot peak around the glass transition. This overshoot peak occurred at lower temperatures and was smaller in magnitude for samples containing more CO2 residues. The TMDSC nonreversing curves also indicated that aPET exhibited a clear cold-crystallization exotherm at 120.0C, but aPET-110-40 exhibited two cold-crystallization exotherms at 109.2 and 127.4C. The two cold crystallizations in the CO2 -treated aPET-110-40 became one after vacuum treatment. The DMA data exhibited multiple tan , peaks in both CO2 -treated poly(ethylene terephthalate) samples. These multiple tan , peaks, attributed to multiple amorphous phases, tended to shift to higher temperatures for longer vacuum times. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

    Studies on thermoplastic polyurethanes based on new diphenylethane-derivative diols.


    Abstract Two series of poly(ether urethane)s and one series of poly(ester urethane)s were synthesized, containing, respectively, poly(oxytetramethylene) diol (PTMO) of Mn = 1000 and 2000 and poly(,-caprolactone) diol of Mn = 2000 as soft segments. In each series the same hard segment, i.e., 4,4,-(ethane-1,2-diyl)bis(benzenethiohexanol)/hexane-1,6-diyl diisocyanate, with different content (, 14,72 wt %) was used. The polymers were prepared by a one-step melt polymerization in the presence of dibutyltin dilaurate as a catalyst, at the molar ratio of NCO/OH = 1 (in the case of the polymers from PTMO of Mn = 1000 also at 1.05). For all polymers structures (by FTIR and X-ray diffraction analysis) and physicochemical, thermal (by differential scanning calorimetry and thermogravimetric analysis), and tensile properties as well as Shore A/D hardness were determined. The resulting polymers were thermoplastic materials with partially crystalline structures (except the polymer with the highest content of PTMO of Mn = 2000). It was found that the poly(ether urethane)s showed lower crystallinity, glass-transition temperature (Tg), and hardness as well as better thermal stability than the poly(ester urethane)s. Poly(ether urethane)s also exhibited higher tensile strength (up to 23.5 MPa vs. 20.3 MPa) and elongation at break (up to , 1950% vs. 1200%) in comparison with the corresponding poly(ester urethane)s. Among the poly(ether urethane)s an increase in soft-segment length was accompanied by an increase in thermal stability, tensile strength, and elongation at break, as well as a decrease in Tg, crystallinity, and hardness. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Synthesis and physical properties of low-molecular-weight redistributed poly(2,6-dimethyl-1,4-phenylene oxide) for epoxy resin

    Hann-Jang Hwang
    Abstract Low-molecular-weight poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was prepared by the redistribution of regular PPO with 4,4,-isopropylidenediphenol (bisphenol A) with benzoyl peroxide as an initiator in toluene. The redistributed PPO was characterized by proton nuclear magnetic resonance, mass spectra, and Fourier transform infrared spectroscopy. The redistributed PPO oligomers with terminal phenolic hydroxyl groups and low molecular weights (weight-average molecular weight = 800,4000) were used in the modification of a diglycidyl ether of bisphenol A/4,4,-diaminodiphenylmethane network system. The curing behaviors were investigated by differential scanning calorimetry and Fourier transform infrared spectroscopy. The effect of molecular weight and the amount of redistributed PPO oligomers incorporated into the network on the physical properties of the resulting systems were investigated. The thermal properties of the cured redistributed PPO/epoxy resins were studied by dynamic mechanical analysis, thermal mechanical analysis, thermogravimetric analysis, and dielectric analysis. These cured redistributed PPO/epoxy resins exhibited lower dielectric constants, dissipation factors, coefficients of thermal expansion, and moisture absorptions than those of the control diglycidyl ether of bisphenol A based epoxy. The effects of the composition on the glass-transition temperature and thermal stability are discussed. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Biobased polyisocyanates from plant oil triglycerides: Synthesis, polymerization, and characterization

    Gkhan ayl
    Abstract In this study, an easy and efficient synthesis of unsaturated plant oil triglycerides having isocyanate groups is reported. In the first step of the synthesis, the triglyceride was brominated at the allylic positions by a reaction with N -bromosuccinimide, and in the second step, these brominated species were reacted with AgNCO to convert them to isocyanate-containing triglycerides. At the end of the reaction, approximately 60,70% of the bromine was replaced by NCO groups, and the double bonds of the triglyceride were not consumed. When the amount of AgNCO was increased, the yield also increased. The final products were characterized with IR and 1H-NMR, and polyurethanes and polyureas were obtained from these fatty isocyanates with alcohols and amines, respectively. The polymers were characterized by differential scanning calorimetry and thermogravimetric analysis. Differential scanning calorimetry curves showed that glycerin polyurethane showed a glass-transition temperature at 19C, castor oil polyurethane showed two glass-transition temperatures at ,43 and 36C, and triethylene tetraamine polyurea showed a glass-transition temperature at 31C. Some properties of the polymers, such as the tensile strength and swelling ratios, were also determined. The swelling rate of glycerin polyurethane was higher than that of castor oil polyurethane in dichloromethane. The equilibrium swelling ratio was highest for the castor oil polyurethane. The polyurethanes synthesized in this study had a Young's modulus around 50 kPa and a tensile strength around 0.01 N/mm2 (100 kPa). The tensile strength of glycerin polyurethane was higher than that of castor oil polyurethane. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Local dynamics in epoxy coatings containing iron oxide nanoparticles by dielectric relaxation spectroscopy

    G. Kortaberria
    Abstract Nanocomposites of photocurable epoxy resin and epoxy-modified iron oxide magnetic nanoparticles were analyzed by dielectric relaxation spectroscopy to study the local dynamics at temperatures well below the glass-transition temperature. Two secondary processes were detected, , and , processes, but the second one was just detected at lower temperatures in the high-frequency part of the spectra and moved out of the frequency range at higher temperatures. Data were fitted to the Havriliak,Negami and Arrhenius models, and the obtained parameters were analyzed. Relaxation times of the , secondary relaxation did not change with the nanoparticle content, but the relaxation strength increased. The increase could not be explained when we took into account the molecular origin of the relaxation. The presence of ferromagnetic nanoparticles enhanced the internal field and increased the relaxation strengths. Transmission electron microscopy images showed that the nanoparticles were well dispersed in the matrix, without magnetic agglomerates. 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source]

    Moisture absorption behavior of epoxies and their S2 glass composites

    Amit Chatterjee
    Abstract The influence of moisture exposure on the behavior of three toughened epoxy,amine systems (scrimp resins SC11, SC15, and SC79, Applied Poleramic, Inc., Benicia, CA) was investigated. Neat resin samples were conditioned by immersion in distilled water at 71C and in an environmental chamber at 85% relative humidity and 87.8C until saturation. The equilibrium weight gain ranged from 1.8 to 3.8% for the resins. The long-chain, low-crosslink-density epoxy system (SC11) absorbed the highest amount of water and was saturated first, and it was followed by the medium-crosslink-density (SC15) and high-crosslink-density materials (SC79). The moisture diffusivity decreased with the increasing crosslink density of the resins. The percentage reduction of the glass-transition temperature (Tg) at equilibrium moisture absorption was highest for the low-crosslink molecule. The percentage reductions for the medium-crosslink and higher crosslink systems were comparable. A net weight loss after drying was observed for the SC11 and SC79 resin systems. Fourier transform infrared analysis confirmed the segment breakage and leaching of molecules from the epoxy,amine network. The effects of moisture cycling on Tg were dependent on the epoxy,amine morphology. During the drying stage, Tg increased to a value higher than that of the unaged dry systems. The S2 glass composite samples were conditioned under identical conditions for the resin system. Composite systems absorbed less moisture than the neat resins as expected. 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source]

    Preparation and properties of physically crosslinked sodium carboxymethylcellulose/poly(vinyl alcohol) complex hydrogels

    Congming Xiao
    Abstract A series of physically crosslinked complex hydrogels of poly(vinyl alcohol) (PVA) and sodium carboxymethylcellulose (CMC) were prepared via physical mixing and a freeze/thaw technique. The morphology of the CMC/PVA complex gels was analyzed with differential scanning calorimetry and wide-angle X-ray diffraction. It was found that the crystallinity and melting temperature of the complex gels decreased, whereas the glass-transition temperature increased, with an increase in the content of CMC. The reswelling of the complex gels was pH-responsive and relied on the content of CMC and the freeze/thaw cycles. A network structure model of the complex gel was presented. PVA crystalline regions served as physical crosslinks; the interaction between CMC and PVA resulted in intramolecular entanglements. It was also found that the model drug hemoglobin was released completely from the complex hydrogels in 4 h, and its release rate increased with an increase in the content of CMC. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Synthesis and characterization of soluble copolyimides containing chalcone and phosphine oxide moieties in the main chain

    Wei Wang
    Abstract The functional diamines 3,3,-diaminochalcone and bis(3-aminophenyl)-3,5-bis(trifluoromethyl)phenyl phosphine oxide were successfully prepared by simple and convenient procedures with short reaction times, and the overall yields were 78 and 70%, respectively. Copolyimides prepared from 3,3,-diaminochalcone, bis(3-aminophenyl)-3,5-bis(trifluoromethyl)phenyl phosphine oxide, and 4,4,-(hexafluoroisopropylidene)diphthalic anhydride exhibited excellent solubility in several organic solvents, such as dimethyl sulfoxide, N,N -dimethylformamide, N -methyl pyrrolidone, tetrahydrofuran, and acetone. They also showed very good thermal stability even up to 450C for 5% weight loss (by thermogravimetric analysis) in nitrogen and a high glass-transition temperature up to 274C (by differential scanning calorimetry) in nitrogen. The copolymers' adhesive and photoreactive properties were also investigated, and it was confirmed that the copolyimide containing chalcone and phosphine oxide moieties in the main chain had good adhesiveness and photoreactivity. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Novel adamantane-containing epoxy resin

    Xiaoming Su
    Abstract A novel adamantane-containing epoxy resin diglycidyl ether of bisphenol-adamantane (DGEBAda) was successfully synthesized from 1,3-bis(4-hydroxyphenyl)adamantane by a one-step method. The proposed structure of the epoxy resin was confirmed with Fourier transform infrared, 1H-NMR, gel permeation chromatography, and epoxy equivalent weight titration. The synthesized adamantane-containing epoxy resin was cured with 4,4,-diaminodiphenyl sulfone (DDS) and dicyandiamide (DICY). The thermal properties of the DDS-cured epoxy were investigated with differential scanning calorimetry and thermogravimetric analysis (TGA). The dielectric properties of the DICY-cured epoxy were determined from its dielectric spectrum. The obtained results were compared with those of commercially available diglycidyl ether of bisphenol A (DGEBA), a tetramethyl biphenol (TMBP)/epoxy system, and some other associated epoxy resins. According to the measured values, the glass-transition temperature of the DGEBAda/DDS system (223C) was higher than that of the DGEBA/DDS system and close to that of the TMBP/DDS system. TGA results showed that the DGEBAda/DDS system had a higher char yield (25.02%) and integral procedure decomposition temperature (850.7C); however, the 5 wt % degradation temperature was lower than that of DDS-cured DGEBA and TMBP. Moreover, DGEBAda/DDS had reduced moisture absorption and lower dielectric properties. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source]

    Mechanical and morphological properties of organic,inorganic, hybrid, clay-filled, and cyanate ester/siloxane toughened epoxy nanocomposites

    S. Nagendiran
    Abstract Organic,inorganic hybrids involving cyanate ester and hydroxyl-terminated polydimethylsiloxane (HTPDMS) modified diglycidyl ether of bisphenol A (DGEBA; epoxy resin) filled with organomodified clay [montmorillonite (MMT)] nanocomposites were prepared via in situ polymerization and compared with unfilled-clay macrocomposites. The epoxy-organomodified MMT clay nanocomposites were prepared by the homogeneous dispersion of various percentages (1,5%), and the resulting homogeneous epoxy/clay hybrids were modified with 10% HTPDMS and ,-aminopropyltriethoxysilane as a coupling agent in the presence of a tin catalyst. The siliconized epoxy/clay prepolymer was further modified separately with 10% of three different types of cyanate esters, namely, 4,4,-dicyanato-2,2,-diphenylpropane, 1,1,-bis(3-methyl-4-cyanatophenyl) cyclohexane, and 1,3-dicyanato benzene, and cured with diaminodiphenylmethane as a curing agent. The reactions during the curing process between the epoxy, siloxane, and cyanate were confirmed by Fourier transform infrared analysis. The results of dynamic mechanical analysis showed that the glass-transition temperatures of the clay-filled hybrid epoxy systems were lower than that of neat epoxy. The data obtained from mechanical studies implied that there was a significant improvement in the strength and modulus by the nanoscale reinforcement of organomodified MMT clay with the matrix resin. The morphologies of the siloxane-containing, hybrid epoxy/clay systems showed heterogeneous character due to the partial incompatibility of HTPDMS. The exfoliation of the organoclay was ascertained from X-ray diffraction patterns. The increase in the percentage of organomodified MMT clay up to 5 wt % led to a significant improvement in the mechanical properties and an insignificant decrease in the glass-transition temperature versus the unfilled-clay systems. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source]

    Properties of nanocomposites based on maleate-vinyl ether donor,acceptor UV-curable systems

    Neena Ravindran
    Abstract UV-curable nanocomposites based on donor,acceptor crosslinking chemistry were prepared containing organically modified montmorillonites. The coatings were characterized for thermal, mechanical, and morphological properties. X-ray diffraction and transmission electron microscopy showed that nanocomposites were formed in all samples. Results showed that an increase in the percentage of clay caused an increased modulus and glass-transition temperature. It was also seen that tensile modulus showed dramatic improvement when compared with the unmodified polyester sample. Real time IR kinetic data showed that higher conversions were obtained at higher clay loadings. Pendulum hardness values and tensile modulus values showed different trends in properties depending on the combination of polymer matrix and organomodification. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source]

    Dynamic mechanical properties and morphology of high-density polyethylene/CaCO3 blends with and without an impact modifier

    Yu-Lin Yang
    Abstract Dynamic mechanical analysis and differential scanning calorimetry were used to investigate the relaxations and crystallization of high-density polyethylene (HDPE) reinforced with calcium carbonate (CaCO3) particles and an elastomer. Five series of blends were designed and manufactured, including one series of binary blends composed of HDPE and amino acid treated CaCO3 and four series of ternary blends composed of HDPE, treated or untreated CaCO3, and a polyolefin elastomer [poly(ethylene- co -octene) (POE)] grafted with maleic anhydride. The analysis of the tan , diagrams indicated that the ternary blends exhibited phase separation. The modulus increased significantly with the CaCO3 content, and the glass-transition temperature of POE was the leading parameter that controlled the mechanical properties of the ternary blends. The dynamic mechanical properties and crystallization of the blends were controlled by the synergistic effect of CaCO3 and maleic anhydride grafted POE, which was favored by the core,shell structure of the inclusions. The treatment of the CaCO3 filler had little influence on the mechanical properties and morphology. 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3907,3914, 2007 [source]

    Master curve and time,temperature,transformation cure diagram of lignin,phenolic and phenolic resol resins

    M. V. Alonso
    Abstract The aim of this work is to generate both a master curve of resol resins based on the time,temperature superposition principle and their TTT cure diagrams. The samples used for this purpose were lignin,phenolic and phenol,formaldehyde resol resins. A TMA technique was employed to study the gelation of resol resins. In addition, a DSC technique was employed to determine the kinetic parameters through the Ozawa method, which allowed us to obtain isoconversional curves from the data fit to the Arrhenius expression. Establishing the relationship between the glass-transition temperature and curing degree allowed the determination of the vitrification lines of the resol resins. Thus, using the experimental data obtained by TMA and DSC, we generated a TTT cure diagram for each of resins studied. 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3362,3369, 2007 [source]

    Synthesis of a [60]fullerene-functionalized poly(vinyl chloride) derivative by stereospecific chemical modification of PVC

    Gerardo Martnez
    Abstract The covalent attachment of [60]fullerene (C60) to two poly(vinyl chloride) (PVC) samples with different isotactic content is achieved by direct reaction in o -dichlorobenzene (o -DCB) solution in the presence of AIBN. The extent of fullerenation is controlled by varying the C60 feed ratio. The pendant C60 -chemically modified PVC polymers are soluble in tetrahydrofuran (THF) and have been characterized by UV,vis, NMR, FTIR, DSC, TGA, cyclic voltammetry, and SEM. The quantitative microstructural analysis after covalent attachment of the bulky C60 moiety to the PVC has been followed by 13C NMR spectroscopy. From the results it can be concluded that the modification of PVC by graft reaction through free radical reaction proceeds by a stereoselective mechanism. This conclusion has been confirmed on the basis of the increase of the glass-transition temperature (Tg) and the thermal stability of the C60 -chemical modified PVC samples. The fullerenated PVCs obtained show good electron acceptor properties, as evidenced by electrochemical investigations. 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5408,5419, 2007 [source]

    Synthesis and properties of polyimides bearing acid groups on long pendant aliphatic chains

    Tomohiro Yasuda
    Abstract A series of novel polyimide electrolytes having long pendant sulfo- or phosphoalkoxy groups were synthesized for fuel-cell applications. Sulfodecyloxy-, phosphodecyloxy-, and sulfophenoxydodecyloxy-substituted benzidine monomers were synthesized from dihydroxybenzidine. These monomers were copolymerized with naphthalene tetracarboxylic dianhydride and fluorenylidene dianiline to give the corresponding polyimides. A flexible, ductile, and self-standing membrane was obtained via casting from the polyimide solution. Because the acid groups were on long pendant side chains and away from the main chains, the polyimide membrane showed improved oxidative and hydrolytic stability in comparison with the polyimides with sulfonic acid groups on the main chains or on the short side chains. High thermal stability (no glass-transition temperature and a decomposition temperature > 200 C) was also obtained. The polyimide membrane displayed high proton conductivity of 10,1 S cm,1 at 120 C. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3995,4005, 2006 [source]

    Synthesis and self-assembly of polystyrene-grafted multiwalled carbon nanotubes with a hairy-rod nanostructure

    Yingkui Yang
    Abstract Polystyrene-grafted multiwalled carbon nanotubes (PS- g -MWNTs) with a hairy-rod nanostructure were synthesized by the in situ free-radical polymerization of styrene in the presence of multiwalled carbon nanotubes (MWNTs) terminated with vinyl groups. To quantitatively study the molecular weight and composition of polystyrene (PS) chains in PS- g -MWNTs, PS- g -MWNTs were fully defunctionalized by hydrolysis. The results showed that 1 of every 100 carbon atoms in MWNTs was functionalized at the tips and outer walls of the carbon nanotubes and grafted by PS with a weight-average molecular weight of 9800 g/mol; therefore, a uniform thin layer (ca. 8,10 nm) of a PS shell was formed on the outer wall of MWNTs. PS- g -MWNTs were soluble in dimethylformamide and tetrahydrofuran. The thermal stability and glass-transition temperature of PS in PS- g -MWNTs were obviously increased. Nanopins were formed on the glass substrates by the self-assembly of PS- g -MWNTs, and the dewetting effect between the glass substrate and PS chains covered MWNTs during the evaporation of the solution. Both the length and diameter of the nanopins increased with the solution concentration. When PS- g -MWNTs were compression-molded, MWNTs were dispersed uniformly in the PS matrix and formed good networks, such as circlelike and starlike structures, because of the entanglements of hairy PS chains on MWNTs. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3869,3881, 2006 [source]

    Synthesis and characterization of core,shell-type polymeric micelles from diblock copolymers via reversible addition,fragmentation chain transfer

    Ping Zhang
    Abstract A method was developed to enable the formation of nanoparticles by reversible addition,fragmentation chain transfer polymerization. The thermoresponsive behavior of polymeric micelles was modified by means of micellar inner cores and an outer shell. Polymeric micelles comprising AB block copolymers of poly(N -isopropylacrylamide) (PIPAAm) and poly(2-hydroxyethylacrylate) (PHEA) or polystyrene (PSt) were prepared. PIPAAm- b -PHEA and PIPAAm- b -PSt block copolymers formed a core,shell micellar structure after the dialysis of the block copolymer solutions in organic solvents against water at 20 C. Upon heating above the lower critical solution temperature (LCST), PIPAAm- b -PHEA micelles exhibited an abrupt increase in polarity and an abrupt decrease in rigidity sensed by pyrene. In contrast, PIPAAm- b -PSt micelles maintained constant values with lower polarity and higher rigidity than those of PIPAAm- b -PHEA micelles over the temperature range of 20,40 C. Structural deformations produced by the change in the outer polymer shell with temperature cycles through the LCST were proposed for the PHEA core, which possessed a lower glass-transition temperature (ca. 20 C) than the LCST of the PIPAAm outer shell (ca. 32.5 C), whereas the PSt core with a much higher glass-transition temperature (ca. 100 C) retained its structure. The nature of the hydrophobic segments composing the micelle inner core offered an important control point for thermoresponsive drug release and the drug activity of the thermoresponsive polymeric micelles. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3312,3320, 2006 [source]

    Novel amorphous perfluorocopolymeric system: Copolymers of perfluoro-2-methylene-1,3-dioxolane derivatives

    Yu Yang
    Abstract Perfluorotetrahydro-2-methylene-furo[3,4- d][1,3]dioxole (monomer I) and perfluoro-2-methylene-4-methoxymethyl-1,3-dioxolane (monomer II) are soluble in perfluorinated or partially fluorinated solvents and readily polymerize in solution or in bulk when initiated by a free-radical initiator, perfluorodibenzoyl peroxide. The copolymerization parameters have been determined with in situ19F NMR measurements. The copolymerization reactivity ratios are rI = 1.80 and rII = 0.80 in 1,1,2-trichlorotrifluoroethane at 41 C and rI = 0.97 and rII = 0.85 for the bulk polymerization. These data show that this copolymerization pair has a good copolymerization tendency and yields nearly ideal random copolymers. The copolymers have only one glass-transition temperature from 101 to 168 C, depending on the copolymer compositions. Melting endotherms have not been observed in their differential scanning calorimetry traces, and this indicates that all the copolymers with different compositions are completely amorphous. These copolymers are thermally stable (the initial decomposition temperatures are higher than 350 C under an N2 atmosphere) and have low refractive indices and high optical transparency from UV to near-infrared. Copolymer films prepared by casting were flexible and tough. These properties make the copolymers ideal candidates as optical and electrical materials. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1613,1618, 2006 [source]