Weight Loss In Air Research Articles

The effect of long‐term ultraviolet light irradiation on polymer matrix composites

AbstractThis study reports the individual and combined effects of ultraviolet light and thermal shock on the physical properties of polymer matrix composites in air and in a “near‐vacuum system.” The longest exposure time was 180 days. It was found that the weight loss of composites increased with irradiation time. In the graphite/epoxy system, the weight loss in air was 2–3 times that in a “near‐vacuum system.” Similarly, the weight loss of the glass/epoxy system in air was 3–6 times that in a “near‐vacuum system.” The weight loss of the glass/epoxy system was always larger than that of the graphite/epoxy system. In all cases, the UV irradiation and 1000 times thermal shock did not change the fracture mechanism—it was always brittle fracture in addition to fiber pullout. Surface erosion was observed in the irradiated surfaces by scanning electron microscopy. For both graphite/epoxy and glass/epoxy composites, the tensile strength decreased with increasing irradiation time irrespective of the irradiation environment. However, the decrease was not significant. By SEM, cracks could be observed in the up‐surface and side‐surface of the glass/epoxy system that was irradiated more than 1 month in air and through 1000 times thermal shock. Obviously, UV light cannot deeply penetrate the sample, and only the surface of the sample will be influenced. The UV radiation initiated microcracks, which propagated through the thermal shock.

Effect of mixing technique on surface characteristics of impression materials

Statement of problem. Previous studies have shown a relationship between the disinfection process, wettability, and mass change of impression materials. Hand-mixed high viscosity impression materials usually result in a material with numerous voids, which contribute to surface roughness and affect the surface characteristics of the material. Purpose. This study evaluated the effect of mixing technique on advancing contact angle, receding contact angle, imbibition, and mass loss of various high and low viscosity polyether and polyvinyl siloxane materials. The null hypothesis tested was no differences exist between the different mixing systems. Material and methods. The Wilhelmy technique was used for deriving wetting properties of the materials used (Impregum F and Penta, Permadyne Syringe, Garant and Penta, Dimension Penta and Garant L, Aquasil). Conditions included no disinfection (0 hours) and 1, 5, and 18 hours of immersion disinfection in a full-strength solution of 2% acid glutaraldehyde disinfectant (Banicide). Weight changes before and after disinfection were measured to detect weight loss or mass increase over time. Weight loss in air was also measured to detect mass loss. Data were analyzed with a one-way analysis of variance at alpha = 0.05. Results. All materials displayed some degree of imbibition of the disinfectant and experienced mass loss with polymerization, except the light viscosity polyvinyl that gained 0.18% at 5 hours. No significant differences were found in wettability among the polyether materials after 1 hour of disinfection. Less imbibition was observed for high viscosity mechanically mixed materials compared with the hand-mixed materials for both polyether and polyvinyl siloxane at 1-hour disinfection time. Conclusions. Polyether materials were more wettable than polyvinyl. Imbibition of high viscosity polyether and polyvinyl materials after 1 and 18 hours of disinfection were affected by the mixing system used. (J Prosthet Dent 1998;79:495-502.)

Synthesis and properties of new aromatic noncyclic poly(imide-amide)s from N,N-bis(aminobenzoyl)anilines and aromatic dicarboxylic acids

Two dianilines containing the noncyclic N-phenylimide group, 4,4′- and 3,4′-diamino-(N,N-dibenzoylaniline), were synthesized as new diamine monomers. The low-temperature solution polycondensation of the diamines with aromatic dicarboxylic acid chlorides afforded poly(imide-amide)s with inherent viscosities of 0.14–0.44 dL/g. The noncyclic N-phenylimide unit in the diamines could be cleaved by nucleophilic attack at the amine function at high temperature. The noncyclic poly(imide-amide)s are soluble in polar solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide. The polymers have glass transition temperatures and temperatures of 10% weight loss in air in the range of 195–265°C and 405–430°C, respectively.

Synthesis and properties of new aromatic noncyclic poly(imide-amide)s fromN,N-bis(aminobenzoyl)anilines and aromatic dicarboxylic acids

Two dianilines containing the noncyclic N-phenylimide group, 4,4′- and 3,4′-diamino-(N,N-dibenzoylaniline), were synthesized as new diamine monomers. The low-temperature solution polycondensation of the diamines with aromatic dicarboxylic acid chlorides afforded poly(imide-amide)s with inherent viscosities of 0.14–0.44 dL/g. The noncyclic N-phenylimide unit in the diamines could be cleaved by nucleophilic attack at the amine function at high temperature. The noncyclic poly(imide-amide)s are soluble in polar solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide. The polymers have glass transition temperatures and temperatures of 10% weight loss in air in the range of 195–265°C and 405–430°C, respectively.

Introduction of a [5]Helicene Unit in Polyimides by Chemical and Thermal Transformations of Precursor Polymers

Several [5]helicene-containing polyimides have been synthesized by chemical and thermal transformation of the precursor polyimides having the tetrahydro[5]helicene unit. The illustrated diamines 4a and 4b were polymerized with two dianhydrides (6FDA and s-BPDA) to form high molecular weight polyimides 5a,b and 6a,b, containing the tetrahydro[5]helicene core. These precursor polyimides showed good solubilities in common solvents and good thermal properties. Chemical transformation in solution or in the film form could be effected by treatment with bromine at elevated temperatures. The resulting [5]helicene-containing polyimides showed a marked increase in thermooxidative stability. The onset temperatures for 5% weight loss in air were over 500 °C for the [5]helicene-based polyimides, about 70 °C higher than those for the precursor polyimides. Furthermore, the [5]helicene-containing polyimides retained the high tensile (Young's) moduli of the precursor polyimides, indicating that the transformation did not result in any chain cleavage or cross-linking. The transformation to yield [5]helicene-containing polyimides could also be effected by heating at 400 °C in air. The thermally induced transformation was supported by the synthesis and transformation of a model compound.

Phenylmaleimide encapped arylene ether imide oligomers

High temperature cure sites for polyimides and related high performance thermosetting systems are important and it has been demonstrated now by several groups that 4-phenylethynylphthalic anhydride and/or 3-phenylethynylaniline are attractive endcappers for polyimides that have wide curing windows and afford solvent resistant networks after 30–90 min at 350–400°C. The present paper has investigated phenylmaleic anhydride (PMA) as an alternate system which is thermally and possibly electron beam curable. Thus, PMA has been successfully utilized as a high temperature crosslinking endgroup for several high performance amorphous polyimides and initial results are described in this paper. Imide oligomers of controlled molecular weights were successfully synthesized by conducting either chemical imidization or by employing a two-step amine-terminated oligomer route followed by endcapping with PMA at about 140°C or lower. The more conventional higher temperature process was complicated by side reactions which are discussed herein. The molecular weights of the oligomers were successfully controlled from 2000 to 15 000 g mol −1. The materials exhibited about at 200°C curing window between oligomer T g and cure exotherm. Glass transition temperatures increased by more than 50°C after curing and produced solvent resistant insoluble materials with about 85% gel content. Curing of the phenylmaleimide endgroups was most successful under a nitrogen atmosphere, but it appears that normal moulding operations are acceptable, wherein only moderate amounts of oxygen are introduced into the specimen. The thermosetting reaction appears to be more sensitive to radical initiation than the earlier studied phenylethynyl systems. Dynamic thermogravimetric analysis on the cured PMA functionalized oligomers showed good behaviour and 5% weight loss in air was only observed above 500°C. The systems are being evaluated as structural adhesives and matrix resins for composite materials and excellent titanium/titanium lapshear values of about 5000 psi (34 MPa) on the cured oligomers has been demonstrated.

Synthesis and Characterization of Poly(benzoyl-1,4-phenylene)s. 2. Catalyst Coligand Effects on Polymer Properties

High molecular weight, soluble poly(benzoyl-1,4-phenylene)s (η inh =0.99-1.6 dL/g) have been prepared by nickel-catalyzed polymerization of 2,5-dichlorobenzophenone in the presence of excess zinc and triphenylphosphine (PBP-A). Polymerization with 2,2'-bipyridine as coligand produces a soluble polymer (PBP-B) which exhibits a higher glass transition temperature of 217 o C (versus 149 o C for comparable PBP-A), a UV-vis λ max at 352 nm (versus 328 nm for PBP-A), and only two 13 C NMR peaks in the carbonyl region at 1966-198 ppm (versus an additional peak at 196.3 ppm for PBP-A). It has been proposed that these two polymers differ in the regiochemical placement of the lateral benzoyl groups along the chain, with PBP-B exhibiting more regular head-to-tail structures.These soluble polymers show no evidence for crystallinity by DSC or by WAXD and exhibit high thermal stability (only 3% weight loss in air or N 2 on heating to 500 o C). Film samples show tensile moduli of 6.4 GPa and tensile breaking strengths in the range of 0.9 GPa

Synthesis and Characterization of Novel Poly(aryl ether pyridyltriazine)s

Poly(aryl ether pyridyltriazine)s were synthesized by two approaches. In the first approach novel pyridyltriazine-containing monomers, 3-(2'-pyridyl)-5,6-bis(4'-fluorophenyl)-1,2,4-triazine and 3-(2'-pyridyl)-5,6-bis(4'-hydroxyphenyl)-1,2,4-triazine, were prepared and reacted with various bisphenols and activated aromatic difluorides, respectively, via a nucleophilic aromatic substitution reaction. High molecular weight polymers were achieved in reactions with 3-(2'-pyridyl)-5,6-bis(4'-hydroxyphenyl)-1,2,4-triazine. However, for polymers prepared with 3-(2'-pyridyl)-5,6-bis(4'-fluorophenyl)-1,2,4-triazine, evidence of cross-linking accompanying the linear polymerization was detected. The second synthetic approach involved preparing poly(aryl ether benzil)s and then reacting them with (2-pyridyl)hydrazidine to form poly(aryl ether pyridyltriazine)s. The polymer modification reaction was quantitative and proceeded with no detectable backbone cleavage. From a synthetic viewpoint, the latter approach proved to be more advantageous, since difficulties associated with either the stability or reactivity of heterocyclic (e.g., triazine) monomers could be bypassed. All of the poly(aryl ether pyridyltriazine)s were amorphous and exhibited T g 's in the range 202-277°C, significantly higher than the T g 's of the parent benzil polymers (167-242°C). The thermooxidative stability of the polymers prepared was excellent; 5% weight loss in air occurred in the range 420-447°C. Some of the polymers were both solution and melt processable, and all formed tough clear creasable films

Polymerization and polymer properties of diarylacetylenes

The polymerization of three diarylacetylenes, namely 1-( p-benzylphenyl)-2-phenylacetylene ( p-BzDPA), 1-( p-phenylphenyl)-2-phenylacetylene and 1-(β-naphthyl)-2-phenylacetylene, was examined. These monomers polymerized in good yields with TaCl 5-cocatalyst systems. Poly( p-BzDPA) was soluble in various organic solvents and had high molecular weights of 6 × 10 5−9 × 10 5 according to gel permeation chromatography. In contrast, the other two polymers were insoluble in all solvents. All these polymers had fairly good thermal stability in air (their onset temperatures of weight loss in air were 330–450°C). The oxygen permeability coefficient of poly( p-BzDPA) at 25°C was 18 barrers, which was close to that of natural rubber (23 barrers).

Thermal behavior of bismaleimide resin

AbstractThe cure of a bismaleimide (BMI) neat resin modified with an aromatic diamine and a siloxane elastomer, has been studied by 13C solid state nuclear magnetic resonance. Two chemical reactions occur during the cure cycle; at a low temperature, Michael's reaction predominates, while at a high temperature the polymerization of the double bond maleimide creates the network.The degradation of this BMI material was characterized with isothermal and dynamic thermogravimetric analyses in air and in nitrogen. The BMI thermal stability is lower in nitrogen than in air. This behavior is an indication of oxygen participating in reactions at high temperatures.The activation energy (Ea) of thermal degradation was determined from isothermal data using an Arrhenius equation (In V vs. 1/T). The global Ea for the weight loss in air was found to be 91 kJ/mol.The nature and the evolution of the thermal degradation products were the combined analyzed by techniques of pyrolysis, gas chromatography and mass spectrometry. The major thermal decomposition products obtained in the temperature range of 300–700°C are identified as benzene, methyl formamide, aniline, toluene and isocyanate‐derived products.

Thermal analysis of GAPTRIOL, an energetic azide polymer

GAPTRIOL is a non-linear glycidyl azide polymer used as the starting material to produce a binder in composite propellant formulations. The mechanism and energetics for the decomposition of GAPTRIOL are therefore of interest. Accordingly, this paper reports results of DSC, TGA and ARC measurements on GAPTRIOL. Discussion of these results and comparison with literature results for GAPDIOL, the linear analogue, are included. The decomposition of GAPDIOL has been reported as a first-order process. Results of kinetic studies on GAPTRIOL using both variable heating rate and isothermal techniques suggest that its decomposition is not a first-order process. In addition, TGA data show a two-stage weight loss in nitrogen and a four-stage weight loss in air. The kinetic information gleaned from the DSC and TGA measurements is compared with that extracted from the ARC data.

Synthesis and properties of poly(arylene ether phenyl‐s‐triazine)s

AbstractA series of new poly(arylene ether phenyl‐s‐triazine)s was prepared by the nucleophilic aromatic substitution polymerization of the potassium salt of bisphenols with 2,4‐bis (halophenyl)‐6‐phenyl‐s‐triazine in N‐methyl‐2‐pyrrolidone at elevated temperature. The polymers with inherent viscosities exceeding 0.5 were obtained after polymerization for 1 h using 2,4‐bis(fluorophenyl)‐6‐phenyl‐s‐triazine as a monomer. The glass transition temperatures of the resulting polymers ranged from 200 to 260°C depending on the bisphenol used in the polymer synthesis. The poly(arylene ether phenyl‐s‐triazine)s demonstrated excellent thermal stabilities in excess of 490°C (5% weight loss in air). The isothermal TGA measurements (400°C under air or nitrogen atmosphere) revealed that the 4,4'‐biphenol‐ and hydroquinone‐based poly(arylene ether phenyl‐s‐triazine)s belong to the most superior class of heat resistant polymers, such as polyimide Kapton™. The mechanical properties of these polymers are also described. © 1994 John Wiley & Sons, Inc.

Preparation and characterization of fluorine‐containing aromatic condensation polymers, 4. Preparation and characterization of fluorine‐containing aromatic polyazomethines and copolyazomethines from perfluoroisopropylidene group‐containing aromatic diamines and/or isopropylidene group‐containing aromatic diamines and phthaladehydes

AbstractA series of novel fluorine‐containing aromatic homopolyazomethines and copolyazomethines were synthesized by solution polycondensation of perfluoroisopropylidene (perfluoropropane‐2,2‐diyl) group‐containing aromatic diamines, 2,2‐bis[4‐(4‐aminophenoxy)phenyl]‐1,1,1,3,3,3‐hexafluoropropane (4,4′‐[1,1,1,3,3,3‐hexafluoropropane‐2,2‐diylbis(1,4‐phenyleneoxy)]dianiline (1a)) and 2,2‐bis(4‐aminophenyl)‐1,1,1,3,3,3‐hexafluoropropane (4,4′‐(1,1,1,3,3,3‐hexafluoropropane‐2,2‐diyl)dianiline (1b)), and/or the corresponding analogous isopropylidene group‐containing aromatic diamines, 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane (4,4′‐[isopropylidenebis(1,4‐phenyleneoxy)]dianiline (1c)) and 2,2‐bis(4‐aminophenyl)propane (4,4′‐isopropylidenedianiline (1d)), with terephthalaldehyde (2a) and isophthaladehyde (2b). The effect of fluorine substitution on the synthesis and properties of these polymers was investigated by comparison with those of the corresponding homopolyazomethines but without fluorine. Film‐forming fluorine‐containing polyazomethines with reduced viscosities up to ηred = 0,44 dL · g−1 were obtained in high yields by using m‐cresol as reaction medium. Incorporation of perfluoroisopropylidene groups in the polyazomethine backbone greatly enhanced the solubility of the polymers in various organic solvents including chloroform and tetrahydrofuran. Their thermal stability was also successfully improved by the introduction of fluorine, and both the temperatures of 5% and 10% weight loss in air increased monotonically with the increase of the fluorine content. The surface properties of the films or the contact angles formed by water and diiodomethane were, however, scarcely affected by fluorine substitution. The mechanical properties of the films, such as tensile strength and initial modulus, fairly decreased by the modification.

Synthesis and characterization of polyarylates derived from 4,4′‐dihydroxy‐meta‐terphenyl and aromatic diacid chlorides

AbstractPolyarylates derived from 4,4″‐dihydroxy‐meta‐terphenyl (DHmTP) were prepared by the phase‐transfer catalyzed, two‐phase polycondensation with aromatic diacid chlorides. The resulting polymers were crystalline, solvent resistant, and produced brittle films. Copolymers with bisphenol‐A were also synthesized using isophthaloyl diacid chloride. At low to moderate levels of DHmTP in the copolymers (25–75%), the materials had high glass transition temperatures (186–201°C), good solvent resistance, and gave tough, clear films. Terpolymers of DHmTP and BPA with 50:50 isophthaloyl and terphthaloyl diacid chloride were prepared with not much improvement over Ardel D‐100®. All the DHmTP‐polyarylates had good thermal stability (5% weight loss in air > 415–460°C) and had a high % char (20–48%). © 1994 John Wiley & Sons, Inc.

Synthesis of aromatic poly(thioether ketone)

AbstractAromatic poly(thioether ketone)s were prepared by the direct polycondensation of aromatic dicarboxylic acids with aryl compounds containing ether or sulfide structures using phosphorus pentoxide/methanesulfonic acid (PPMA) as a condensing agent and solvent. Polycondensation proceeded smoothly and produced aromatic poly(thioether ketone)s with inherent viscosities up to 0.73 dL/g. The synthesis of substituted aryl ketones by the reaction of substituted benzoic acids with aryl compounds in PMMA was studied in detail to demonstrate the feasibility of the reaction for polymer formation. The thermogravimetry of the aromatic poly(thioether ketone)s showed a 10% weight loss in air and nitrogen at around 450 and 460°C, respectively. © 1992 John Wiley & Sons, Inc.

Synthesis and physical properties of amorphous poly(aryl ether isoquinoline)s

Poly(aryl ether isoquinoline)s (PAEI) are prepared by intramolecular ring closure reaction of poly(aryl ether ketone)s (PAEK) [OPhCO-Ph(R) 2 (R') 2 -COPhOAr] n (R=H,Ph; R'=H,Ph; Ar=Ph, PhPh, PhC(Me) 2 Ph, PhC(CF 3 ) 2 Ph) with benzylamine. The synthesis of copolymers of PAEI and PAEK is demonstrated and the copolymer contents are determined. Fluorinated isoquinoline monomers were prepared and condensed with bisphenols to give high molecular weight polymers with T g s ranging from 225 to 320°C. Studies by TGA showed 5 % weight losses in air and nitrogen above 500°C for these polymers.

Unique Characteristics Derived From Poly(Arylene Ether Phosphine Oxide)s

Arylene ether phosphine oxide homopolymers were prepared via nucleophilic aromatic substitution polycondensations of bis(4-ftuorophenyl)phenyl (or methyl) phosphine oxide with various aromatic bisphenols in the presence of a weak base and an aprotic dipolar solvent. These thermoplastic materials with Tg values in the range of about 200°C-285°C showed 5% weight loss in air around 500°C with substantial amounts of char yield at 800°C, which was related to their excellent' self-extinguishing characteristics relative to other engineering thermoplastics. Additionally, the presence of phosphorus in the char after such high temperature heating implied that these materials should also be resistant to aggressive oxygen plasma environments. Indeed, these systems showed extremely low amounts of etching in oxygen plasma when compared with other engineering polymers. The presence of phosphorus residues after either burning or etching with oxygen plasma could play crucial roles in areas of commercial importance and aerospace applications.

Synthesis of Aromatic Poly(ether sulfone)s by Nickel-Catalyzed Coupling Polymerization of Aromatic Dichlorides

Aromatic poly(ether sulfone)s were prepared by the nickel-catalyzed coupling polymerization of aromatic dichlorides containing ether sulfone structures. Polymerizations were carried out in N,N-dimethylacetamide (DMAc) in the presence of nickel chloride, zinc, triphenylphosphine, and bipyridine and produced aromatic poly(ether sulfone)s with inherent viscosities up to 0.38 dl g−1 under mild conditions. The effects of various factors, such as amount of catalyst, ligand, zinc and solvent, reaction temperature, and sonication, were studied. The thermogravimetry of the aromatic poly(ether sulfone)s showed 10% weight loss in air and in nitrogen at 525–565 and 530–570°C, respectively.

Characterization of acetylene terminated sulfone (ATS) resin. II. Thermal analysis of the resin

AbstractThe kinetics and thermodynamics of the cure and post‐cure reactions of an acetylene terminated sulfone (ATS) resin mixture and pure fractions from that mixture were studied using differential scanning calorimetry. Thermal stabilities were measured by programmed thermogravimetry under helium, and oxidative stabilities using isothermal thermogravimetry in air. Microstructural changes accompanying the cure reaction were identified using infrared spectroscopy. Early products of thermal degradation were trapped for identification and quantitative analysis using the technique of sub‐ambient thermal volatilization analysis. We found that glass transition temperatures increase with crosslink density in the resin, that oxygen is able to copolymerize or couple with the polyenes to produce peroxides or hydroperoxides (respectively) which subsequently decompose to form terminal alcohols on the polyene, that weight loss in air at 600°F is an oxidative process that is insensitive to resin crosslink density, and that sulfone functionality constitutes the thermal weak link in the ATS resin system.

Rigid‐Rod benzobisthiazole polymers with reactive fluorene moieties: Synthesis and characterization

AbstractHigh purity 2,7‐fluorenedicarboxylic acid chloride was synthesized in a multistep reaction scheme from 2,7‐dibromofluorene. Subsequent polycondensation in polyphosphoric acid of 2,5‐diamino‐1,4‐benzenedithiol dihydrochloride with terephthaloyl chloride and 2,7‐fluorenedicarboxylic acid chloride led to rigid‐rod benzobisthiazole polymers with reactive fluorene moieties. The proportion of fluorene in the resultant polymers was controlled through reaction stoichiometry. Soluble polymers with intrinsic viscosities as high as 33.7 dL/g (methanesulfonic acid, 30°C) were obtained if the polymerization temperature was not allowed to exceed 165°C. Insoluble, presumably crosslinked polymers were obtained at higher temperature (190–200°C). Thermal characterization of the polymers by differential thermal analysis and thermal gravimetric analysis/mass spectroscopy did not disclose any thermal transition to 450°C. Onset of weight loss in air did not occur until over 550°C.