Soluble and curable prepolymers from polyallyl ester monomers containing aromatic imide groups

Five polyallyl ester monomers that contain aromatic imide groups were synthesized as thermally stable laminating resins. From these monomers soluble and low-melting prepolymers were obtained by radical polymerization in aprotic polar solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, or N-methyl -2-pyrrolidone. The prepolymers are oligomeric compounds in which DP = 3–6 and have lower melting points than the corresponding monomers. It is assumed that the reaction of solvent molecule participates in the polymerization. Whereas, the bulk and the solution polymerization in n-butyl acetate or n-propyl alcohol yielded insoluble and infusible polymer. The relatively low-melting prepolymers were curable at 150–180°C without the evolution of volatile by-products. Resulting glass-fiber laminates have no glass transition point below 300°C and thermooxidative stability at 330°C.     

Thermal behaviour and kinetic study of some triazoles as potential anti-inflammatory agents

Thermogravimetric (TG), differential thermogravimetric analysis and differential scanning calorimetry had been used to characterize the thermal stability of four new heterocyclic compounds with triazolic structure. The four analysed compounds have similar thermal behaviours, namely the thermal mal curves of these new compounds show three thermal events. These compounds were thermally stable up to 110 °C. Above this temperature, the evolution of hydrochloric acid took place as observed by EGA. Identification and the monitoring of gaseous species released during thermal decomposition of pure triazoles in air atmosphere have been carried out by coupled TG–FTIR. Between 110 and 220 °C the main gaseous product is HCl which was identified on the basis of these FTIR spectra. Arguments for a rapid thermooxidation of the four molecules were brought by EGA by identifying the substances which arise from both the destruction of side chains and of triazolic ring. The kinetic analysis of the destruction process of triazolic structure was investigated using the TG data in air for the substance’s decomposition in non-isothermal conditions. The isoconversional methods, Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa and Friedman, were applied to determine the activation energy from the analysis of four curves measured at different heating rates. In order to obtain realistic kinetic parameters, even if the decomposition process is a complex one, the non-parametric kinetics method was also used. A good agreement between the data obtained from the four applied methods was found.     

The synthesis and thermal polymerization of 4,4′-diethynylphenyl ether

Diethynylphenyl ether (DEPE) was synthesized and its thermal polymerization studied by NMR, IR, and DSC techniques. DEPE is a crystalline solid that melts at 72–73°C and undergoes polymerization beginning at about 150°C. The heat of polymerization measured by DSC was 53 ± 2 kcal/mole. Thermomechanical analysis (TMA) of the fully cured resin showed softening behavior at temperatures in excess of 400°C. Weight loss up to 720°C was only 21%. A mechanism of polymerization based on the analysis of IR and NMR data for party polymerized material below 300°C is proposed.     

Preparation of poly-p-benzenesulfonamide

The poly-p-benzenesulfonamide (PBS) structure has been prepared by the transamidation of N¹,N¹-dimethylsufanilamide hydrochloride in a melt reaction at 180°C. The polymeric nature of the product is exhibited by brittle film formation and a glass transition temperature of 180–190°C. Infrared and NMR spectroscopy are consistent with the proposed structure. The number-average degree of polymerization was measured by NMR. The maximum degree of polymerization was 14. Failure to obtain an optimum molecular weight did not appear to be due to monomer purity. Increasing the reaction temperature from 180 to 220°C led to side reactions giving insoluble and infusible product. PBS underwent thermal decomposition near 310°C. The decomposition temperature is independent of molecular weight.     

Synthesis of novel hyperbranched poly(ester‐amide)s based on neutral α‐amino acids via “AD + CBB′” couple‐monomer approach

A series of novel hyperbranched poly(ester‐amide)s (HBPEAs) based on neutral α‐amino acids have been synthesized via the “AD + CBB′” couple‐monomer approach. The ABB′ intermediates were stoichiometrically formed through thio‐Michael addition reaction because of reactivity differences between functional groups. Without any purification, in situ self‐polycondensations of the intermediates at elevated temperature in the presence of a catalyst afforded HBPEAs with multihydroxyl end groups. The degrees of branching (DBs) of the HBPEAs were estimated to be 0.40–0.58 and 0.24–0.54 by quantitative ¹³C NMR with two different calculation methods, respectively, depending on polymerization conditions and structure of monomers. The influences of catalyst, temperature, and intermediate structure on the polymerization process and molecular weights as well as properties of the resultant polymers were investigated. FTIR, NMR, and DEPT‐135 NMR analyses revealed the branched structure of the resultant polymers. The HBPEAs possess moderately high molecular weights with broad distributions, glass transition temperatures in the range of ?25.5 to 36.5 °C, and decomposition temperatures at 10% weight loss under nitrogen and air in the regions of 243.4–289.1 °C and 231.4–265.6 °C, respectively. Among them, those derived from D ,L ‐phenylalanine display the lowest degree of branching, whereas the highest glass transition temperature and the best thermal stability. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Development of Oligomeric Phthalonitrile Resins for Advanced Composite Applications

Phthalonitrile endcapped oligomers containing aromatic ether and imide linkages have been synthesized and characterized. The phthalonitrile terminated oligomers were prepared in two step (one spot) method by the reaction of an excess amount of pyromellitc dianhydride (PMDA) with aromatic diamines, in a N,N-dimethylacetamide (DMAc)/toluene solvent mixture to form anhydride terminated oligomeric intermediate that was terminated by the reaction with 4-(aminophenoxy) phthaloitrile. The average molecular weights of the prepared oligomers were determined by GPC analysis. The oligomeric phthalonitrile monomers have been converted to network polymers using 4,4'-diaminodiphenyl sulfone (DDS) (5.0 wt %) curing additive at elevated temperatures. Differential scanning calorimetric (DSC) analysis was used to follow the polymerization as the oligomeric phthalonitrile/diamine mixtures and prepolymers. An isothermal rheometric analysis was conducted to determine the complex viscosity of the prepolymers during polymerization reaction. Viscosity increases as a function of time due to crosslinking, which depends upon the concentration and reactivity of the curing agent. The TGA analysis of cured resins showed superior thermal and thermo-oxidative stability. The temperature of 10% weight loss from TGA are in the range of 498-511 °C in N₂ and 448–461 °C in air atmosphere. Char yield at 800 °C is 41.7–50.2% in air and 70.6–83.1% in N_2.     

Synthesis and Characterization of Poly(allyl methacrylate) Obtained by Free Radical Initiator

Allyl methacrylate was polymerized in CCl₄ solution by α,α′‐azoisobutyronitrile at 50, 60, and 70°C. The kinetic curves were auto‐accelarated types at 60 and 70°C, but almost linear at 50°C. Arrhenius activation energy was 77.5 kJ/mol. The polymer was insoluble in common organic solvents. It was characterized by FT‐IR, NMR, DSC, TGA and XPS methods. About 98–99% of allyl side groups were remained as pendant even after completion of the polymerization. The spectroscopic and thermal results showed that polymerization is not a cyclopolymerization type, but may have end group cyclization. The high molecular weight is the main cause of a polymer being insoluble even in the early stage of the polymerization. Molecular weight of 1.1×10⁶ for a soluble polymer fraction was measured by light scattering method. The Tg of polymer was 94°C, and after curing at 150–200°C, increased to 211°C. The thermal pyrolysis of polymer at about 350°C gave an anhydride by linkage type degradation, and side group cyclization. The XPS analysis showed the presence of radical fragments of AIBN (initiator) and CCl₄ (solvent) associated with oligomers.     

Synthesis,Characterization and Stability of Triblock Copolymer Based on Tetrahydrofuran and Glycidylazide as Binder

In this work, a triblock copolymer polytetrahydrofuran–block-poly(glycidyl azide)–block-polytetrahydrofuran was synthesized through ring-opening polymerization of epichlorohydrin and tetrahydrofuran catalyzed by BF₃-diethyl ether at 30°C, and further modification. The structure of the polymer was verified by IR, ¹H and ¹³C NMR spectroscopy. The decomposition and kinetic parameters of the block copolymer such as its activation energy and frequency factor were determined using the differential scanning calorimetry and thermo-gravimetric analysis. The results revealed that the main thermal degradation for the copolymer occurs in the temperature range of 220–250°C. Finally, the effect of polytetrahydrofuran content on the thermal stability and decomposition temperature of the overall copolymer was investigated.     

Preparation of high molecular weight polybenzoxazine prepolymers containing siloxane unites and properties of their thermosets

High‐molecular‐weight polybenzoxazine prepolymers containing polydimethylsiloane unit in the main‐chain have been synthesized from α,ω‐bis(aminopropyl)polydimethylsiloxane (PDMS) (molecular weight = 248, 850, and 1622) and bisphenol‐A with formaldehyde. Moreover, another type of prepolymers was prepared using methylenedianiline (MDA) as codiamine with PDMS. The weight average molecular weight of the obtained prepolymers was estimated from size exclusion chromatography to be in the range of 8000–11,000. The chemical structures of the prepolymers were investigated by ¹H NMR and IR analyses. The prepolymers gave transparent free standing films by casting their dioxane solution. The prepolymer films after thermally cured up to 240 °C gave brown colored transparent and flexible polybenzoxazine films. Tensile test of the films revealed that the elongation at break increased with increasing the molecular weight of PDMS unit. Dynamic mechanical analysis of the thermosets showed that the T_gs were as high as 238–270 °C. The thermosets also revealed high thermal stability as evidenced by the 5% weight loss temperatures in the range of 324–384 °C from thermogravimetic analysis. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Functionalized monomers based on N-(4-hydroxy phenyl)maleimide

N-(4-Hydroxy phenyl)maleimide (HPMI) is functionalized with acryloyl, methacryloyl, allyl, propargyl and cyanate groups and the structures of the materials are characterized by FTIR, ¹H NMR and ¹³C NMR. Thermal curing behaviours of the monomers and thermal stabilities of the polymers are studied using thermal analysis. Introduction of polymerizable groups shifts the curing exotherm to low temperatures, and the curing behaviour is dictated by the polymerizable substituent present in the aromatic ring. Polymer from acryloyl-functionalized monomer shows the highest thermal stability (402 °C), whereas the highest char value (49 % at 700 °C) is noted for the polymer obtained from propargyl-functionalized monomer. Polymers derived from functionalization of HPMI with acryloyl and methacryloyl showed better thermal stabilities. Thermosets formed by the thermal polymerization of HPMI functionalized with propargyl and cyanate groups showed higher char values at 700 °C in nitrogen atmosphere.     

Synthesis and Characterization of the Monomer 2,2′ diallylbisphenol-A (ABFA) for obtaining Proton Exchange Membranes based on Crosslinked Sulphonated Poly(Arylene ether sulphone)s

Summary: In the present work, a methodology of synthesis and characterization of the monomer 2,2′ diallylbisphenol-A (ABFA) was developed, aiming at getting a precursor, with adequate purity, for obtaining cross-linked membranes based on sulphonated poly(arylene ether sulphone)s. The monomer synthesis involved the synthesis of 2,2′ bis(4-allyloxiphenyl)propane (Bisphenol-A, diallyl ether - BFAAE), from Bisphenol-A (BFA), followed by Claisen rearrangement of BFAAE, for the production of the target compound 2,2′ diallylbisphenol-A (ABFA). All the compounds, reagent BFA and obtained products, intermediate product BFAAE and final product ABFA, were characterized by FTIR (Fourier Transform infrared spectroscopy), TGA (Thermo-gravimetric analysis) and HPLC (High-performance liquid chromatography). The compound BFAAE was obtained with a yield of 94.5% and a purity of 97.3%, the latter characterized by TGA and by HPLC. The structure of the product was confirmed by FTIR. The thermal Claisen rearrangement process was conducted by using Differential Scanning Calorimetry (DSC) technique, from a factorial experiment planning, with two factors and three levels, with temperature and time being the variables. The above cited techniques were used for monitoring the Claisen rearrangement and for the characterization of the final product. The best results yield ABFA purity between 85 and 90%, approximately, for 220 °C/60min, 230 °C/30min and 210 °C/90min conditions. The obtained results suggest that, in the studied range, polymerization and degradation of the monomer ABFA occur, simultaneously to its formation.     

Reaction control in radical polymerization of di‐n‐butyl itaconate utilizing a hydrogen‐bonding interaction

We have reported that intramolecular chain‐transfer reaction takes place in radical polymerization of itaconates at high temperatures and/or at low monomer concentrations. In this article, radical polymerizations of di‐n‐butyl itaconate (DBI) were carried out in toluene at 60 °C in the presence of amide compounds. The ¹³C‐NMR spectra of the obtained poly(DBI)s indicated that the intramolecular chain‐transfer reaction was suppressed as compared with in the absence of amide compounds. The NMR analysis of DBI and N‐ethylacetamide demonstrated both 1:1 complex and 1:2 complex were formed at 60 °C through a hydrogen‐bonding interaction. The ESR analysis of radical polymerization of diisopropyl itaconate (DiPI) was conducted in addition to the NMR analysis of the obtained poly(DiPI). It was suggested that the suppression of the intramolecular chain‐transfer reaction with the hydrogen‐bonding interaction was achieved by controlling the conformation of the side chain at the penultimate monomeric unit of the propagating radical with an isotactic stereosequence. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4895–4905, 2004     

Thermooxidative stabilization of acrylonitrile terpolymers obtained under reversible chain-transfer conditions: Effects of synthesis temperature and initiation method

The terpolymerization of acrylonitrile, methyl acrylate, and itaconic acid mediated by a reversible addition-fragmentation chain transfer agent, dibenzyl trithiocarbonate, and initiated by AIBN at 80°C, potassium persulfate at 45–55°C, and radiolysis at 20°C is studied. In all the cases, polymerization proceeds via the pseudoliving mechanism, which is preserved up to ultimately high monomer conversions (80–90%). According to FTIR ATR and NMR spectroscopy, all the synthesized terpolymers are characterized by close monomer compositions and their degree of branching is too low to be detected spectroscopically. However, the thermal behaviors of terpolymers obtained by polymerizations at various temperatures are different, namely, the lower the temperature of terpolymer synthesis, the slower the thermooxidative stabilization processes occurring in it.     

Study on the condensation and crosslinking reactions of furfuryl alcohol and tris(2-hy-droxyethyl)isocyanurate by thermal methods

Condensation and crosslinking reactions of furfuryl alcohol (FA) and FA with tris (2-hydroxyethyl )isocyanurate (THEIC) are studied by means of DSC, TG, TBA, NMR and elemental analysis. Four exothermic peaks are observed on the DSC curves of thermal condensation of FA and FA with THEIC in the presence of sulfuric acid. The peaks I, II (50–80°C), III (110–130°C) and IV (150–190°C) correspond to linear polycondensation of FA through head-to-tail condensation, head-to-head etherification, crosslinking dehydration reaction between methylene group and terminal hydroxy group of FA polymeric chain and to further crosslinking reaction at higher temperature, respectively. The reactivity of FA and THEIC increases sharply at 130–150°C and THEIC is reacted completely at 150°C. Addition of THEIC raises the initial decomposition temperature of FA polymer by 60°C.     

Synthesis and thermal behavior of gem-dinitro valerylated polystyrene

Commercial polystyrene has been chemically modified with 4,4-dinitro valeryl chloride by use of Friedel–Crafts acylation reaction in the presence of anhydrous aluminum chloride in a mixture of 1,2-dichloroethane and nitrobenzene. The modified polystyrene containing –COCH₂CH₂C(NO₂)₂CH₃ fragments in side phenyl rings, named gem-dinitro valerylated polystyrene (GDN-PS), was characterized by an Ubbelohde’s viscometer, FTIR, and ¹H NMR spectroscopy. Simultaneous thermogravimetry–differential thermal analysis and differential scanning calorimetry (DSC) have been used to study thermal behavior of the polymer. The results of TG analysis revealed that the main thermal degradation for the GDN-PS occurs during two temperature ranges of 200–300 and 300–430 °C. The DTA curve of GDN-PS is showing a visible exothermic peak at 253.8 °C corresponding to the decomposition of gem-dinitro valeryl groups. The decomposition kinetic of the gem-dinitro groups for GDN-PS with degree of substitution (DS) 11 % was studied by non-isothermal DSC under various heating rates. Kinetic parameters such as activation energy and frequency factor for thermal decomposition of GDN-PS with DS 11 % were evaluated via the ASTM E698 and two isoconversional methods.     

A differential scanning calorimeter study of the crystal forms and polymerization kinetics of 2,4-hexadiynyl-1,6-bis(p-toluenesulfonate)

The thermal properties of 2,4-hexadiynyl-1,6-bis(p-toluenesulfonate) have been explored by program temperature and isothermal differential calorimetry. The heat of fusion for the rapidly heated pure solid was 8254 cal/mole (34,540 J/mole) at 367.1°K (93.8°C). This amounts to an entropy change of 22.5 cal/mole °K (94.1 J/mole °K). The energy of activation for the thermal polymerizations was 18.97 kcal/mole (79.37 kJ/mole). The thermal polymerization appears to follow a solid–solid phase transition which proceeds by random homogeneous nucleation throughout the process. The kinetics were simple first order over 70% of the reaction. Programmed temperature studies indicate that during the first 10% of the polymerization a new high temperature (mp 375.4°K) solid phase is formed which acts as the monomer form during the bulk of the reaction.     

Cocuring behaviors of benzoxazine and maleimide derivatives and the thermal properties of the cured products

The cocuring behaviors of 3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine (P‐ABz) and various N‐phenylmaleimide compounds were studied with DSC, FTIR, and TGA‐GC/MS. The presence of benzoxazine compound promoted the polymerization of maleimide groups. In contrast, 4‐hydroxyphenylmaleimide (MI‐OH) and 4‐maleimidobenzoic acid (MI‐COOH), which possess acidic moieties, showed an acid‐catalytic effect on the polymerization of benzoxazine groups. The cocuring composition of P‐ABz/MI‐COOH showed low polymerization temperatures, high glass transition temperature above 220 °C, and comparable thermal stability to conventional polybenzoxazines. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1890–1899, 2006     

Mechanism of thermal polymerization of cyanate ester systems: Chromatographic and spectroscopic studies

The mechanisms and kinetics of polymerization of mono- and difunctional cyanate esters are investigated using chromatographic (HPLC) and spectroscopic methods (UV, liquid and solid-state NMR, and FTIR). The results obtained after chromatographic separation and identification of the chemical species present in the reaction medium have enabled us to propose a reaction path and a kinetic model for these thermally polymerized systems. Finally, the polymerization of cyanate ester was studied in the presence of different catalysts (imidazole, AcAcCu and AcAcCr) added directly, without solvent, and showed their influence on mechanisms. © 1996 John Wiley & Sons, Inc.     

The curing of epoxy resins with aminophenoxycyclotriphosphazenes

Aminophenoxycyclotriphosphazenes have been used as curing agents for epoxy resins. The thermal curing was performed in stages at 120–125 and 175–180°C followed by postcuring at 225°C to give tough brown polymers. The thermal curing reaction was monitored using FTIR and differential scanning calorimetry. Thermogravimetric analysis of the cured resins has shown thermal stability up to 350–340°C. The char yield obtained in nitrogen at 800°C was about 55–42% and in air at 700°C was about 40–32%. Graphite cloth laminates were prepared. The mechanical properties evaluated were found superior to those of commonly used epoxy resin systems. These resins are useful for making fire- and heat-resistant composites, laminates, molded parts, and adhesives.     

Degradation of epoxy polymers: Part 1—Products of thermal degradation of bisphenol-A diglycidyl ether

The principal characteristics and products of thermal degradation of a commercial epoxy resin prepared by reaction of 2,2-bis(4′-hydroxy phenyl)propane (bisphenol-A) with 1-chloro-2,3-epoxy propane (epichlorhydrin) have been studied. The principal volatile products, acrolein, acetone and allyl alcohol, are formed at 280°C and, although cross-linking is detectable at 220°C, it only becomes significant at 320°C when the residual resin is brittle and insoluble. Decomposition of the cross-linked resin occurs above 340°C when phenolic compounds appear together with more complex products with higher molecular weights whose structures have been speculated upon from examination of their mass spectral characteristics.