Investigation of the curing kinetics of polyurethane/nitrocellulose blends through FT-IR measurements

Polyester (HTPS) based polyurethane (PU) elastomers were currently established to be effective binders for high-energy composites with improved performances. Conventional PU binders are mostly non-energetic materials, and consequently reduce the energy performance significantly. Nitrocellulose (NC), is an energetic polymer widely used as an ingredient in propellants, explosives, fireworks, and gas generators, it may be introduced in PU-based compositions to overcome their performance drawback. Kinetic parameters must be specified in order to build PU binders with the most convenient and appropriate features. Therefore, the cure kinetics of polyester based polyurethane binder systems were investigated by Fourier transform infrared spectroscopy (FT-IR) isothermal method. The polyester prepolymer (Desmophen^® 1200) was cured with hexamethylene diisocyanate (HDI: Desmodur^® N100) at various molar ratios (R_[NCO]/[OH] = 0.6, 1, 1.25, and 1.5) and under different isothermal conditions (T = 60°C, 80°C, 100°C, and 120°C). In addition, the effect of the addition of nitrocellulose on the kinetics of polymerization of PU was investigated. The progression of the reaction was followed based on the decrease of the peak intensity of –NCO group at 2271 cm⁻¹ as a function of the reaction time. The curing kinetic model and the apparent activation energy (E_α) were determined by the use of Kamal autocatalytic model and Friedman isoconversional method, respectively.     

Comparison between properties of polyether polytriazole elastomers and polyether polyurethane elastomers

In order to explore the application of click chemistry in the field of elastomer materials, the comparison between the properties of polyurethane and polytriazole elastomers has been carried out. Propargyl‐terminated ethylene oxide‐tetrahydrofuran copolymer (PTPET) has been prepared from the ethylene oxide‐tetrahydrofuran copolymer (PET) by end modification. Using polyisocyanate N100 and polyazide compounds as cross‐linkers, PET polyurethane and PTPET polytriazole elastomers have been prepared through urethane and copper‐catalyzed azide‐alkyne huisgen [3 + 2] dipolar cycloaddition reactions, respectively. Mechanical properties indicate that, to be different from those of polyurethane elastomers, the modulus E and stress σ_b of polytriazole elastomers increase at first, and then decrease with the increase in R. At around the stoichiometric ratio, the modulus E and stress σ_b reach a maximum, and the strain ε_b reaches a minimum. Swelling tests demonstrate that the M_c of polytriazole elastomers has a minimum value at the stoichiometric ratio. The dynamic mechanical analysis indicates that both polyurethane and polytriazole elastomers have the same glass transition temperature of ?64°C, although polytriazole elastomers exhibit lower dissipation factor tan δ. Thermal analysis shows that polytriazole elastomers have better thermal stability than polyurethane elastomers. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and Characterization of a New Energetic Plasticizer: Acyl-Terminated GAP

A new energetic plasticizer, acyl-terminated glycidyl azide polymer (GAP), was synthesized through the reaction between 2,4,6-trinitrobenzoyl (TNB) chloride and GAP. The TNB-GAP structure was confirmed by FT-IR, UV-vis, ¹H NMR, and ¹³C NMR. The glass transition temperature (T _g ) of TNB-GAP was evaluated by differential scanning calorimetry (DSC), and the thermal stability of TNB-GAP was tested by thermogravimetric analysis (TGA). DSC traces showed that TNB-GAP had a T _g of ?46.01°C. TGA curves showed that the thermo-oxidative degradation of TNB-GAP in air was a two-step reaction, and the percentage of degraded TNB-GAP nearly reached 100% at 650°C. Exothermic decomposition reaction kinetic parameters of TNB-GAP were also studied using the non-isothermal DSC method. Results indicated that the values of apparent activation energy of TNB-GAP were 80.16 and 162.92 kJ/mol, and the values of the pre-exponential constant were 1.75 × 10¹⁰ and 1.22 × 10¹⁶.     

Research on the Blocking Reaction Kinetics and Mechanism of Aqueous Polyurethane Micelles Blocked by 2,4,6-Trichlorophenol

The blocked terminal-isocyanate (NCO) aqueous polyurethane micelles were prepared by using the 2,6-hexamethylene diisocyanate (HDI), polyethylene glycol (PEG), dimethylol propionic acid (DMPA), and 2,4,6-trichlorophenol (TCP) as blocking agent. This paper was focused on the kinetics research of the TCP blocking terminal-NCO of pre-polymer, which occurred during the preparation process of TCP blocked aqueous polyurethane micelles. The kinetics parameters were obtained in the absence and presence of dibutyl tin dilaurate (DBTDL) as catalyst, respectively. Furthermore, the mechanism for TCP blocking terminal-NCO of pre-polymer was explored. The results showed that the blocking reaction was second order reaction, and the reaction activation energy was 43.890 KJ/mol without catalyst. In the presence of DBTDL, the blocking reaction activation energy was reduced to 34.412 KJ/mol, and the reaction rate was improved significantly. In addition, TCP blocking terminal-NCO of pre-polymer could be ascribed to the nucleophilic addition between nucleophilic phenolic hydroxyl of TCP and the carbon atom of -NCO group.     

Transesterification kinetics of poly(ethylene terephthalate) and poly(ethylene 2,6‐naphthalate) blends with the addition of 2,2′‐bis(1,3‐oxazoline)

The kinetics of the transesterification reaction between poly(ethylene terephthalate) (PET) and poly(ethylene 2,6‐naphthalate) (PEN) with and without the addition of a chain extender were studied with ¹H NMR. Different kinetic approaches were considered, and a second‐order, reversible reaction was accepted for the PET/PEN reactive blend system. The addition of 2,2′‐bis(1,3‐oxazoline) (BOZ) promoted the transesterification reaction between PET and PEN in the molten state. The activation energy of the transesterification reaction for the PET/PEN reactive blend with BOZ (94.0 kJ/mol) was lower than that without BOZ (168.9KJ/mol). The rate constant k took an almost constant value for blend samples with different compositions mixed at 275 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2607–2614, 2001     

N-Aryltetramethylguanidines,living catalysts for polyurethane foams

N-Aryltetramethylguanidines catalyze the formation of polyurethane foams by a novel exchange reaction involving C?N double bond of the guanidines and the isocyanate groups of the polyisocyanates. The catalyst sites are transferred to the growing polymer network, achieving a rapid catalytic build-up of the foam.     

Homopolymerization of methyl methacrylate by novel salicylaldiminate‐nickel/methylaluminoxane catalysts obtained by oxidative addition of the chelate ligand to a nickel(0) precursor

Salicylaldimine ligands, such as 5‐nitro‐N(2,6‐diisopropylphenyl)salicylaldimine, 3,5‐dinitro‐N(2,6‐diisopropylphenyl)salicylaldimine, and 3‐phenyl‐N(2,6‐diisopropylphenyl) salicylaldimine were checked in the oxidative addition to bis(1,5‐cyclooctadiene)nickel(0) to prepare, after activation by methylaluminoxane (MAO), novel nickel‐based catalytic systems active in the polymerization of methyl methacrylate. The catalytic behavior of the aforementioned systems, in terms of activity, molecular weight, and polydispersity of the resulting poly(methyl methacrylate) as well as its stereoregularity degree, was investigated as a function of the Al/Ni molar ratio, reaction temperature, and nature of the salicylaldimine ligand. The effect of ethylene atmosphere present during the preparation of the catalyst precursors was also investigated. The results are discussed and compared with those previously obtained by bis(salicylaldiminate)nickel(II)/MAO catalytic systems. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1716–1724, 2003     

Ethylene Oligomerization Catalyzed by Nickel（Ⅱ） Diimine Complexes

Ethylene oligomerization has been investigated by using catalyst systems composed of nickel(II) diimine complexes (diimine = N, N′‐o‐phenylene bis (salicylideneaminato), N, N′‐o‐phenylenebisbenzal, N, N′‐ethylenebisbenzal) and ethylaluminoxane (EAO). The main products in toluene and at 110–200 °C were olefins with low carbon numbers (C₄—C₁₀). Effects of reaction temperature, Al/Ni molar ratio and reaction period on both the catalytic activity and product distribution were explored. The activity of 1.84 × 10⁵ g of oligomer/(mol_NI · h), with 87.4% of selectivity to C₄—C₁₀ olefins, was attained at 200 °C in the reaction when a catalyst composed of NiCl₂ (PhCH = o‐NC₆H₄N = CHPh) and EAO was used.     

Non-isothermal decomposition kinetics of the interaction of poly(ethylene terephthalate) with alkyd varnish

The recycling of soft drink bottles poly(ethylene terephthalate) (PET) has been used as an additive in varnish containing alkyd resin. The PET, called to recycled PET (PET-R), was added to the varnish in increasing amounts. Samples of varnish containing PET-R (VPET-R) were used as a film onto slides and its thermal properties were evaluated using thermogravimetry (TG). Throughout the visual analysis and thermal behavior of VPET-R it is possible to identify that the maximum amount of PET-R added to the varnish without changing in the film properties was 2%. The kinetic parameters, such as activation energy (E) and the pre-exponential factor (A) were calculated by the isoconversional Flynn-Wall-Ozawa method for the samples containing 0.5 to 2.0% PET-R. A decrease in the values of E was verified for lower amounts of PET-R for the thermal decomposition reaction. A kinetic compensation effect (KCE) represented by the lnA=−13.42+0.23E equation was observed for all samples. The most suitable kinetic model to describe this decomposition process is the autocatalytic Šesták-Berggren, being the model applied to heterogeneous systems.     

Thermosetting epoxidized polybutadiene/low-molecular weight polyphenylene oxide compatible system with quite low-dielectric constant and loss prepared through co-curing reaction

Through the redistribution reaction of PPO, the hydroxyl-terminated low molecular weight PPO (PPO-OH) was prepared. Furthermore, after the reacting of PPO-OH with methacrylic anhydride, the double-bond-terminated low-molecular weight PPO (R-PPO) were synthesized, its M_n was 2631 g/mol. The R-PPO were co-cured with epoxidized polybutadiene (JP-100) to prepare JP-100/R-PPO cured systems. The JP-100/R-PPO cured systems showed single-phase morphology. The co-curing reaction with R-PPO could effectively improve the thermal performance of JP-100, the glass transition temperature (T_g) of cured JP-100/R-PPO systems raised greatly. For the cured JP-100/R-PPO (100/30) system, its T_g was 192°C. The dielectric constant and dissipation factor of cured JP-100/R-PPO systems were both decreased and showed good frequency stability. The dielectric constant and dissipation factor at 1 MHz of cured JP-100/R-PPO (100/30) system were 2.61 and 0.0038, respectively, were obviously lower than those of cured JP-100 system (which were 3.10 and 0.0099, respectively). The JP-100/R-PPO systems exhibited an excellent thermal stability. The 5% weight loss temperature (T_5%) of cured JP-100/R-PPO system was around 340°C.     

Insights into Nitrogen-doped Carbon for Oxygen Reduction: The Role of Graphitic and Pyridinic Nitrogen Species

Nitrogen-doped carbons (N/Cs) manifest good catalytic performance for oxygen reduction reaction (ORR) for fuel cell systems. However, to date, controversies remain on the role of active sites in N/Cs. In the present study, ORR test was conducted on three N/Cs in O₂-saturated 0.1 M KOH aqueous solution, where apparent linear correlation between graphitic N contents and ORR activity was observed. Theoretical calculations demonstrated that graphitic N doping is energetically more favorable than that of pyridinic N doping for ORR and the pyridinic N leads to more preferential with 2 e^– ORR pathway. These results reveal that graphitic N plays a key role in N/Cs mediated ORR activity. This work lays a solid foundation on identifying the active sites in heteroatom-doped carbons and can be exploited for rational design and engineering of effective carbon-based ORR catalysts.     

Cu/CuxS-Embedded N,S-Doped Porous Carbon Derived in Situ from a MOF Designed for Efficient Catalysis

The reasonable design of the precursor of a carbon-based nanocatalyst is an important pathway to improve catalytic performance. In this study, a simple solvothermal method was used to synthesize [Cu(TPT)(2,5-tdc)] ⋅ 2H₂O (Cu-MOF), which contains N and S atoms, in one step. Further in-situ carbonization of the Cu-MOF as the precursor was used to synthesize Cu/Cu_xS-embedded N,S-doped porous carbon (Cu/Cu_xS/NSC) composites. The catalytic activities of the prepared Cu/Cu_xS/NSC were investigated through catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The results show that the designed Cu/Cu_xS/NSC has exceptional catalytic activity and recycling stability, with a reaction rate constant of 0.0256 s⁻¹, and the conversion rate still exceeds 90 % after 15 cycles. Meanwhile, the efficient catalytic reduction of dyes (CR, MO, MB and RhB) confirmed its versatility. Finally, the active sites of the Cu/Cu_xS/NSC catalysts were analyzed, and a possible multicomponent synergistic catalytic mechanism was proposed.     

Efficient peroxide decoloration of azo dye catalyzed by polyethylene glycol-linked manganese chlorin derivative

We reported here that polyethylene glycol (PEG)-linked manganese pyrochlorophyllide a (PEG-MnPChlide a) possesses remarkable catalytic activity comparable to horseradish peroxidase (HRP). The PEG-MnPChlide a catalyzed the oxidation decoloration reaction of C.I. Acid Orange 7 by hydrogen peroxide under a mild aqueous condition, pH 8.0 at 25 °C. The manganese pyrochlorophyride a methylester (MnPChlide a ME) dissolved in a Triton X-100 micellar solution also exhibited the catalytic activity, indicating the micellar environment plays an important role in the catalytic reaction. The reaction rate was accelerated by addition of imidazole. The catalytic reactions were analyzed by Michaelis–Menten kinetics, revealing that the higher reactivity of catalyst–substrate complex is responsible for the present catalytic reaction system.     

Anionic synthesis of poly[ethylene methylene bis(4-phenyl-carbamate)-g-acrylonitrile]

A relatively high-molecular-weight polyurethane based on MDI and ethylene glycol was prepared and characterized. This polymer was metalated with sodium hydride in N,N-dimethylformamide (DMF) at about 0°C. Metalation was confirmed principally by spectroscopic identification of the N-methyl derivative obtained by coupling the metalated polymer with methyl iodide. Under appropriate reaction conditions the metalated polyurethane was used for the anionic graft polymerization of the reactive monomers acrylonitrile and ethylene and propylene sulfides. Attempted anionic graft polymerizations with other monomers, including styrene and ethylene and propylene oxides, were unsuccessful. The polyurethane grafted with acrylonitrile was separated by fractionation from accompanying small amounts of polyacrylonitrile, a low-molecular-weight homopolymer. One sample of polyurethane grafted with acrylonitrile was identified by microanalysis, IR, NMR, and increase in weight and was also characterized by differential thermal analysis.     

Group IV Organometallic Compounds Based on Dianionic “Pincer” Ligands: Synthesis,Characterization, and Catalytic Activity in Intramolecular Hydroamination Reactions

Neutral Zr^IV and Hf^IV diamido complexes stabilized by unsymmetrical dianionic N,C,N′ pincer ligands have been prepared through the simplest and convenient direct metal‐induced C_aryl? H bond activation. Simple ligand modification has contributed to highlight the non‐innocent role played by the donor atom set in the control of the cyclometallation kinetics. The as‐prepared bis‐amido catalysts were found to be good candidates for the intramolecular hydroamination/cyclization of primary aminoalkenes. The ability of these compounds to promote such a catalytic transformation efficiently (by providing, in some cases, fast and complete substrate conversion at room temperature) constitutes a remarkable step forward toward catalytic systems that can operate at relatively low catalyst loading and under milder reaction conditions. Kinetic studies and substrate‐scope investigations, in conjunction with preliminary DFT calculations on the real systems, were used to elucidate the effects of the substrate substitution on the catalyst performance and to support the most reliable mechanistic path operative in the hydroamination reaction.     

Compatibilizing effect of isocyanate functional group on polyethylene terephthalate/low density polyethylene blends

To evaluate the compatibilizing effects of isocyanate (NCO) functional group on the polyethylene terephthalate/low density polyethylene (PET/LDPE) blends, LDPE grafted with 2-hydroxyethyl methacrylate-isophorone diisocyanate (LDPE-g-HI) was prepared and blended with PET. The chemical reaction occurred during the melt blending in the PET/LDPE-g-HI blends was confirmed by the result of IR spectra. In the light of the blend morphology, the dispersions of the PET/LDPE-g-HI blends were very fine over the PET/LDPE blends. DSC thermograms indicated that PET microdispersions produced by the slow cooling of the PET/LDPE-g-HI blends were largely amorphous, with low crystallinity, due to the chemical bonding. The tensile strengths of the PET/LDPE-g-HI blends were higher than those of the PET/LDPE blends having a poor adhesion. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 447–453, 1998     

Dmap-Catalyzed Synthesis of Novel Pyrrolo[2,3-D]Pyrimidine Derivatives Bearing an Aromatic Sulfonamide Moiety

4-(N,N-Dimethylamino)pyridine (DMAP), with a dual role as a basic nucleophilic catalyst, was shown to be a highly efficient catalyst for the synthesis of some new N-(2-aryl-7-benzyl-5,6-diphenyl-7H-pyrrolo[2,3-d]pyrimidin-4-yl)benzenesulfonamides through the reaction of 2-aryl-7-benzyl-5,6-diphenyl-7H-pyrrolo[2,3-d]pyrimidin-4-amines (7-deazaadenines) with benzenesulfonyl chlorides. It was also found that the use of DMAP under solvent-free conditions is much more effective than other catalytic systems such as pyridine as both the catalyst and solvent, t-BuOK in t-BuOH, Et₃N in ethanol (EtOH), and even DMAP in dimethylformamide (DMF). The influences of the reaction parameters, temperature, and the catalyst amount, on the catalytic performance have been studied. All synthetic compounds were characterized on the basis of their full spectral data.     

Synthesis of diimine ligands with cycloalkyl substituents based on 4,6-dibenzofuran-and 4,6-dibenzothiophenedicarboxaldehydes

A formic acid-catalyzed reaction of substituted cycloalkylanilines with 4,6-dibenzofuran-and 4,6-dibenzothiophenedicarboxaldehydes in methanol-dichloromethane mixture afforded a number of the corresponding diimines, which can be of interest as components of catalytic systems for polymerization of olefins. Dedicated to the memory of Academician N. N. Vorozhtsov on the 100th anniversary of his birth. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1131–1134, June, 2007.     

Studies on PNPP Hydrolysis Catalyzed by Schiff Base Cobalt（Ⅱ） Complexes Containing Benzoaza-15-crown-5

Three novel Schiff base cobalt（Ⅱ） complexes containing benzoaza-15-crown-5, CoL^1, CoL^2 and CoL^3 were synthesized and characterized, and these complexes were used in catalytic hydrolysis of carboxylic ester （PNPP, p-nitrophenyl picolinate） as mimic hydrolytic metalloenzyme. The analysis of specific absorption spectra of the hydrolytic reaction systems indicated that the catalytic hydrolysis involved the key intermediates formed by PNPP with cobalt（Ⅱ） complexes. The CoL^3 bearing the electron withdrawing group shows better catalytic activity due to its stabilization effect on active species MLS^-. The catalytic mechanism of PNPP hydrolysis was also proposed. The kinetic parameter of PNPP catalytic hydrolysis has been calculated and the activation energy for the catalytic hydrolysis is 43.69, 39.76 and 35.44 kJ·mol^-1, respectively.     

Preparation of high molecular weight polyurethane particles by nonaqueous emulsion polyaddition

A versatile nonaqueous emulsion polyaddition process for the one-step fabrication of spherical polyurethane nanoparticles is presented. Three different emulsion systems were used consisting of N,N′-dimethylformamide (DMF) dispersed in n-hexane, acetonitrile dispersed in cyclohexane, and acetonitrile dispersed in tetradecane. After successful stabilization of the emulsion systems by using a poly(isoprene)-poly(methylmethacrylate) block copolymer, the fabrication of the polyurethanes was carried out within the dispersed polar phase. The polyurethane particles showed average diameters as small as 35 nm. Additionally, infrared (IR) characterization revealed that the formation of any urea, which decreases the mechanical properties of the polyurethanes, was prevented during the polyaddition. This was attributed to the anhydrous reaction conditions. Gel permeation chromatography (GPC) analysis demonstrated the average molecular weights (M _n) of the polyurethanes to be as high as 16,500 g/mol, corresponding to conversions of 0.98. Comparable molecular weights and conversions have not previously been achieved without the formation of urea.