Diels-Alder-Reaktionen. IX. Über Bildung und Thermolyse der isomeren Tricyclopentadiene

Diels-Alder-Reactions. IX. On the Formation and the Thermolysis of Isomeric Tricyclopentadienes The formation of isomeric tricyclopentadienes by codimerisation of cyclopentadiene with endo- and exo-dicyclopentadiene between 100 and 140°C in the liquid phase, and the retrodiene reaction of the main isomeres of the tricyclopentadiene fraction by gas phase thermolysis were studied kinetically between 230 and 310°C. The rate constants and the parameters of activation were determined.     

Diels-Alder-Reaktionen. VIII. Kinetische Untersuchungen zur Bildung und zur Pyrolyse von Tetracyclo[6.2.1.13.6.02.7]dodec-4-en

Diels-Alder-Reactions. VIII. Kinetic Investigations of the Formation and the Pyrolysis of Tetracyclo [6.2.1.1^3.6.0^2.7]-dodec-4-en The formation of tetracyclo[6.2.1.1^3.6.0^2.7]dodec-4-ene by codimerisation of cyclopentadiene with bicyclo[2.2.1]hept-2-ene between 60 and 140°C in the liquid phase and the inverse reaction by gas phase pyrolysis between 240 and 300°C were studied kinetically. The activation parameters were determined.     

Investigations of chromatic transformations of polydiacetylene with aromatic compounds

Thermochromic changes of 10,12‐pentacosadiynoic acid (PCDA) were investigated in combination with four aromatic compounds, benzene, furan, thiophene, and cyclopentadiene, with subsequent exposure to UV radiation. Using Raman spectroscopy and solid‐state Fluorometry, no differences were observed between benzene, furan, or thiophene from the PCDA itself, with respect to the blue to red color change, which took place from 80°C to 100°C. However, the addition of cyclopentadiene exhibited the color change at a significantly higher temperature, ranging from 180°C to 200°C. Lack of new products formed during the initial mixing period was ruled out by analysis using solid‐state NMR MAS and differential scanning calorimetry (DSC), with only monomer peaks at 69.61°C for the PCDA and 72.37°C for PCDA in combination with cyclopentadiene, as recorded by the DSC. It is believed that a chemical bond between PCDA and cyclopentadiene is formed after polymerization from catalysis by the UV radiation. Solid‐state NMR MAS revealed a chemical shift peak of 131.55 ppm for the PCDA and a much larger peak at 130.84 ppm for the PCDA and cyclopentadiene. The DSC exhibited melting point peaks at 193.26°C and 194.88°C for PCDA and PCDA with cyclopentadiene, respectively. Because the color change involves C C bond rotation of side groups, stressing π‐bond overlap, the cyclopentadiene bond is thought to prevent rotation by steric hindrance until a higher temperature or melting occurs at the DSC stated temperature of 194.88°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Diffusion and sorption of organic liquids through polymer membranes. VIII. Elastomers versus monocyclic aromatic liquids

Sorption and diffusion of five monocyclic aromatic liquids—three halogenated benzenes, nitrobenzene, and aniline—with five engineering polymers—ethylene propylene diene ter-polymer, nitrile butadiene rubber, styrene butadiene rubber, natural rubber, and neoprene—have been investigated in the temperature interval of 25–60°C. Solvent diffusivity into polymer membranes was determined from the immersion/weight gain experiments. Permeability coefficients were also calculated from the diffusion and sorption data. A temperature dependence of sorption and transport was also investigated to estimate the activation parameters. The experimental results and computed quantities were used to study the type of transport mechanism and the nature of polymer-solvent interactions.     

Synthesis and characterization of a new class of thermosetting resins: Allyl and propargyl substituted cyclopentadiene derivatives

A series of all-hydrocarbon resins were synthesized by reacting cyclopentadiene allyl chloride, propargyl chloride, or a mixture of allyl chloride and propargyl ide, under phase transfer conditions. Phase transfer reactions with and without added solvents, and with either quaternary ammonium or crown ether catalysts, yielded similar products consisting of a mixture of 1,1-disubstituted cyclopentadiene (minor amount) and 2-3 isomers each of tri-, tetra-, penta-, and hexa-substituted derivatives. No further reaction of each these components possible. The overall substitution pattern varied little with changes in reaction conditions although limiting the allyl chloride content led to still reactive, partially substituted products. Incorporation of all-propargyl and high propargyl-to-allyl mixed functionalities on cyclopentadiene yielded products whose stability was very hindering their thorough characterization. Preliminary evaluation was there-carried out for mixed resins with lower propargyl functionality. The allyl substituted resin (allylated cyclopentadiene, ACP) underwent thermal cure lout initiator at around 200°C while allyl/propargyl substituted resin (7:1 ratio, APCP) showed a faster, lower temperature cure at around 120°C. Cationic cure of ACP was also initiated by a novel sulfonium salt at around 100°C. Neat resin when cured at 200°C gave material with a flexural storage modulus 2 of about 300 MPa. Further cure at 250°C raised the modulus to 1.2 GPa. resin gave composites with excellent properties when used with glass and on fibers. Flexural modulus values (by DMA) of ∼ 66 GPa were obtained for ACP/carbon fiber composites compared with 42 GPa for epoxy/carbon composites made in our laboratories using commercially available materials. The modulus values at 300°C dropped to 10% of the room temperature value for the epoxy composites, while the ACP/carbon composite maintained 60% of its room temperature value at 300°C. When brought back to ambient temperature, the modulus of latter sample had increased to 80 GPa and that of the epoxy composite dropped to 23 GPa. Glass fiber ACP composites performed similar to an epoxy composite up to 200°C but maintained properties up to 300°C while those of the epoxy were drastically reduced. TGA analysis of both cured ACP resin and its composites showed decomposition beginning at 375°C. Three-point-bending tests indicated very high modulus with brittle failure for ACP composites. Scanning electron micrographs showed moderate bonding of the new resin to both carbon glass fiber surfaces. This new class of thermosetting resins offers excellent potential for application in low-cost glass and carbon composites with good thermal and physical properties.     

Semiempirische MO-Berechnungen zur Diels-Alder-Reaktion. I. EHT-Berechnungen zur endo-exo-Produktverteilung einiger Dien-Additionen des Cyclopentadiens

Semi-empirical MO-Calculations on the Diels-Alder-Reaction. I. EHT-Calculations on the endo-exo-Product Distribution of Some Diene Additions of Cyclopentadiene In order to explain the endo-exo product distribution of the diene addition of cyclopentadiene with acroleine, methacroleine, crotonaldehyde, butadiene, isoprene and piperylene, EHT calculations have been carried out on a coplanar endo-orientated complex of cyclopentadiene with acroleine. Variations of distances in the region of 2.6—4.0 Å and subsequent correction of the EHT energies by means of a Madelung term have been made. In the region of intermolecular distances investigated the endo orientation was favoured energetically compared with the exo alternative. The charge transfer from diene to dienophile also prevailed in the endo complex of cyclopentadiene and acroleine. A consideration of the bond interactions by an analysis of the energy distribution points to asynchron formation of the σ-bonds. Secondary interaction between the carbonyl carbon atom and the nearest centre of the diene stabilizes the endo complex more strongly than the exo complex, so that the cyclic arrangement of the components should be retained. Therefore, the formulation of a “one-step-two-phases” mechanism seems to be justified for these diene additions. The influence of the methyl groups on the endo-exo product distribution of the DIELS-ALDER-reaction of cyclopentadiene with acroleine or butadiene and the favoured attack at the methyl-free diolefin double bond have been described with similar models, yielding principal correspondance with kinetical results, but partially differing from ALDER's “endo-rule”.     

A kinetic model of the cycloaddition reactions between cyclopentadiene and 1,3-butadiene for synthesis of 5-vinyl-2-norbornene

Under high temperature and pressure, a continuous tubular reactor was successfully utilized to investigate the kinetics of 5-vinyl-2-norbornene (VNB) production. The process involved multiple cycloaddition reactions between cyclopentadiene (CPD) and 1,3-butadiene (BD). The results, spanning a wide range of operating conditions, indicate that higher temperature (180°C) and proper residence time (72 min) were conducive to efficient synthesis of VNB. The apparent kinetic parameters, including activation energies and pre-exponential factors, were acquired by fitting experimental data under integral operating conditions. The kinetic model was proven effective from a practical point of view in predicting the concentration changes of each product in the range 140 to 180°C and 30 to 80 wt.% concentration. This work provides a solid basis for the optimization of the VNB synthesis process.     

Improvement in Low Temperature Izod Impact Strength of SAN/ASA/HNBR Ternary Blends Considering Competing Effects of Glass Transition Temperature and Compatibility

The competing effects of glass transition temperature (T_g) and compatibility on the low temperature Izod impact toughness of styrene–acrylonitrile copolymer/acrylonitrile–styrene‐acrylate terpolymer (SAN/ASA, 75/25, w/w) blends were investigated by using a series of hydrogenated nitrile butadiene rubbers (HNBRs) with different acrylonitrile (AN) contents. The results showed that the HNBR with AN mass content ranging from 21% to 43% had good compatibility with polymer matrix and exhibited dramatic toughening effect at 25°C. Owing to their low T_gs, only the HNBRs (AN = 21% and 25%) remained favorable toughening effect at 0 and ?30°C, respectively. Furthermore, the HNBR with 0% AN content was represented by butadiene rubber (BR). Although, BR has an extremely low T_g (?94.5°C), it is incompatible with polymer matrix, and then could not toughen the material at three temperatures (?30, 0, and 25°C, respectively). Various characterizations including solubility parameters, scanning electron microscopy (SEM), dynamic mechanical thermal analysis (DMTA), Fourier transform infrared (FTIR) spectroscopy, and so on were carried out to elucidate the toughening mechanism. J. VINYL ADDIT. TECHNOL., 25:225–235, 2019. © 2018 Society of Plastics Engineers     

Synthesis,cure analysis,and composite properties of allylated cyclopentadiene resins

Allylated cyclopentadiene was synthesized through the phase transfer reaction of cyclopentadiene and allyl chloride in the presence of a strong base. The reaction yielded a mixture of isomers with 2 to 6 allyl groups per cyclopentadiene ring. Variations in reactant ratios changed product ratios only slightly; however, lower ratios of allyl chloride to cyclopentadiene (4:1 and 2:1) produced lower substituted products. DSC analysis of the ACP showed thermal cure without added catalyst. The total enthalpy of cure was ∼750 J/g with a peak energy at 310°C. FTIR analysis of the thermal cure showed the predominate cure mechanisms to be ene reactions and polyadditions of allyl groups with a small amount of oxidation. Partial curing (B-staging) of ACP was conducted thermally at 180 and 200°C. An increase in viscosity with time was found in each case with gelation occurring at ∼15 h and 3 h, respectively. ACP resin was also cured using various concentrations of peroxide and BF₃₀ dibutyl etherate catalysts. In all cases gelled materials were formed. ACP/carbon fiber and ACP/glass fiber composites gave flexural moduli of 165 and 42 GPa, respectively. Flexural strength values were found to be 956 MPa for ACP/carbon and 681 MPa for ACP/glass. Treatment of ACP/carbon fiber composites in boiling water or refluxing toluene had no significant effect on their mechanical properties.     

Thermoanalytical Investigations on the Effect of Atmospheric Oxygen on HTPB resin

TG-DSC studies, carried out on hydroxy-terminated polybutadiene (HTPB) in air and nitrogen atmospheres show three transitions which give rise to (1) an exothermic DSC peak and mass gain in TG at 170°C–240°C, seen only in air (2) exothermic peak and low mass loss, both in air and nitrogen, due to depolymerization, cyclization and cross linking, and (3) final mass loss corresponding to pyrolysis in nitrogen and combustion in air, appearing respectively as an endothermic peak and as a sharp exothermic peak in the two atmospheres. The FTIR spectrum of the product isolated from TG after the mass gain step shows addition of oxygen to the butadiene back bone. Arrhenius activation parameters (E and A) were computed for the exothermic oxygen addition reaction. The Ozawa method refined by MKN two-term approximation for p(x) function gave results quite comparable to those from Kissinger method.     

Diffusion and sorption of organic liquids through polymer membranes. II. Neoprene,SBR, EPDM,NBR, and natural rubber versus n-alkanes

Diffusion and sorption of n-alkanes (C₆–C₁₀) through commercial polymer membranes such as neoprene, styrene butadiene rubber, ethylene propylene diene terpolymer, nitrile butadiene rubber, and natural rubber have been studied from 25 to 60°C. The diffusion results have been explained in terms of the size of liquid molecules and the diffusion mechanism was found to follow the Fickian trend. Nitrile butadiene rubber and neoprene showed much smaller values of diffusivities and sorption constants than the other polymer membranes. Arrhenius parameters for the activated diffusion process and the thermodynamic quantities for the process of equilibrium sorption have been estimated.     

Viscous behavior of some liquid rubber resins

The flow behavior of several low molecular weight polymers has been studied as a function of shear rate and temperature. These polymers, which had terminating hydroxyl or bromine groups, included homopolymers of polybutadiene and acrylonitrile–butadiene and styrene–butadiene copolymers. Viscosity was measured as a function of shear rate for the temperature range 25°–35°C, and the limiting zero shear viscosities were obtained for the range 25°–60°C. A cone plate viscometer was employed to measure the effect of shear rate on viscosity, and a Brookfield viscometer was used to verify the zero-shear rate values. A tendency of the fluid to flow out of the cone-plate gap was observed for some of the materials studied. From the viscosity data, characteristic times were estimated, and the data were compared with two constitutive equations. A modified Arrhenius equation was fitted to the zero-shear viscosity data. In the case of one material, it was possible to test the Nakajima relationship between viscosity and molecular weight distribution. The dependence of material parameters on temperature is discussed in detail.     

Thermogravimetric and mass-spectrometric study of the thermal decomposition of PBCT resins

The thermal decomposition of three commercial samples of carboxy-terminated polybutadiene (PBCT) resins was studied by thermogravimetric analysis (TGA) at heating rates varying from 2° to 100°C/min. Kinetic parameters of the decomposition process at different heating rates were evaluated by means of the Fuoss method.¹ The decomposition process and the activation energy values are found to be dependent on heating rate. Mass-spectrometric analysis of the decomposition products shows that the pyrolysis products of PBCT resins are mainly low molecular weight hydrocarbons: ethylene, acetylene, butadiene, propadiene, vinylcyclohexene, etc. The rates of evolution of these hydrocarbon products vary with the carboxy content of the PBCT resin. Based on this, a carbonium ion mechanism has been suggested for the thermal decomposition. The data generated from this work are of importance for a consideration of the mechanism of combustion of composite solid propellants based on PBCT binders.     

Alternierende copolymerisation von butadien und ethen

The copolymerization of butadiene and ethene in the presence of the catalyst dineopentyloxyvanadiumoxychloride/triisobutylaluminum was investigated. Basic reaction parameters, such as the [A1]/[V] ratio, the composition of monomer mixture and the polymerization temperature result in a significant influence on the progress of reaction, the conversion of monomers and on the molecular weight and polydispersity of copolymers obtained. NMR measurements demonstrate a high degree of alternation. A maximum of conversion and molecular weight was found by variation of the ratio of catalyst components at [A1]/[V] ≈? 7. An increase of ethene content in the monomer mixture also results in a maximum of conversion but, in contrast, in a continuous decrease in molecular weight. The increase of polymerization temperature from ?25°C up to +40°C results in different effects on the yield of copolymers and appropriate data of molecular weight. The microstructure of products with a high content of trans-butadiene units exhibits an increase of 1,2-addition of butadiene and the beginning of crosslinking reactions at temperatures above 20°C.     

The effect of CTBN concentrations on the kinetic parameters of decomposition of blends of cardanol‐based epoxidized novolac resin modified with carboxyl‐terminated liquid copolymer

Cardanol‐based novolac resins were separately prepared with different mole ratios of cardanol‐to‐formaldehyde with different acid catalysts. These resins were epoxidized with epichlorohydrin, in basic medium, at 120°C. The resins were, separately, blended with different weight percentages of carboxyl‐terminated butadiene acrylonotrile copolymer and cured with polyamine. Structural changes during blending were studied by FTIR spectroscopic analysis. Coats–Redfern equation was utilized to calculate the kinetic parameters, viz., order of decomposition reaction (n), activation energy (E), pre‐exponential factor (Z), and rate decomposition constant (k), for the decomposition of the samples. It was found that the degradation of the epoxies and their blend samples proceeded in two steps. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of Carbon Black/Silica Hybrid Filler on Thermal Properties,Fatigue Life,and Natural Weathering of SBR/Recycled NBR Blends

The utilization of nitrile glove waste will spark a great deal of interest in the rubber industry in developing cost-effective techniques to convert waste and used rubber into a processable form. Blends of styrene butadiene rubber/recycled acrylonitrile butadiene rubber (SBR/NBRr) reinforced at 85/15 blend with different ratios of a carbon black/silica (CB/Sil) hybrid filler (50/0, 40/10, 30/20, 20/30, 40/10, 0/50 phr) were tested either with or without the silane coupling agent, Si69. Results showed that the increased thermal stability of blends with Si69 is highly related to the formation of crosslinks between the filler. Thermogravimetric (TG) thermograms showed that the percentage of char residue for blends with Si69 was higher than without Si69. The differential scanning calorimetry (DSC) thermograms of both blends revealed a glass transition temperature (Tg) between 65.0°C and 66.9°C. At all blend ratios, the fatigue life of blends with Si69 was better than blends without Si69. After six months’ exposure to natural weather, blends with Si69 exhibited better tensile properties, retention, and morphology compared to blends without Si69.     

Carbonization and CO<Subscript>2</Subscript> activation of scrap tires: Optimization of specific surface area by the Taguchi method

This research demonstrates the production of activated carbon from scrap tires via physical activation with carbon dioxide. A newly constructed apparatus was utilized for uninterrupted carbonization and activation processes. Taguchi experimental design (L16) was applied to conduct the experiments at different levels by altering six operating parameters. Carbonization temperature (550–700 °C), activation temperature (800–950 °C), process duration (30–120 min), CO₂ flow rate (400 and 600 cc/min) and heating rate (5 and 10 °C/min) were the variables examined in this study. The effect of parameters on the specific surface area (SSA) of activated carbon was studied, and the influential parameters were identified employing analysis of variance (ANOVA). The optimum conditions for maximum SSA were: carbonization temperature=650 °C, carbonization time=60 min, heating rate=5 °C/min, activation temperature= 900 °C, activation time=60 min and CO₂ flow rate=400 cc/min. The most effective parameter was activation temperature with an estimated impact of 49%. The activated carbon produced under optimum conditions was characterized by pore and surface structure analysis, iodine adsorption test, ash content, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The process yield for optimized activated carbon was 13.2% with the following properties: specific surface area=437 m²/g, total pore volume=0.353 cc/g, iodine number=404.7 mg/g and ash content=13.9% along with an amorphous structure and a lot of oxygen functional groups. These properties are comparable to those of commercial activated carbons.     

Preparation and characterization of epoxidate poly(1,2‐butadiene)–toughened diglycidyl ether bisphenol‐A epoxy composites

By the oxidation of liquid poly(1,2‐butadiene) (LPB) with H₂O₂/HCOOH, epoxidate poly(1,2‐butadiene) (ELPB) was obtained as a toughening agent to prepare diglycidyl ether bisphenol‐A (DGEBA) epoxy composites by using V115 polyamide(PA) as a cross‐linking agent. DGEBA, ELPB, and the composites were effectively cured by PA at 100°C for 2 h followed by postcuring at 170°C for 1 h. Thermal gravimetric analysis results in air and nitrogen atmosphere showed that the thermal stability of composites could be improved by the addition of ELPB. Compared with DGEBA/PA, the composites exhibited a decrease in strength at yield but an increase in strain at break with the increase in ELPB amount. The composite with 10% ELPB exhibited both thermal stability and tenacity superior to those of DGEBA/PA and composites with 5 and 20% ELPB, respectively. The improvements in thermal and mechanical properties of composites depended on the formation of Inter Penetrating Networks (IPN) among DGEBA/PA/ELPB and their distributions in the matrix. At an appropriate ELPB amount, the IPN, mostly made of DGEBA/PA/ELPB, may be distributed more evenly in the matrix; less ELPB resulted in the formation of IPN mainly made of DGEBA/PA; excessive addition of ELPB resulted in the local aggregation of ELPB/PA and phase separations. The toughening mechanism was changed from chemically forming IPN made of DGEBA/PA/ELPB to physically reinforcing DGEBA/PA by ELPB/PA with the increase in ELPB addition. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Polymer‐modified bitumen of recycled LDPE and maleated bitumen

Maleated bitumen was prepared by the reaction of penetration grade bitumen (80/100) with maleic anhydride at 150°C for 2 h under nitrogen atmosphere. The effectiveness of maleation was assessed in bitumen–recycled low‐density polyethylene (LDPE) blends in terms of their softening point and elastic recovery. It was observed that the softening point and elastic recovery of the blends increased after maleation of the base bitumen owing to the formation of an asphaltene‐linked‐LDPE system. To obtain the desired elasticity, a recoverable composition was worked out with the help of maleated bitumen, recycled LDPE and styrene–butadiene–styrene. The storage stability of the blends was assessed in terms of their difference in softening points, rheological parameters, and microstructure of the top and bottom portions of test tube samples. The difference in softening point of the recoverable maleated bitumen blend was 5°C as compared to 60°C for the base bitumen blend. The phase angle was also reduced to 7.4° at 70°C compared with the 44.30° for the base bitumen blend. Scanning electron micrographs indicate that polymers existed in both the top and the bottom portions of the aged test tube maleated blend samples. The stability of the blend was further improved when LDPE is colloidal milled with maleic anhydride in the blend preparation. Roofing bitumen was also made with maleated bitumen containing 9 wt % recycled LDPE content. Based on the rheological data, it was found that the maleated bitumen–LDPE blend exhibited superior time‐/temperature‐dependent response and higher creep recovery compared with the base bitumen blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013     

Hydrogenation of 1,3-butadiene and isoprene prepolymers having carboxyl end groups

The hydrogenations of butadiene and isoprene prepolymers having carboxyl and cyano end groups were investigated by two methods: Heterogenous hydrogenations were carried out at 45°C and 50 psi of hydrogen pressure with palladium on carbonate as catalyst. The best degree of saturation and carboxyl retention were 95 and 79% for butadiene prepolymers and 84 and 95% for an isoprene prepolymers, respectively. Dimide reduction was made in xylene at 130–140°C and normal pressure with p-toluenesulfonylhydrazide (TSH) as the diimide source. A nearly 100% degree of saturation for butadiene prepolymers and 91% for isoprene prepolymers were achieved. The effects of reaction conditions on the degree of saturation and the carboxyl retention, calculation of molecular weight before and after hydrogenation based on H-NMR spectral data, and diimide reduction with TSH are discussed. © 1995 John Wiley & Sons, Inc.