Kinetics of polyesterification: modelling and simulation of unsaturated polyester synthesis involving 2-methyl-1,3-propanediol

The kinetics of the individual key reactions involved in the formation of unsaturated polyester resins have been studied using the very reactive glycol, 2-methyl-1,3-propanediol (MPD). This diol has been reacted in turn with maleic anhydride (MA), phthalic anhydride (PA) and isophthalic acid (IA) under isothermal conditions in the temperature range 180-210 °C and the kinetic constants for the following reactions have been obtained MA+MPD, PA+MPD, IA+MPD, MA+PA+MPD and MA+IA+MPD. The relative reactivities of MPD with MA and PA measured by monitoring the loss of carboxyl groups at 180 and 200 °C were found to be 2.26 and 1.70, respectively. At 200 °C PA is more reactive than IA (ratio approximately 1.31) in homopolyesterification. In the copolyesterifications involving PA and IA where cross catalysis can occur, the PA reacted approximately 1.25 times faster than IA at 200 °C. The differences in reactivity might be expected to have a significant effect on the coreactant sequence lengths in prepolymers formed by the concurrent reaction of PA, IA and MPD particularly at low conversions thus on the final properties of the cured resins in which they are employed. The properties of the products are not examined in this paper.     

Synthesis of epoxy–amine multiacrylic prepolymers by reactive extrusion

Epoxy-amine multiacrylic prepolymers were prepared by reactive extrusion using a one-step competitive reaction of diglycidyl ether of bisphenol A (DGEBA) and glycidyl methacrylate (GMA) with diamines. The technical and chemical limitations of the process were analyzed through a reactive extrusion diagram. Diphenyl was used as a tracer for residence time distribution (RTD) studies. Extrusion parameter analysis showed that the reactions are kinetically controlled and that an increase in reaction temperature leads to higher residence time and broader distributions. At constant temperature, we found a linear evolution of the average residence time (t_m ) with kneading disk blocks and left-handed screw element length. The structure of the obtained oligomers was analyzed using a conversion distribution concept. © 1996 John Wiley & Sons, Inc.     

Extruder synthesis of a new class of polyurethanes: Polyacylurethanes based on poly(ε-caprolactone) oligomers

Using a micro-extruder a new class of polyurethanes, polyacylurethanes (PAUs), based on poly(ε-caprolactone) (PCL) oligomers and terephthaloyl diisocyanate was synthesized. These polymers are anticipated to have potential for biodegradable and/or biomedical applications. Therefore, PAUs were synthesized without the use of any, possibly toxic, catalysts.PCL diols of different molecular mass were used, namely 750, 1000, 1250, 1500, 2000, 3000 and 4000 g/mol. These diols were synthesized by thermal polymerization at 150 °C without the use of any catalyst. The PAUs of terephthaloyl diisocyanate were synthesized by reactive extrusion using a micro-extruder of 5 cm³ at 130 °C.The PAUs obtained were characterized using DSC, GPC, DMTA, SAXS and tensile testing.Surprisingly, PAUs based on PCL chains of 750, 1000, 1250 and 1500 g/mol were found to show microphase separation/micro crystallization as proven by SAXS data combined with DSC. This microphase separation creates elastomeric properties as is known from polyurethanes.In the PAUs based on PCL chains of 2000, 3000 and 4000 g/mol part of the PCL was found to crystallize and no evidence of any phase separation of the acylurethane block was found.     

The synthesis and characterisation of reactive poly(p-phenylene terephthalamide)s: A route towards compression stable aramid fibres

Herein we report on the synthesis of reactive poly(p-phenylene terephthalamide) (PPTA) oligomers and the preparation and characterisation of aramid fibres thereof. Methacrylate and maleimide reactive end-groups were found to be sufficiently stable in H₂SO₄ at 85 °C and they were used to prepare reactive PPTA oligomers. Lyotropic spin-dopes could be prepared with up to 20 wt% of reactive oligomer (M_n = 3900 g mol⁻¹) and this modification did not interfere with the fibre spinning process and had no effect on the fibre tensile properties. The as-spun fibres did indeed show a modest (+0.1 GPa) improvement in compression strength. A high temperature treatment at 380 °C resulted in fibres which all show a significant increase in compressive strength over their as-spun precursors, i.e. from 0.7 to 0.9 GPa. When fibres were treated at 430 °C the compression values of the oligomer-modified fibres dropped somewhat, whereas unmodified PPTA displayed a compressive strength of 1.1 GPa. Other favourable fibre properties such as modulus and tenacity were not compromised.     

The use of model compounds in interpreting the thermal degradation of poly(methy methacrylate)

Summary Methyl methacrylate oligomers have been synthesised and used as models to probe the effect of groups formed during termination of polymerization on the thermal stability of poly(methyl methacrylate). Oligomers containing a head-to-head linkage were found to be the least thermally stable, degrading at temperatures around 190°C. In comparison, oligomers containing unsaturated end groups degrade at 255°C, while models containing saturated terminal units are relatively stable and only degrade at temperatures in excess of 300°C.     

In-situ13C magic-angle-spinning NMR measurements of the conversion of ethene to aliphatic hydrocarbons over structurally different zeolites

Solid-state¹³C NMR analysis of the oligomerisation of ethene over H-ZSM-5, H-Y and H-mordenite, indicates that the degree of branching of the final products increases with increasing pore dimensions of the zeolite. In order to monitor the formation of intermediate reaction products, we investigated the oligomerisation of ethene in zeolite H-ZSM-5 at lower temperature. Ethene sorbed in ZSM-5 is stable below 0 °C, but at higher temperatures it is oligomerised to higher, branched reaction products. The use of sealed capsules enabled us to identify several (apparently highly reactive) higher olefins as intermediates. Although the observation of intermediate olefinic oligomers is in line with the classical reaction mechanism of acid-catalysed oligomerisation via carbenium ions, no such charged species could be detected. Alkoxide species, on the other hand, were observed, and these may very well be involved in the reactions.     

Effective recovery of pure aluminum from waste composite laminates by sub- and super-critical water

An innovative and environment-friendly sub- and super-critical water processes have been proposed for successful recovery of aluminum from composite laminated wastes. The effects of reaction temperature (190-400 °C) and residence time (10 and 30 min) were mainly investigated to recover aluminum in an intact form from two commercially available packaging materials, which were made by dry and extrusion lamination methods (samples A and B), respectively. After the reaction, carbon and oxygen contents in the solid-phase were measured by CHNS/O analyzer and the aqueous-phase was subjected for TOC, ICP and ethylene glycol analyses. The results suggested that, the dry laminated ‘sample A’ exhibited a gradual decrease in carbon and oxygen level with increase in reaction temperatures indicating separation of polymers from aluminum. At 10 min, temperature ranges from 340 to 400 °C and at 30 min, from 310 to 340 °C were optimum for the aluminum recovery, showing the lowest percentage of carbon and oxygen in the solid-phase. The aluminum was oxidized above the optimum temperatures. On the other hand, the extrusion laminated ‘sample B’ showed resistance to separation of polymers and the carbon and oxygen level decreased drastically only near the critical point of water. At 30 min, 370-400 °C led to an efficient recovery of aluminum. The results revealed that, temperature, reaction time and the lamination method were the key parameters that determined the recovery of aluminum. This study provides a framework for the effective material cycling of huge wastes of laminated composites using sub- and super-critical water technology.     

Cationic oligomerization of 3-methylene-p-menth-4(8)-ene and 2-methyl-3-methylene-5-isopropylbicyclo [3.1.01,5] hexane

Summary The title monomers were synthesized via Wittig reaction from thujone and pugelone. The monomers were found to react rapidly with cationic initiators at temperatures from -15° to 22°C. The products of these reactions were found to be low molecular weight oligomers. The reaction temperature, presence of solvent or initiator type and concentration seemed to have some effect on the molecular weights of the products obtained.     

The behavior of silicocarbonatite aggregates from the Montreal area

In a previous paper, it was concluded that silicocarbonatite aggregates from the Francon quarry, Montreal contributed to durability problems in Portland cement concrete. Results show that, at 2 days after casting, concrete made with silicocarbonatite aggregates contained over 1.5% more Na₂O than similar bars made with Exshaw limestone aggregates. A reaction involving the rare mineral dawsonite in the silicocarbonatite is thought responsible for the higher Na₂O content. In turn, this caused increased expansion of concrete bars made with alkali expansive aggregates. Also, concrete made with alkali-carbonate reactive Pittsburg aggregate showed more expansion when cured at 80 °C than bars cured at 23 °C. Concrete bars made with Exshaw limestone aggregates cured for 4 h at 85 °C showed late-stage expansion, which is attributed to delayed ettringite formation (DEF). However, no expansion was shown by heat-cured concrete prisms or mortar bars made with silicocarbonatite aggregates. Release of alkalis, aluminates and carbonates by the dawsonite reaction may have inhibited DEF. Concrete bars made with nonreactive Nelson dolostone and 10% silicocarbonatite cured at 80 °C for 4 h showed up to 0.15% expansion after several years at 23 °C and 100% relative humidity (R.H.), indicating that a deleterious reaction did occur.     

Toughening of Epoxy Resins by Amine Terminated Poly(arylene ether ketone)s having Pendant Tertiary Butyl Groups

Summary The objective of this study was to investigate the effects of the amine terminated poly(arylene ether ketone) (PAEK) oligomers as epoxy tougheners on the mechanical and thermal properties of diglycidyl ether of bisphenol A based epoxy resin. The reactive oligomers including pendant tertiary butyl groups were synthesized by nucleophilic aromatic substitution reaction and molecular weight of the oligomers were controlled through end group functionalization and characterized by FTIR spectroscopy. The stoichiometrical amount of the reactive oligomers as toughener and the curing agent, 4,4’-diaminodiphenyl sulfone (DDS) were mixed and degassed. The homogenous mixtures were cured at 120 °C into the preheated molds. The mechanical and thermal characterizations of toughened epoxy resin system were evaluated. It has been shown that the mechanical and thermal properties of toughened epoxy system vary as a function of the chemical structure and the concentration of reactive oligomers. The paper has been dedicated to Prof. Dr. Abdülkadir Kuyulu     

The current state of the accelerated concrete prism test

Expansions due to alkali-silica reaction (ASR) in the accelerated concrete prism test (ACPT-60 °C) show a significant reduction at 13 weeks compared to 52 week testing in the standard concrete prism test (CPT-38 °C). Previous work indicated that increased leaching, higher mass loss and a reduction in the pH were observed when temperature was increased from 38 to 60 °C. After further investigation the authors have revealed that non-reactive fine aggregate from certain sources combined with the same reactive coarse aggregate exhibited further reduction in expansion in the ACPT. Expansion data for a wide range of reactive coarse aggregates in 38 and 60 °C testing regimes is shown. Data investigating the Spratt reactive coarse aggregate combined with seven different non-reactive sands will be shown to demonstrate the dramatic effect of the non-reactive sand. Selected pore solution analyses will be given to further elucidate this issue.     

Recession behavior of Lu2SiO5 under a high speed steam jet at high temperatures

Study of recession behavior of Lu₂SiO₅ bulk was performed in high speed steam jet with a velocity of ∼50 m/s temperature range between 1300 and 1500 °C for 100 h. X-ray results showed that no phase change was observed for all samples after steam exposure. Detailed scanning electron microscopy examinations showed some cracks formation was observed on the bulk surface for the samples of 1400 and 1500 °C. Also, porous structure was formed on the bulk surface for the samples of 1300 and 1400 °C. As for 1500 °C sample, the porous structure disappeared after exposure test. The high magnification images of 1300 °C sample showed the depletion of grain boundary glassy phase. However, for 1400 °C sample, boundary phase was formed again, and the grain growth can be identified for the sample of 1500 °C. The recession mechanism can be explained by a mass transfer of evaporated species from the bulk surface and the weight loss rate measured can be expressed by Arrhenius plot.     

Novel intramolecular blocked isocyanates as stable one-component systems for poly(urea urethane)s

Several poly(urea urethane) oligomers 14a-e were prepared by polycondensation of N-(hydroxyalkyl)-2-oxo-1,3-diazepane-1-carboxamides 11a-e in bulk. The latter compounds were obtained under mild reaction conditions from a novel type of activated urethane/intramolecular blocked isocyanate 8 and a homologous series of amino alcohols. The influence of several catalysts (DABCO, Sn(octoate)₂, and Bu₂Mg) and reaction temperatures (100-150 °C) on molecular weight and microstructure of the polymers obtained was studied. The poly(urea urethane)s are semicrystalline materials and their melting points show the odd/even effect observed earlier for [n]-polyamides, [n]-polyurethanes, poly(ester amide)s, and poly(amide urethane)s. TGA analysis showed that the polymers are stable up to approximately 205-230 °C, the polymers with lower number of methylene groups in the amino alcohol decomposing at the lowest temperature.     

Catalytic hydrothermal conversion of cellulose over SnO2 and ZnO nanoparticle catalysts

The hydrothermal conversion of cellulose in the presence of nanometal oxide particles (SnO₂ and ZnO) was investigated in this study. Both catalysts were synthesized hydrothermally and characterized using TEM, FESEM-EDX, X-ray diffraction spectroscopy and BET (Brunauer, Emmett and Teller) methods. In order to reveal the effect of nano-scale catalysts, experiments were conducted using bulk (non-nano) metal oxide and pure cellulose without any catalyst. The hydrothermal conversion experiments were carried out in a micro autoclave at 300, 400, 500, 600 °C and 1 h reaction time. The compositions of the gaseous products and the aqueous phase were determined with various analytical techniques (GC, ion chromatography, HPLC, UV-vis). Contribution of carbon containing products to the carbon mass balance was also represented. The results indicated both nano and bulk ZnO and SnO₂ to have an effect on the water-gas shift reaction at varying temperatures. The water-gas shift reaction (WGS) proceeded fast at 300 °C in the presence of ZnO, while the rate of WGS was lower at 300 °C in the presence of SnO₂. Nano ZnO led to improved hydrogen yield, while ethane and propane were formed as a result of side reactions in the presence of nano and bulk SnO₂.     

Long-term effectiveness and mechanism of LiOH in inhibiting alkali-silica reaction

A practical alkali reactive aggregate-Beijing aggregate was used to test the long-term effectiveness of LiOH in inhibiting alkali-aggregate reaction (AAR) expansion. In this paper, the most rigorous conditions were so designed that the mortar bars had been cured at 80 °C for 3 years after being autoclaved for 24 h at 150 °C. At this condition, LiOH was able to inhibit long-term alkali-silica reaction (ASR) expansion effectively. Not only was the relationship between molar ratio of n(Li)/n(Na) and the alkali contents in systems established, but also the governing mechanism of such effects was studied by SEM.     

Control of molecular weight distribution of petroleum pitches via multistage supercritical extraction

Packed-column supercritical extraction (SCE), followed by low-pressure gas stripping, was used to produce a dimer-rich pitch fraction from an oligomeric petroleum pitch, Marathon M-50, of broad molecular weight distribution (MWD). Both solvent-to-pitch ratios (S/P) >5 and a positive retrograde temperature gradient of 380-330 °C at 70 bar were found to reduce significantly the amount of trimer+ oligomers in the overhead product from the SCE column. This monomer- and dimer-rich overhead was subsequently stripped of monomer with gaseous toluene in a second packed column at 380 °C and 1.5 bar to obtain an 80+ mol% dimer product with an overall yield, based on the original feed, of 30%. To our knowledge, this is the first reported fractionation of a dimer-rich cut from a petroleum pitch with a demonstrably low level of both lower and higher mol wt impurities.     

Comparative study of carbide-derived carbons obtained from biomorphic TiC and SiC structures

Biomorphic carbide ceramics, TiC and SiC, derived from paper performs by chemical vapor infiltration were converted into high porous carbon by carbide-derived carbon (CDC) approach using selective etching in chlorine or hydrogen/chlorine gas mixture in a temperature range of 400-1200 °C. A comparative study of both carbide precursors was performed regarding reaction kinetics, influence of hydrogen as well as microstructure of the resulting carbon. SiC showed lower reactivity than TiC. Temperatures below 650 °C are not sufficient to remove Si from SiC. Addition of hydrogen to the reactive gas inhibits the chlorination reaction. A linear decrease of etching rate with increasing hydrogen/chlorine ratio was observed for both carbide precursors. A critical ratio, where no etching takes place, was estimated to be 0.72 for TiC-CDC and 0.66 for SiC-CDC. The etching rate of TiC is independent from the temperature. In the case of SiC activation energy of the chlorination reaction of about 50 kJ/mol was estimated in the temperature range 650-800 °C. The structural ordering of CDC with increasing synthesis temperature affects also its oxidation resistance as shown by thermo gravimetric analysis.     

Star oligomers with different reactivity in low VOC polyurethane coatings: Part II

Conclusions  In this paper the effects of the reactivity of hydroxyl functional oligomers with a polyisocyanate crosslinking agent have been demonstrated by comparing the potlife/hardness of a 3.5 VOC two-component polyurethane clear coat based on a low TG, high reactive against a high TG, low reactive oligomer. The reaction rate of two polymers forming a crosslinked network becomes diffusion controlled when, during the reaction, the increasing TG comes close to the reaction temperature.⁴ If this reaction takes place in the presence of a solvent which evaporates during film formation and crosslinking, the speed of evaporation will affect both the reaction rate and the film TG. The results of this study have shown that the reactivity determines the potlife whilst the TG controls the hardness. The reactivity of blends of such oligomers against pure oligomers is different as can be calculated using the theory of branching processes and as shown from practical measurements. Blends of oligomers or a pure oligomer with up to 75% of the properties of the high TG, low reactive oligomer do show a hardness close to the properties of the low TG, high reactive oligomer which further proves that the chemical reactivity controls the overall drying performance. A fast chemical reactivity shortens the potlife with a risk of solvent entrapment near to and at the gel point which results in low hardness.     

Synthesis and thermal stability of Cr2AlC

A new reaction route with AlCr₂ and C as starting materials has been developed to produce Cr₂AlC. A Cr₂AlC bulk ceramic was achieved by hot pressing the AlCr₂ and C powders at 1400 °C with 20 MPa for 1 h in Ar. The mechanism to form Cr₂AlC in a temperature range of 1050-1400 °C was studied. It was confirmed that Cr₂AlC is formed directly by a reaction between C and AlCr₂. The reaction process, phase composition and microstructure were characterized with differential thermal analysis, X-ray diffractometry and scanning electron microscopy. The produced Cr₂AlC ceramic is stable up to 1500 °C in an Ar atmosphere, but decomposes into Al₈Cr₅ and Cr₂₃C₆ above 1500 °C.