Preparation of unsaturated poly(ε‐caprolactone) with a new titanium alkoxide initiator

Titanium alkoxides are widely used in the ring‐opening polymerization of ε‐caprolactone. In this study, functional poly(ε‐caprolactone) was synthesized with a new titanium initiator by a two‐step procedure: First, the titanium initiator, with an unsaturated group, was prepared by a classical organic reaction between 2‐hydroxyethylmethacrylate or 2‐allyloxyethanol with titanium tetrapropoxide; then, we initiated the polymerization of the ε‐caprolactone monomer in a glass reactor or twin‐screw extruder. By means of NMR spectroscopy, the structures of the initiators and polymers were determined. When 2‐hydroxyethylmethacrylate was used, there was a side reaction (transesterification) during the preparation of the initiator, and so it was impossible to obtain the expected product. With 2‐allyloxyethanol, the designed titanium initiator was synthesized with high purity, and the allyl moiety remained intact after the polymerization of ε‐caprolactone. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanism and kinetics of transesterification in poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalene dicarboxylate) polymer blends

In a previous work [L. Alexandrova, A. Cabrera, M.A. Hernández, M.J. Cruz, M.J.M. Abadie, O. Manero, D. Likhatchev, Polymer 43 (2002) 5397. [1]], a model compounds study on the kinetics of a transesterification reaction in poly(ethylene terphthalate)-poly(ethylene naphthalene 2,6-dicarboxylate), PET-PEN blends, resulting from melt processing, was simulated using model compounds of ethylene dibenzoate (BEB) and ethylene dinaphthoate (NEN). A first-order kinetics was established under pseudo first-order conditions for both reactants, and thus the overall transesterification reaction was second-order reversible. Direct ester-ester exchange was deduced as a prevailing mechanism for the transesterification reaction under the conditions studied.In this work, the actual PET-PEN system was melt processed by mixing the polymers below the critical reaction temperature in a twin-screw extruder. Thereafter, the reaction was induced by temperature in open glass ampoules. A second order reversible kinetics was measured, in agreement with the kinetics established in the previous model compounds study. The equilibrium constant value corresponds to a forward rate constant which is four times larger than the reverse rate constant. The activation thermodynamic parameters confirmed the direct ester-ester exchange mechanism for the reaction.     

Transesterification in poly(ethylene terephthalate) and poly(ethylene naphthalate 2,6-dicarboxylate) blends: model compounds study

Kinetics of transesterification reaction in poly(ethylene terephthalate)-poly(ethylene naphthalate 2,6-dicarboxylate), PET-PEN, blends resulting from melt processing was simulated using model compounds of ethylene dibenzoate (BEB) and ethylene dinaphthoate (NEN). The exchange reaction between BEB and NEN was followed by ¹H NMR spectroscopy using signals from the aliphatic protons of ethylene glycol moieties at 4.66 and 4.78 ppm, respectively. The first-order kinetics was established under pseudo-first-order conditions for both reactants. Thus, the overall transesterification reaction was second order reversible. The reversibility was confirmed experimentally by heating a mixed sequence of 1-benzoate 2-naphthoate ethylene (BEN) under similar conditions. Both forward reaction of the equimolar amounts of the reagents and reverse reaction came to equilibrium at the same molar ratio of the reactants and reaction products of roughly 0.25:0.50:0.25 for BEB, BEN, and NEN, respectively. The rate equation for the transesterification reaction in the model system was modified using half-concentration of BEN, which is the only effective in the intermolecular exchange. Direct ester-ester exchange was deduced as a prevailing mechanism for the transesterification reaction under the conditions studied, and the values of equilibrium and rate constants, as well as other basic thermodynamic and kinetic parameters were determined. The use of Zn(OAc)₂ as a catalyst resulted in a significant decrease in the activation enthalpy of transesterification, which might be due to the partial switch of the reaction mechanism from primarily pseudo-homolytic to more heterolytic where Zn^II acts as a Lewis base which binds to the ester carbonyl oxygen.     

Modification of poly(ethylene ether carbonate) polyols by transesterification

Poly(ethylene ether carbonate) polyols are the reaction products of alkylene carbonates or alkylene oxides and CO₂ with alcoholic initiators. These polyols can be modified with aliphatic hydroxyl compounds by transesterification reactions. The modifier becomes chemically bound into the polymer during reaction and modifies the properties of the polyol. The extent of reaction is very easy to follow by size exclusion chromatography. Molecular weight is controlled by the molecular weight of the reactants and by their stoichiometry. This transesterification process is compared to the previously described transesterification/advancement process. The transesterification process has the advantage of using milder temperature conditions and runs at ambient pressures. Therefore, modifiers can be used in the transesterification process that are unstable or undergo different chemistry under the reaction conditions of the transesterification/advancement process. Although the modifiers used in the transesterification/advancement process must be less volatile than DEG, more volatile modifiers can be used in the transesterification process. The two processes compliment each other, allowing the preparation of a wide variety of modified poly(ethylene ether carbonate) polyols. These polyols are useful in polyurethane applications.     

Influence of catalyst on transesterification between poly(lactic acid) and polycarbonate under flow field

This paper investigated the effect of catalyst on transesterification and transesterification mechanism between poly(lactic acid) (PLA) and polycarbonate (PC) under flow field. Three catalysts (zinc borate, titanium pigment and tetrabutyl titanate) were evaluated. It is found that transesterification reaction can take place without any catalyst, while three catalysts can all promote the transesterification reaction between poly(lactic acid) and polycarbonate to a greater extent. ¹H nuclear magnetic resonance spectroscopy, gel permeation chromatography and dynamic mechanical analysis revealed that structures of copolymers are not identical in the blends with and without catalyst. For pure blend, most of copolymers have relatively high molecular weight with low PC content, which implies that transesterification reaction most likely happens only once between a PLA chain and a PC chain during mixing process, and only a small amount of multiple reactions happen. However, for the catalyst systems, catalysts induce much more multiple reactions accompanying with the reducing molecular weight in copolymers and increasing PC content. Moreover, it is found that the catalysts not only affect the chain compositions of the product copolymers, but also influence the amount of polymers involved in the reaction. Tetrabutyl titanate is found to be the most effective catalyst in this study where the amount of reacted polycarbonate is more than 4 times of that in pure blend. It is found that PLA segments in copolymer are easily aligned on the interface due to its relatively high Deborah number, which increases the probability of its contact with more PC chains. Although the flow effect on the alignment of chain segment is similar in blends with and without catalysts, the acceleration of reaction due to catalyst makes it possible for multiple reactions. The match of the reaction time and contact time of chain segment of PC and PLA at interfaces is then of key importance in the interfacial transesterification reaction. The effect of flow field on the interfacial reaction is then not only from the interfacial update, but also from the change of chain conformation near the interface.     

Efficient method for recycling poly(ethylene terephthalate) to poly(butylene terephthalate) using transesterification reaction

A method of recycling postconsumer poly(ethylene terephthalate (PET) using transesterification was studied. Shredded flakes of postconsumer PET waste were transesterified with higher diols, such as 1,4‐butanediol, 1,4‐cyclohexane dimethanol, and 1,6‐hexanediol, to yield copolyesters in the presence of Ti(iPrO)₄ and Sb₂O₃ as catalysts. The extent of the formation of undesirable tetrahydrofuran side products was dependent on the molar ratio of PET to1,4‐butanediol and the time of reflux during transesterification. Quantitative insertion of the butylene moiety into PET could be achieved under appropriate reaction conditions. The mechanical properties of PBT obtained by a transesterification reaction of PET with 1,4‐butanediol were comparable to those of virgin PBT (obtained by direct reaction of dimethyl terephathalate with 1,4‐butanediol). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3720–3729, 2004     

Investigation of exchange reactions and rheological response of reactive blends of poly(trimethylene terephthalate) and phenoxy resin

BACKGROUND: Reactive melt blends of poly(trimethylene terephthalate) (PTT) with a phenoxy resin (Ph) are some of the most interesting classes of reactive blends in which different kinds of exchange reactions can occur. This work is devoted to the study of these reactions and their effect on the rheological and morphological properties of the blends. RESULTS: The occurrence of transesterification reactions was confirmed by ¹H NMR analysis. Scanning electron microscopy observations confirmed that all the blends, except PTT/Ph 90/10 (w/w), which exhibits a droplet‐in‐matrix morphology, are homogeneous. At the beginning of transesterification, the melt viscosity of the blends is more influenced by molar mass increasing reactions than by molar mass decreasing ones. After extension of the reaction time and increase in temperature the molar mass reducing reactions become predominant, which results in a reduction of the complex viscosities. CONCLUSION: This work provides new data on the transesterification reactions involving the secondary hydroxyl groups of phenoxy. The properties of PTT/Ph blends are strongly determined by the transesterification reactions, which on the one hand results in the formation of PTT‐grafted phenoxy chains and on the other hand a decrease in the molar mass of non‐bonded PTT. These reactions exert a distinct compatibilizing effect between the blend components. Copyright © 2008 Society of Chemical Industry     

Synthesis of economically viable biodiesel from waste frying oils (WFO)

In present communication, waste frying oil (WFO) has been used as a feedstock for biodiesel synthesis. WFO, procured from a local Indian restaurant possessed an acid value of 0.84 mg KOH/g, which is low enough for single step transesterification reaction. Biodiesel (fatty acid methyl esters) was washed after transesterification reaction and the yield got lowered substantially (from 96% to 86.36%) after water washing owing to loss of esters. 30:100 vol% (methanol to oil), 0.6 wt% NaOCH₃, 60°C temperature and 600 rpm agitation in 1 h reaction time was found to be optimum for transesterification reaction. ¹H NMR spectrum showed a high conversion (95.19%) of fatty acids in WFO to biodiesel in 2 h reaction time. Almost complete conversion (99.68%) was attained in 2 h reaction time. © 2011 Canadian Society for Chemical Engineering     

碳酸二甲酯和乙酸苯酯合成碳酸二苯酯催化剂研究进展

综述了碳酸二甲酯和乙酸苯酯合成碳酸二苯酯工艺路线及其反应机理,并对该反应的催化剂体系进行了系统的概述,包括均相催化剂体系(锡和钛的有机化合物等)和多相催化剂体系(MoO3和WO3等金属氧化物)。并分析了以锡、钛以及金属氧化物作催化剂时合成碳酸二苯酯的优势和劣势;指出固载化的有机锡/有机钛与其他金属氧化物的复合化合物是今后碳酸二甲酯和乙酸苯酯合成碳酸二苯酯催化剂的重要研究方向。     

PET/PBT共混过程中酯交换反应的~(13)CNMR研究

用13C NM R 考察了添加扩链剂进行反应性共混后PET/PBT 的结构变化。在共混初期,检测不到嵌段共聚物的存在,可能与其含量极少有关。随着共混时间的增加,开始出现酯交换反应,且酯交换度随共混时间和温度而增加。扩链剂的加入能促进酯交换反应,但扩链剂的用量对酯交换的影响并不大     

Review on transesterification in polycarbonate–poly(butylene terephthalate) blend

Various polycarbonate - poly(butylene terephthalate) polyester (PC-PBT) blend prepared by reactive melt blending primarily in extruder with range of temperature and time are discussed in this review article. In the melt blended PC-PBT blend system, transesterification plays a major role in formation of PC-PBT blend. Transesterification reactions between these two polymers have been analyzed by proper polymer sample, end-capped or having reactive chain end group. The kinetics of mechanism is a function of temperature and PC-PBT ratio. Trace catalyst residue present in PBT catalyzes the transesterification reaction. As the extent of transesterification is increased, it forms various composition of copolymer. Inhibition in the transesterification reaction of PC-PBT blend has been observed when different type of alkyl, aryl, and alkyl-aryl group of phosphite are introduced into it, otherwise there has been collateral change in the morphology, thermal, and mechanical property of blend. Therefore, this PC-PBT blend has been an interesting topic of research in academia and industries.     

STUDIES OF TRANSESTERIFICATION OF KARANJA (Pongamia pinnata) OIL IN A PACKED BED REACTOR

Studies were made to determine the influence of different reaction temperatures and residence times on biodiesel yield by transesterification of karanja oil (Pongamia pinnata) in the presence of methanol using a solid acid heterogeneous catalyst in a continuous process. Recycle runs were conducted by further transesterification of the organic phases (first run mixture of methyl ester and unconverted oil) in the presence of methanol under similar conditions. High-pressure liquid chromatography (HPLC) reveals poor biodiesel yield even with an increase in the reaction temperature and residence time in the first run. Biodiesel yield obtained from the recycle runs, however, was greatly increased over that of the first-run biodiesel yield. Recycle transesterification at a reaction temperature of 240°C and residence time of 50 min gives a maximum yield value of 97.74%. Consequently, irrespective of the presence of high free fatty acids and other impurities in karanja oil, recycling the organic phase of the first run significantly enhances the biodiesel yield.     

Stable Organic Titanium Catalysts and Reactive Distillation Used for the Transesterification of Dimethyl Carbonate with Phenol

The transesterification of dimethyl carbonate with phenol to methyl phenyl carbonate (MPC) was investigated on novel catalysts such as titanium diisopropoxide bis(ethyl acetoacetate) and titanium dibutoxide bis(ethyl acetoacetate) in a closed batch reactor at 185–206 °C under high pressure. The produced methanol could be removed efficiently by reactive distillation in order to overcome the equilibrium. The prepared catalysts have higher resistance to water than titanium alkoxides. Phenol conversion as high as 86.4 % with an MPC selectivity of 99.4 % was achieved under optimal reaction conditions within 9 h. Most of the catalytic activity was retained after repeated use for ten times.     

Partly alcoholized poly(vinyl acetate) polymers: kinetics of formation and reaction with iodine

Methoxide-catalysed transesterification of poly(vinyl acetate) with methanol was examined kinetically. Polymer specimens were isolated at various stages of hydrolysis and the extent of their colourimetric reaction with iodine determined. Polymers with up to 60 mol % degree of hydrolysis can be prepared reproducibly by careful kinetic control of the reaction conditions. The analytical sensitivity for formation of the red I₂-PVA complex was consistent with a developing hydroxyl group block structure as transesterification proceeds.     

醇交换反应催化剂的研究与应用

对醇交换反应中使用的催化剂进行了评述,介绍了碱或碱金属化合物、L酸、有机金属化合物的均相催化剂和SiO₂、Al₂O₃为载体的金属氧化物及分子筛的非均相催化剂的研究与应用。认为开发有机锡和有机钛类固载化催化剂是醇交换反应催化剂研究的重要方向。     

Transesterification reactions in triphenyl phosphite additivated‐poly(ethylene terephthalate)/poly(ethylene naphthalate) blends

The occurrence of transesterification reactions in poly(ethylene terephthalate) (PET)/poly(ethylene naphthalate) (PEN) blends prepared in presence of triphenyl phosphite (TPP) was investigated. When PEN was processed with TPP, which is a known chain extender for PET, chain extension reactions also took place. Torqueprocessing time curves obtained during preparation of 75/25 PET/PEN blends containing TPP, showed a build‐up profile followed by a fast decrease that was interpreted as chain extension between blend components and degradation due to phosphite residues formation, respectively. Although transesterification inhibition was expected, this type of reaction was not suppressed by TPP.     

Eco-friendly protective coatings based on poly(urethane sulfone amide) dispersions for carbon steel

Eight eco-friendly protective coatings (PU, PUA1, PUA3, PUA5, T30PUA5, T60PUA5, T90PUA5, and T120PUA5), were formulated based on series of laboratory-synthesized poly(urethane co-sulfone amide) copolymer dispersions (CPDs) as binders. The first four formulations were based on CPDs prepared by the copolymerization reaction of PU based on castor oil (CO) with aromatic polyamide sulfone (APAS) in four different concentrations (0%, 1%, 3%, and 5% solid to solid). The other four formulations were based on CPDs synthesized by the copolymerization reaction of PU based on transesterified CO with triethanolamine (CON) at different time intervals (30, 60, 90, and 120 min) with APAS at only one concentration. The effect of the degree of copolymerization and transesterification reactions on the physical, chemical, and mechanical properties of the formulated coatings was studied. The results showed that the copolymerization and transesterification reactions led to an increase in the density and viscosity of the coating formulations. Additionally, the hardness of the dried films increased with copolymerization and transesterification reactions. The transesterification reaction decreased the adhesion force of the coated films. The copolymerization process caused a decrease in the water uptake of the coated films. However, the transesterification reaction increased the water uptake. The prepared formulations were applied on carbon steel substrates to estimate their efficiency as eco-friendly protective coatings for steel. The weight loss of the coated steel panels decreased with an increase in the amount of the copolymerized APAS within the PU chains, while it increased with an increase in the transesterification time of the CON used in the preparation of the coated copolymers. From the corrosion test results, PUA5 and T30PUA5 showed the best anticorrosive performance as estimated from the degree of rusting, weight loss measurements, and failure at scribe.     

Studies on the formation of poly(ethylene terephthalate): 2. Rate of transesterification of dimethyl terephthalate with ethylene glycol

The transesterification of dimethyl terephthalate (DMT) with ethylene glycol (EG) was kinetically investigated in the presence of various catalysts at 197°C. The reaction was followed by the measurement of the quantity of methanol which distilled from the reaction vessel. This distillation made corrections of reactant and catalyst concentrations necessary. The transesterification was assumed to obey first-order kinetics with respect to DMT and EG, and a rate equation was derived. The reaction was found to be first order in catalyst concentration as well and when this finding was incorporated in the rate equation, excellent agreement between the observed and calculated values was recognized throughout the reaction. The first-order dependence on the catalyst concentration is valid below a critical concentration which was found to be dependent on the catalyst type. Above this concentration a lower reaction order was observed.     

The General Applicability of in Situ Transesterification for the Production of Fatty Acid Esters from a Variety of Feedstocks

We previously described a method for fatty acid methyl ester (FAME) production wherein acylglycerol transesterification was achieved by reacting flaked full fat soybeans with alkaline methanol to create a product that met ASTM specifications for biodiesel. In the present work we explore the general applicability of this approach, termed in situ transesterification, to feedstocks other than soybeans. Materials investigated were distillers dried grains with solubles (DDGS), which is a co-product of the production of ethanol from corn, and meat and bone meal (MBM), a product of animal rendering. For both feedstocks, reaction conditions giving maximum lipid transesterification were predicted by statistical experimental design and response surface regression analysis, and then verified experimentally. Successful transesterification was achieved at ambient pressure and 35 °C. For DDGS, partial drying markedly reduced the methanol requirement to achieve a high degree (91.1% of maximum theoretical) of transesterification. Elevated reaction temperatures (to 55 °C was explored) caused little or no shortening of the time to completion. Protein was not removed from the DDGS during this treatment. For MBM, drying was not required to achieve a high degree (93.3%) of transesterification. The remaining meal retained approximately 90% of the protein originally present. Coupled with the previous work with soybeans, the data presented here indicate that in situ transesterification is generally applicable to lipid-bearing materials, which could substantially increase the supply of biodiesel. Mention of brand or firm names does not constitute an endorsement by the US Department of Agriculture over others of a similar nature not mentioned.     

Transesterifications of poly(bisphenol A carbonate) with aromatic and aliphatic segments in ethylene terephthalate–caprolactone copolyester

In this article, transesterification of poly(bisphenol A carbonate) (PC) with a ethylene terephthalate–caprolactone copolyester at a weight ratio 50/50 (TCL50) was investigated by infrared spectroscopy (IR), proton nuclear magnetic resonance spectroscopy (¹H‐NMR), and a model compound. The IR and ¹H‐NMR results showed that transesterification occurred between PC and ethylene terephthalate (ET) segments in TCL50 and resulted in the formation of bisphenol A–terephthalate ester units as in the annealed blend of PC with the PET homopolyester. By comparison with a model compound, the new signal at 2.55 ppm in the ¹H‐NMR spectrum confirmed the appearance of bisphenol A–caprolactone ester units resulting from the exchange reaction of PC with caprolactone (CL) segments. The ¹H‐NMR analysis of the transesterification rates revealed that the reactions of PC with aromatic and aliphatic segments in TCL50 proceeded in a random or free manner. In addition, we separately examined the interchange reaction between a PC and poly(ε‐caprolactone) (PCL) homopolyester in an annealed blend. It was found that in the presence of a Ti compound catalyst the predominant reaction was a transesterification rather than a thermooxidative branching reaction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1558–1565, 2001