Polycondensation catalysts

Lewis acid-free catalysts for acyclic diene metathesis obviate the formation of carbocations, which in turn completely eliminates competing reactions, mostly involving cationic oligomerisation via 1-alkene bonds. Thus, metathesis polycondensation occurs quantitatively to yield high molecular weight poly(l-alke-nylenejs with vinyl end groups and ethylene as a byproduct. 

Efficient catalysts capable of promoting metathesis condensation polymerisation are based on tungsten, molybdenum and ruthenium complexes [1]. Usually, the Schrock alkylidenes, especially their tungsten version, which have been shown to be the fastest metathesis polycondensation catalysts known to date, are employed [14,18-21,24,25]  

It should be noted that these catalysts ensure rapid conversions of any type of monomer susceptible to metathesis polycondensation, even of heteroatom-containing (functionalised) a,co-dienes [1]. 

The ruthenium-based catalyst provided by Grubbs et al. [19] also promotes acyclic diene metathesis polycondensation, although with higher concentrations being required to achieve reasonable reaction rates [24,25]  

Ruthenium-based catalysts are relatively easy to synthesise and are tolerant of alcohol functionality in the acyclic diene monomer [26]. 

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Starting with DMT, methanol is removed from the reaction starting with TA, water is removed. Catalysts ate used to transesterrfy DMT but not for direct esterification of TA. The second step is the polycondensation reaction which is driven by removing glycol. A polycondensation catalyst is used. 

A PEIT of 50/50 (molar ratio) composition is synthesized by a two-step reaction sequence as follows. In the first step, 97.10 g (0.5 mol) dimethyl terephthalate (DMT), 97.10 g (0.5 mol) dimethyl isophthalate (DMI), 136.55 g (2.2 mol) 1,2-ethanediol, and zinc acetate dihydrate ester interchange catalyst (2.7 x 10 4% mass of the total amount of DMI and DMT mixture) are weighed into a threenecked flask fitted with a mechanical stirrer, a nitrogen inlet, and a condenser. The medium is stirred for 2.0-2.5 h at 180-210°C under nitrogen. Ninety-two percent of the theoretical amount of methanol is removed by distillation. In the second step, antimony acetate polycondensation catalyst and trimethyl phosphate thermal stabilizer (9.9 x 10-4 and 1.5 x 10 3% mass of the total amount of DMI... 

With values between 13 and 16, the equilibrium constant is still high enough to regard the formation of DEG from EG to be irreversible in an open industrial system. DEG formation is not only an important side reaction during esterification, polycondensation and glycolysis, but also during distillation of EG and water in the process columns. In particular, the residence time in the bottom reboiler of the last separation column is critical, where the polycondensation catalyst and... 

The esterification of TPA is catalyzed by protons and in standard industrial operations neither an additional esterification catalyst nor a polycondensation catalyst is added to the esterification reactor. Some new antimony-free polycondensation catalysts [125-128] also affect the speed of esterification significantly and it could be advantageous to add them directly into the slurry preparation vessel. Co-monomers, which should be randomly incorporated into the polymer chains, are usually fed into the slurry preparation vessel. How and when additives, catalysts, colorants and co-monomers are added influences the overall reaction rate and therefore affects the product quality. 

Cannon, K. C., Seshadri, S. R. and Dirkx, R. R., Preparation of polyesters using lithium titanyl oxalate polycondensation catalysts, EP Patent EP 0 970 983 A2 (2000). 

For the polymerization, either in the melt or solid phase, the reaction is driven to the polymer by removing ethylene glycol. The polymerization reaction is typically catalyzed by solutions consisting of antimony trioxide or germanium oxide. Both polycondensation catalysts also catalyze the reverse reaction, which is driven by an excess of ethylene glycol at melt conditions, generally above 255 °C. The polymerization reaction follows second-order kinetics with an activation energy of 22 000 cal/mol [6],... 

Polymer was prepared as follows. Bis (/3-hydroxyethyl) terephthalate (4/14 mole) reacted with terephthalic acid (TA) (3/14 mole) at 275°C using Sb203 as polycondensation catalyst. To the resulting polymer ([17] 0.41, COOH content 51.3 eq/10 g, and diethylene glycol content 0.60 mole %/TA) was added POC, followed by 15 minutes at high vacuum. 

Once the transesterification step is complete, the metal salt is always deactivated by complexation with a phosphate or phosphite compound [18], preventing unwanted side reactions as the reaction temperature is increased during polycondensation. Such side reactions lead to polymer chain scission and loss of molecular weight, as well as development of unwanted discoloration of the polymer. Care has to be taken that excess phosphorous compounds are not added to the reaction, as these compounds can significantly reduce the effectiveness of the polycondensation catalyst. 

With the help of DTA method effect of interesterification and polycondensation catalysts on PETP stability at thermooxidation [214] has been studied. Thermooxidative destruction is accelerated by the presence of metal catalysts. 

Uses Esteritication/transesteritication/polycondensation catalyst for prep, of polyesters, unsat. polyesters, alkyds suitable for food and pharmaceutical contact applies., such as coatings, epoxies, hybrid resins food pkg. adhesives, closures with sealing gaskets for food containers food-contact oaDer/oaDerboard... 

Fitz, H. and Kalle, A. G. Process for the Manufacture of a Linear Polyester Using Stannous Oxalate as a Polycondensation Catalyst US Patent 3,425,994, February 4, 1%9. 

Nakajima, T, and Tsukamoto, K. (2005) Polycondensation catalysts with high catalytic activity for preparation of heat-resistant polyesters with decreased foreign matter content, JP 2005023160, Jpn. Kokai Tokkyo Koho,... 

Kim et al. [19] fabricated PET/clay composites using a two-step in-situ polymerization method. In the first step, a slurry mixture of monomer (purified tereph-thalic acid and ethylene glycol), polycondensation catalyst, clays, and some additives was kept at 250 °C for 5-6h in the esterification step. Then, it was transferred to a polycondensation reactor until the intrinsic viscosity (IV) value reached 0.6dlg" . Then, the materials were pelletized. Furthermore, a solid-state polymerization (SSP) process is carried out to conduct the polymerization process further. SSP was carried out at between 220 and 145 °C for around 8h until the IV reached 0.8dlg . ... 

Catalysts, such as manganese, zinc, calcium, cobalt, and titanium, have been widely used as effective ester-exchange catalysts. Polycondensation catalysts, such as antimony, are commonly employed. Phosphorus compoimds can be added to increase the thermal stability of the finished resin. 

Jabarin [31] in his study of isothermal crystallization kinetics of PET samples received from different manufacturers observed that molecular weight and polycondensation catalyst affect the crystallization mechanism and crystallization rate. 

The transesterification step can last 3 to 4 h, so that 90 to 95% of the theoretical methanol amount is liberated (about 330 kg methanol per 1000 kg DMT). The reaction product formed contains 40% BHET, 30% dimer, and 30% oligomers with low molecular weight [2]. When the transesterification step is over, excess EG is distilled at 220 to 245°C and then polycondensation catalyst is introduced (in the form of EG solution) along with other additives. Some metal oxides (TiOz, SbOj, or GeOj) are used as polycondensation catalysts. The use of a Bronsted acid (H2SO4) as the catalyst diminishes the oligomer content in the polymer [3]. 

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