Dimethyl terephthalate studies with

Energy Transfer Studies with Dimethyl Terephthalate (DMT) and 4,4 -BPDC. Several attempts were made to determine if energy transfer could occur from an excited DMT molecule to a 4,4 -BPDC molecule in a rigid ethanol glass at 77°K. These studies were accomplished by adding various amounts (20 - 50 mole percent) 4,4 -BPDC to a known concentration (5.0 x 10"4 M) of DMT. The change in emission intensity at 418 nm, which is exclusively emission from DMT, was then measured with excitation at 298 nm. 

The studies carried out on the alcohol distillate obtained from the co-transesterification of dimethyl terephthalate with ethylene glycol in the presence of the sodium salt of diethyl phosphite or the di-sodium salt of 1,2-dicarbomethoxyethylphosphonic acid in various concentrations showed (Table I) that the side reactions were markedly suppressed. 

With the advances in experimental solid-state NMR and computational resources (both software and computing power), it is now possible to use both the experimental and computational results (sometimes in a complementary way) to study biologically important macromolecules such as proteins. The quantum-chemical computation (particularly by density functional theory) of NMR parameters in solids has found important application in protein structure determination.30-36 Tesche and Haeberlen37 calculated the proton chemical shift tensor of the methyl groups in dimethyl terephthalate and found the theoretical results were in good agreement with the multiple pulse experiment. 

As far as quantitative chemical derivatization GC analysis is concerned, it is necessary to mention especially the work of Gehrke and his collaborators, who specified the fundamental concepts of quantitative GC analysis combined with the chemical derivatization of sample compounds and applied them to the accurate determination of the twenty natural protein amino acids and other non-protein amino acids as their N-TFA-n-butyl esters [5 ], the urinary excretion level of methylated nucleic acid bases as their TMS derivatives [6], TMS nucleosides [7] and other investigations. Further examples include a computer program for processing the quantitative GC data obtained for seventeen triglyceride fatty acids after their transesterification by 2 NKOH in n-butanol [8], a study of the kinetics of the transesterification reactions of dimethyl terephthalate with ethylene glycol [9] and the GC-MS determination of chlorophenols in spent bleach liquors after isolation of the chlorophenols by a multi-step extraction, purification of the final extract by HPLC and derivatization with diazoethane [10]. 

All these plastics are essentially the same compound, composed of terephthalic acid (para-phthalic acid) esterified with ethylene glycol. This polyester is made by a base-catalyzed transesterification of dimethyl terephthalate with ethylene glycol at a temperature around 150 °C. At this temperature, methanol escapes as a gas, driving the reaction to completion. We will study polyesters and other polymers in more detail in Chapter 26. 

Voltammetric data for ester reductions are available for several aromatic esters [51-54], and in particular cyclic voltammetry shows clearly that in the absence of proton donors reversible formation of anion radical occurs [51]. In dimethylfonnamide (DMF) solution the peak potential for reduction of methyl benzoate is —2.29 V (versus SCE) for comparison dimethyl terephthalate reduces at —1.68 V and phthalic anhydride at —1.25 V [4]. Half-wave potentials for reduction of aromatic carboxylate esters in an unbuffered solution of pH 7.2 are linearly correlated with cr values [51] electron-withdrawing substituents in the ring or alkoxy group shift Ei/o toward less negative potentials. Generally, esters seem to be more easily reducible than the parent carboxylic acids. Anion radicals of methyl, ethyl, and isopropyl benzoate have been detected by electron paramagnetic resonance (epr) spectroscopy upon cathodic reduction of these esters in acetonitrile-tetrapro-pylammonium perchlorate [52]. The anion radicals of several anhydrides, including phthalic anhydride, have similarly been studied [55]. 

PIT is a semicrystalline polymer synthesized by the condensation of PDO with either terephthalic acid or dimethyl terephthalate, followed by polymerization. Studies of PTT had never gone beyond academic interest until recent years because one of its raw materials, PDO, was very expensive and available only in a small volume. PTT received less attention compared with PET and PBT. However, recent breakthroughs in PDO synthesis made PTT available in industrial quantities, thus offering new opportunities in carpet, textile, film, packing, and engineering thermoplastics markets. 

The PTT is aromatic polyester prepared by the melt polycondensation of 1,3-propanediol (1,3-PDO) with either TPA or dimethyl terephthalate (DMT). The PTT is synthesized by the transesterification of propanediol with dimethylene terephthalate or by the esterification of propane diol with TPA. The reaction is carried out in the presence of hot catalyst like titanimn butoxide (Ti(OBu) ) and dibutyl tin oxide (DBTO) at a temperature of 260°C. The important by-products of this reaction include acrolien and allyl alcohol (Chuah, 2001). Direct esterification of propane diol and TPA is considered as the least economic and industrial method. The reaction is carried out in the presence of a heel imder a pressure of 70-150 kPa at a temperature of 260°C. The heel is usually referred to the added PTT oligomers which act as a reaction mediiun and increase the solubility of TPA (Chuah, 2001). Recent studies by different groups show that the selection of the catalyst plays a major role on the reaction rate and PTT properties. Commonly used catalysts like titanium (Doerr et al., 1994), tin (Kurian and Liang, 2001 Fritz et al., 1969) and antimony (Karayannidis et al., 2003 Fitz et al., 2000) compounds have their own limitations. Titanimn-based catalysts are active but the PTT is discolored, antimony-based catalysts are toxic and only active in polycondensation while tin-based compounds have lower catalytic activity. Karayannidis and co-workers (2003) reported the use of stannous oetoate ([CHj(CH2)3CH(C2Hj)COO]jSn) as the catalyst for PTT synthesis but its catalytic activity is poor, resulting in a low molecular weight PTT which was confirmed... 

The blends of aliphatic-aromatic copolyesters synthesized from dimethyl succinate, dimethyl terephthalate and butanediol with starch was studied by soil burial [141]. Blends of copofyes-ters with starch posssessed higher degradation rate but lower tensile strength as compared with unfilled copofyesters. 

In single layer devices the low efficiency frequently is due to the imbalance of electrons and holes. Inserting a hole-transport (electron-blocking) or electron transport (hole-blocking) layer provides a means to enhance minority carriers and block the majority carriers and confine them to the emitter layer, which increases the probability of recombination. Poly(N-vinylcarbazole) (PVK) has been used as a hole transport layer and occasionally in blends with the emitter polymer. PVK is a well-studied photo-conductive polymer which often forms exciplexes with organic molecules, e.g., dimethyl terephthalate. An exciplex is a transient donor-acceptor complex between the excited state of the donor and the ground state of the acceptor. ... 

Investigation of template poly condensation kinetics has only been studied within a very narrow scope. Polymerization of dimethyl tartrate with hexamethylene diamine was found to be enhanced by using as a template poly(vinyl pyrrolidone), poly(2-vinyl pyridine), or polysaccharides and poly(vinyl alcohol), poly(4-vinyl pyridine). In this case, the template can be treated as a catalyst. No information exists on the influence of the template on the order of reaction. The increase in molecular weight of the polymerization product by the template can be induced by a shift of equilibrium or by an increase in the reaction rate. A similar increase in the reaction rate was observed when poly(4-vi-nyl pyridine) was used in the synthesis of poly(terephtalamides) activated by triphenyl phosphite.The authors suggested that a high molecular weight template was involved in the increase of the local concentration of the substrate (terephthalic acid) by adsorption and activation via N-phosphonium salt of poly(4- vinyl pyridine). 

After having studied in our laboratory, polymer blends of amorphous polymers poly-c-caprolactone and poly (vinyl chloride) (1,2) (PCL/ PVC), blends with a crystalline component PCL/PVC (3,4), poly(2,6-dimethyl phenylene oxide) (PPO) with isotactic polystyrene (i-PS) (5) and atactic polystyrene (a-PS) with i-PS (6), we have now become involved in the study of a blend in which both polymers crystallize. The system chosen is the poly(1,4-butylene terephthalate)/poly(ethylene terephthalate) (PBT/PET) blend. The crystallization behavior of PBT has been studied extensively in our laboratory (7,8) this polymer has a... 

The information drawn from polarizability and polarization studies seems, in general, to compare reasonably with that from other physical methods, if the natures of these methods are borne in mind. The techniques of X-ray, neutron and electron diffraction and microwave spectroscopy provide metrical structural details of the highest precision relating to the crystalline or gaseous states flexible molecules in solution may be expected to adopt conformations between the extremes found in the states mentioned. Thus dimethyl oxalate, diethyl terephthalate, 1,2-dibromoethane, and 1,4-dimethoxybenzene all exhibit dipole moments as solutes, but nevertheless assume trans—and therefore nonpolar—forms in their solid phases (cf. Chemical Society Tables, 1958). Accordingly it is difficult to assess the correctness of the findings summarized in Table 23 when available, results secured in other ways have been quoted in the papers cited. 

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