When melt‐extruded in the presence of triphenylphosphite (TPP), the molecular weight of polyesters such as poly(ethylene terephthalate) (PET) increases with time. Analysis of the PET chain end groups and model studies of high‐temperature reactions indicate that, most likely, the process leading to chain extension of PET in the presence of TPP takes place in two steps. In the first step, TPP rapidly reacts with the hydroxyl end groups by displacing one phenoxy group from the TPP. In the second step, a slow reaction takes place between the alkyldiphenyl phosphite and carboxylic chain end groups, forming an ester bond between the carboxyl and alkyl groups, and producing diphenylphosphite (DPP) as a reaction by‐product. The DPP tautomerizes to its pentacovalently bonded stabler form of diphenylphosphate, the form in which the DPP was usually detected in our analyses. The ester formation results in the extension of the PET chains. Model studies are presented which support the proposed mechanism.

The redox chemistry of a model compound of polyaniline, N,N'-diphenyl-p-phenylenediamine, has been studied in acidic media. The redox processes of this "dimer" have been shown to be highly reversible and pH-dependent. The dimer undergoes a two-step oxidation from amine to radical cation to imine forms. An equilibrium constant was determined for the conversion of a 50:50 mixture of amine and imine forms to the radical cation as a function of proton concentration. A 50% conversion to the radical form occurs at a pH of 2.2. This pH value corresponds very well with the midpoint of the metal-to-insulator transition in polyaniline as a function of pH. ESR measurements were used to study the radical cation in solution. Spin density was found to be highest on the nitrogens, but considerable delocalization into central and end phenyls was found.There is a current resurgence of interest in the polymer known as polyaniline. The reversible redox chemistry, high charge storage capacity, good environmental stability (1, 2), and electrochemical properties (3) have been an incentive for many studies concerning its ability to function as an electrode in various applications. The synthesis of polyaniline involves the chemical (4) or electrochemical (5) oxidation of aniline in aqueous media and results in the production of highly conducting salts. When this material is undoped by reaction with a Bronsted base, a material composed of N-phenyl-p-phenylenediamine and Nphenyl-p-benzoquinonediimine units results (4, 6). This form can be most simply called poly(p-phenyleneamineimine) and is often called polyemeraldine base. It can be written asThe redox chemistry of polyaniline is complicated by a myriad of possible structures, especially in aqueous media where protonation and deprotonation occur in concert with electrochemical oxidation and reduction. Ambiguity about the role of protons in the successive redox reactions of polyaniline has resulted, due in part to uncertainty about the degree of protonation of the various intermediates.The most interesting property of polyaniline is its ability to undergo an insulator-to-metal transition as a function of the concentration of a Bronsted acid in the surrounding electrolyte without net oxidation or reduction of the polymer backbone (2b, 7). Another interesting property is the reversible loss of conductivity in acidic media as the electrochemical potential is swept to high values [greater than about 0.4V vs. standard calomel electrode (SCE)] (8). These considerations prompted us to undertake a study of model polyaniline compounds which could be unequivocally characterized in various stages of oxidation in contrast to the intractable polymer. We have previously reported results of a study of a phenyl-end-capped "tetramer" of polyaniline, [4-(phenylamino)phenyl]-l-4-benzenediamine (II). We obtained large single-crystal charge-transfer complexes (III) (9a), which enabled us to make a complete structure determination. Electron density mapping fixed the exact chemical composition and degree of pr...

Reaction of 1-phenyl-4-mono-or disubstituted thiosemicarbazides with platinum(I1,IV) salts affords the diamagnetic intensely colored neutral complexes Pt(C6Hb,R,R'-atf)s (8, R = R' = CH3; R = H, R' = CeH5, tert-CaH~). The nature of these complexes has been elucidated by a combination of electrochemical, epr, and electronic spectral studies. They have been shown to be the central members of five-membered electron transfer series Pt(C8Ha,R,R'-atf)zz whose component species (z = 2 --, 1--, 0, 1+, 2 + ) are interrelated by one-electron-transfer reactions. Polarographic half-wave potentials in acetonitrile solution occur in the range of ca. -1.2 to +0.8 V vs. sce. Cyclic voltammetric studies of the Pt(CaH5,tert-C4Ho-atf)gz series indicate reversible behavior for the processes 2 -1 -, 1t 0, and 0 * 1+ a t scan rates of 0.1-10 V/sec. Electronic spectra of all five members of this series are reported together with epr data for the spin-doublet z = 1 -, 1 + members of all three series This study provides a detailed demonstration of the validity of the electron-transfer series concept as applied to planar complexes containing unsaturated five-membered chelate rings.

The EPR spectra of Cr3+ in single crystals of alexandrite (Al2−xCrxBeO4, x<0.01) have been obtained at temperatures between RT and 4.2 K in the frequency range 9.5–9.1 GHz. The orthorhombic structure of Al2BeO4 has two distinct Al3+ sites in the unit cell corresponding to Cs and Ci symmetry. The EPR spectra at 35 GHz of Cr3+ in the Cs site have been previously analyzed by other investigators. This study reports the observation of Cr3+ in the Ci site and the refined spin-Hamiltonian parameters for both magnetic centers. The absolute sign of the fine structure tensor elements for the Ci site has been determined to be positive. The observed orientations of both the chromium mirror and inversion magnetic axes are consistent with the crystallographic symmetry relationships of pure Al2BeO4. A comparison of the measured Cr3+ EPR intensities for resonances from both sites indicates that for two magnetically dilute crystals, the mirror site is preferentially occupied with a relative site occupancy of 78%±3%.

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