A study of the microstructure of the copolyesters formed in the exchange reactions which occur during the melt mixing of polyethylene adipate) (PEA) and polyethylene terephthalate) (PET) is reported. A PET sample stripped of the low molecular weight oligomers was melt-mixed with an equimolar amount of an PEA sample, and the exchange kinetics at 290 °C was followed by analyzing the reaction mixture by NMR and FAB-MS. Mass spectra of partially aminolyzed melt-mixed samples were also examined. The copolyester initially formed in the exchange reaction proved to be a block copolymer containing an excess of EA units, as expected for a reaction proceeding by the attack of PEA on the PET chains. In the later stages of the exchange reaction, the copolyester microstructure was observed to approach a Bernoullian distribution and equimolar composition. The determination of the composition and microstructure of the copolyesters formed was attempted by NMR and mass spectra of the melt-mixed samples. This proved to be a difficult task by 200-MHz NMR spectroscopy, since only dyads were detected here because of the large repeating units in the copolymer. Instead, the FAB mass spectra showed series of oligomers up to the octamers, and the composition and microstructure of the copolyesters was monitored by applying some methods of statistical modeling of mass spectra of copolymers.

A covalently assembled monolayer of 61-(p-hydroxyphenylmethano)fullerene [C60] molecules has been synthesized. Both static and dynamic contact angle measurements show that the hydrophobic character increases upon the fullerene linkage. Atomic force microscopy lithography shows that the depth of the monolayer is about 19 Å. UV−vis spectra are well-tuned with the presence of the fullerene on the silica surfaces. The surface atomic composition, investigated by angle-resolved X-ray photoelectron spectra, shows a monotonic increase of the carbon signal upon decreasing the photoelectron takeoff angles, thus confirming the upper layer nature of this signal. Room-temperature photoluminescence spectra, under controlled atmosphere, show that the oxygen presence influences considerably the luminescence quantum yield.

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and CONCETTO PUGLISI, DANIELE VITALINI, Istituto per la Chimica e la Tecnologia dei Materiuli Polimerici, Consigh Nazion.uk deUe Ricerche, Viak A. Doria, 6-95125 Cataniu, Italy, and S . CUCINELLA, Enichern SPA.-Sun Donuto Milanese, 20100 Milam, Italy synopsisThe mechanism of action of aromatic sulfonates as flame retardant (FR) agents on poly(bisphenol-A carbonate) (PC) has been investigated. These compounds are capable of inducing a self-extinguence in PC even when present in very low amounts (0.2-1%). Thermogravimetric and flash pyrolysis-GC-M!3 data show the thermal degradation rate of PC enhanced, and the distribution of the volatile pyrolysis products was modified by these additives. Oxygen Index (01) and Nitrous Oxide Index (NOI) measurements indicate a FR condensed-phase mechanism of these additives. Traces of polymer surface temperature against time, measured under forced flame conditions, show that the expanded carbon layer formed in the combustion of polycarbonatearomatic d f o n a t e blends produces a heat insulating effect toward the undecomposed bulk. The overall evidence leads us to conclude that aromatic sulfonates cause the flame extinguishment in polycarbonate by an intumescent phenomenon.

SynopsisThe thermal decomposition products that evolve from poly(viny1 chloride) (PVC), poly(viny1 bromide) (PVB), poly(viny1 alcohol) (PVA), and poly(viny1 acetate) (PVAc) were analyzed by direct pyrolysis in the ion source of a mass spectrometer (MS). Our results indicate that in both stages of the decomposition process which occurred in the four vinyl polymers investigated several aromatic hydrocarbons were produced and that the relative amounts of benzene, napthalene, and anthracene were different in the two stages. This previously unreported information determines in a single scheme the thermal behavior of the title compounds.

A new method for the determination of reliable molecular weight averages (MW) and polydispersity index (MWD) values for polydisperse polymers, directly analyzing their matrix-assisted laser/desorption ionization time-of-flight (MALDI-TOF) mass spectra, is reported. Our success is due to the concerted effect of an off-line procedure of MALDI-TOF spectrum processing that includes: (i) signal smoothing to improve the recorded traces of the spectra up to high m/z values; (ii) a subtraction of the misleading contribution to the signals introduced by the offset used in spectrum recording; (iii) examination of the spectrqup to the highest possible m/z value for a better accuracy in estimating the MW values. To illustrate this method, three polymers with a wide polydispersity index, a polydimethylsiloxane, a polymethylmethacrylate, and a bisphenol-A copolyether, have been analyzed. Contrary to the general opinion that MW values can be measured directly by MALDI-TOF only for polymers with a very narrow mass distribution, the data reported here show that our off-line procedure is also able to measure reliable MW values for polydisperse materials.The soft ionization which occurs in matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry allows the detection of very large molecules, even if they are in a complex mixture.'-'' In polymer analysis, the MALDI technique may be used for the direct determination of the polymer structure by the identification of mass-resolved macromolecules including oligomers and terminal groups."-'4 In this field, the prospect of a simultaneous measurement of molecular weight averages (MW) and molecular weight dispersion (MWD) has attracted the interest of polymer scientists. However, for this purpose, the MALDI technique, originally developed for proteins,', has shown serious limitations up to the present time.Several authors have found that MW values provided by MALDI-TOF agree with those obtained by conventional tools (viscosity, gel-permeation chromatography (GPC), laser light scattering) only in the case of polymer samples with narrow MWD (< 1.2>,'. '*-I7 whereas with polydisperse polymers MALDI fails to yield reliable MW estimate^.'^-^' It has been suggested that MALDI underestimates the higher molecular weight species so that, as the polydispersity index of the sample increases, the measured MW values become much lower than those obtained by other methods2 ' Recently, in an attempt to solve this problem, MW and MWD values of polydisperse polymers such as dextrans, polyesters and polysiloxanes, were determined using MALDI as a detector for GPC.'2.'7.2' According to this procedure, during the GPC experiment, several fractions of the polymer solution eluted from the columns were Author for correspondence. collected and the contained materials separately analyzed off-line by MALDI-TOF MS. Since these polymer fractions have a narrow MWD, they give good MALDI spectra with MW values in agreement with those obtained by other techniques. The eluted volumes of the o...

The optical O(2) recognition capability of a covalently assembled monolayer (CAM) of 5,10,15-tri-{p-dodecanoxyphenyl}-20-(p-hydroxyphenyl) porphyrin on silica-based substrates was studied at room temperature by both UV-vis and photoluminescence (PL) measurements. The optical properties of this robust monolayer setup appear to be highly sensitive to the O(2) concentration in N(2). Both UV-vis and PL measurements were used to study the porphyrin-oxygen interactions. The monolayer-based sensor exhibits a short response time and can be restored within seconds. The oxygen-induced luminescence quenching of the monolayer involves both ground and excited states. The proposed mechanism responsible for the luminescence quenching involves different kinds of interactions between the monolayer and O(2).

The optical gas recognition capability of a covalently self-assembled monolayer of 5,10,15-tri-{p-dodecanoxyphenyl}-20-(p-hydroxyphenyl) porphyrin molecules on silica substrates was studied. The following analytes have been investigated: NO 2 , CO, CH 4 , H 2 , NH 3 , HCl, CHCl 3 , C 2 H 5 OH, CH 3 OH, pyridine, tetrahydrofurane, triethylamine, and dimethylformamide. The self-assembled porphyrin monolayer appears highly sensitive to 1 ppm of NO 2 in both anhydrous and humid conditions. The selectivity of the self-assembled porphyrin monolayer with respect to other analytes was also examined and present data show that the presence of CO, CH 4 , H 2 , and NH 3 does not influence its UV-vis spectrum. Many common solvents slowly affect the position of the Soret band. The presence of HCl vapors results in a broad band extending over the entire 440-500 nm range while the starting Soret disappears. UV-vis measurements on a n-hexane 1.0‚10 -5 solution of the 2, 3,7,8,12,13,17,18-octaethyl-21H,23H-porphine, that does not contain phenyl substituents in the meso positions, show no changes in the optical spectrum upon NO 2 interaction. It emerges that aromatic substituents in the meso positions play a crucial role in determining the optical sensing properties.