Kinetic studies of multi-step thermal degradations of copolymers or polymer mixtures

A kinetic analysis of multi-step thermogravimetric curves was developed for separation of overlapping decomposition steps to determine their individual reaction order, activation energy and weight loss. The method was applied in three instances: (a) separation of evaporation from decomposition for an isobutene-butadiene copolymer; (b) effects of drying conditions on the volatile content of a styrene-indene resin; (c) separation of dehydrochlorination from cyclodecomposition of poly(vinyl chloride).

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Zusammenfassung Eine kinetische Analyse von mehrstufigen thermogravimetrischen Kurven wurde entwickelt, um überlappende Zersetzungsstufen zu trennen, ihre individuellen Reaktionsordnungen, Aktivierungsenergien und Gewichtsverluste zu bestimmen. Die Methode wurde in drei Fällen eingesetzt: (a) Trennung der Verdampfung des Isobuten-Butadien-Kopolymers von der Zersetzung; (b) die Wirkung der Trocknungsbedingungen auf den Gehalt an flüchtigen Substanzen eines Styrol-Inden-Harzes; (c) Trennung der Dehydrochlorierung des Poly-Vinylchlorids von der Ringspaltung.

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Résumé On a mis au point une méthode d'analyse cinétique des courbes thermogravimétriques en plusieurs termes pour séparer les étapes de décomposition qui se chevauchent et déterminer pour chacune d'elles l'ordre de réaction, l'énergie d'activation et la perte de poids. On a utilisé cette méthode dans trois cas: a) pour distinguer l'évaporation de la décomposition du copolymère isobutène-butadiène, b) pour étudier l'influence des conditions de séchage sur la teneur en substances volatiles d'une résine styrène-indène, c) pour distinguer la déchlorhydratation du chlorure de polyvinyle de la décomposition du cycle.

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Paper presented at the International Symposium on Macromolecular Chemistry, Budapest, 1969.     

Elaboration of nanohybrid materials by photopolymerisation of 3,4-ethylenedioxythiophene on TiO2

A method for the elaboration of a heterojunction composed on n-type inorganic semiconducting nanoparticles, TiO(2), and a p-type organic semiconducting polymer poly(3,4-ethylene dioxythiophene) by UV illumination is described.     

聚[1—（三甲硅基）1—丙炔]—一种有希望的气体分离膜材料

聚[1-(三甲硅基)]-丙炔(PTMSP)膜的气体透过速率高于目前已知的,不管在室温是玻璃态还是橡胶态的任何聚合物.PTMSP在室温是玻璃态.PTMSP的高透气性主要来源于极高的对气体溶解度及高扩散系数,而这是因为在这种玻璃态聚合物中,有大量处于非松弛区域的自由体积.PTMSP的最大问题是它的高透气性随着时间的过去和热历史而衰减.近来,为解决这一问题进行了大量的努力,如加入低挥发材料,氟化、溴化,与其它单体共聚,与其它聚合物共混等.     

Synthesis,characterization and self-assembly of amphiphilic block copolymer poly(4-vinyl benzene chloride)-b-poly(N-vinylpyrrolidone) in aqueous solution

The synthesis, characterization and self-assembly of a novel amphiphilic block copolymer containing a poly(N-vinylpyrrolidone) as a segment of hydrophilic and poly(4-vinyl benzene chloride) (PVBC) arms are reported. The copolymer was characterized by FT-IR spectroscopy ¹H NMR. The composition and the molecular weights of the block copolymers were established using gel permeation chromatography and ¹H NMR. The water-soluble fraction of poly(N-vinyl-2-pyrrolidone) (PVP)/PVBC block copolymers formed micelles which were investigated at 25 °C in water at 5 mg/ml concentration using a tensiometer. The morphology of micelles in aqueous solution was determined by the AFM, SANS, and SAXS methods.     

The Baire category theorem and the evasion number

In this paper we prove that where is the evasion number defined by Blass. This answers negatively a question asked by Brendle and Shelah.

     

Existence of ergodic retraction for noncommutative semigroups in Banach spaces

We prove the existence of ergodic retraction for a noncommutative semigroup which is right Eberlein-weakly almost periodic in a uniformly convex Banach space.

     

Impact of electronic coupling, symmetry, and planarization on one- and two-photon properties of triarylamines with one, two, or three diarylboryl acceptors

We have performed a study of the one- and two-photon absorption properties of a systematically varied series of triarylamino-compounds with one, two, or three attached diarylborane arms arranged in linear dipolar, bent dipolar, and octupolar geometries. Two-photon fluorescence excitation spectra were measured over a wide spectral range with femtosecond laser pulses. We found that on going from the single-arm to the two- and three-arm systems, the peak in two-photon absorption (2PA) cross-section is suppressed by factors of 3-11 for the lowest excitonic level associated with the electronic coupling of the arms, whereas it is enhanced by factors of 4-8 for the higher excitonic level. These results show that the coupling of arms redistributes the 2PA cross-section between the excitonic levels in a manner that strongly favors the higher-energy excitonic level. The experimental data on one- and two-photon cross-sections, ground- and excited-state transition dipole moments, and permanent dipole moment differences between the ground and the lowest excited states were compared to the results obtained from a simple Frenkel exciton model and from highly correlated quantum-chemical calculations. It has been found that planarization of the structure around the triarylamine moiety leads to a sizable increase in peak 2PA cross-section for the lowest excitonic level of the two-arm system, whereas for the three-arm system, the corresponding peak was weakened and shifted to lower energy. Our studies show the importance of the interarm coupling, number of arms, and structural planarity on both the enhancement and the suppression of two-photon cross-sections in multiarm molecules.     

n‐Doping of Organic Electronic Materials Using Air‐Stable Organometallics: A Mechanistic Study of Reduction by Dimeric Sandwich Compounds

Several 19‐electron sandwich compounds are known to exist as “2×18‐electron” dimers. Recently it has been shown that, despite their air stability in the solid state, some of these dimers act as powerful reductants when co‐deposited from either the gas phase or from solution and that this behavior can be useful in n‐doping materials for organic electronics, including compounds with moderate electron affinities, such as 6,13‐bis[tri(isopropyl)silylethynyl]pentacene ( 3 ). This paper addresses the mechanisms by which the dimers of 1,2,3,4,5‐pentamethylrhodocene ( 1 b₂ ), (pentamethylcyclopentadienyl)(1,3,5‐trialkylbenzene)ruthenium (alkyl=Me, 2 a₂ ; alkyl=Et, 2 b₂ ), and (pentamethylcyclopentadienyl)(benzene)iron ( 2 c₂ ) react with 3 in solution. Vis/NIR and NMR spectroscopy, and X‐ray crystallography indicate that the products of these solution reactions are 3 ^.? salts of the monomeric sandwich cations. Vis/NIR kinetic studies for the Group 8 dimers are consistent with a mechanism whereby an endergonic electron transfer from the dimer to 3 is followed by rapid cleavage of the dimer cation. NMR crossover experiments with partially deuterated derivatives suggest that the C? C bond in the 1 b₂ dimer is much more readily broken than that in 2 a₂ ; consistent with this observation, Vis/NIR kinetic measurements suggest that the solution reduction of 3 by 1 b₂ can occur by both the mechanism established for the Group 8 species and by a mechanism in which an endergonic dissociation of the dimer is followed by rapid electron transfer from monomeric 1 b to 3 .     

Synthesis of functionalized poly(1,3-dioxolane)

Classical initiation induces polymerization through cyclic tertiary oxonium ions which are responsible for the formation of an important quantity of cyclic oligomers. The activated monomer mechanism, i.e. polymerization in the presence of a diol, has been successful in the case of some substituted oxiranes such as epichlorohydrine and propylene oxide. It has also been used in the case of cyclic acetals [1,3-dioxolane (DXL) and 1,3-dioxepane (DXP)] and allows the preparation of dihydroxylated homopolymers as well as that of triblock copolymers. It was nevertheless shown that transacetalization leads to complications at the onset of the reaction. In order to shed some light on the reactions involved, we used a monoalcohol - methanol - instead of a diol. The products were separated and characterized: a monoadduct (methanol-DXL) was observed, confirming the occurence of the active monomer mechanism, but dimethoxymethane was also observed, evidence of transacetalization between methanol and DXL. It was shown that fast equilibration takes place between the following compounds: (methanol + DXL), (monoadduct of methanol and DXL), (dimethoxymethane + ethyleneglycol). When p-isopropenylbenzyl alcohol was used, it was possible to prepare macromonomers, i.e. poly(DXL) chains carrying polymerizable double bonds at their ends. Nevertheless because of the transacetalization reaction described above, a mixture of products was obtained.