Katalysatoren beim thermischen Abbau von Polymeren, 1. Über den katalytischen Abbau von Polypivalolacton

The ability of different metal oxides and acetates to catalyze the thermal degradation of poly(pivalolactone) into cyclic oligomers has been investigated. Magnesium oxide was found to be the most active catalyst which converts poly(pivalolactone) completely into oligomers within less than two hours at 547 K. The influence of temperature and catalyst concentration and the distribution of cyclic oligomers is discussed.     

Über die thermischen umwandlungen des chloroprens

The kinetics of the conversion of chloroprene into cyclic dimers and polychloroprene was investigated using gel-chromatography. The temperature dependences of velocity constants for the formation of individual dimers were determined within the range from 50 to 70°C. The order of dimerization equaled two at the beginning of the reaction and decreased during its course. The polymerization was inhibited by diphenylpicrylhydrazyl and accelerated by iodine. The rate of polymerization in the solutions of dimethyl sulphoxide and dimethyl sulphate was several times higher than that in pure chloroprene. The addition of 2.4-pentadione-bis-ethylene-rhodium accelerated the polymerization; however, it slowed down the formation of 1.2-dichloro-1.2-divinylcyclobutane. The equations for the formation of the last dimer and for the conversion of monomer were derived.     

Über den einfluß des lösungsmittels beim thermischen zerfall des azoisobuttersäuredinitrils

The thermal decomposition of azo-bis-isobutyronitrile in a series of 10 solvents was investigated. The reaction is strictly of first order. The rate is different in all solvents, the maximum difference at 60°C amounts 40% (malonic ester/cyclohexanol), which corresponds to a difference of 250 cal/mole in the free enthalpy of the transition state. The greater differences of the activation enthalpy are compensated by similar differences of the entropy of the transition state.     

Über den thermo-oxidativen Abbau von Polyvinylacetat unter thermogravimetrisch-dynamischen Bedingungen

The present work discusses the results of studies on the elimination of acetic acid from poly(vinyl acetate) in air under thermogravimetric-dynamic conditions. The dependence of the kinetic parameters on the degree of transformation, the heating rate and on the average molecular weight of the studied samples, as well as the presence of an exothermic process at the end of the first degradation step indicate a modification of the reaction mechanism, probably because of the superposition of an oxidation process at higher temperatures.     

Über die kinetik des thermischen abbaues von polystyrolen

The results of the kinetic isothermal, thermal-dynamic (i.e. with constant heating rate) and of the gaschromatographic-pyrolytic study of the thermal degradation of different polystyrenes show the mechanism of the degradation reaction to be complex and not simple depolymerisation. The kinetic parameters of the thermal degradation depend as well on the molecular weight as on the nature of the polystyrene and the degree of conversion. On these reasons, one observes under thermal-dynamic conditions an influence of the heating rate on the total activation energy.     

Über den thermischen abbau des poly(ε-caprolacton)s

The thermal and electron impact induced degradation reactions of poly(ε-caprolactone) {poly[oxy(1-oxohexamethylene)]} were investigated in a mass spectrometer. It can be shown that the favorated thermal degradation reaction is the cleavage of the ester bond and formation of ω-hydroxyl and ketene endgroups (Eq. (iii)) and with a lower intensity the cleavage of the O? CH₂-bond and formation of carboxyl-and pentenyl endgroups (Eq. (vii)). After electron impact and fragmentation of the pyrolysis products to carboxonium ions an elimination of caprolactone via a “zip”-mechanism can be observed (Eq. (v)).     

Über den thermischen und den thermisch-oxydativen abbau von polyoxymethylenen in lösung 30. Mitt. über polyoxymethylene

High polymers with C?C-double bonds are suited for modifications by simple, chemically obvious reactions provided they exist as solutions in non-polar solvents, free from H₂O and H-acid compounds. Long-chain branching can be achieved in diolefins by FRIEDEL -CRAFTS catalysts. One obtains non-gelled products of much higher molecular weight. By different routes long-chain branching in unsaturated polymers is produced with 4-isocyanate-phenyl sulfene chlorid. Addition type reactions of the NCO-groups incorporated in the polymers produce a variety of copolymers. Cis 1,4-polybutadiene as a model substance is chosen to demonstrate the effect and the range of application of the above-mentioned reagent. The addition reactions of the NCO-group can be studied with NCO-containing polybutadiene in extreme dilution.     

Über die kinetik des thermischen und thermooxidativen abbaus von polyäthylenterephthalat

The apparent kinetic parameters of the thermal and the thermal and thermooxidative degradation of poly(ethylene terephthalate) for non-isothermal conditions were evaluated. The dependence of these parameters on the heating rate, the mean molecular weight, and the degree of conversion was also established. It is shown that the degradation in nitrogen probably occurs by a short chain mechanism, while the degradation in air is more complex. In the latter case, the exothermic character of the DTA-curves suggests that the chain degradation reaction is overlapped by oxidation processes.     

Über den einfluß von reglern auf die polymerisation des trioxans

Chain transfer of cationic trioxane polymerisation with several transfer agents was investigated, showing that during polymerisation a hydride shift takes place as side-reaction. This was confirmed by analytical investigations. The intramolecular hydride shift yields methyl cations which on their part release polymerisation or transacetalisation. Hydride shift and transacetalisation are characteristic for the cationic polymerisation of trioxane and formaldehyde. Several new chain transfer agents such as esters of boric acid and alkyl substituted aromatic compounds were found. Furthermore polyoxymethylenes with unsaturated, nitrile, and peroxy end groups were prepared.     

Über den Abbau der Bluthistiocyten

Zusammenfassung Nach Einspritzung von Tusche und Zinnober in Blutadern nehmen die Endothelien von Leber, Milz, Lunge, Knochenmark, Nebenniere, und Darm Tusche auf. Die tuschebeladenen Endothelien lösen sich los und werden zu Bluthistiocyten. Diese Histiocyten gehen in Leber und Milz zugrunde.In der Leber werden sie in den Capillaren der Läppchenränder festgehalten, dort zusammengeballt und aufgelöst. Ihr unverdaulicher Tusche- bzw. Zinnoberinhalt bleibt hier in großen Haufen liegen.In der Milz werden Histiocyten von den Reticulumzellen aufgenommen und ein Teil geht in den Reticulummaschen zugrunde. Auch hier findet sich Tuscheablagerung als Zeichen des Abbaues.Die Lunge beteiligt sich nicht am Abbau der Histiocyten. Im Gegensatz zu Milz und Leber wird sie bald nach der Einspritzung fast völlig tuschefrei. Gelegentlich in den Capillaren zu findende Bilder, die den Verdacht auf Histiocytenabbau erwecken könnten, sind als Embolien aus den Lebercapillaren stammenden Materials anzusehen. Intimagranulome in Lungenvenen, dieSiegmund für den Abbau der Histiocyten verantwortlich macht, wurden nicht gefunden.Mit 5 Abbildungen im Text.     

Über den einfluß ungesättigter verbindungen auf die polymerisation des trioxans

The Polymerization of trioxan in the presence of small amounts of unsaturated compounds acting as chain transfer agents is described, The resulting polymers contain a larger alkali and temperature stable fraction. The chain transfer action of the unsaturated compounds can be explained by addition of the Polyoxymethlene cation to the carbon double bond followed by cleavage of a proton. Copolymerization may also occur to a smaller extent, this explains the increasing amounts of stable polymer. Most of the unsatitrated compounds investigated lower the conversion of the trioxan polymerization. The reason for this is an inhibiting interaction the between the catalyst and the unsaturatedc compound.     

Über den einfluß einiger alkylhalogenide auf die durch titanhalogenide katalysierte polymerisation des isobutens

The effect of some alkyl halides (tert-butyl fluoride, butyl fluoride, benzyl fluoride, benzyl chloride and benzyl bromide) on the polymerization of isobutene in heptane catalyzed with Ti(IV) halides was investigated. It was found that additions of tert-butyl fluoride and benzyl fluoride to a solution of isobutene and titanium(IV) chloride, bromide or iodide in heptane led to a very fast polymerization. The effect of butyl fluoride was found to be similar, but considerably weaker compared to tert-butyl fluoride and benzyl fluoride. Polymerizations with the catalyst system titanium(IV) chloride/benzyl fluoride were studied in greater detail. As it could be seen from the results, alkyl fluorides do not act as cocatalysts, but the polymerization of isobutene is due to catalytically active products arising from an exchange of halogen atoms between titanium halides and alkyl fluorides. The mechanism of initiation with the catalytic system titanium(IV) chloride/benzyl fluoride is discussed in connection with the results of the UV spectroscopic investigations of the polymers obtained.     

Über den einfluß der aufheizgeschwindigkeit auf die kinetik des thermogravimetrischen abbaues von polymeren

An explanation for the observed influence of the heating rate on the activation energy of thernimogravimetric polymer destruction is presented in this work. Thereby it is shown, that for complex reactions (thus also for depolymerisations) the known displacement of the domain of destruction temperatures with the heating rate may not remain parallel, if there exists an influence of the conversion degree on the activation energy. Because the impossibility of stationarity in thermogravimetric conditions, complex reactions will show every-time such influences. However, a modification of the slope of the conversion curves for various heating rates determines a modification of the temperature coefficient and thus of the activation energy. The thermogravimetric method becomes in this way an useful one to distinguish between elementary and complex reactions, because elementary processes will not show a conversion dependence of the activation energy and therefore in this case neither the displaced conversion curves, are showing an variation of the slope, nor the activation energy a modification with heating rate.     

Über den aufbau von block- und pfropfcopolymeren

After briefly introducing the basic possibilities for the formation of graft and blockcopolymers, the important methods of the radical-initiated block and graft copolymerization are discussed on the basis of the characteristic examples, which are available in the literature. Thereafter the discussion is carried out on the few a t that time known syntheses in the field of the anionic block copolymerization, which then finally loads to the own work with polyfunctional macromolecular anionic initiators. Thus the addition of dialkylaluminium hydrides to macromolecules with C?C double bonds in side chains or at chain ends, and treating the products with transitionmetal halides (e.g. TiCl₄), macromolecular ZIEGLER -NATTA -Catalysts are formed. These initiate graft and block copolymerization of ethylene and α-olefines, whereby the poly-α-olefine molecules, which are already grown, can have a stereoregular structure. Macromolecules containing RC?NM linkages are formed on addition of organometallic compounds of lithium (LiR) or magnesium (MgRhal) to the N≡C triple bond in styrene-acrylonitrile copolymers, and they initiate anionic graft copolymerization of acrylonitrile (AN), methylmethacrylate (MMA), 2-vinylpyridine (2-VP), and 4-vinylpyridine (4-VP). Reactions of macromolecules containing O?C, N≡C, or C?C linkages in side chains with sodium or naphthalene sodium give macromolecular radical anions (e.g., high-polymeric ketyls in the case of poly-p-vinylbenzophenone) or dianions, formed by electron-transfer from the metal to the multiple bond. Both the radical anions and the dianions initiate anionic graft copolymerization of AN, MMA, 2-VP, 4-VP, butadiene, and styrene, and in this way pure graft copolymers are formed, free from “backbone molecules” and from homopolymers of the grafted monomer. Pure graft copolymers are formed also on use of macromolecular organometallic initiators, such as those formed by metallation of poly-4-chlorostyrene or 4-chlorostyrene styrene copolymers with stoichiometric amounts of naphthalene sodium. Since the anionic end groups of the growing side chains remain “living” during these processes, second and third monomers can be added to afford graft copolymers whose side chains are block copolymers. If the growing chains are terminated, e.g., by chlorosilanes containing functional groups, then reactive end groups are introduced into the side chains. Finally, graft and, in particular, block copolymers can be obtained when “finished” macromolecules containing very reactive silicon side or end groups (e.g., H? Si-, Cl? Si-, HO? Si-, CH₂?CH? CH₂? Si-groups) are joined together by chemical reactions. These methods open a route to block copolymers having stereoregular blocks. Macromolecules containing suitable functional groups attached to silicon atoms also provide a bridge to anionic processes. For instance, macromolecules containing p-vinyl-phenylsilicon end groups surprisingly react readily with sodium to radical anions which effect block copolymerization of vinyl monomers.     

Über die bestimmung des zahlenmittels des molekulargewichts von polyoxymethylenen. 36. Mitt. Über polyoxymethylene

The paper gives a review on methods of determining the number average molecular weight M?_n of polyoxymethylenes, especially by osmosis, kryoscopy and both chemical and infrared -spectroscopic determination of end-groups. Osmotic measurements in phenol at 90°C succeeded much better with cellophane membranes than with glass membranes. Kryoscopic determinations in camphor by RAST 's method were reliable only in the presence of an antioxydant. End-group determination of polyoxymethylene diacetates by infrared has been improved by using the CH₂-band at 6,8 μ as a reference for the carbonyl absorption at 5,70 μ. Calibration was achieved by chromic acid oxidation and titration of acetic acid. This infrared method may also be applied to formate end-groups. Further, a calibration for the determination of hydroxylendgroups by IR is given. Orthoformate units in polytrioxane are determined by acid hydrolysis of the polymer and titration of the liberated formic acid.     

Ueber den Abbau des Nahrungs-Eiweisses in der Leber

Ohne Zusammenfassung     

Untersuchungen über den Abbau von Bakterien durch Abwehrfermente

Ohne ZusammenfassungDie Untersuchungen wurden zum großen Teil bereits im Jahre 1913/14 ausgeführt. Der Abschluß der Arbeit und die Zusammenstellung der Versuchsergebnisse waren infolge des Krieges erst jetzt möglich.     

Über den mechanismus der anionischen polymerisation von acrylnitril mit triäthylphosphin, 8. Über makrozwitterionen

The anionic polymerization of acrylonitrile with triethylphosphine as initiator in dimethylformamide was studied at different temperatures and various monomer/initiator ratios. ¹H-NMR spectroscopy and gel permeation chromatography as well as emission spectra analysis of phosphorus were employed on both the crude polymer and the polymer samples obtained by reprecipitation and by gel permeation chromatography. In addition, the number of polymer anions was determined by spectroscopic end group analysis. Thus, it was possible to show the occurrence of a polymerization via macrozwitterions besides the dominant transfer mechanism and also the necessity of minimum values of the polymerization temperature as well as the monomer/initiator ratio for the formation of macrozwitterions, . If these conditions are not realized, a transfer reaction to the monomer through proton abstraction takes place by means of the zwitterion , which is formed by the interaction of triethylphosphine and acrylonitrile, and the resulting anion, , initiates the polymerization chain. As a result ofthe increase ofthe initiator concentration as well as that of the temperature, more side-reactions in the polymerization occur, as can be noted by IR- or UV-spectroscopical analysis of the polymer.