Umsetzung von Metall- und Metalloidverbindungen mit mehrfunktionellen Molekülen, 31. Mitteilung

The reaction of galliumtrichloride and galliumtribomide resp. with 2,6-dimethyl- and 2,4,6-trimethyl-N-trimethylsilyl-trifluoroacetanilide leads to the trifluoracetanilidodihalogenogallanes1–3. The 2,6,9-trioxa-4,8-diaza-1,5-digalla-bicyclo-[3.3.1]-nonadiene derivatives1 a–3 a are formed probably as by products.N-Trimethylsilyltrifluoroacetamide reacts with galliumtrichloride to yield the trifluoroacetamido-dichlorogallane4.N-Trimethylsilyl-N,N,N-triorganyl-thioureas react with galliumtrichloride under elimination of chlorotrimethylsilane to give the thio-ureido-gallanes5 and6. IfN,N-diorganylureas andN,N-diorganyl-thio-ureas resp. are reacted with galliumtrichloride and methyl-gallium-dichloride resp., the thio-ureido- and ureido-gallanes7–9 are obtained by elimination of hydrogenchloride. The compounds are characterized by analysis and spectral data (NMR:¹H,¹⁹F; MS; IR). The substances are monomeric in the gas phase, obviously due to internal coordination.

30. Mitt.:W. Maringgele undA. Meller, J. Organomet. Chem., im Druck.     

Electrode kinetics and thermodynamic study of complexes of palladium(II) at D.M.E.

Polarographic study of Pd(II) reveals that it reduces quasireversibly at d.m.e. in 0.2M-pyridine+0.1N-HCl medium. Kinetic parameters of Pd(II) in various concentrations of -resorcyclic acid were calculated usingGellings method and thus the effect of concentration of -resorcyclic acid on the kinetics of the reduction of Pd(II) has been explained.DeFord/Hume graphical extrapolation method and the mathematical method ofMihailov have been employed for the evaluation of overall formation constants of the complexes formed with -resorcyclic acid. The logarithmic values of overall formation constants ₁, ₂ and ₃ obtained by the two methods are 7.47, 8.60, 9.66 (DeFord andHume Method) and 7.44, 8.64, 9.66 (Mihailov Method) at 298 K. Thermodynamic parameters of these complexes are reported.

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Elektrodenkinetik und thermodynamische Untersuchungen an Pd(II)-Komplexen mittels polarographie

Zusammenfassung Pd(II) zeigt eine quasireversible Reduktion in 0,2M-Pyridin/0,1N-HCl. Kinetische Parameter wurden mittels der Methode vonGelling ermittelt und damit der Effekt verschiedener -Resorcylsäurekonzentrationen erklärt. Bildungskonstanten der entsperechenden Komplexe wurden nachDeFord/Hume und nachMihailov ermittelt. Die logarithmischen Werte der Gesamtbildungskonstanten ₁, ₂ und ₃ bei 298 K betragen nach derDe Ford/Hume-Methode 7,47, 8,60 und 9,66, nach derMihailov-Methode 7,44. 8,64 und 9,66. Die thermodynamischen Parameter der Komplexbildung werden angegeben.

     

ESR and ENDOR Investigations on Various <Emphasis Type="Italic">Wurster</Emphasis>’s Radical Cations in Solution. Experimental Results,Theoretical <Emphasis Type="Italic">Ab Initio</Emphasis>, and DFT Calculations

Summary. ESR and ENDOR spectra are reported of several symmetrical substituted N,N,N,N-tetraalkyl-p-phenylenediamine radical cations in solution. Different N,N-alkyl substituted para-phenylenediamines, like the ethyl, n-propyl, and iso-propyl derivative are compared with the parent N,N,N,N-tetramethyl-p-phenylenediamine (Wursters Blue Cation). N,N,N,N-Tetrabenzyl-p-phenylenediamine, 1,4-dipyrrolidinylbenzene, and N,N-bis[4-(dimethylamino)phenyl]piperazine are additionally investigated. Experimental and calculated hyperfine coupling constants are compared. Characteristic UV-VIS data and redox potentials in acetonitrile are reported, together with the syntheses of the compounds.     

Das Schwingungsspektrum von Barium-Divanadat

The infrared and laser-Raman spectra of crystalline Ba₂V₂O₇ are reported and discussed by means of a Site Symmetry analysis.

28. Mitt. der Reihe Orthovanadate und verwandte Verbindungen. 27. Mitt.:E. J. Baran undM. E. Escobar, J. Phys. Chem. Solids, im Druck; 26. Mitt.:E. J. Baran, I. L. Botto, J. F. Ramos undP. J. Aymonino, Mh. Chem.109, 1139 (1978); 25. Mitt.:E. J. Baran, J. Mol. Struct.48, 441 (1978); 24. Mitt.:E. J. Baran undI. L. Botto, J. inorg. nucl. Chem.40, 1603, (1978); 23. Mitt.:M. E. Escobar undE. J. Baran, Z. Anorg. allg. Chem.,441, 273 (1978).     

Synthesen von Aminomethylen-γ-halogenacetessigsäurederivaten und deren Ringschlußreaktionen zu 3-Hydroxypyrrolen,Pyrido[1,2-a]pyrimidonen bzw. 4-Chinolonen β,β-Diacyl-enamine und-enole, 5. Mitt.

Condensation of alkyl -haloacetoacetates (or -chloroacetoacetanilide) with triethoxymethane and primary (hetero)aromatic amines gives in a one step synthesis under mild conditions new ,-diacyl-enamines (2 a-m, 3 a-d). In contrast, the N-alkylsubstituted derivatives could be synthesized only in a two step procedurevia the enolethers6 a, b. According to their ir-specra, most of the aminomethylene--haloacetoacetic acid derivatives are stereochemically fixed either in theE- orZ-form. The pmr-spectra, however, show that they exist as mixtures of at least two isomers in solution.With KOH or sodium acetate, a ring closure to 3-hydroxy-pyrroles (8, 9) could be achieved whereas with pyridine only quarternary pyridinium salts (11) are formed. Acidic (orLewis acidic) condensing agents leave the chloroacetyl group unaffected and give either free carboxylic acids (2 p-r) pyrido-[1,2-a]pyrimidones (12) or 4-quinolones (13), depending on the type of the molecule and the reaction temperatures employed.

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Synthesen von Aminomethylen--halogenacetessigsäurederivaten und deren Ringschlußreaktionen zu 3-Hydroxypyrrolen, Pyrido[1,2-a]pyrimidonen bzw. 4-Chinolonen ,-Diacyl-enamine und-enole, 5. Mitt.

     

Absorption spectra of 2-styryl-4-phenyl-thiazole ethiodides in organic solvents of varying polarities and determination of the formation constant of the charge transfer complex formed

The electronic absorption spectra of some 2-styryl-4-phenyl-thiazole ethiodides are studied in organic solvents of different polarities. The shorter wavelength band appearing in the visible region is assigned to an intramolecular charge transfer (CT)-transition originating from the phenyl moiety to the positively charged hetero ring, while the longer wavelength one is due to an intermolecular CT-transition from the iodide ion to the 2-styryl-4-phenyl-thiazolinium cation. These assignments are based on the nature of the aldehydic residue and effects of solvent, concentration, and temperature on both the position and absorptivity of the CT complex-band. It is concluded that the CT complex formed will be highly solvated inDMF, DMSO, ethanol and methanol relative to in CHCl₃, dioxane and acetone. The formation constant of the CT complex in solutions of different polarities is determined at different temperatures. Furthermore, the thermodynamic parameters H ^o, G ^o and S ^o for complex formation are calculated and discussed.

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Absorptionsspektren von 2-Styryl-4-phenyl-thiazol-ethiodiden in verschiedenen Lösungsmitteln und Bestimmung der Bildungskonstanten der Charge-Transfer-Komplexe

Zusammenfassung Die Elektronenanregungsspektren einiger substituierter 2-Styryl-4-phenyl-thiazol-ethiodide wurden in einigen Lösungsmitteln unterschiedlicher Polarität untersucht. Die Absorption bei kürzerer Wellenlänge wird einem intramolekularen Charge-Transfer (CT)-Übergang zugeordnet, die langwellige Bande einem intermolekularen CT-Übergang (Jodid—organ. Kation). Die Diskussion erfolgt basierend auf Substitutions-, Lösungsmittel-, Konzentrations-, und Temperatur-Effekten. Die Komplexbildungskonstanten und die thermodynamischen Parameter H ^o, G ^o und S ^o werden angegeben.

     

Influence of o-benzoquinone nature on initiation of radical polymerization by the o-benzoquinone—tert-amine system

o-Benzoquinones initiate radical polymerization of methacrylates under visible light irradiation in the presence of tertiary amines. Spectral sensitivity of the initiating system coincides with absorption bands of o-benzoquinone attributed to the S(*) (_max 400 nm) and S(n*) (_max 600 nm) transitions. The amine radicals (Am^·) initiating polymerization are generated by the photoreduction of Q in the presence of AmH from the triplet radical pair ³(QH^·, Am^·). The yield of Am^· depends on the difference between the volumes of substituents in the 3 and 6 positions of the quinoid ring and is maximal for symmetrically substituted o-benzoquinones. For a series of derivatives of symmetrical 3,6-di-tert-butyl-o-benzoquinone, the rate of photopolymerization of ,-bis(methacryloyloxyethyleneoxycarbonyloxy)ethyleneoxyethylene (OCM-2) in the presence of N,N-dimethylaniline is determined by the free energy (G _e) of electron transfer from the amine to photoexcited o-benzoquinone. The G _e value includes the energies of oxidation of the amines and reduction of the o-quinones and the energy of the 00 transition of the triplet excited state of o-benzoquinones, which are equal to their redox potentials. The photopolymerization rate is maximal for G _e 0.     

Complexes of dioxouranium(VI) with zwitter-ionic forms of Bi- and tetra-dentateSchiff bases

Potentially bi- and tetra-dentateSchiff bases derived from salicylaldehyde react with hydrated uranyl salts to give complexes: UO₂H₂ LX ₂, UO₂H₂ LX ₂ and UO₂(HL)₂ X ₂ [H₂ L=N,N-propane-1,3-diylbis(salicylideneimine), H₂ L=N,N-ethylenebis(salicylideneimine) and HL=N-phenylsalicylideneimine;X ^–=Cl^–, Br^–, I^–, NO₃ ^–, ClO₄ ^–, and NCS^–]. Because of marked spectral similrities with the structurally known Ca(H₂ L) (NO₃)₂, theSchiff bases are coordinated through the negatively charged phenolic oxygen atoms and not the nitrogen atoms of the azomethine groups which carry the protons transferred from phenolic groups on coordination. Halide, nitrate, perchlorate and thiocyanate groups are covalently bonded to the uranyl ion, resulting a 6-coordinated uranium ion in the halo and thiocyanato complexes and 8-coordinated in nitrato and perchlorato complexes.

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Komplexe von Dioxouranyl(VI) mit zwitterionischen Formen von zwei- und vierzähnigen Schiff-Basen

Zusammenfassung Von Salizylaldehyd abgeleitete zwei- und vierzähnigeSchiff-Basen reagieren mit hydratisierten Uranylsalzen zu Komplexen folgenden Typs: UO₂H₂ LX ₂, UO₂H₂ LX ₂ und UO₂(HL)₂ X ₂ [H₂ L=N,N-Propan-1,3-diylbis(salicylidenimin), H₂ L=N,N-Ethylen-bis(salicylidenimin) und HL=N-Phenylsalicylidenimin;X ^–=Cl^–, Br^–, I^–, NO₃ ^–, ClO₄ ^– und NCS^–]. Auf Grund eindeutiger spektraler Ähnlichkeiten mit dem bekannten Ca(H₂ L) (NO₃)₂ wird auf Koordination über die negativ geladenen phenolischen Sauerstoffatome (und nicht über die Azomethin-Stickstoffe) geschlossen. Die AnionenX ^– sind kovalent an das Uranyl-Ion gebunden; damit ergibt sich ein hexakoordiniertes Uranyl-Ion für die Halogen- und Thiocyanat-Komplexe und Oktakoordination für die Nitrat- und Perchlorat-Komplexe.

     

Volumetric and viscometric study of aqueous binary mixtures of some glycol ethers at T = (275.15 and 283.15) K

The experimental data for the density (ρ) and viscosity (η) are reported for aqueous binary mixtures of different glycol ethers, namely ethylene glycol monomethyl ether (EGMME), ethylene glycol monoethyl ether (EGMEE), diethylene glycol monomethyl ether (DEGMME), and diethylene glycol monoethyl ether (DEGMEE), at different temperatures (T = 275.15 K and 283.15 K) within the concentration range 0 mol · kg⁻¹ to 0.1 mol · kg⁻¹. The values of density (ρ) and viscosity (η) of the solutions were used to compute different derived parameters, such as apparent molar volume (?_V) of the solute, excess molar volume (V^E) of the solution, viscosity B and D coefficients of solution and temperature coefficient of viscosity B-coefficient (dB/dT) of solution. The limiting apparent molar volume of the solutes () have been obtained for aqueous binary mixtures of these glycol ethers by smooth extrapolation of ?_V–m curves to zero concentration. By using the values of , the limiting excess partial molar volumes () have also been calculated. The results are interpreted in term of various interactions such as solute–solvent interactions and hydrogen bonding.     

Detector quantum efficiency: An important parameter for FT-IR spectroscopy

Spectral detectivities (D ^*()) are commonly used to characterize the sensitivity of infrared detectors, but for most spectroscopic purposes they are very misleading.For photon detectorsspectral detector quantum efficiencies ( _q ()) are needed in order to calculate the (S/N) ratio for the photon-noise limited situation. An equation to calculate _q(#x03C3;) fromD ^*() values is presented. The results for some common IR-detectors are surprising.As an application for the use of _q () values theS/N ratio of an FT-IR spectrum from an optimized FTS instrument under photon-limited conditions is given.     

Concerning the absorption and emission properties of phenanthro[1,10,9,8,o,p,q,r,a]perylene-7,14-dione

Summary In contrast to hitherto published data, phenanthro[1,10,9,8,o,p,q,r,a]perylene-7,14-dione, the fundamental chromophoric system of hypericin type compounds, exhibits an absorption with a long wavelength band at 423 nm in aprotic solvents like dimethylsulfoxide (7000). Its fluorescence in these solvents is below the detection limit. In protic solvents like methanol, the long wavelength absorption is bathochromically shifted to 546 nm, and a fluorescence at 565 nm is observed. This behavior was interpreted from the reversal ofn – * and – * transitions. The data have not been recorded yet due to the very low solubility of this compound. Its monoprotonation in ground and excited states is characterized bypK _a andpK* _a values of –6 and 2; diprotonation occurs at apK _a=–7.

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Absorptions- und Emissions-Eigenschaften von Phenanthro[1,10,9,8,o,p,q,r,a]perylen-7,14-dion (Kurze Mitt.)

Zusammenfassung Im Gegensatz zu bislang publizierten Daten zeigt Phenanthro[1,10,9,8,o,p,q,r,a]perylen-7,14-dion, das fundamentale chromophore System der Hypericintyp-Verbindungen, in aprotischen Lösungsmitteln wie Dimethylsulfoxid eine Absorption mit einer langwelligen Bande bei 423 nm (7000). In diesen Lösungsmitteln ist Fluoreszenz nicht nachweisbar. In protischen Lösungsmitteln wie Methanol wird die langwellige Bande bathochrom verschoben (546 nm) und bei 565 nm tritt Fluoreszenz auf. Dieses Verhalten wurde mit der Umkehr in der Reihenfolge vonn – * und – * Übergängen interpretiert. Die Daten wurden wegen der extremen Schwerlöslichkeit dieser Verbindung bislang nicht erhalten. Die Monoprotonierung im Grund- und Anregungszustand ist durchpK _a- undpK* _a -Werte von –6 und 2 charakterisiert; die Diprotonierung tritt beipK _a=–7 ein.

     

Dampfdruckmessungen und Protonenresonanzuntersuchung an Hydriden der intermetallischen Phasen Ti2(Ni,Co) und Ti2(Ni,Fe)

NMR and hydrogen equilibrium pressure measurements were performed on hydrides of the intermetallic compounds Ti₂(Ni, Co) and Ti₂(Ni, Fe). The following values of enthalpy H and entropy S for the formation of the hydrides of the intermetallic phases Ti₂Co and Ti₂Ni were found: H(Ti₂CoH _y )=–47.6 kJ/mol H₂, H(Ti₂NiH _y )=–53.7 kJ/mol H₂; S(Ti₂CoH _y )=–119.8 J/(K·mol H₂), S(Ti₂NiH _y )=–127.5 J/(K·mol H₂). By substitution of Ni or Co by Fe, the values of H and S of the corresponding quaternary hydrides become less negative. An interpretation of the experimental results is tried by the model ofShaltiel and coworkers.Proton diffusion was investigated in a series of the intermetallic hydrides Ti₂(Ni, Co)H _x and Ti₂(Ni, Fe)H _x . The diffusion rate is lowered by increased Ni/Fe substitution. Substitution of Ni by Co scarcely effects the hopping process. The activation energies were found to be smaller for the Ti₂Ni-hydrides compared with the Ti₂Co-hydrides.

Herrn Prof. Dr.H. Nowotny zum 70. Geburtstag gewidmet.     

Kinetics of oxidation of glycine and valine by chloramine-T in hydrochloric acid medium

The kinetics of oxidation of glycine and valine by chloramine-T in hydrochloric acid medium has been studied. The rate of disappearance of chloramine-T shows a first order dependence on both chloramine-T and the amino acid, and an inverse first order with respect to [H⁺]. The solvent isotope effect was studied using heavy water. The kinetic parameters,E _a ,Arrhenius factorA, H and S and G have been calculated. A rate law in agreement with experimental results has been derived. A mechanism is proposed.

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Über die Kinetik der Oxidation von Glycin und Valin mit Chloramin-T in salzsaurem Medium

Zusammenfassung Die Kinetik der Oxidation von Glycin und Valin mit Chloramin-T in Salzsäure wurde untersucht. Die Geschwindigkeitskonstante des Wegreagierens von Chloramin-T zeigt eine Abhängigkeit erster Ordnung sowohl von Chloramin-T als auch von der Aminosäure und ist invers erster Ordnung bezüglich [H⁺]. Der Lösungsmittel-Isotopeneffekt wurde mit D₂O untersucht. Es wurden die kinetischen Parameter,E _a , derArrhenius-FaktorA, H , S und G , bestimmt. Ein Mechanismus, der in Übereinstimmung mit den experimentenllen Daten ist, wird vorgeschlagen.

     

Extremal hexagonal chains concerning k-matchings and k-independent sets

Denote by _n the set of the hexagonal chains with n hexagons. For any B _{n n} , let m _k (B _n ) and i _k (B _n ) be the numbers of k-matchings and k-independent sets of B _n , respectively. In the paper, we show that for any hexagonal chain B _{n n} and for any k0, m _k (L _n )m _k (B _n )m _k (Z _n ) and i _k (L _n )i _k (B _n )i _k (Z _n ), with left equalities holding for all k only if B _n =L _n , and the right equalities holding for all k only if B _n =Z _n , where L _n and Z _n are the linear chain and the zig-zag chain, respectively. These generalize some related results known before.     

Bakterieninhaltsstoffe,V: Alkylchinoline und derenN-Oxide ausPseudomonas aeruginosa

Alkyl and alkenyl quinolines (so-called Pyo-substances) and theirN-oxides were isolated fromPseudomonas aeruginosa. Structures proposed earlier could be confirmed; a new representative (Pyo V) is described.

IV. Mitt.:A. Römer, H. Budzikiewicz, H. Korth undG. Pulverer, Tetrahedron Letters1979, 509.     

Magnetische Messungen im Nahordnungsbereich vonHeusler-Phasen (Co,T)2 XY

Magnetic measurements onHeusler alloys (Co,T)₂ XY (field and temperature dependence) are performed around theCurie points (temperature range:T _C–50 toT _C+50). A method otherwise used to get rid of ferromagnetic impurities only ( _g versus 1/H plot) is applied to pure ferromagnets and yields completely new _g (extrap.) versusT curves with a maximumT _max> T _C. The method was applied to pure gadolinium first which has aCurie point within the accessible region of the susceptibility measuring device.

     

Synthese neuer Indolderivate

The synthesis of the ,-unsaturated ketones4, 5 und6 via the regiospecific aldol- andWittigreaction with some indolealdehydes is described.4 and5 are stable enough for NaBH₄-reduction to the corresponding alcohols.

     

Prins-Reaktionen mit Arylaldehyden, 5. Mitt.: Zur Umsetzung mit 2-Buten und mit Cyclohexen

By reaction of 2-[(1RS, 2RS)-2-hydroxy-1-methyl-propyl]-2-phenyl-1,3-dithiane (1 a) withcis-2-butene oxide, subsequent reduction and acetalizationc-4,t-5-dimethyl-r-2,c-6-diphenyl-1,3-dioxane (3 a) andt-4,c-5-dimethyl-r-2,c-6-diphenyl-1,3-dioxane (3 b) were synthesized as model compounds. For the same purpose by aldol reaction of cyclohexanone and reduction (1RS, 2SR)-2[(RS)-hydroxy-(4-methoxyphenyl)methyl]cyclohexanol (7 a), (1RS, 2RS)-2[(SR)-hydroxy-(4-methoxyphenyl)methyl]cyclohexanol (8 a), and (1RS, 2RS)-2[(RS)-hydroxy-(4-nitrophenyl)methyl]cyclohexanol (8 b) and by acetalization (2 , 4 , 4 a, 8 a)-2,4-bis(4-methoxyphenyl)hexahydro-4H-1,3-benzodioxin (9 a) and (2 , 4 , 4 a, 8 a)-2,4-bis(4-nitrophenyl)hexahydro-4H-1,3-benzodioxin (10 b) were obtained. FromPrins reactions, starting with 2-butene3 a,c-4,c-5-dimethyl-r-2,c-6-diphenyl-1,3-dioxane (3 c),r-4,t-5-dimethyl-c-6-phenyl-1,3,2-dioxathiane-2,2-dioxide (4), and (2Z, 4E)-1,5-diphenyl-4-methyl-2,4-pentadien-1-on (5), and starting with cyclohexene (E)-3-(4-methoxybenzylidene)cyclohexenyl-4-methoxyphenyl ketone (11) have been isolated in low yields.

4. Mitt.:Griengl, H., Nowak, P., Mh. Chem.109, 11 (1978).     

Ligational behaviour of thiosemicarbazide and thiosemicarbazone-(III): Tetragonal complexes of cobalt(II) derived from 4-benzylamidothiosemicarbazide and 1-(α-) furyl-4-benzylamidothiosemicarbazone

Zusammenfassung Es wurden eine Anzahl von neuen Kobalt(II)-Komplexen von 4-Benzylamidothiosemicarbazid (BTSC) und 1-(-)Furyl-4-benzylamidothiosemicarbazon (FBTS) von der allgemeinen Zusammensetzung CoL ₂ X ₂ (L=BTSC, FBTS;X=Cl, Br, I, NO₃ and NCS) synthetisiert. Die Untersuchugen erfolgten mittels Elementaranalyse, magnetischer Messungen, Elektronenanregungsspektroskopie und IR-Spektroskopie (einschließlich des fernen IR); aus diesen Messungen ließ sich eine im wesentlichen tetragonale Symmetrie für alle Komplexe dieser Reihe ableiten.

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Ligational behaviour of thiosemicarbazide and thiosemicarbazone-(III): Tetragonal complexes of cobalt(II) derived from 4-benzylamidothiosemicarbazide and 1-(-) furyl-4-benzylamidothiosemicarbazone

A number of new complexes of cobalt(II) have been prepared with 4-benzylamidothiosemicarbazide (BTSC) and 1-(-)furyl-4-benzylamidothiosemicarbazone (FBTS) which conform to the general formula CoL ₂ X ₂ (whereL=BTSC andFBTS andX=Cl, Br, I, NO₃ and NCS). These have been characterized by chemical analyses and physical measurements. The tetragonal symmetry has been proposed on the basis of electronic spectral studies for all these complexes. The explanation for the slightly lower magnetic moments for cobalt(II) complexes has been sought in the possible presence of low symmetry component. The tetragonal radial parametersDq(E),Dq(A),Dt andDs and molecular orbital parameters d and d have been evaluated. The S–N, bidentate nature of the ligands and the presence of the various anions in the coordination sphere have been confirmed on the basis of additional Co–N, Co–S and Co–X frequencies in the far infrared spectra of the complexes. The nitrato and thiocyanato groups act as monodentate and are coordinated through oxygen and nitrogen atoms, respectively.

     

Effects of ionization on the phase behavior of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-co-acrylic acid) and poly(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diethylacrylamide-co-acrylic acid) in water

Phase transitions of poly(N-isopropylacrylamide-co-acrylic acid) (PiPA-AA) and poly(N,N- diethylacrylamide-co-acrylic acid) (PdEA-AA) in water have been investigated by means of turbidimetry, Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The phase transition temperatures (T_p) of these copolymers increase with the degree of ionization () of the acrylic acid (AA) units, which in turn is dependent on the pH of the solutions. Apparent values of pK_a for the AA units, determined from the pH dependencies of T_p, are 4.7 and 5.4 for PiPA-AA and PdEA-AA, respectively. Differences between T_p for PiPA-AA and T_p for PiPA homopolymer (T_p) are +1.5 and –0.2 °C/mol% of AA at =1 and 0, respectively. The values of T_p for PdEA-AA are +2.6 (ionic) and –0.5 (nonionic)°C/mol%, indicating that the incorporated AA units have a larger effect on PdEA than on PiPA. DSC measurements performed with each of these copolymers at different pH values show a linear relationship between T_p and the enthalpy of transition (H). IR measurements of PiPA-AA show that the profiles of IR bands from both iPA and AA units exhibit critical changes at T_p of the copolymer. Heating the solution above T_p leads to shifts of the amide II, C–H stretch, and C–H bend bands from the iPA units toward lower wavenumbers, as well as a shift of the amide I band from the iPA units toward higher wavenumbers. A decrease in the intensity of the symmetric C=O stretch IR band from carboxylate anions (1560 cm^–1), and an increase in the intensity of the C=O stretch band from COOH groups (1705 cm^–1) suggest that a partial protonation of the carboxylate groups (COO^–+H⁺COOH) takes place upon the phase transition.