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  • 1
    Electronic Resource
    Electronic Resource
    An investigation of the self-aggregation process of syndiotactic poly(methyl methacrylate) in solution by using infrared spectra (1988)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 189 (1988), S. 2099-2105 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The time dependence of self-aggregation of syndiotactic (s) poly(methyl methacrylate) (PMMA) in dilute toluene or CCl4 solutions was investigated using infrared (IR) spectra measurements. The IR spectra were also recorded in s-PMMA solutions where no self-aggregation takes place (benzene, acetonitrile). It was found that the helix conformation with a large number of units per turn (near-tt) in aggregated s-PMMA is formed in parallel with intermolecular interactions of ester groups of s-sequences. The connection between the fraction of s-sequences in the helix conformation determined for unaggregated s-PMMA in various solvents using IR spectra and the ability of s-PMMA to form self-aggregates (double helix) in a certain solvent is discussed. Intersegmental contacts which occur in s-PMMA in CCl4, i.e. in a thermodynamically poor solvent, lead to a decrease in the equilibrium aggregated fraction, to the slowing-down of the aggregation process and to the decomposition of the majority of aggregated structures during evaporation of the solvent; their effect is similar to that of chemical crosslinking.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1988.021890912
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  • 2
    Electronic Resource
    Electronic Resource
    Mechanisms and kinetics of the anionic polymerization of acrylates, 2Part 1: cf. ref.1. Polymerization of tert-butyl acrylate in a flow tube reactor and effect of lithium chloride and lithium tert-butoxide (1992)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 193 (1992), S. 101-112 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics and the molecular weight distributions (MWD) in the anionic polymerization of tert-butyl acrylate (tBuA) in tetrahydrofuran at 23 ± 3°C were investigated. Tert-butyl α-lithioisobutyrate (tBiB-Li) was used as the initiator in the absence and presence of the additives lithium chloride and lithium tert-butoxide (tBuOLi). A flow tube reactor was used which allowed very rapid mixing of reagents, within milliseconds. The polymerization is extremely fast, half-lives being 0,01 s for the system without additive, 0,05 s for LiCl and 3 s for tBuOLi as an additive. The rate of termination was estimated from the strong UV absorption of the enolized β-oxoester end group formed. The number-average degree of polymerization is a linear function of conversion, the absolute values, however, demonstrate initiator efficiencies of only ca. 30%. The MWD's of the polymers formed are narrow (Mw/Mn = 1,35 without additive, M/Mn = 1,08 in the presence of LiCl and Mw/Mn = 1,77 in the presence of tBuOLi). After precipitation these values are reduced to 1,17; 1,06 and 1,32, respectively. Experiments in a stirred tank reactor and in ampoules lead to much broader MWD's. This shows that the rate of mixing has a strong effect on the MWD and is of substantial importance in these rapid polymerizations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1992.021930110
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  • 3
    Electronic Resource
    Electronic Resource
    13C cross polarization/magic-angle spinning NMR and infrared spectroscopic study of poly(ε-caprolactam) and of poly(ε-caprolactam)/polystyrene blends (1993)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 194 (1993), S. 1757-1763 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Infrared and 13C cross polarization/magic-angle spinning nuclear magnetic resonance (13C CP/MAS NMR) spectra and TH1ρ relaxation times of differently treated poly(ε-caprolactam)1Systematic IUPAC name: poly[imino(1-oxohexamethylene)]. (PCL) and of poly(ε-caprolactam)/polystyrene blends were measured and the fractions of the α- and α-crystalline and mesomorphous PCL forms were determined. The amounts of the α-form obtained from the infrared and 13C CP/MAS NMR spectra are in agreement. In the blends, the fraction of the PCL α-crystalline form is higher as compared with extruded pure PCL. The existence of a single TH1ρ parameter for PCL in each of the samples indicates small dimensions of the crystalline regions; the obtained TH1ρ values correspond to the PCL phase composition.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1993.021940622
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  • 4
    Electronic Resource
    Electronic Resource
    Study of the propagation centre in the anionic polymerization of lactams, 2Part 1: cf. ref.1.. Model study of the interaction between an activated monomer and N-acyllactam in dimethyl sulfoxide (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 197 (1996), S. 483-495 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Interaction of potassium 3,3-dimethyl-2-piperidone with 1-benzoyl-3,3-dimethyl-2-piperidone in DMSO as a model of the complex propagation centre in the anionic polymerization of lactams has been studied by 1H and 13C NMR, infrared spectroscopy, and, for the Li counterion, by MNDO calculations. The reactants were found to form a loose complex which can emerge in various geometries sharing the equivalence and relative motional freedom of both lactam moieties. Types of internal motions in the complex are suggested and their implications for the detailed idea of the propagation mechanism are discussed.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1996.021970205
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  • 5
    Electronic Resource
    Electronic Resource
    Study of the propagation centre in the anionic polymerization of (meth)acrylic monomers, 5Part 4: cf. ref.16. Nuclear magnetic resonance study of the model dimer in tetrahydrofuran (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 196 (1995), S. 3005-3014 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (1) as a model of the living dimer of tert-butyl methacrylate was studied in deuterated tetrahydrofuran (THF-d8) solution by 6Li, 7Li, 1H and 13C NMR. In agreement with earlier observations from infrared spectroscopy and with quantum chemical ab initio and semiempirical self-consistent field calculations, 1 is shown to have a strong tendency to an intramolecular coordination of Li to the penultimate ester carbonyl group. The competing linear form of 1 (with uncoordinated penultimate ester group) is shown to exist due to its stabilization by self-aggregation to form a dimer of 1. In contrast to the monomeric form of 1, the dimer does not bind THF into a specific solvate. Given the entropy-driven solvation at low temperatures, the occurrence of the dimeric aggregate is enhanced by higher temperature and concentration of 1. Both the cyclic and linear form of 1 are shown to exist in at least two different conformers and various solvation states. Their mutual exchange is several orders of magnitude slower than the anionic propagation reaction of tert-butyl methacrylate.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1995.021960923
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  • 6
    Electronic Resource
    Electronic Resource
    Study of the propagation centre in the anionic polymerization of (meth)acrylic monomers, 4Part 3: cf. ref.22 NMR and quantum chemical study of the initiation systems containing tert-butyl 2-lithioisobutyrate and lithium tert-butoxide or lithium 3-methylpentan-3-olate (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 196 (1995), S. 3117-3132 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In contrast to methyl 2-lithioisobutyrate (I), tert-butyl 2-lithioisobutyrate (A) in tetrahydrofuran (THF) appears to have one form only, irrespective of concentration (0,1-0,8 mol/L) or temperature (203-273 K). According to its relaxation characteristics, this form probably is a tetramer. The results indicate, however, that about 20% of A do not provide well-developed NMR signals and may be present as a partly organized pseudophase. A is shown to form 2:2 and 1:3 complexes with lithium tert-butoxide (B) and lithium 3-methylpentan-3-olate (C) in THF in dependence on their mole ratio and partly on storage time. The 7Li, 1H and 13C NMR relaxation behaviour of these complexes support their essentially tetrameric nature. Although intramolecular exchange of Li atoms in a complex appears to be rapid, intermolecular exchange of any of the components is vanishingly slow on the NMR time scale. The complexes of A with either B or C exhibit remarkable stability above 273 K, in contrast to that of A itself. The quantum chemical analysis of the complexes shows that they are held together by a cooperative system of polycentric bonds and electrostatic interactions. Thus they are not easily destroyed by thermal activation but they react readily with monomer. Implications of the results for anionic polymerization of (meth)acrylates are discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1995.021961004
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  • 7
    Electronic Resource
    Electronic Resource
    Study of the propagation centre in the anionic polymerization of acrylic monomers, 1. Spectroscopic study of methyl 2-lithioisobutyrate, an initiator for the anionic polymerization of acrylic monomers (1994)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 195 (1994), S. 3039-3056 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: As the simplest model for the propagation centre in the anionic polymerization of methyl methacrylate, the solution of methyl 2-lithioisobutyrate (1) in tetrahydrofuran was studied by means of 1H, 6Li, 7Li and 13C nuclear magnetic resonance (NMR), and Raman spectroscopy at various concentrations and temperatures. A system of equilibria of differently solvated dimeric, tetrameric and two isomeric trimeric aggregates was found and their thermodynamic constants were established. On the basis of the analysis of NMR chemical shifts, heteronuclear nuclear Overhauser effect correlation spectroscopy (NOESY) spectra and relaxation data, structures of the aggregates are suggested. The kinetics of the exchange between the aggregates and the lifetime of individual aggregates was established. The results suggest that the aggregation can interfere with initiation in the early steps of anionic polymerization of acrylics.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1994.021950904
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  • 8
    Electronic Resource
    Electronic Resource
    Study of the propagation centre in the anionic polymerization of (meth)acrylic monomers, 7Part 6: cf. ref.19. Study of the interaction of the living dimer with lithium tert-butoxide in tetrahydrofuran (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 197 (1996), S. 1889-1907 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Using 1H, 6I i, 7Li and 13C NMR, di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (A) as a dimeric model of the living poly(tert-butyl methacrylate) is shown to form well-defined aggregates with lithium tert-butoxide (B) in tetrahydrofuran. The prevailing aggregates with the composition A2B2 and AB3 are controlled mainly by the ratio A:B. The initial mixture of aggregates is formed very fast but is metastable. Using 1D and 2D spectra, 1H-1H and 1H-6Li nuclear Overhauser effect and relaxations of 1H, 7Li and 13C, both aggregates are shown to exist mainly in three conformational forms (b, c, d) of the A-part which are very similar in both aggregate types. In agreement with the previously published infrared spectra, form d has the γ-ester group of A coordinated to Li. d does not exchange with the ‘open’ forms b or c with perceptible rate on the NMR time scale. Its population is promoted by a larger content of B in the aggregate. By modified neglect of differential overlap (MNDO) quantum calculations, the aggregates A2B2 and AB3 are predicted to have a roughly cubical core (O—Li)4 which is distorted in the d form where one (AB3) or two (A2B2) Li atoms are pulled out of the cube by coordination to the γ-ester group. The stabilization of the supramolecule A2B2 or AB3 and the promoting effect of B on intramolecular coordination to the γ-ester group in A is explained in terms of a cooperative system of polycentric bonds and electrostatic interactions.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1996.021970610
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  • 9
    Electronic Resource
    Electronic Resource
    Ordered structures of syndiotactic poly(methyl methacrylates) studied by a combination of infrared, Raman, and NMR spectroscopy. (1986)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 24 (1986), S. 657-674 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The C — O stretching vibrations in Raman and infrared spectra of poly(methyl methacrylate) (PMMA) samples of various stereoregularity in solutions and in the solid state were measured. It was found that for ordered structures of syndiotactic (s) PMMA, transition dipole coupling of ester groups in ordered s-PMMA sequences leads to a splitting of the C — O stretching vibration into three components with wavenumbers equal in the solid state and in solution, and of different activity in Raman and infrared spectra. A comparison of the time dependences of self-aggregation of s-PMMA as measured by NMR and infrared spectroscopy indicates that the first phase of the aggregation process is detected by both methods. NMR analysis of the effect of the degree of stereoregularity on the self-aggregation of s-PMMA shows that the prerequisite for the generation of a stable ordered structure is the mutual interaction of two s-sequences of a minimum length of 9 monomer units. The experimental data obtained lead to the conclusion that, in self-aggregated s-PMMA, some of the ester groups are in close contact, with the interacting s-sequences probably forming a double helix.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1986.090240312
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  • 10
    Electronic Resource
    Electronic Resource
    Stereoselectivity of an early propagation step in the anionic polymerization of methyl methacrylate - ab initio SCF, MNDO and AM1 study (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 6 (1997), S. 437-450 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: On the basis of previous experimental and theoretical studies of low-molecular models of living poly(methyl methacrylate) and their coordination interactions, molecular states preceding and involving the propagation step of the anionic polymerization of methyl methacrylate (MMA) were investigated. Previously published structures of the intracoordinated form of the model dimer dimethyl 2-lithio-2,4,4-trimethylglutarate (DMMALi) and its free anion (DMMA) optimized using ab initio SCF 3-21G were reinspected and a new, similar but more stable, geometry was found. AM1 and ab initio 3-21G calculations of the addition of MMA to the anion derived from methyl isobutyrate were used to explore the applicability of semiempirical methods to the present problem. Intermediate complexes and transition states of the iso- and syndiotactic addition of MMA to DMMA and DMMALi were simulated using MNDO and AM1. The activation energy of MMA addition to DMMA is predicted to be substantially lower for the syndiotactic transition state. In contrast, only isotactic MMA addition is possible to the energetically favored intra-coordinated form of DMMALi (c-DMMALi). Syndiotactic addition to the uncoordinated form of DMMALi is apparently possible according to MNDO. Considering the earlier finding that c-DMMALi is favored by dilution and lower temperature in solvating media such as tetrahydrofuran, the differences in stereoregularity of the anionic polymerization of MMA caused by concentration, temperature or solvent polarity can be plausibly explained.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1997.040060209
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