bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Analysis of the Concentration Effects on Elution Volumes by Using the Preferential Solvation Parameter in Two SEC Packings
Authors: García‐Lopera Rosa , Gómez Clara M. , Abad Concepción , Campos Agustín 
Published: February 2003

AbstractSize exclusion chromatography (SEC) elution behavior of different solvent/polymer systems has been analyzed from chromatographic, thermodynamic, and hydrodynamic points of view in two organic column packings based on polystyrene/divinylbenzene (PS/DVB) copolymer, μ‐styragel and TSK‐Gel HHR. Although both packings present similar chromatographic properties, some differences arise when eluting the same systems. The values of the adsorption distribution coefficients, Kp, have been correlated with the preferential solvation coefficient, λ (see Figure), for both packings, showing that those systems with lower and negative λ values (denoting higher preferential solvation of the polymer by the gel packing) are those with Kp > 1. In addition, the main goal has been to make use of the λ values to adequately interpret the dependence of the elution volumes on injected polymer concentration. In this regard, the experimental concentration effects have been completely explained by taking into account not only the conventional hydrodynamic factors but also thermodynamic aspects such as the preferential solvation phenomenon.Plot of the preferential solvation coefficient, λ, as a function of the volume fraction of polymer (2), ϕ2, at three hydrodynamic volumes, Vh = 106 (○ •); 107 (□ ▪), and 108 (▵ ▴) mL · mol−1 for the system THF/PBD/PS (μ‐styragel: empty symbols; TSK‐Gel HHR (solid symbols).magnified imagePlot of the preferential solvation coefficient, λ, as a function of the volume fraction of polymer (2), ϕ2, at three hydrodynamic volumes, Vh = 106 (○ •); 107 (□ ▪), and 108 (▵ ▴) mL · mol−1 for the system THF/PBD/PS (μ‐styragel: empty symbols; TSK‐Gel HHR (solid symbols).
Synthesis of Poly(propylene oxide) with Strict Control of End Functionality, 1. Initiation with (4‐Methoxy)phenoxy Tetraphenylporphynatoaluminum
Authors: Lopitaux Garance , Ricart Guy , Faven Catherine , Coqueret Xavier 
Published: February 2003

AbstractThe polymerization of propylene oxide (PO) initiated by (4‐methoxy)phenoxy tetraphenylporphynatoaluminum (TPPAl‐O‐PMP) was studied with the aim of strictly controlling the end‐group functionality of the resulting poly(propylene oxide) (PPO), together with the molecular weight, in terms of average values and of narrow chain‐length distribution. The influence of the relative amount of reactants used for the preparation of the initiator on the nature and number of end groups was studied by various analytic methods including 1H NMR and UV spectroscopies and matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF) spectrometry. In spite of apparent living behavior observed from size exclusion chromatograpy (SEC) measurements, large variations in the yield of polymerization, determined after several hours of reaction, indicated a strong dependence of the propagation rate on slight variations around the 1:1 stoichiometry of triethylaluminum to the unmetallated porphyrin and to the phenolic ligand. Associated with the anomalous kinetic behavior, differences in the nature of the end groups were unambiguously evidenced by MALDI‐TOF spectrometry for narrow molecular weight (MW) distributed PPOs obtained with a slight excess of triethylaluminum and a slight deficit in added phenol with regard to porphyrin. A mechanism involving side reactions is proposed to account for the observed kinetic and structural features. Immortal polymerization of PO with strict control of MW distribution and functionality is obtained under appropriate conditions and consistently supported by various methods of MW determination.Principle of end‐group functionalization in porphyrin catalyzed PO polymerization.magnified imagePrinciple of end‐group functionalization in porphyrin catalyzed PO polymerization.
Quantitative Aspects of the Dendronization of Dendronized Linear Polystyrenes
Authors: Shu Lijin , Göossl Illdiko , Rabe Jürgen P. , Dieter Schlüter A. 
Published: February 2003

AbstractThe paper describes in detail how amine‐terminated dendronized polystyrenes 1(G2), 2(G3), and 3(G1) of varying generations (first: G1, second: G2, third: G3) were reacted with the G1 (and G2) dendrons 4, 5c, and 6b carrying active esters at their focal point to furnish polymers 7(G4), 8(G2), 9(G3), and 10(G4). All these dendronization steps were monitored using UV absorbance measurements after labeling the unreacted amines with the Sanger reagent, 2,4‐dinitrofluorobenzene, providing a quantitative assessment of the overall structural integrity achievable for dendronized polymers synthesized according to this divergent growth scheme. Polymers 3(G1), 8(G2), 9(G3), and 10(G4) represent a quasi‐homologous series of high molar mass dendronized polymers whose lengths and length distributions, in their deprotected (and thus charged) state, was determined by contour‐length histograms using scanning force microscopy (SFM). Finally, the decoration of representatives of this series with long alkyl chains is also reported.
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Copolymers from Methacrylic Acid and Trimethylsilyl Methacrylate ‐ Synthesis, Reactivity Ratios and Thermal Properties
Authors: Mormann Werner , Ferbitz Jens 
Published: February 2003

AbstractCopolymers from methacrylic acid (1) and trimethylsilyl methacrylate (2) have been synthesized by free radical copolymerisation and by controlled desilylation of poly(trimethylsilyl methacrylate) (3). The reactivity ratios were r1 = 2.75, r2 = 0.004. Differential scanning calorimetry showed a linear correlation between the peak temperature of the endotherm for the formation of cyclic anhydrides and the content of methacrylic acid in the copolymer. Obviously, the acid catalyses this reaction. The copolymers as well as poly(trimethylsilyl methacrylate) have a ceiling temperature. Sequence distributions were calculated and used to predict glass transition temperatures for comparison to the experimental results. The microstructure of the copolymers obtained by the different synthetic routes is different as shown from Tg and from their solubility. Those from desilylation are random with “reactivity ratios” of 1, those from copolymerisation seem to have longer sequences of methacrylic acid leading to formation of intermolecular aggregates.
Dependence of DSC peak temperature of anhydride formation on methacrylic acid content.magnified imageDependence of DSC peak temperature of anhydride formation on methacrylic acid content.
Cross‐Linked Poly(ε‐caprolactone/D,L‐lactide) Copolymers with Elastic Properties
Authors: Helminen Antti O. , Korhonen Harri , Seppälä Jukka V. 
Published: February 2003

AbstractCross‐linked ε‐caprolactone (CL) and D,L‐lactide (DLLA) copolymers with elastic properties were synthesized in three steps. First, the monomers were copolymerized in ring‐opening polymerization to obtain telechelic star‐shaped oligomers with almost completely random monomer distribution. The oligomers were methacrylated with methacrylic anhydride in the second step and cured in a third. Molar CL/DLLA compositions of 30/70, 50/50, 70/30, 90/10, and 100/0 were used to obtain elastic structures with a wide range of properties. The effect of the average length of the copolymer block on the properties of the networks was evaluated with three different co‐initiator contents (0.5, 1.0, and 2.0/100) in the oligomer synthesis. The oligomers were characterized by 13C NMR spectroscopy, size‐exclusion chromatography (SEC), and differential‐scanning calorimetry (DSC). The formation of elastic networks was confirmed by the absence of a flow region in dynamic mechanical analysis (DMA), the increase in Tg in DSC, and the full recovery of the sample dimensions after tensile testing. In addition, gel contents were high and the samples swelled in CH2Cl2. The networks possessed break stresses from 0.7–9.7 MPa with elongations from 80–350%. Networks with 100 or 90% of ε‐caprolactone retained their form in vitro for 12 weeks, but an increase in lactide content made the networks more vulnerable to hydrolysis.
Water absorption of the polymers during hydrolysis.magnified imageWater absorption of the polymers during hydrolysis.
Nano‐Scale Molecular Shapes of Water‐Soluble Chitin Derivatives Having Monodisperse Poly(2‐alkyl‐2‐oxazoline) Side Chains
Authors: Aoi Keigo , Takasu Akinori , Okada Masahiko , Imae Toyoko 
Published: February 2003

AbstractThe molecular shapes and the sizes of structures formed by chitin derivatives with monodisperse poly(2‐alkyl‐2‐oxazoline) side chains were investigated using atomic force microscopy (AFM), cryo‐transmission electron microscopy (cryo‐TEM), and small‐angle neutron scattering (SANS) analyses. A ring structure with an outside diameter of 45–60 nm and a cross‐sectional diameter of 10–18 nm was observed in the AFM image for chitin‐graft‐poly(2‐methyl‐2‐oxazoline) 1d (DP of the side chain, 8.5; [side chain]/[glucosamine unit], 0.53). From the cryo‐TEM observation of the graft copolymer 1d in 0.5 wt.‐% D2O solution, an average diameter of 40 nm for the particles was determined, with a narrow size distribution. SANS measurements of the 0.5 wt.‐% D2O solution of 1d revealed that the outside diameter of the particles and the cross‐sectional diameter were 57 nm and 8 nm, respectively. The absolute weight average molecular weight of 1d was determined to be 5.4 × 105 by static light scattering. From these results it was concluded that 1d can form a unimolecular ring structure in aqueous solution. However, graft copolymers with fewer side chains (1c; [side chain]/[glucosamine unit], 0.30) and with more side chains (1e; [side chain]/[glucosamine unit], 0.96) did not form rings but instead formed monodisperse unimolecular spherical particles of diameters of 28–36 nm by AFM. A graft copolymer 1f with relatively long side chains (DP of side chain, 19.6; [side chain]/[glucosamine unit], 1.00) was also observed as a spherical particle by AFM (diameter: 30–40 nm by AFM; 40 nm by SANS). On the other hand, an intermolecular aggregate formation (diameter of the aggregate: 36–143 nm) was observed for graft copolymers 1a and 1b having short side chains (DP of side chains, 5.6; [side chain]/[glucosamine unit], 0.35 and 0.48, respectively), with a spherical molecular particle of diameter 36 nm by the AFM analysis. Chitin‐graft‐poly(2‐ethyl‐2‐oxazoline) (2) (DP of side chains, 21.7; [side chain]/[glucosamine unit], 0.95) generated larger aggregates of diameter 100–400 nm by AFM. The complexation behavior of graft copolymer 1d with magnesium 8‐anilino‐1‐naphthalenesulfonate (ANS) and with N‐phenyl‐1‐naphthylamine (PNA) was also examined by fluorescence measurement in an aqueous solution. It was found that graft copolymer 1d complexed with both ANS and PNA, and the binding constants were calculated to be 7.5 × 104 M−1 and 5.3 × 104 M−1, respectively.
Chemical structure of chitin‐graft‐poly(2‐alkyl‐2‐oxazoline).magnified imageChemical structure of chitin‐graft‐poly(2‐alkyl‐2‐oxazoline).
Critically Evaluated Termination Rate Coefficients for Free‐Radical Polymerization, 1. The Current Situation
Authors: Buback Michael , Egorov Mark , Gilbert Robert G. , Kaminsky Vladimir , Olaj Oskar F. , Russell Gregory T. , Vana Philipp , Zifferer Gerhard 
Published: February 2003

AbstractThis is the first publication of an IUPAC‐sponsored Task Group on “Critically evaluated termination rate coefficients for free‐radical polymerization.” The paper summarizes the current situation with regard to the reliability of values of termination rate coefficients kt. It begins by illustrating the stark reality that there is large and unacceptable scatter in literature values of kt, and it is pointed out that some reasons for this are relatively easily remedied. However, the major reason for this situation is the inherent complexity of the phenomenon of termination in free‐radical polymerization. It is our impression that this complexity is only incompletely grasped by many workers in the field, and a consequence of this tendency to oversimplify is that misunderstanding of and disagreement about termination are rampant. Therefore this paper presents a full discussion of the intricacies of kt: sections deal with diffusion control, conversion dependence, chain‐length dependence, steady state and non‐steady state measurements, activation energies and activation volumes, combination and disproportionation, and theories. All the presented concepts are developed from first principles, and only rigorous, fully‐documented experimental results and theoretical investigations are cited as evidence. For this reason it can be said that this paper summarizes all that we, as a cross‐section of workers in the field, agree on about termination in free‐radical polymerization. Our discussion naturally leads to a series of recommendations regarding measurement of kt and reaching a more satisfactory understanding of this very important rate coefficient.
Variation of termination rate coefficient kt with inverse absolute temperature T−1 for bulk polymerization of methyl methacrylate at ambient pressure.[6] The plot contains all tabulated values[6] (including those categorized as “recalculated”) except ones from polymerizations noted as involving solvent or above‐ambient pressures.magnified imageVariation of termination rate coefficient kt with inverse absolute temperature T−1 for bulk polymerization of methyl methacrylate at ambient pressure.[6] The plot contains all tabulated values[6] (including those categorized as “recalculated”) except ones from polymerizations noted as involving solvent or above‐ambient pressures.
Homo‐ and Copolymerization of ω‐Functional Polystyrene Macromonomers via Coordination Polymerization
Authors: Lahitte Jean‐François , Peruch Frédéric , Plentz‐Meneghetti Simoni , Isel François , Lutz Pierre J. 
Published: February 2003

AbstractMacromonomers have been extensively used, as well defined building blocks for various macromolecular architectures via anionic, ROMP and free radical homo‐ or copolymerization processes. The purpose of the present work was to examine the homopolymerization and copolymerization of ω‐allyl, ω‐undecenyl and ω‐vinylbenzyl polystyrene (PS) macromonomers, in the presence of early or late transition metal catalysts. The influence of several parameters (type of catalytic system, nature of polymerizable end‐group and molar mass of the macromonomer) on the homopolymerization was first investigated. Whereas ω‐allyl or ω‐undecenyl PS macromonomers were not very reactive in homopolymerization whatever the catalyst, ω‐vinylbenzyl PS macromonomers gave interesting results with CpTiCl3/MAO and Cp*TiCl3/MAO. The copolymerization of these macromonomers with ethylene was also studied in the presence of the following palladium catalyst: [(ArNC(Me)C(Me)NAr)Pd(CH2)3(COOMe)]+BAr4′−(VERSIPOL™) (Ar = 2,6‐iPr2–C6H3 and Ar′ = 3,5‐(CF3)2C6H3). ω‐vinylbenzyl PS macromonomers could not be incorporated into poly(ethylene) chains. On the contrary, the incorporation of ω‐allyl PS macromonomers was achieved. Moreover, for macromonomers containing an alkyl spacer between the allylic unit and the PS chain, the incorporation rate, the copolymerization yield and the molar masses of the copolymers were increased, giving access to a new type of graft copolymer structure.
Synthesis of polystyrene macromonomers.magnified imageSynthesis of polystyrene macromonomers.
Controlled Ring‐Opening Polymerization of Lactones and Lactide Initiated by Lanthanum Isopropoxide, 2. Mechanistic Studies
Authors: Save Maud , Soum Alain 
Published: February 2003

AbstractThe mechanism of ring‐opening polymerization of some lactones and lactide initiated by lanthanum isopropoxide has been comprehensively investigated. NMR and viscosity analyses demonstrated that three active polymer chains grow per lanthanum atom and that, depending on the coordinating ability of the monomer, propagation proceeds on aggregated or unaggregated active species. It is also demonstrated that inter‐ and intramolecular side reactions are limited and that lanthanum‐based initiator selectivity in ring‐opening polymerization is analogous to that of aluminum ones.
Part of the proposed mechanism for the lanthanum alkoxide initiated polymerization of ε‐caprolactone.magnified imagePart of the proposed mechanism for the lanthanum alkoxide initiated polymerization of ε‐caprolactone.
Stereochemical Pseudohexad 13C NMR Resonances and Regioregular Propylene/Ethylene‐1‐13C Copolymers
Authors: Sessa Irene , Ferro Dino Romano , Grisi Fabia , Liguori Dario , Milano Giuseppe , Zambelli Adolfo 
Published: February 2003

AbstractThis paper reports the assignment of the 13C NMR resonances of the Sββ and Sαγ methylenes observed in the spectra of copolymers of propylene with trace amounts of enriched ethylene‐1‐13C. The assignment is achieved by comparing the chemical shifts calculated by an empirical method (at the CH2 stereochemical pseudohexad level), with the experimental spectra of regioregular copolymers with different stereochemical structure. The implications of the observed Sββ and Sαγ resonances on the stereochemical polymerization mechanisms are also discussed.
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Change of Tacticity during Thermal Degradation of PMMA
Authors: Wondraczek Katrin , Adams Jörg , Fuhrmann Jürgen 
Published: February 2003

AbstractThe change of tacticity during thermal treatment of commercial poly(methyl methacrylate) (PMMA) at 200 °C in air was studied in detail. The coupling between de‐ and repolymerization is contrasted by NMR analysis. The parameter of tacticity opens up a new perspective in describing the consequences of degradation. The analysis of the configuration of the residue was performed by 1H NMR spectroscopy. The ratios of the three characteristic triads – of isotactic (I), syndiotactic (S), and heterotactic (H) sequences – depend on degradation time and approach a constant value of S/H/I = 0.3:0.4:0.3 at about 80% of mass loss when starting with an initial ratio of S/H/I = 0.5:0.4:0.1. A two‐parameter two‐state model is proposed to calculate the transition from the initial to the final stereo‐sequence distribution generated by de‐ and repolymerization. The correlation between the evaluated parameters and the degradation processes leads to information on repolymerization, which is dominant after about 50% weight loss, i.e., from about 20 h on, and afterwards in two consecutive steps with a rapid change in tacticity, when 50% of the residual material is converted into a new sequence distribution. This type of tacticity conversion has its maximum speed at about 80% weight loss in the second of the consecutive steps.
Triad portions during degradation determined by 1H NMR spectroscopy: • syndio‐, ♦ hetero‐, ▴ isotactic triads.magnified imageTriad portions during degradation determined by 1H NMR spectroscopy: • syndio‐, ♦ hetero‐, ▴ isotactic triads.
Grafting of Vinyl‐Type Polynorbornene on Polybutadiene and Polyisoprene
Authors: Schroers Michael , Demeter Jürgen , Dehnicke Kurt , Greiner Andreas 
Published: February 2003

AbstractHigh molecular weight vinyl‐type polynorbornene was obtained by polymerization of norbornene initiated by [NiBr(NPMe3)]4/B(C6F5)3. Polymerization in the presence of olefins resulted in termination of polynorbornene chains by olefinic moieties. Molecular weights of polynorbornenes terminated by vinylidene compounds are lower than those terminated by vinyl and vinylene compounds. Corresponding polymerizations with polybutadiene and polyisoprene yielded graft copolymers with polynorbornene as grafts without contamination by homopolymerized polynorbornene. Grafting reactions were proved by spectroscopy, GPC, and degradation experiments using OsO4.
GPC traces (refractometer detector) of PN obtained for the polymerizations of 2 in the presence of 4d.magnified imageGPC traces (refractometer detector) of PN obtained for the polymerizations of 2 in the presence of 4d.
Synthesis, Characterization, and Thermal Properties of Block Copolymers Containing Poly(styrene‐co‐4‐vinylpyridine) and Poly(styrene‐co‐butyl acrylate) by Controlled Radical Polymerization
Authors: Taube Carsten , Fernández García Marta , Schmidt‐Naake Gudrun , Fischer Hartmut 
Published: February 2003

AbstractRadical polymerization of styrene and mixtures of styrene and 4‐vinylpyridine was performed in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) producing polymers with controlled molecular weights and molecular weight distributions. The living nature of these polymers was confirmed by using them as macroinitiators in the block copolymerization of styrene and butyl acrylate. The thermal properties of the synthesized statistical diblock copolymers measured by differential scanning calorimetry indicated that a phase‐separated morphology was exhibited in most of the block copolymers. The results were confirmed by transmission electron microscopy (TEM) and small angle X‐ray scattering (SAXS) showing microphase‐separated morphology as is known for homo A‐B diblock polymers.
SAXS of a block copolymer synthesized from S/V 70:30 macroinitiators (03) with one detected Tg.magnified imageSAXS of a block copolymer synthesized from S/V 70:30 macroinitiators (03) with one detected Tg.
Ethene/Norbornene Copolymerization using the Catalyst System Pri[(3‐Pri‐Cp)Flu]ZrCl2: Determination of the Copolymerization Parameters and Mechanistic Considerations
Authors: Wendt Ralf A. , Mynott Richard , Fink Gerhard 
Published: February 2003

AbstractThe 13C NMR spectra of ethene/norbornene copolymers in which there are no norbornene microblocks are much simpler than those of copolymers in which norbornene microblocks are present, making it possible to completely assign all the 13C resonances to the corresponding pentads in the copolymer chain. However, there is disagreement in the literature over several assignments of the ethene 13C NMR signals. In this paper these discrepancies are summarized and discussed. This contribution also reports ethene/norbornene copolymerizations carried out at various temperatures using the homogeneous catalyst system Pri[(3‐Pri‐Cp)Flu]ZrCl2. The 13C NMR spectra of the copolymers were analyzed in the light of the discussion above and the triad distributions were used to determine the copolymerization parameters by Markov first‐ and second‐order statistical models. On the basis of these results, the mechanism generating such an alternating microstructure in these copolymers is discussed and compared with the mechanism previously proposed in the literature.
The 13C NMR spectrum with signal assignments of an ethene/norbornene copolymer without norbornene microblocks.magnified imageThe 13C NMR spectrum with signal assignments of an ethene/norbornene copolymer without norbornene microblocks.