ISSN:0749-1581    

DOI:10.1002/mrc.1260321302

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:0749-1581    

DOI:10.1002/mrc.1260321303

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractIt has been demonstrated that1H 2D NMR of solids allows the correlation of structural information [1H chemical shift via combined rotation and multiple pulse spectroscopy, (CRAMPS)] in one frequency dimension with information on the dynamics (1H wideline) in the second dimension. Furthermore, domain sizes of individual phases found in heterogeneous solids can be determined by modelling1H‐1H spin diffusion occurring during a mixing periodtm. The experiment was applied to a poly(ethylene oxide)—polystyrene (PEO‐b‐PS) diblock copolymer. With standard double resonance magic angle spinning equipment, mobile poly(ethylene oxide) and mainly rigid polystyrene blocks in the polymer can be discriminated. By calibration with small‐angle x‐ray scattering data for the diblock copolymer, the spin diffusion coefficient for a system of intermediate mobility can be established. Thereby one can to fill the gap within the series of spin diffusion coefficients of highly mobile systems on the one hand and rigid systems on the other. Further applications of the experiment ar

ISSN:0749-1581    

DOI:10.1002/mrc.1260321304

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractMethyl 2‐lithioisobutyrate (LIMIB) is shown to form 3:1, 2:2 and 1:3 complexes with lithiumtert‐butoxide (LTB) in THF, depending on their molar ratio and storage time. The rate of formation of the complexes varies inversely as their stability: the 3:1 (LIMIB:LTB) complex is formed immediately but is not very stable; the full formation of the 1:3 complex takes about 20 h at −15°C but the product can be kept for several hours at room temperature without marked change.1H,13C,6Li and7Li NMR and MNDO results suggest that the core of any kind of the complex is formed by a cubic (Li‐0)4structure with each of the four Li atoms bound to three equivalent oxygens. The structure of the complexes with lesstert‐butoxide is less tightly packed. The complexes do not exhibit intermolecular exchange of Li atoms; their intramolecular exchange was not found but cannot be excluded. Preliminary results are presented for living MMA oligomers prepared by initiation with the LIMIB‐LTB system. The structure of these oligomers is not significantly affected by the equilibrium state of the initiation system. The living centre is found to be coordinated both to LTB and to the penultimate ester group. Although improved in stability by LTB coordination, the living oligomers exhibit marked self‐termination in THF

ISSN:0749-1581    

DOI:10.1002/mrc.1260321305

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractProton spin diffusion measurements were made using the Goldman—Shen technique of bisphenol‐A polycarbonate containing 10 wt% trioctyl phosphate at temperatures below the glass transition temperature. The proton lineshapes reveal the existence of dynamic heterogeneities in the glass and spin diffusion can be observed from the more mobile to the less mobile domain. The time‐scale for spin diffusion is 4–10 ms and the mobile domain size is estimated at 11 Å at 339 K. This estimate is consistent with a mobile domain of approximately two diluent molecules and 11 polymer repeat units. This grouping can be compared with the results of a statistical lattice model used to estimate local environments at this com

ISSN:0749-1581    

DOI:10.1002/mrc.1260321306

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractMost binary mixtures of polymers are not miscible on the molecular level in the absence of specific intermolecular interactions. Solid‐state13C and 2D13C,1H NMR has been used to study miscible polymer blends in an attempt to identify the interacting groups and gain a molecular level understanding of the forces that drive irascibility. Selective polarization transfer methods, either solid‐state nuclear Overhauser effects or windowless isotropic mixing, were used to study these interactions, and the interacting groups in several strongly and weakly interacting polymer blends were identif

ISSN:0749-1581    

DOI:10.1002/mrc.1260321307

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractNatural abundance13C chemical shift anisotropy (CSA) spectra of the aromatic CH carbons of bisphenol‐A (BPA) residues were measured for BPA polycarbonate (BPAPC) and polyarylate (PAr) films at different temperatures by selective excitation switching angle sample spinning (SESASS) NMR spectroscopy. The CSA spectra thus obtained were analysed in terms of the two‐site exchange model for the flip motion of the phenylene group. In BPAPC, wide distributions in flip angle around 0° and 180° are well revealed under the situation of the first exchange limit for the flip motion and the widths become significantly broader with increasing temperature. These results are in good agreement with those of the previous2H NMR analyses. Similar wide distributions in flip angle are also recognized even at lower temperatures for PAr, which is a non‐crystalline polymer composed of BPA and phthalic acid residues, suggesting more enhanced phenylene motion in this polymer. Moreover, the CSA spectra obtained for PAr above 60°C are found not to be reproduced by using the simple two‐site exchange model primarily based on the flip motions around 0° and 180°, probably owing to the onset of larger scale random motion of t

ISSN:0749-1581    

DOI:10.1002/mrc.1260321308

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe results of proton NMRT1xzmeasurements on poly(ethylene terephthalate) (PET) films and fibers processed under various conditions are presented. Consistent with previous results, two domains are found in isotropic, amorphous PET. The NMR results provide an accurate measure of crystallinity in PET films and fibers, without requiring any assumptions about the semi‐crystalline morphology of the polymer. The NMR technique is particularly advantageous for PET fibers where orientation effects interfere with the more traditional density determination of crystallinit

ISSN:0749-1581    

DOI:10.1002/mrc.1260321309

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractNMR was used to provide evidence of site—site interactions in bifunctional polymers. A series of polymer‐supported phosphonic acid and phosphonate ester ligands was examined by solid‐state31P NMR spectroscopy. Interaction between phosphonate monoethyl ester sites was demonstrated and disruption of this interaction by the addition of diethyl ester groups was shown. The effect of the synthesis conditions on the bifunctionality of resins containing both phosphonic acid and quaternary amine groups was examined. The spectra indicated that the phosphonic acid groups exists as phosphonate ions in the bifunctional amine/acid polymers and are capable of displacing chloride as the counterion on the amine

ISSN:0749-1581    

DOI:10.1002/mrc.1260321310

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractPolymorphs of highly syndiotactic polypropylene were studied by magic angle spinning13C NMR. The conversion of one crystalline form into another was observed by the formation of different conformers of the polymer chain. The reversion of the metastable forms to the conventional crystalline phase was followed directly by variable‐temperature experiments and the addition of plasticizers. The multiplicity of signals associated with these structures were fully assigned in terms oftrans,gaucheconformations, by taking into account a sequence of four bonds in the main chain. Additional signals due to the packing of helical chains of opposite chirality are discussed in terms of the packing disorder present in the structure. The spectral pattern due to the amorphous region depends on temperature and thermal history, because the chain sequences can be observed under conditions of static and dynamic disorder as compared with the NMR time‐scale. The chains are fairly elongated, because they contain a considerable amount oftranssequences. Phase distribution and interfaces were characterized by hydrogen relaxation times in the rotating frameT1pH. Phase specificity was retained by recovering the magnetization on the13C nucleus under high‐resolution conditions. Apparently spin diffusion cannot average out theT1pH value over the whole material when the thickness of the crystalline lemellae is increased by the annealing treatment. In the stretched material crystalline and amorphous phases are intimate and the chains in the amorphous phase also appear to be partly ext

ISSN:0749-1581    

DOI:10.1002/mrc.1260321311

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY