摘要:

AbstractRaman spectra have been obtained of the longitudinal acoustic mode (LAM) in α‐BrC20H41and α, ω‐BrC20H40Br, and compared with such spectra forn‐C20H42. Normal coordinate analyses of these three molecules clearly account for (i) the frequency decreases on Br substitution; (ii) the presence of doublet LAM modes in both brominated molecules; and (iii) the decrease in the total intensity of the LAM mode resulting from the added masses, as distinct from the increase predicted by the elastic rod model. These results thus provide experimental support for predictions made from normal coordinate and intensity analyses regarding the influence on LAM bands of mass perturbations at the ends of paraffini

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240701

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractDetailed normal‐coordinate analysis has been carried out on a large number of conformers of model molecules of poly(oxyethylene); the model molecules treated are CH3(OCH2CH2)nOCH3withn= 2,3, and 6. The systematic treatment provides well‐defined correlations between conformation and vibrational spectra of poly(oxyethylene). The vibrations in the region 1050–800 cm−1, which are associated with the CO and CC stretching and CH2rocking modes, are highly dependent on the conformation of the polymer chain. On the basis of these correlations, the infrared and Raman spectra of the molten state and of the aqueous solution are interpreted in terms of the conformational states. The analysis indicates that the following conformational fragments are present in these phases:GT‐TG(T:trans;G: gauche),TT‐TG,GT‐GG,TT‐TT, andTT‐GGfor the CH2CH2OCH2CH2group, andTGTandTGGfor the OCH2CH2O group. Conformational fragmentsGT‐TG′ andGT‐G′G′ are

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240702

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractModel butanediol–MDI–polypropylene oxide polymers have been synthesized to explore the structure–property relationships in urethane/polyether polymers. The results of mechanical, thermal, and spectroscopic analyses agree remarkably well. The phase mixing in these polymers decreases with increasing hard‐segment length, while the hard‐segment stability increases with increasing hard‐segment length. This is demonstrated clearly by dynamic mechanical, differential scanning calorimetry, infrared, and NMR studies. The importance of hydrogen bonding to the stability of the hard segment is strongly supported by the variable‐temperature infrared experiments. The critical hard‐segment size for phase segregation was shown to be two butanediols per hard segment. The temperature limit of the flatness of the storage modulus was tied to the thermal stability of the hard‐segment hydrogen bonding which is controlled largely by the length of the hard segment and the extent of the

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240703

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractMolecular aggregation in polytrimellitamideimide (PAI) was investigated by small‐angle x‐ray scattering (SAXS). PAI films annealed above the glass transition temperature show a scattering peak characteristic of two‐phase structure. A one‐dimensional model was used to analyze these SAXS curves. The more ordered phases are produced at higher annealing temperature. The average thickness of the ordered lamellae is comparable with the repeating length of the main chain. The relative difference of electron density between two phases is only a few percent, which shows that the two‐phase structure of PAI, like that of aromatic polyimide, differs essentially from that of ordinary crystalline

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240704

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractWe have combined pressure–volume–temperature measurements and high‐temperature x‐ray diffraction to calculate the heat of fusion of the poly(4‐methyl pentene‐1) crystal from the Clapeyron equation. We find ΔHf= 14.8 cal/g, only about half as large as several literature values. The new value of the heat of fusion leads to increased degrees of crystallinity, in agreement with the highly crystalline appearance of the x‐ray patterns of typical samples, in particular oriented fibers. The new entropy of fusion at constant pressure of 2.46 cal/deg per mole of monomer units is significantly lower than the values for polypropylene, polybutene‐1, and polypentene‐1, indicating possible ordering in the me

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240705

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractA study of molecular orientation in a series of five one‐way‐drawn sheets of poly(ethylene terephthalate) is reported. Five orientation averagesP lmnrwhich characterize the benzene‐ring orientation were determined directly by Raman spectroscopy. Two further averagesP 202randP 222rwere determined from a combination of Raman spectroscopy and refractive index measurements on the basis of two different conformational models. As in a previous publication, the seven averagesP lmnrwere used to estimate all theP lmnrup to fourth order for the benzene rings on the assumption that in each case the actual distribution of orientations is close to the most probable distribution. The seven orientation averagesP lmnrfor each drawn sheet were also compared with those calculated on the basis of two simple models for the development of molecular orientation during drawing, the pseudoaffine deformation scheme and the rubber network model. It was shown that the orientation of the chain axes is closer to that predicted by the rubber network model, the pseudoaffine deformation scheme greatly overestimating the degree of chain biaxiality. The results also show that the benzene ring planes are preferentially oriented toward the planes of the sheets. The chain axis orientation is, however, nearly uniaxial and similar to that observed for uniaxially drawn samples, suggesting that there is no direct connection between the processes of chain axis orientation and preferential orientation of the be

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240706

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThe aggregate model is extended to examine the relationship between mechanical anisotropy and molecular orientation in one‐way drawn sheets of poly(ethylene terephthalate). It is assumed that both the aggregate and the unit of structure have orthorhombic symmetry. On the basis of a number of detailed assumptions regarding the appropriate application of the model, calculated bounds are obtained for the elastic constants that are in reasonable agreement with the experimental values. The implications of these results with regard to molecular orientation are considered, and it is concluded that both the chain orientation and orientation around the chain axis are important in determining the mechanical anisotrop

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240707

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractAn aromatic semirigid polyquinoline, poly[2,2′‐(p,p′‐oxydi‐p‐phenylene) 6,6′‐oxybis(4‐phenylquinoline)], has been studied in dilute solution using viscometry, light scattering, and size‐exclusion chromatography coupled with low‐angle light‐scattering detection (SEC/LALS). The SEC/LALS technique permits determination of the intrinsic viscosity and absolute molecular weight for a series of narrow fractions without preparative fractionation. Aggregation that was observed in dilute chloroform solutions was found to be related to protonation of the polyquinoline by HCI present in chloroform. Unperturbed dimensions calculated from the SEC/LALS results show the chain to have nearly freely rotating dimensions, as expected for a chain composed of long (12‐Å) rigid segments c

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240708

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractThrough x‐ray diffraction, the changes in the unit‐cell parameters of crystal forms I and II of polybutene‐1 were followed from room temperature to the melting point. These data were combined with the results of other measurements to computer the heats and entropies of fusion by use of the Clapeyron equ

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240709

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY

摘要:

AbstractAn Abbé refractometer with a rotatable polarizer mounted on the eyepiece is used for determining the two principal refractive indices of birefringent concentrated solutions of ethyl cellulose in m‐cresol and in acetic acid. At a certain concentration, birefringence appears for both systems, and the concentration agrees with that for the onset of iridescence (here defined as the critical concentrationCafor formation of the liquid‐crystalline phase). The birefringence of concentrated solutions depends strongly on concentration and temperature and can be generalized by a master curve. The refractive index increments for both systems are almost independent of temperature at high concentrat

ISSN:0887-6266    

DOI:10.1002/polb.1986.090240710

出版商:John Wiley&Sons, Inc.    

年代:1986

数据来源: WILEY