摘要:

AbstractDifferential scanning calorimetry (DSC) studies show that poly(ethylene oxide) (PEO) exhibits three transition regions below its melting point. The effects of annealing on the intensity and temperature of these transitions enable us to locateT

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150801

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractPoly(ethylene oxide) (PEO) was spin‐labeled with 3‐chlorocarbonyl‐2,2,5,5‐tetramethylpyrroline‐1‐oxyl. Correlation times were calculated from 173 to 375°K. For estimating slow‐motion rotational correlation times three models were used: Brownian diffusion, “moderate jump” diffusion, and “large jump” diffusion. Analysis of the changes in the extrema separation and spectra shape with temperature strongly suggests the presence of β and γ processes in solid poly(ethylene oxide). The Brownian diffusion model gives, for the γ relaxation, an activation energy of 8 kcal mole−1which is in good agreement with that found using dielect

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150802

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractRaman depolarization (ρ) measurements have been made over the temperature range 20>T>60°C for solutions of poly(dimethyl siloxane) (mol wt 7.7 × 104and 2.0 × 104) for several concentrations up to 100%. The band studied was the highly polarized methyl stretch at 2907 cm−1. Computer calculations of the probabilityptof a rotational isomer beingtransallow the ρ values to be related to ΔG, the free energy of mixing. ΔGis plotted as a function of concentration and minima are observed at 60 ± 3% (mol wt = 7.7 × 104) and 70 ± 3% (mol wt

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150803

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe spin‐lattice relaxation time and the nuclear Overhauser enhancement (NOE) of19F nuclei in dilute solutions of poly(p‐fluorostyrene) and poly(m‐fluorostyrene) were measured as a function of molecular weight, concentration, temperature, solvent, and field strength. Models for local motion of the chain backbone based on independent internal rotations or on one‐dimensional defect diffusion failed to provide a quantitative description of bothT1and the NOE. A model based on three‐bond crankshaft motions and a cutoff of coupling along the backbone gives a consistent account of these results as well as13C nuclear magnetic resonance (NMR) relaxation data on polystyrene from the literature. The model provides a finite set of exponential correlation times to describe local motion, the center of the distribution lying in the nanosecond region for dilute solutions of polystyrenes in normal solvents. The apparent activation energy for the backbone motion obtained from the temperature dependence of the average correlation time based on NMR data is about 20 kJ mole−1. The local correlation times based on NMR are appreciably shorter than those determined by dielectric relaxation. This discrepancy points to the existence of several different local motions which make different contributions depending upon the experimental techniq

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150804

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe effect of molecular orientation on the linear swelling of nylon 6 caused by absorption of water was studied using two kinds of oriented films, melt drawn and cold drawn. The molecular orientation causes anisotropy in swelling at all humidities such that the swelling is larger in the orientation direction than in the directions perpendicular to it. The large contribution of crystalline orientation to this phenomenon was expected for the melt drawn film which has practically no amorphous orientation. An analysis with a two‐phase morphological model reveals that the distance between the crystallites is a prominent factor controlling the degree of linear swelling, and that the anisotropy of swelling arises from the change in the distribution of crystallites due to orientation. By comparing the result for the melt drawn film with that for the cold drawn film, which has considerable amorphous orientation, it was proven that molecular orientation in the amorphous phase where swelling actually occurs does not depend so much on the degree of swelling as on the distribution of crystallite

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150805

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractFourier transform infrared spectroscopy has been used for the detection of thermally induced conformational changes in atactic poly(vinyl chloride) (PVC). Difference spectra emphasize changes in the distribution ofgauchedefects in the chains as functions of temperature and annealing. Specific bands in the ν(CCl) and δ(CH2) regions varied with inverse temperature, allowing a calculation of the activation energies of the rotamer species. Conformational changes were also detected in quenched PVC films as a result of annealing below the glass transition temperature,T

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150806

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractDielectric constants have been determined for a fraction of poly(diethylene terephthalate) in benzene at several temperatures. The data indicate that the dipole moment ratio 〈μ2〉/Nm2is somewhat higher than that of poly(ethylene oxide), and its temperature coefficient is in the vicinity of zero. Both the dipole ratio and its temperature coefficient are in very good agreement with those predicted by the rotational isomeric state theory. Using this theory, the unperturbed dimensions of poly(diethylene terephthalate) were calculated and it was found that (〈r2〉/M)∞= 0.80 Å2(g mol wt)−1, a value intermediate between those of poly(ethylene oxide) (0.57) and poly(ethylene terephth

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150807

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractLow‐density polyethylene was modified by the inclusion of phosphonate ester pendent groups by using an oxidative chlorophosphonylation reaction followed by esterification of the polyethylene poly(phosphonyl chloride) with an alcohol. Two different types of phosphonate esters were prepared: dimethyl phosphonate from the reaction with methanol and a phosphonate graft copolymer from the reaction with hydroxy‐terminated poly(ethylene oxide) (PEO). For the latter, oligomers with molecular weights of 350 and 750 were used. For each type of phosphonate, a series of polymers were prepared with pendent group concentrations ranging from 0 to 9.1 substituents per 100 carbon atoms. The modified polymers were characterized by infrared spectroscopy, differential scanning calorimetry, and by measurement of the tensile modulus. Infrared spectroscopy proved to be useful for determining if the polymer modification reaction resulted in entirely phosphonate ester pendent group substitutions or if unesterified phosphonic acid groups were also present. The polymers prepared in this investigation exhibited no infrared absorbances arising from phosphonic acid groups. The presence of phosphonate ester groups resulted in a decrease of crystallinity with increasing phosphonate concentration and with the exception of the polymers containing 9.1 PEO–phosphonate grafts per 100 carbon atoms, the effect of phosphonylation on the melting temperature of the polymers was consistent with Flory's theory for the melting point depression of random copolymers. The tensile modulus measured from a constant uniaxial elongation experiment decreased with increasing phosphonylation. The behavior of all three phosphonate series was identical and could be attributed to the effect of decreasing polymer crystall

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150808

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractSamples of ultradrawn high density polyethylene were studied by thermomechanical analysis. The purpose was to study the dimensional changes in polyethylene morphologies of extreme orientation. Dimensional changes were measured from −140 to +70°C with a precision of better than 1%. A negative thermal expansion coefficient was observed along the length (caxis) of the fibers containing the polyethylene morphologies of extreme orientation. A change in negative coefficient is observed between −35 and −45°C. The sign and magnitude of the expansion coefficient confirm, along with other evidence, the existence of extended chain structures in these morphologies. A series‐parallel model has been developed for the ultradrawn polyethylenes to describe the dimensional changes with te

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150809

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe first order intramolecular rate constant for the reaction between the terminal groups of flexible macromolecules is calculated in the partial draining case, following the theory formulated by Wilemski and Fixman for diffusion controlled reactions. Substantial differences with respect to the nondraining and free‐draining limits are evidenced, and it is shown that the rate constant in the partial‐draining case has relevant contributions from all the modes of the bead‐spring chain. The effects of chain flexibility and hydrodynamic interaction in macromolecules of increasing molecular weight are examined. The effective diffusion constant of the end groups increases with both the flexibility and the length of the chain. Numerical results for polystyrene (PS) and polydimethylsiloxane (PDMS) are presented and employed to calculate the relative quantum yield for fluorescence quenching. For highly flexible chains, like PDMS, quenching effects are expected in a range of molecular weight well above the limit of validity of the bead‐spring model. On the contrary, for more rigid polymers, like PS, the quenching can be observed only at molecular weights lower than this limit. The calculated behavior is compared with some experimental results recently obtained by the

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150810

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY