摘要:

AbstractLaser light scattering experiments with polyacrylamide gels containing diffusing bovine plasma albumin are described. Complete heterodyne beating hasnotbeen assumed, and an account is given of a novel method for finding the degree of spectral broadening by scanning angles of scatter while measuring the temporal autocorrelation function. Results obtained by this method for polyacrylamide gels and un‐cross‐linked solutions in the absence of diffusing protein, are compared with those of other authors. In the presence of the protein there is a complex interaction between the diffusion coefficient of the protein and the coefficient associated with the diffusing fluctuations in segment density of polyacrylamide. The diffusing protein dominates at low gel concentrations, and the gel density fluctuations dominates at high gel concentrations. It is proposed that the protein preferentially occupies the less dense regions of the gel, so that at low gel concentrations, where it diffuses faster than the gel fluctuations, it tends to cancel them out, whereas at high gel concentrations where the protein is highly impeded by the gel structure, it tends to be carried along by the gel density fluctuati

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250401

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractWe examine the influence of high‐energy radiation and subsequent aging and orientation on the degree of crystallinity of poly(vinylidene fluoride) (PVDF) films. In particular, PVDF films were exposed to electron beam radiation (doses up to 50 Mrad) and aged at room temperature for varying lengths of time followed by uniaxial orientation. The degree of crystallinity of these films was found to increase significantly with increasing radiation dose. In addition, a further substantial increase in the degree of crystallinity was observed upon subsequent aging of irradiated films at room temperature. Upon orientation, in addition to a further rise in the degree of crystallinity, the crystallites were observed to undergo the α form → β form transformation, the latter phase being the polar phase effective for piezo‐electric/pyroelectric a

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250402

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe melting points of miscible blends prepared from two crystalline polymers, poly(caprolactone) (PCL), and Saran a random copolymer of vinylidene chloride with vinyl chloride [P(VCl2‐VC)], vinyl acetate [P(VCl2‐VA)], or acrylonitrile [P(VCl2‐AN)], have been measured by differential scanning calorimetry as a function of the crystallization temperature. The equilibrium melting points of these blends have been determined by Hoffman‐Weeks plots. From two series of data, one of which was obtained by measuring the melting points of PCL crystals and the other by measuring the melting points of Saran crystals, the thermodynamic polymer‐polymer interaction parameters of PCL/Saran blends have been calculated over the full range of composition. The two series of data merge into a smooth curve, which is composition dependent, despite the fact that the melting points of PCL and P(VCl2‐VC) or P(VCl2‐VA) are very different at 58.1, 183.5, and 184.2°C, respectively. Calculations using the “equation of state” Prigogine‐Flory thermodynamic theory indicate that the temperature dependence of the thermodynamic interaction parameter in typical polymer blends is small, which agrees with the

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250403

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractWe present a theoretical treatment of nematic‐isotropic phase equilibria in mixtures which consist of random coils and comblike polymers, the latter components being composed of a rigid backbone and flexible side chains. The mixing partition function is evaluated by using the Flory lattice model. The comblike component is characterized by the axial ratioxrof its rigid main chain and the number of flexible side chainsz, each containingmsegments. The coiled component is described by its number of segmentsxc. The net exchange energy of mixing is assumed to be zero; i.e., we consider athermal solutions. It is shown that the flexible side chains attached to the rigid main chains markedly enhance the compatibility in the isotropic phase. If the ratio of the volume fraction of the side chains to the volume fraction of the main chains is high enough, there is even a finite range of concentration where the random coils mix homogeneously with the comblike component. This is in contrast to mixtures of rods and coils, which have been shown by Flory to be incompatible over nearly the full range of composition. These conclusions hold true only when ordered states are involved. For comblike polymers with flexible backbones mixed with random coils in isotropic melts, the resulting free energy of mixing is given by the familiar Flory‐Huggins express

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250404

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractWe report ultrasonic attenuation and velocity measurements on poly(dimethylsiloxane) (PDMS), poly(phenylmethyl siloxane) (PPMS), and copolymer poly(dimethyl phenylmethyl siloxane) in the temperature range of 10–50°C and frequency 0.3–45 MHz. The present data complement previously reported Brillouin spectra at hypersonic frequencies. Whereas the ultrasonic velocityu0is virtually independent of frequency, the ultrasonic absorption exhibits strong dispersion which can be ascribed to the viscoelastic normal mode relaxation. The ultrasonic attenuation data for PPMS at low temperatures display an additional relaxation process related to localized segmental motion. This mode is also responsible for the relatively large dispersion of the sound velocity and attenuation in the gigahertz frequency range accessible to the Brillouin scattering experiment. The extended information, which can be extracted by studying hypersonic dispersion, is discussed in de

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250405

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractDilute solutions of polystyrene in chloroform were filtered through track‐etched mica membranes. The pores of each membrane were smaller than the mean unperturbed dimension of the polymer molecules. Three configurations of polystyrene were used: linear, comb‐branched, and star‐branched. The data for the linear polystyrenes show that the reflection coefficient σ decreases with solvent flow rate per poreqin a manner independent of molecular weight. At low flow rates the rejection is quantitatively described by 1 − σ ∼q1.69. Comparisons among the three configurations show that as the extent of branching increases, σ increases at given solvent flow rate. It is concluded that filtration studies with well‐defined porous membranes can provide a relative measure of deformability among various configurations of pol

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250406

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe structure of ethylene copolymers modified by α‐olefins has become an area of intense investigation since the successful commercialization of so‐called linear low‐density polyethylene (LLDPE) resins. The molecular structure of a series of typical commercial LLDPE copolymers was investigated and compared to LDPE and HDPE. The commercial LLDPE resins studied contained about 7% by weight of butene‐1. The resins were fractionated according to short‐chain branching content by a technique called temperature rising elution fractionation. Size exclusion chromatography, x‐ray diffraction,13C nuclear magnetic resonance, intrinsic viscosity, and differential scanning calorimetry were used to fully characterize the whole polymers as well as fractions of a selected LLDPE resin. A broad set of data was assembled in this work to investigate the short‐chain branching, long‐chain branching, and the molecular‐weight distribution of these commercial resins. The melting behavior of the LLDPE resins was found to be strikingly different from that of LDPE and HDPE. The broad and multimodal melting envelope of the LLDPE resins was found to be due to a broad and multimodal short‐chain branching distribution. No significant long‐chain branching was found in the LLDPE resins. The short‐chain branching was found to decrease with the increase of molecular weight in a typical commercial LLDPE resin. The unique physical properties of these resins are certainly strongly controlled by the expression of the distinctive heterogeneous comonomer incorporation in the solid‐state morphological structure. The physical and mechanical properties of these materials should be ultimately understandable on the basis of the unique morphology which results from the extremely heterogeneous incorporation of modifying α‐olefin in

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250407

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe low‐frequency acoustic vibrational modes of solid poly(ethylene) (PE) oriented by stretching and hydrostatic extrusion are studied with Brillouin spectroscopy. The experimental results evidence a damping of the longitudinal acoustic mode propagating in the direction parallel to the orientation axis of the samples. The results are discussed in terms of the theoretically derived acoustic dispersion relations for the PE crysta

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250408

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractFibers were spun from the nematic phase of the copolymer of polyethylene terephthalate having 60 mol % ofp‐oxybenzoate units. A capillary rheometer was used for spinning with a shear rate at the wall of 6.4 sec−1, and capillary (length/diameter) ratio of 14.1. The spinning temperature was varied from 250° to 300°C and, at each temperature, the spin‐draw ratio was examined as a variable. Spinning was performed under two conditions. When spinning from the melt without preheating, the initial modulus of the fibers increased with spin‐draw ratio and increased with increasing spinning temperature for a fixed spin‐draw ratio. In the second case, the melt was preheated and then cooled to the desired temperature before spinning the fibers. The preheating temperature was 280°C for spinning at 250°C, and 300°C for spinning at 280°C. Preheating increased the fiber modulus to the value obtained by spinning at the preheating temperature. A reduction of the viscosity due to the melting of poly(p‐hydroxybenzoic acid) (PHB) crystallites produces better orientation and higher modulus. However, with increasing spin‐draw ratio, the modulus of the preheated fibers decreased to the values expected for the spinning temperature. This decrease in modulus is due to recrystallization of PH

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250409

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe effect of high‐energy ion implantation of oxygen into a thin film of poly(ethylene terephthalate) (PET) was studied by Fourier transform infrared spectroscopy and differential scanning calorimetry (DSC). Mylar samples 13 μm thick were implanted with 6‐MeV oxygen ions at fluences ranging from 5 × 1012to 2 × 1014ions/cm2. The DSC data showed a substantial loss of crystallinity, even at the lowest fluence, which extended deeper into the polymer film than the predicted range for oxygen deceleration in PET. Solubility measurements indicated the presence of cross‐linking, especially at the highest fluence, but bands due to cross‐linking could not be detected in the infrared. The trans/gauche ratio for the glycol group conformation was measured by a pair of conformationally sensitive infrared bands. Surprisingly, the conformation of the glycol segments did not change appreciably with increasing fluence, although crystallinity decreased and degree of cross‐linking increased. The implications these results have on possible mechanisms of chemical and physical alterations of the polymer structure by ion implantation a

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250410

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY