ISSN:0032-3888    

DOI:10.1002/pen.760240502

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760240503

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe morphology of two series of polyurethane/polyvinyl interstitial composites is characterized by scanning electron microscopy, small‐angle light scattering, and small‐angle X‐ray scattering. Thermal and mechanical properties are measured using differential scanning calorimetry and dynamic mechanical analysis. The polyurethane networks examined are microphase separated segmented block copolymers. A variety of linear and network vinylic components are studied including polymethacrylonitrile homopolymer and copolymer, and polyacenaphthalene homopolymer and copolymer. The polyurethane and polyvinyl components phase separate during thein situpolymerization resulting in a three‐phase morphology. Detailed small‐angle X‐ray scattering analysis provides measurements of phase mixing, domain spacings, and diffuse phase boundary thicknesses. A comparison of these parameters for parent polymers and composites reveals only slight differences; indicating that the microdomain structures of the phase‐separated polyurethane networks are preserved in the composite. Appreciable molecular interpenetration of components is not observed. Dynamic mechanical loss measurements for several of the composites demonstrate the presence of loss processes occurring over extremely broad ranges of temperature. The strong mechanical interaction between components observed suggest that the urethane and vinyl phases may be bicontinuous in th

ISSN:0032-3888    

DOI:10.1002/pen.760240504

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractPoly(vinylidene fluoride), PVF2, as well as blends of PVF2with poly(methyl methacrylate), PMMA, develop a variety of crystalline morphologies at low undercoolings. Both the α and γ crystal forms grow from the melt and the former undergoes a solid‐solid phase transition to the latter, though its morphology remains unaltered. Three melting temperatures which decrease with increasing PMMA content are observed. Hoffman‐Weeks analysis shows the equilibrium melting points of the blends to be depressed. Using these equilibrium values, the thermodynamic interaction energy density is calculated to go from −5.40 × 106to −2.96 × 107j/m3as the blend composition goes from 40.1 volume percent to pure PVF2. The band periodicity in the α form spherulites increases with crystallization temperature and PMMA content and it appears to be from a lamellar reorientation process with an apparent activation energy of 322 cal/mole. Electron diffraction patterns taken along the radial direction in a given spherulite reveal lamellar twisting which causes the banded appearance. Light scattering results suggest that the lamellar are formed into rod‐like structures on a local scale but that on a larger scale they develop a disoriented spheruli

ISSN:0032-3888    

DOI:10.1002/pen.760240505

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractAn investigation was carried out in order to study the effect of prestrain on the subsequent crystallization of a specific copolyester based on lactic and glycolic acid. This polymer, which can be easily quenched into an amorphous glass, has aTgof 43°C and when in crystalline form has a melting point of 210°C. Using amorphous films, samples were prestrained to various levels at temperatures not far aboveTg. In some cases films were immediately quenched at the prestrain level so as to retain the elongation while others were allowed to immediately retract whereby they showed a relatively small degree of permanent Set. Utilizing birefringence, quenched samples whose initial elongation was maintained showed linear behavior with prestrain while those that retracted showed essentially zero birefringence until a prestrain of about 150 percent after which a small degree of positive birefringence resulted. Wide angle x‐ray diffraction (WAXS) showed no signs of crystallinity in all cases. These same films were then quickly taken to 150°C and rapidly crystallized. Again, one series of the prestrained samples were in the elongated state during crystallization whereas the second series was unrestrained during crystallization. Using microscopy and small angle light scattering (SALS), the morphological textures of these crystallized films were investigated. In all cases, spherulitic textures were observed of equivalent size up to a value of about 200 percent elongation the spherulite size systematically decreased with the prestrain an increase in clearly showing that prestrain had a pronounced effect upon the nucleation density. Increasing draw rate displayed a similar effect on nucleation density. Since spherulite size was noted to be the same in either series, it indicated that nucleation was induced as a result of the prestrain and remained irrelevant of whether the sample was allowed to relax or not. The morphology above the transitional state was similar to row structure common to polymers crystallized in the oriented state. WAXS and birefringence was applied to the crystallized materials and it was found that up until the transitional zone, no crystal orientation was observed in either series indicating that although nucleation density was strongly affected up until that point, no orientation was retained within the sample upon crystallization. A simplified model is used to explain the observed res

ISSN:0032-3888    

DOI:10.1002/pen.760240506

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA quantitative model which described the microscopic and macroscopic refractive index properties of uniaxially oriented crystalline polymers has been extended in relation to molecular bond polarizabilities in this work. Application of this extended modeling methodology in analyzing measured refractive index data for a series of unoriented and oriented samples of linear polyethylene provided Δ co= 0.0585 and Δ ao= 0.194 as the most probable crystalline and noncrystalline intrinsic birefringences for samples exhibiting spherulitic morphology. With these intrinsic birefringences, noncrystalline orientation functions were determined from the optical measurements coupled to the model and the results compared to values obtained from infrared measurements. This comparison of noncrystalline orientation functions, as well as from low density polyethylene reported by other investigators, provided experimental justification for our modeling methodology to examine the possibility of changing intrinsic birefringences for polyethylene as a function of orientation and morphology. The results of this examination demonstrated that values for Δ co= 0.0585 and Δ ao= 0.12 should be used for both low and high density polyethylene samples oriented above the spherulitic to fibrillar transi

ISSN:0032-3888    

DOI:10.1002/pen.760240507

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractSmall angle X‐ray scattering (SAXS) has been used to evaluate the size and concentration of voids in poly(N,N′‐bis‐(phenoxyphenyl)pyromellitimide), PMDA‐ODA. Analysis of the angular dependence of the scattering indicates the presence of voids ranging from 50 to 150 Å in radius. Integrated SAXS demonstrated that the volume fraction of voids was 7 × 10−4. These results were supported by measurements of the attenuation factor as a function of the sam

ISSN:0032-3888    

DOI:10.1002/pen.760240508

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA large number of studies have been devoted in recent years to the miscibility behavior of linear polyesters with chlorinated polymers, including poly(vinyl chloride) (PVC), chlorinated PVC, chlorinated poly(ethylenes), and copolymers of vinylidene chloride (Saran). However, similar studies with aromatic polyesters are lacking. It is the purpose of this paper to compare the properties of blends made of poly(ethylene terephthalate), poly(butylene terephthalate) or poly(hexamethylene terephthalate) and of various chlorinated polymers. It is shown that a high concentration of chlorine atoms is required to achieve miscibility. Moreover, there is a “miscibility window” in terms of the carbonyl concentration of polyesters, immiscibility being found for carbonyl concentrations outside this window, A similar behavior was observed before for linear polyester/chlorinated polymer blends and for polyester/polycarbonate blends. Solid state small‐angle light scattering experiments were also conducted to follow the morphology of the blends as a function of composition. Spherulites were found but their size vary with compos

ISSN:0032-3888    

DOI:10.1002/pen.760240509

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractTransmitted light intensities were measured by means of the polarized light technique for the nematic liquid crystal phase of racemic poly(γ‐benzyl glutamate) (PBG) inm‐cresol at 25°C after cessation of steady flow at shear rates ranging from 0.2 to 110 s−1. Weight‐average molecular weights of PBG used were 1.5, 2.1, and 2.6 × 105, while the concentrations varied between 20, 30, and 40 wt percent. Transmitted light intensities with crossed and parallel polarizers,IxandI|, show wavy changes with time after cessation of steady flow, indicating the retardation decreases with time. An attempt was made to explain experimental results on the basis of a simple model, in which not only relaxation of molecular orientation but also effects of the wall and disclination were taken in

ISSN:0032-3888    

DOI:10.1002/pen.760240510

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe dynamic tensile deformation mechanism of spherulitic poly‐alpha‐olefins, high‐density polyethylene, isotactic polypropylene, and isotactic polybutene‐1, was investigated by dynamic X‐ray diffraction at various temperatures and frequencies in order to assign the α and β mechanical dispersions explicitly. The uniaxial orientation distribution function qj(ζj, 0) of thej‐th crystal plane and its dynamic response Δqj′(ζj, 0) in‐phase with dynamic strain were observed for several crystal planes, and then the orientation distribution function ω(§, 0, η) of crystallites (crystal grains) and its dynamic response Δω′(§, 0, η), also in‐phase with the dynamic strain, were determined by a mathematical transformation procedure proposed by Roe and Krigbaum on the basis of the Legendre addition theorem. The temperature and frequency dependences of Δω′(§, 0, η) were analyzed in terms of a spherulite deformation model combining affine orientation of crystal lamellae with several types of preferential reorientation of the crystal grains within the orienting lamellae. The following assignments are made: (1) the a mechanical dispersion must be assigned to the dynamic orientation dispersions of crystal grains within lamellae involving two types of preferential rotations of the grains associated with lamellar detwisting mostly in the equatorial zone of uniaxially deformed spherulites and with lamellar tilting mostly in the polar zone of the spherulites. Both processes are intralamellar grain‐boundary phenomena, and the former process of lamellar detwisting is hardly activated for polypropylene and polybutene‐1 spherulites in contrast to polyethylene spherulites. (2) The β mechanical dispersion must be assigned to the dynamic orientation dispersion of the crystal lamellae behaving as rigid bodies unaccompanied by reorientation of crystal grains within the orienting lamellae. This process is

ISSN:0032-3888    

DOI:10.1002/pen.760240511

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY