ISSN:0032-3888    

DOI:10.1002/pen.760321702

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThe mesophase structures of some flexible chain polymers, which do not contain mesogenic groups, but are able to form thermodynamically equilibrium mesomorphic states, were studied by means of the X‐ray analysis, the differential scanning calorimetry, and other methods. The mesophase polyethylene in bicomponent polymer blends, mesomorphic ultra‐high molecular weight polyphosphazenes, and membrane polyvinylorganosilanes were investigated. The scheme of polymer phase transitions is discussed. Besides conformational disordering, the step‐by‐step loss of different levels of the positional order (i.e. the multiple‐step character of melting) of flexible, semiflexible, and stiff chain polymers is deduced and illustrated by examples from the authors' experience and from the l

ISSN:0032-3888    

DOI:10.1002/pen.760321703

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractTemperature dependencies of the thermal expansion coefficient for segments of macromolecular helices, α(T), were obtained for polymers by infrared (IR) spectroscopy. It was shown that the α(T) are complicated (nonlinear) over a wide temperature range. Wunderlich and Bauer's idea concerning “freezing out” of normal vibrations of polymer chains was used to describe them. It was shown that the substitution of the classical rather than quantum statistics for both torsional and bending vibrational modes of macromolecules causes complications in α(T). Mechanical properties of drawn linear polymers are connected with the thermal expansion. Therefore, such an approach may be used to describe the temperature dependence of Young's modulus and failure strength for drawn polymers in the range from cryogenic to melting temper

ISSN:0032-3888    

DOI:10.1002/pen.760321704

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThe study of single‐molecule single‐crystals of isotactic polystyrene was carried out by scanning tunneling microscopy (STM) and transmission electron microscopy (TEM). It was shown that STM provided more information than TEM. By means of STM, the single‐molecule single‐crystals were found even in the case of aggregation. Regular strips were also found on the top surface of single‐molecule single‐crystals. This seems to imply regular adjac

ISSN:0032-3888    

DOI:10.1002/pen.760321705

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractWith specially shaped samples it is possible to study the stress‐strain relation σ(γ) in simple shear up to large shear deformation γ. Measurements of σ(γ) on synthetic polyisoprene, IR 305, differently crosslinked with dicumylperoxide, are reported and compared with those for uniaxial extension on the same materials. Using the simple deformation geometry including shearbands proposed in the meander model (1), both stress‐strain relations can be converted into each other. These results favor the applied superstructural model and moreover show that the deformation behavior of rubbers is governed by one material l

ISSN:0032-3888    

DOI:10.1002/pen.760321706

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractChalk‐filled isotactic polypropylene (iPP) toughened by modifying the interfaces with liquid oligomer of ethylene oxide was subjected to high deformation at elevated temperature. Oriented chalk‐filled material exhibits interesting properties: high concentration of open interconnected pores, high elastic modulus, high tensile strength, ability to absorb large quantities of liquids, white color and roughness of the surface. A continuous process for the production of oriented, toughened, chalk‐filled isotactic polypropylene is described. The stretching ratios which can be achieved range from 4 to 8 for modified chalk concentrations with compositions of 60 and 40 wt%, respectively. Solid state extruded, toughened, chalk‐filled iPP prepared for comparison exhibits similar morphology and properties as drawn toughened chalk‐filled iPP although it contains much l

ISSN:0032-3888    

DOI:10.1002/pen.760321707

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractIsotactic poly(vinyl cyclohexane) (PVCH) was studied by thermal analysis. The deduced equilibrium melting point,T m°, is 405°C (678 K). The heat of fusion, ΔH ƒ°was found to be 50.82 J/g (5.60 kJ/mol) and ΔCpatTg, is 0.273 J/(gK) [30.1 J/(molK)]. The glass transition temperature,Tg, of the amorphous PVCH is 80°C (353 K). In semicrystalline samples,Tgincreases up to 165°C (438 K) for crystallinities>40%. Beside crystalline and flexible amorphous, a rigid amorphous phase is postulated in the semicrystall

ISSN:0032-3888    

DOI:10.1002/pen.760321708

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThe effectiveness of thermal analysis as a technique for screening polymeric candidates for high temperature composite application is described. DSC, DMA, and TGA were employed to measure glass transition temperature, characterize blend phase morphology, and assess thermo‐oxidative stability. The materials studied were polybenzimidazole (PBI), polyimide copolymer (6FCoPI), and blends of PBI with Ultem 1000™ and 6FCoPI. The potential of misinterpretation of thermal analysis as the primary screening tool was also demonstrated. It was shown that if thermal analysis was used with insufficient understanding of the chemistry and physics of the materials under investigation, highly misleading conclusions may be deri

ISSN:0032-3888    

DOI:10.1002/pen.760321709

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractA large collection of data on Young's modulus and density of unfilled polyethylenes at ambient conditions has been compared with various competing theoretical mixing rules developed for composite micromechanics. The objective was to see if such theories usefully predict the dependence of stiffness on crystalline content in an archetypal isotropic semicrystalline thermoplastic polymer above its glass trnsition temperature. It was found that the self‐consistent scheme derived by Hill and Budiansky from continuum micromechanics appears to have valid application to this system. The scheme naturally and coherently incorporates information on bulk and shear moduli and Poisson's ratios, while giving a good account of the main trend in the Young's modulus data. Conversely, other theoretical models frequently invoked in the polymer literature were explicitly found to be unsuitable for representing principal features of modulus‐density relationships dectated by the d

ISSN:0032-3888    

DOI:10.1002/pen.760321710

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractAvailable literature data, augmented with a few mild and plausible assumptions, have been used to derive an estimated empirical compliance matrix for orthorhombic crystalline polyethylene at ambient conditions. Compared with this representation of experimental observations, reported theoretical compliance surfaces, derived from molecular mechanics, are shown to be in quantitative disagreement, although qualitatively their shapes are not dissimilar.It is further shown that if an accurate theoretical determination were to be available, it would yield an ability to translate (in surprisingly few, and rather simple, theoretical steps) directly from interatomic forces, acting over nanometer lengths, into realistic, crystallinity‐dependent, estimates of macroscopic moduli of isotropic semicrystalline polyethylene

ISSN:0032-3888    

DOI:10.1002/pen.760321711

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY