摘要:

AbstractThe sizes and shapes of star‐shaped poly(vinyl ether)s, prepared by living cationic polymerization, were studied by dynamic light scattering and molecular mechanics‐based computer simulation. The hydrodynamic radii (Rh) of star poly(isobutyl vinyl ether)s (4a; M̄w= 2.2 × 104− 1.7 × 105) determined by dynamic light scattering were in the range from 30 to 90 Å in tetrahydrofuran or ethyl acetate. Consistent with the expected multiarmed architecture of 4a, the radius for a given number (f) of arms per molecule increased with the degree of polymerization [DP(arm)] of the arms, and for a fixed DP(arm), the radius increased withf. The relationship between arm numberfand the “shrinking” factorh[Rh(star)/Rh(linear)] was consistent with multibranched structures for the star polymers. These results are supported by those for the molecular weight itself; the apparent weight‐average molecular weights by size‐exclusion chromatography are less than the corresponding absolute values by static light scattering. The dependence ofhonfsuggests some degree of asymmetry in the star shape. Similar results were also obtained by the computer simulation of potential energy‐minimized conformations of the arms, which implied almost spherical but slightly asymmetric shapes. The computer simulation also demonstrated that the star polymer (4b) with pendant hydroxyl groups in the arms is smaller in size than the corresponding alkyl (isobutyl) (4a) with the identical arm number and arm degree of polymerization. © 1995

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330401

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe mixing of electrically conducting polymers in the undoped state with flexible polymers has been limited due to the stiffness of the delocalized coplanar backbone. The substitution with alkyl side chains has resulted in the distortion of the aromatic rings in the backbone with an increase of the flexibility. The alkyl substituents also prevent the thiophene back‐bones from packing together, thus making blending with other polymers promising. We have investigated the phase behavior of poly(3‐octylthiophene) (P3OT) with a flexible polymer, poly(ethylene‐co‐vinylacetate) (vinylacetate composition 20%, EVA20), and defined a miscibility window based on melting point data, on cloud point measurements, and on analysis by optical microscopy. The miscible region has been studied by UV‐VIS and CPMAS NMR spectroscopies. A UV absorption in the visible region originates from a π‐π*transition in the delocalized structure of P3OT, and a change in the length of the conjugated segment in the backbone results in a shift of this absorption. A gradual solvatochromatic shift of P3OT in the solid state with dilution was observed in the miscible region.T1relaxation times for the methylene carbons in solid state show a gradual change in the relaxation process as a function of composition. © 1995 John W

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330402

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe dimensional stability of crystalline polymers such as polyethylene and polypropylene is a critical property in structural applications requiring known dimensional stability. It is essential to evaluate how such structural systems will respond when exposed to thermal fluctuations. Utilizing the molecular composite approach, oriented polyethylene has been modeled as a macroscopic composite of its constituent crystalline and amorphous phases. The molecular composite model, originally developed to describe the isotropic behavior of crystalline polymers, has been refined to account for the anisotropic micromorphological behavior of oriented polyethylene solids. This refinement accounts for the deformation and orientation of both constituent phases; the variation of the amorphous phase mechanical and expansional properties due to the taut tie molecules has likewise been considered. Furthermore, a theoretical expression relating the crystalline orientation descriptors, λ andfc, has been developed. A detailed calculational format for the prediction of the expansivity of oriented polyethylene is outlined. The overall pattern of anisotropic dimensional behavior has been correctly predicted when compared with experimentally measured thermal expansivities of various types of polyethylene. © 1995 John Wiley&Sons, In

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330403

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe processing of poly(imide) films from poly(amic acid) solutions involves the simultaneous loss of solvent and chemical conversion, and may involve structural reorganization such as orientation or crystallization. Here, we describe weight loss, solvent sorption. Fourier transform infrared (FTIR), and wide‐angle x‐ray scattering (WAXS) studies during thermal imidization of the commercially important poly(imide) PMDA‐ODA. The results indicate that imidization proceeds nearly to completion before significant crystallization occurs. The experimental data are interpreted in terms of a triangular phase diagram that makes it possible to plot the processing pathway during the conversion from poly(amic acid) solution to solid poly(imide). In constructing this triangular phase diagram the extent of imidization (i.e., the composition of the poly(amic acid‐co‐imide) copolymers during conversion) is treated as an independent thermodynamic variable. The form of the triangular phase diagram can be predicted from the Flory‐Huggins lattice theory of mixing. There is inevitably a two‐phase region present due to the relatively poor solubility of the poly(imide) in the poly(amic acid) solvent (NMP). The specific processing pathway taken depends on the relative amount of solvent loss and imidization during conversion. Further details about the triangular phase diagrams of poly(imides) will require such studies as solvent swelling at intermediate stages of conversion. © 1995 John W

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330404

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

Abstract1H nuclear magnetic resonance (NMR) imaging techniques have been used to image the extrusion aid (EA) in polyethylene (PE) pipe samples. The resulting two‐dimensional images show the distribution of EA within the pipe. EA is found to be uniformly distributed in a normal pipe. Examples of degraded pipes, due to exposure to extreme conditions, show migration of EA to the pipes' wall surfaces. NMR images of a normal pipe and two examples of damaged pipes are presented. The imaging technique and the results are discussed. © 1995 John Wiley&Sons, I

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330405

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractA molecular composite of rigid‐rod poly(p‐phenylene benzobisthiazole) and flexible‐coil poly(benzimidazobenzophenantroline) has been prepared, characterized, and shown to be thermally stable to at least 300°C. These results suggest that stable miscible blends of rodlike and coil‐like polymers can be prepared by controlling the glass transition temperature of the flexible‐coil polymer. © 1995 John Wile

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330406

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractIsothermalcis‐transisomerization behavior was studied by differential scanning calorimetry for conventional Shirakawa polyacetylene (S‐PA) film and highly stretchable polyacetylene (hs‐x) films synthesized using catalysts aged at high temperature. The rate of isomerization is slower for S‐PA than for hs‐x. Kinetic results of isomerization are analyzed by a stretched exponential function with exponentn(0

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330407

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractTwo DSC exotherms forcis‐transthermal isomerization of polyacetylene (PA) films were found near 145 and 170°C. These exotherms are related to the higher‐order structure of PA films, depending on the sample preparation conditions. The high‐temperature peak corresponds to ordered crystallites (A state), which is prominent in conventional Shirakawa polyacetylene (S‐PA) and moderately stretchable PA (ms‐PA) films. The low‐temperature peak corresponds to disordered crystallites (B‐state) found in highly stretchable PA (hs‐x) films. The distribution of crystalline order in the B state depends on the materials. The A state is transformed to B state upon stretching of ms‐PA, but the B state is not transformed to A state by stretching. The supermolecular structure is discussed. © 1995 J

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330408

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractLiquid‐liquid demixing, following spinodal quenches of poly‐2‐chlorostyrene/polystyrene blends, was followed by light scattering at 632.8 nm. The dependences of demixing on H/D substitution and molecular weight of the polystyrene, and on pressure, are reported. In the region of interest, the phase diagram is of the lower critical solution (LCS) type, and demixing is induced by raising the temperature. The transition temperature is lowered by deuterium substitution. At constant quench depth the transition proceeds more rapidly at elevated pressure. © 1995 John Wiley&Son

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330409

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractPolycarbonate of bisphenol‐A (PC)/copolyetherester (Hy) blends have been obtained by melt mixing over the complete composition range. After testing the lack of interchange reactions and degradation under the conditions studied, the miscibility state was studied by DSC and DMTA. The blends appeared to be miscible in the melt state. A fairly complex phase behavior was obtained in the solid state withTg‐composition plots showing a singleTgat most of the compositions but very different after the first and second scans. This was attributed to the different crystalline content of the blends before the two scans. The presence of a Hy crystalline phase and a single PC/Hy amorphous phase in all the blends, with the exception of the 20/80 composition, was verified by DMTA. Several thermal treatments showed the presence of an immiscibility range and, thus, the presence of a UCST. A LCST, which in the case of the 50/50 and 40/60 blends would be at roughly 75°C, will also probably exist. © 1995 John Wiley&Sons

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330410

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY