摘要:

AbstractMixtures are expected to show anomalous behavior in their viscoelastic properties close to a critical point. In this study, the reheological behavior of blends of polystyrene and poly (vinyl methyl ether) below, close to, and above the phase separation temperature Tswas investigated. Rheological measurements were carried out at three different compositions in the melt. Below and far fromTs, a satisfactory superposition of the storage and loss moduliG'andG″ was observed at all temperatures and frequencies. Close toTsdeviations were observed forG'at low frequencies (the so‐called terminal zone). AboveTsG″ values was still observed over the whole range of frequencies and temperatures. The deviations observed forG'nearTscan be interpreted as due to the presence of significant concentration fluctuations. Plots of log (G'/G″2) as a function of temperature were shown to be sensitive to this anomalous b

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291301

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe miscibility of poly (ϵ‐caprolactone) (PCL) with poly (styrene‐co‐acrylic acid) (SAA) and of poly (styrene‐co‐acrylonitrile) (SAN) with SAA was examined as a function of the comonomer composition in the copolymers. For PCL/SAA blends it was found that PCL is miscible with SAA within a specific range of copolymer compositions. Segmental interaction energy densities were evaluated by analysis of the equilibrium melting point depression and application of a binary interaction model. The results suggest that the intramolecular repulsion in SAA copolymer plays an important role in inducing the miscibility. Additionally, the critical AA content in SAA for the blend to be homogeneous was predicted by correlating the segmental interaction energy densities with the binary interaction model. For SAN/SAA blends, it was also found that SAA is miscible with SAN within a specific range of copolymer compositions. From the binary interaction model, segmental interaction energy denisties between different monomer units were estimated from the miscibility map and were found to be positive for all pairs, indicating that the miscibility of the blends is due to the strong repulsion in the SAA

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291302

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractIntrinsic viscosities and gel permeation chromatography data were used to evaluate the Mark–Houwink constants of the soluble electronically conducting polymer, poly(3‐hexylthiophene) (P3HT):Kandaare 2.28 × 10‐3cm3/g and 0.96, respectively, in tetrahydrofuran (THF) at 25°C. Mark–Houwink constants were used to calibrate gel permeation chromatography (GPC) columns for P3HT. Number‐average molecular weights of P3HT determined with modified calibration curves agreed well with those determined by an absolute method, embulliometry. Molecular weights estimated using unmodified polystyrene calibration procedures were significantly larger than

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291303

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA new model is presented for describing the time‐dependent flow of entangled polymer liquids at high shear rates. The results were obtained by extending the Doi and Edwards theory to include the effect of chain stretching. This nonlinear phenomenon is predicted to occur when the product of the shear rate and longitudinal relaxation time of the polymer exceeds one. If a constant‐shear‐rate flow is started under these conditions, it is shown that the shear stress and the normal stress are considerably larger than that predicted by the original reptation model. We also find thatbothof these stresses can pass through maxima before reaching a steady state and that the times required to reach these maxima are constants independent of the shear rate. In general the new model requires the numerical solution of coupled partial differential equations. However, at the highest shear rates where reptative relaxation is no longer important, an analytical solution for the stresses is found. The results obtained here are shown to agree well with experimental data and to be an improvement over a simpler model recently pro

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291304

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThere is little or no trifluoroacetylation of cellulose dissolved in TFA‐CH2Cl2admixtures. Both cellulose and cellulose triacetate (CTA)are slowly degraded in the solvent. Cellulose forms a mesophase as low as 4%(w/w)concentration, but CTA has a much higher critical concentration, 20% (w/w), in TFA‐CH2Cl2. The cellulose behaves as a rigid rod in TFA‐CH2Cl2(70/30v/v) and its persistence length calculated using the lattice model approximates its chain length, presumably due to extensive interaction with the solvent. As expected, due to low polymer‐solvent interactions, the persistence length of CTA in TFA‐CH2Cl2is only one‐fourth the c

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291305

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractSmall‐angle neutron scattering (SANS) has been used to investigate macromolecular orientation of uniaxially hot‐stretched partially deuterated polystyrene. Principle radii of gyration and degree of eccentricity were measured over a range of hot‐stretch temperatures, strain rates, and external draw ratios (EDR). Results show affine deformation for EDR<4 and an increase in the degree of local molecular orientation with increasing rate of strain and decreasing stretching temperature. It also is found that although the macromolecules follow the external stretching affinely on average, they do not deform unif

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291306

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractLow‐frequency Raman spectra were recorded for α‐methyl, ω‐methoxy‐oligo(oxyethylene)s, C1EmC1withmin the range 4–25 (i.e., 15–78 atoms). Longitudinal acoustical mode (LAM‐1) frequencies were identified and compared with those determined previously for α‐hydro, ω‐hydroxy‐oligo (oxyethylene)s. Nonlinear relationships between LAM‐1 frequency and reciprocal chain length were explained as an effect of

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291307

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA novel technique which utilizes a two‐stage staining approach, (i.e., styrene absorption followed by osmium tetraoxide staining) is introduced for staining saturated polyacrylate rubbers. This novel staining approach, which stains and hardens polyacrylate rubber, is found to be useful for room temperature microtomy of polyacrylate rubber‐modified polymers. Therefore, both the morphology and the crack tip toughening mechanisms of polyacrylate rubber‐modified systems can be studied. Details concerning staining time, staining media, and use of solvents are disc

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291308

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA solution to Fick's equation is presented which accurately predicts the transfer of mass out of a polymeric rod or sheet undergoing relaxation by a solvent permeating it by Case II transport. There is a critical length. Before the solvent permeates to this length the diffusible material can diffuse away from the moving boundary faster than it is becoming available at the boundary. Afterward the reverse is true. Five sets of experimental data from three different sources have been used to test the model. The agreement is excellent.

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291309

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

ISSN:0887-6266    

DOI:10.1002/polb.1991.090291310

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY